I am going to wait until roughly 10 AM to make the major update--I like to wait to get the latest computer runs. However, from what I can see everything is one track...and this is a high confidence forecast situation. The models have been steady and consistent and in agreement. The action will wait until later this afternoon..with strong easterly winds cranking up after 3 PM. And snow coming in during the late afternoon. But there are complications..including the potential for rain tomorrow afternoon. Nothing is more fun than preparing for a good storm.
This weekend storm
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I have waited to write this until I have taken a careful look at all the observations and model output. The storm coming in Saturday evening and Sunday morning is potentially much more disruptive than Wednesday's event...and includes both snow and wind.
But before I talk about it how about some fun?...take a look at the latest satellite picture (attached). You see the narrow cloud band over the Sound? That is being forced by a convergence of land breezes on both sides of the Sound over the water. Land breezes occur when the land is colder than the water and the air flows from land to water. Last night with snow on the ground, the land was colder than the relatively warm Puget Sound. The air converges and rises forcing the land breeze convergence zone cloud band. An image from a webcam at the UW shows it (see pic) and if you really like this kind of thing...look at the video (http://www.atmos.washington.edu/cgi-bin/latest.cgi?webcam0_movies). I explain such features in some depth in my book.
Ok, lets get serious. An energetic and wet Pacific weather system is now approaching our coast and will start impacting us on Saturday...particularly later in the day. It will bring a low pressure trough to our coast and will force moist, warmer air above us...producing clouds and precipitation. As pressures fall along the coast on Saturday due to the approaching system the pressure difference across the Cascades will greatly intensify (low pressure west, high pressure associated with the colder air east) and southeasterly winds will increase near crest level. As a result, winds will accelerate over the Cascades, particularly across lower areas in the mountains. The result--very strong easterly winds along the western slopes of the Cascades, particularly around Enumclaw, Black Diamond, North Bend, and Maple Valley. The winds could easily gust to 40 to 80 mph, with serious potential for loss of tree branches, falling trees, and power outages. The winds will start accelerating tomorrow morning and will be powerful by afternoon and peak during the early morning hours Sunday (see graphics for 4 AM Sunday) Weaker easterly winds...but still notable.. will extend towards the Sound.
But the winds are only a warm up. Now lets talk about snow.
The precipitation shield from the incoming system (actually its warm front) will reach the Puget Sound lowlands around dinner time. We will have sufficiently cold air for this to fall as snow. There should be a huge east-west difference in the amount of snow that falls
tomorrow night and Sunday morning. The easterly downslope flow causes drying. On the other hand the easterly flow will rise as it approaches the Olympics--producing greatly enhanced snow. As are result, I would expect a huge snowfall gradient by say 4 AM on Sunday AM--with the western Cascade slopes and far eastern suburbs only getting a few inches of snow. (see the graphics of 24-h snowfall from the latest high resolution forecast model). Seattle and west shore of Puget Sound communities should receive 2-6 inches, and the Kitsap hit by 1-2 FEET. If you are living west of the Sound this will be serious. Better buy some food and be prepared to hunker down. The heavy snow will continue there until at least 9 AM Sunday.But there is so much more.... This includes powerful southeasterlies in the western portion of the Strait that will develop tomorrow evening...with winds gusting to 50-75 mph and substantial snow at the western exit of the Strait. Lots of snow in the mountains--at least a foot. And the potential for freezing rain south of Tacoma and over SW Washington late in the event as warm air moving in aloft causes a layer of air to be above freezing.
This is classic active weather situation where numerous major local weather features occur at once...the complexity caused by our local terrain...that is why we love it here!
Update
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This is clearly turning into a significant event in portions of central Puget Sound with some areas getting 3-6 inches. We have had the northerlies moving southward from NW Washington at low levels, and moist unstable flow from the southwest surmounting it. Thus, the thundersnow and snow showers. Looking at 11 AM at the latest radar, it appears that the worst will be over by 1-2 PM. ...cliff
Seattle's turn and this weekend
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Right now there is a band of snow over central Puget Sound...including Seattle...produced by convergence over the area...but with a twist. Take a look at the surface map. Instead of converging airstreams from off the Pacific, we are getting convergence between southwest flow from off the Pacific and northerly flow from the Strait of Georgia and the Fraser River Valley, with the northerly airstream being rather cold. The convergence is producing a band of snow around Seattle--which is not good for the morni
ng commute. (see radar image) The northerly flow is occurring because the low pressure trough has moved south enough to draw the BC flow
southward. The convergence zone band should move southward and weaken later this morning and the Puget Sound region will be left in scattered snow showers. But an inch or two is possible.The latest infrared satellite picture shows the swirling clouds from the low. You can see instability clouds (cumulus type) develop offshore around the Queen Charlottes as cold continental air goes over warmer water. See the clouds over Las Vegas? They had record SNOW there yesterday.
There have been all kinds of comments about the accuracy about yesterday's forecasts. But even the most critical must admit that the models were absolutely correct about the rainshadowing over Seattle....take a look at the output graphics of my previous posts. Seattle should never have cancelled school. The model underplayed the Whidbey snow...but was correct in showing greater amounts north of Lynnwood and over the south Sound. The timing of the convergence zone snow in the north Sound was off (the models were too early by roughly 3-5 hrs). Twenty years ago we could not have provided any of the regional insights into this event...the models didn't even have the local terrain right. A major problem with weather prediction now is communication....and yesterday shows that my profession needs to do better at that. And communicating uncertainy has to be big part of it.
Now a really threatening even is possible for Saturday night and Sunday. Not a wimpy convergence zone...but a major pacific weather features coming in while cold air is over the region. The models's indicate a threat of serious snow over the region....but this is a difficult forecast. Will the cold air hold as strong, moist SW flow invades aloft? This is what we will have to determine in the next few days.
PS: Book availability. A number of local books stores and online locations have run short of my weather book. During the next few days there should be a major restocking as the 5000 printed last week become available. Some local stores like Barnes and Noble and Edmonds Book Store still have copies.
Snow Situation Today
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noon update: The forecast needs an update. Some parts have worked out well...the rainshadow appeared as predicted and snow--heavy in places--occurred to the north and south of it (mainly north). So what about the CZ snow? It is occurring...but is further north the predicted...but probably will move southward later. Look at the latest radar...you see the heavy shower from roughly Port Townsend that extend to the NE...thats the cz showers...and some areas are getting substantial snowfalls in it. There is heavy snow north of Everett...with lots of places getting 3-6 inches. There appears to have been more troughing (lowering of pressure) offshore and t
hat has resulted in the winds aloft being more southwesterly than expected..the result...the cz being further north. The latest computer models suggest that later this afternoon and evening the winds will turn more westerly and the CZ will move southward and finally give some snow over central PS. I know some people are disappointed and some school districts cancelled classes...The weather system from the north started bringing light precipitation (generally snow away from the coast) to the region after midnight--with the precipitation extending over the area by 5 AM (see radar). As predicted by the high resolution models there is a profound snow shadow extending from the Olympics to Seattle....the radar image is really quite amazing. The borders of the rainshadow have moved a bit over the past few hours...but this feature is shielding central Puget Sound. Away from the shadow, light to occasionally moderate snow is fall...from Snohomish County up to Bellingham and the far eastern suburbs of Seattle where upslope on the Cascades brings back the snow. There is also snow south of the rainshadow...particularly south of Tacoma.
With the system, the winds aloft have switched to southerly or southwesterly and temps have increased aloft...even at the surface many temperatures are near or just below freezing. Along the coast it is warm enough for rain.
Now this is a snow event with two acts. We are in the first one now, and light snow will continue in the non-snow shadowed areas through commute time, with several inches possible.
Act II will start between commute time and 1 PM: convergence zone snow. The latest computer models suggest a band of enhanced CZ snow will form north of Seattle --probably centered in Snohomish County-and then move slowly southward during the afternoon and early evening before dissipating later tonight. In the CZ far heavier snow amounts are possible...4-8 inches are not unreasonable. See the attached model snow forecast for the 24-h ending 4 AM tomorrow. And the mountains are getting a very good dump, with at least of foot.
There is a long history of convergence zone snows in the area...one of the most memorable being the event of Dec 18 1990 when Seattle had a foot and virtually nothing fell at Everett and Sea-Tac airport (my book has a section on this storm). That cz snow was completely unforecast...we didn't have the high resolution models we use today.
Tomorrow things should dry out..but then ANOTHER surge of cold air and strong NE w
inds out the Fraser River valley should develop. And yes, the weekend snow storm is still out there.The coming system
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Update: 8 PM....looks like the central Puget Sound region will be snowfree for the morning commute due to Olympic rainshadowing through perhaps 9am...at least according to the latest forecast model output. The most serious snow in the urban corridor should be north of Seattle during the afternoon..in the Puget Sound convergence zone--lowest amounts 1-3 inches near the sound, increasing to 6-8 inches to the east. The map you see gives the output from the latest computer model run...with the 24h snow amounts ending 4 AM Thursday and clearly shows the convergence zone snow north of Seattle. Healthy amounts of snow...12-16 inches... will fall in the mountains. Heaven for skiers. And also note the moderate amounts from Bellingham southward to Everett. And keep in mind this is a forecast with inherent uncertainties.
This morning, temperatures across the region varied from the low teens in the cold spots away from the water (e.g, Arlington, North Bend) to mid 20s near major water bodies. Some super cold spots in valleys mights have dropped below 10F.
The big concern is tonight and tomorrow. A trough of low pressure will move southward tonight and will bring precipitation to the area. Temperatures will also warm a bit as more onshore flow develops. I think it will start around 3 AM in the general area. The low center at the surface will be inland and thus this will not be a large regional snow event. With northwesterly flow, the Puget Sound region will be initially rainshadowed...certainly from lower PS basin to the west. As the trough and associated low moves south, a Puget Sound convergence zone will form north of Seattle and then move southward. The snow will mainly be between 4 am and 4 PM. With Convergence Zone snow events the greatest amounts are generally east of the Sound....and 4-6 inches is possible there, with amount trailing off to 1-2 inches near the water. NW Washington, which is less rainshadowed could get 3-6 inches away from the water. Near the coast the temps should be high enough to have precip as rain. The mountains will get snow of course...a substantial accumulation (roughly a foot) that may allow the ski areas to open for the holidays.
Colder air moves in again on Thursday....and we all have to watch the situation on late Saturday and Sunday....when a stronger system will approach from off the Pacific.
This morning, temperatures across the region varied from the low teens in the cold spots away from the water (e.g, Arlington, North Bend) to mid 20s near major water bodies. Some super cold spots in valleys mights have dropped below 10F.
The big concern is tonight and tomorrow. A trough of low pressure will move southward tonight and will bring precipitation to the area. Temperatures will also warm a bit as more onshore flow develops. I think it will start around 3 AM in the general area. The low center at the surface will be inland and thus this will not be a large regional snow event. With northwesterly flow, the Puget Sound region will be initially rainshadowed...certainly from lower PS basin to the west. As the trough and associated low moves south, a Puget Sound convergence zone will form north of Seattle and then move southward. The snow will mainly be between 4 am and 4 PM. With Convergence Zone snow events the greatest amounts are generally east of the Sound....and 4-6 inches is possible there, with amount trailing off to 1-2 inches near the water. NW Washington, which is less rainshadowed could get 3-6 inches away from the water. Near the coast the temps should be high enough to have precip as rain. The mountains will get snow of course...a substantial accumulation (roughly a foot) that may allow the ski areas to open for the holidays.
Colder air moves in again on Thursday....and we all have to watch the situation on late Saturday and Sunday....when a stronger system will approach from off the Pacific.
More snow
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This morning the low center and
associated clouds/snow has moved south of us...with snow still falling over Oregon (see image). Low temps last night dropped into the low 20s in Seattle and in the teens in the cooler hinterlands. If you think this is cold...head to the upper plains where low records have been broken (such as the -15F at Denver). As noted in earlier blogs, this cold will be around for a while. But first lets talk snow.
An upper level disturbance...known as an upper level short wave trough in the business...will move southward out of Alaska and BC late Tuesday and Wednesday morning (see upper level map). This is close to the canonical situation for NW snow. Right now it looks like snow will begin falling over our area early Wed morning (perhaps very la
te Tuesday) into early Wed afternoon. As this point, it looks like amounts will be modest, roughly 1-4 inches, with some scattered higher amounts. To get really major snow we need a low developing off of the SW Washington coast and this is not being predicted (see map). The reason this is such a favorable pattern is that the low draws cold air in the from the north, while rotating Pacific moisture up and over it. But at this point, the low is too far inland for such heavy snow. So be ready for a modest snow event.
But the real threat is on Sunday. A far stronger weather system is forecast to approach the area...and with cold air in place we could have a major snow event that would make Wednesday look small. But this far out this is still a lot of uncertainty.... But if you need to buy car chains...I would do it.
associated clouds/snow has moved south of us...with snow still falling over Oregon (see image). Low temps last night dropped into the low 20s in Seattle and in the teens in the cooler hinterlands. If you think this is cold...head to the upper plains where low records have been broken (such as the -15F at Denver). As noted in earlier blogs, this cold will be around for a while. But first lets talk snow.
An upper level disturbance...known as an upper level short wave trough in the business...will move southward out of Alaska and BC late Tuesday and Wednesday morning (see upper level map). This is close to the canonical situation for NW snow. Right now it looks like snow will begin falling over our area early Wed morning (perhaps very la
te Tuesday) into early Wed afternoon. As this point, it looks like amounts will be modest, roughly 1-4 inches, with some scattered higher amounts. To get really major snow we need a low developing off of the SW Washington coast and this is not being predicted (see map). The reason this is such a favorable pattern is that the low draws cold air in the from the north, while rotating Pacific moisture up and over it. But at this point, the low is too far inland for such heavy snow. So be ready for a modest snow event. But the real threat is on Sunday. A far stronger weather system is forecast to approach the area...and with cold air in place we could have a major snow event that would make Wednesday look small. But this far out this is still a lot of uncertainty.... But if you need to buy car chains...I would do it.
End of snow today but cold here to stay
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The air over us is cold enough for snow everywhere in Western Washington and it will be getting considerable colder over the next day. Later yesterday, the weak disturbance from the north began circulating snow showers into our region and with sufficiently cold air in place finally, light snow occurred during the evening and morning hours. The reports I have seen indicate general amounts of 1-2 inches, but with heavier falls north of the city and to the east..parti
cularly in places with some elevation. The
National Weather Service did a good job of forecasting these amounts yesterday afternoon (they went 1-3 inches). Of course, the mountain passes have secured 1.5 to 2 feet during this event.
So what is happening now (7 AM)? Some moisture is still rotating around the offshore low (see radar), but most of the snow showers...and particularly the heavy stuff, is on the eastern side of the Sound and Strait of Georgia.
The reason is that strong easterly flow has developed aloft over the western slopes of the Cascades. To see that look at the observations above Seattle (image) and the surface wind plot (image). Remember the way winds are plotted..the pennant points in the direction the wind is blowing and and a big line mean 10 knots and and small
one is 5 knots. Two big lines is 20 knots, etc. The downslope easterly flow works against precip, but as it rises on the eastern side of the Olympics and Vancouver Island, it enhances the snow.
Strong winds from the NE are now blowing into Bellingham. This air is not only cold, but dry. Strong easterly winds are also blowing in the Gorge at locations such as Troutdale.
Anyway, today the offshore disturbance will move south and the showers we lessen. As the low moves south of us, the really cold air will be drawn southward and skies will clear. Having some snow on the ground will promote cooling, since snow is very good in radiating heat to space. So today will not get much above freezing, but tonight will be much colder...dropping down near 20F in most of the region...and into the teens in colder spots. The cold air will be in all week, with some minor modifications. We are still watching a weak system on Wednesday. Perhaps some snow showers. The question is a major system approaching over the weekend...things could get very interesting...but too soon to talk about that.
cularly in places with some elevation. The
National Weather Service did a good job of forecasting these amounts yesterday afternoon (they went 1-3 inches). Of course, the mountain passes have secured 1.5 to 2 feet during this event.So what is happening now (7 AM)? Some moisture is still rotating around the offshore low (see radar), but most of the snow showers...and particularly the heavy stuff, is on the eastern side of the Sound and Strait of Georgia.
The reason is that strong easterly flow has developed aloft over the western slopes of the Cascades. To see that look at the observations above Seattle (image) and the surface wind plot (image). Remember the way winds are plotted..the pennant points in the direction the wind is blowing and and a big line mean 10 knots and and small
one is 5 knots. Two big lines is 20 knots, etc. The downslope easterly flow works against precip, but as it rises on the eastern side of the Olympics and Vancouver Island, it enhances the snow.Strong winds from the NE are now blowing into Bellingham. This air is not only cold, but dry. Strong easterly winds are also blowing in the Gorge at locations such as Troutdale.
Anyway, today the offshore disturbance will move south and the showers we lessen. As the low moves south of us, the really cold air will be drawn southward and skies will clear. Having some snow on the ground will promote cooling, since snow is very good in radiating heat to space. So today will not get much above freezing, but tonight will be much colder...dropping down near 20F in most of the region...and into the teens in colder spots. The cold air will be in all week, with some minor modifications. We are still watching a weak system on Wednesday. Perhaps some snow showers. The question is a major system approaching over the weekend...things could get very interesting...but too soon to talk about that.
Major Cold
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The winds have subsided now as the strong low has moved east. There are a lot of lessons regarding that low and intense winds it produced...not the least, it being a good example of the difficulty of forecasting rapidly developing systems over the oceans. On one hand, the computer models were extraordinary...predicting the rapid development of an intense low from nothing, days in advance. The problem was the track...and keep in mind that we were only talking ab
out a 100 mile error of the models a day before. Meteorologists do better than economists...at least we saw it coming! The low brought max 40-60 mph gusts in the interior and some gusts to 80-90 mph on the coast. There was some light snow last night at higher interior elevations...but nothing serious. And a key issue is that the road surfaces are relatively warm since our air temps have been fairly warm. This protection will be gone in a few days.
The big...and serious story...now is the cold. We are about to go into the most significant cold spell in years, and you should prepare for it. Remove hoses from exterior pipes, wrap vulnerable pipes, leave water dripping in vulnerable areas..you know what I am talking about.
Today, we have some residual moisture from the storm, but will progressively dry during the day (see radar image). The air is fairly warm right now, with onshore flow from the ocean. The freezing level is about 2000 ft over Puget Sound, snow level about 1000 ft. Today the cold air will start to move in...and particularly tonight. We will get into the mid and upper 30s today, but tonight temps will drop in the 20s. Cool air will start to push into the Fraser RIver valley and strong outflow will begin..with NE winds moving SE over Bellingham, over the San Juans and then will hit the Olympics. This can produce upslope flow and snow on the NE side of the Olympics...so those near Sequim and Port Angeles should prepare for it. I have inserted a series of model output below showing sea level pressure and low level temps...you can see the cold pushing in. Note also that even colder air will be east of the Cascades...next week they will have HIGHS in the single digits and subzero minima. A large pressure difference will develop across the Cascades (due to the colder, denser air east of the crest)...and this will produce strong easterly winds in the Columbia Gorge. I love how everything happens at once in these intense weather periods.
What about snow in the lowlands? By later today the air will be cool enough for snow almost everywhere...but it will be generally dry..a disappointment for the kids. A disturbance from the north will increase the chances of clouds and precip (snow) tonight...BUT by that time there will be a strong easterly, downslope component off the Cascades. I suspect the result will be little, if any snow, east of the Sound and light snow (0-3 inches) on the western side and over the Olympic Peninsula.
Then we settle down to an extended cold period that could last a week. There is a possibility of light snow midweek...but lets wait to talk about that.
PS: Several has asked me about getting the book in times of the holidays....particularly since amazon and barnes.com are temp out. Several local bookstores have lots of books...including university book store...an
d several, like UBS, ship...just like amazon. A number of barnes and noble locations have books. 5000 more books were printed in the past week...and should be 
getting into the system by the end of next week. Anway, check my web page (click on book icon) to get more info on availablility issues.
out a 100 mile error of the models a day before. Meteorologists do better than economists...at least we saw it coming! The low brought max 40-60 mph gusts in the interior and some gusts to 80-90 mph on the coast. There was some light snow last night at higher interior elevations...but nothing serious. And a key issue is that the road surfaces are relatively warm since our air temps have been fairly warm. This protection will be gone in a few days.The big...and serious story...now is the cold. We are about to go into the most significant cold spell in years, and you should prepare for it. Remove hoses from exterior pipes, wrap vulnerable pipes, leave water dripping in vulnerable areas..you know what I am talking about.
Today, we have some residual moisture from the storm, but will progressively dry during the day (see radar image). The air is fairly warm right now, with onshore flow from the ocean. The freezing level is about 2000 ft over Puget Sound, snow level about 1000 ft. Today the cold air will start to move in...and particularly tonight. We will get into the mid and upper 30s today, but tonight temps will drop in the 20s. Cool air will start to push into the Fraser RIver valley and strong outflow will begin..with NE winds moving SE over Bellingham, over the San Juans and then will hit the Olympics. This can produce upslope flow and snow on the NE side of the Olympics...so those near Sequim and Port Angeles should prepare for it. I have inserted a series of model output below showing sea level pressure and low level temps...you can see the cold pushing in. Note also that even colder air will be east of the Cascades...next week they will have HIGHS in the single digits and subzero minima. A large pressure difference will develop across the Cascades (due to the colder, denser air east of the crest)...and this will produce strong easterly winds in the Columbia Gorge. I love how everything happens at once in these intense weather periods.
What about snow in the lowlands? By later today the air will be cool enough for snow almost everywhere...but it will be generally dry..a disappointment for the kids. A disturbance from the north will increase the chances of clouds and precip (snow) tonight...BUT by that time there will be a strong easterly, downslope component off the Cascades. I suspect the result will be little, if any snow, east of the Sound and light snow (0-3 inches) on the western side and over the Olympic Peninsula.
Then we settle down to an extended cold period that could last a week. There is a possibility of light snow midweek...but lets wait to talk about that.
PS: Several has asked me about getting the book in times of the holidays....particularly since amazon and barnes.com are temp out. Several local bookstores have lots of books...including university book store...an
d several, like UBS, ship...just like amazon. A number of barnes and noble locations have books. 5000 more books were printed in the past week...and should be 
getting into the system by the end of next week. Anway, check my web page (click on book icon) to get more info on availablility issues.
Major Change in the Forecast
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UPDATE at 4 PM: The low center has moved north of us and wind have increased greatly...some locations are getting 40-50 mph gusts! No snow anywhere in the lowlands. PS: Several people have asked me about how we can get snow in the lowlands...if you have my book I have whole chapter on it (chapter 3).
The bottom line: the low appears to be going further north than yesterday's model output suggested...making snow much less likely today and this evening. Cold is still coming tomorrow and Sunday. The National Weather Service (NWS) will have to amend their forecasts.
This is a perfect example of why we need a coastal weather radar. The big issue...where is the incoming low and how intense is it. This low only formed last night and was forecast to develop very, very rapidly. These are the circumstances that the models can make major errors...either in intensity of position. During the pas
t few days the models have had varying solutions...and the location of landfall has varied. Two days ago it looked like it was going north...giving us strong winds and less lowland snow. Yesterday they went south...and the NWS went towards lowland snow. I hate to say it...but the new model runs, initialized with the latest data, and recent satellite pictures suggest the northern route will be it (see satellite picture--the low is in the center of the hooked shaped cloud). If we had a radar on the coast we would know without any doubt what would happen today and be able to provide you with an excellent and confident forecast...so tell you congressman and senators you want one (see my web site formore info--http://www.atmos.washington.edu/~cliff/coastalradar.html)
The precipitation shield of the system is now upon us (see radar). Looking at the pressure changes along the coast...the greatest falls are on the north-central Olympic coast. The low should move over the N. Olympic Peninsula and be just north of us around 4 PM. Winds will pick up from the south this afternoon over Puget Sound...so be ready for 20-30 mph winds. Then a strong westerly surge will occur the Strait...that will effect Mukilteo, Everett, and Whidbey Island. (good night to have dinner at Ivars in Mukilteo for you storm watchers). Virtually no snow in the lowlands...but there could be some snow just to the SE of the Olympics (much less extensive than the earlier forecast).
Then as the low moves east, northernly winds down Georgia Strait will increase and then overnight strong winds will pour out of the Fraser River valley into Bellingham. There could be some upslope snow on the NE side of the Olympics Saturday morning.
A positive thing of this change is more snow in the WA Cascades...the skiing industry needs it.
And did I mention the strong southeasterlies over NW Washington this morning and afternoon and the very strong winds on the coast!
More later...
A Difficult Forecast
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Things have changed. The forecast models, which indicated substantial uncertainty yesterday, appear to be locked on to a solution--one in which a strong low center will move SOUTH of Seattle, not north, as previously predicted (see attached sea level pressure forecast for tomorrrow at 4 PM). This will have a huge impact on the forecast tomorrow. Forget strong southerly winds along our coast and in Puget Sound. Forget the strong westerly surge in the Strait of Juan de Fuca. Thats history now. Just so you can appreciate
how difficult this forecast problem is.... consider that the low doesn't even exist now...but will form shortly. That this low is forecast to amplify explosively. That a 100 mile error in its position can radically change the forecast. But as I will note, there is no doubt about cold air coming...the big issue is snow.
So this is how I see it. Today w
ill be cloudy and dry. It better not rain...the weather radar is broken (I swear that hardware knows when challenging weather is coming.... similar to the fact the copy machines malfunction when you REALLY need them). The low will develop rapidly tomorrow, spreading rain over the area tomorrow, starting in the late morning . When the low was going north of us we didn't have to worry about snow, because there would be strong southerly and southwesterly flow. Now we have to worry.
I think it will be too warm for snow over much of the lowlands initially...except for one place...southeast of the Olympics around the lower hood canal and the Kitsap. If you live there, better be prepared. Second, as the air gets colder later in the day there is the possibility of snow reaching the ground where showers are strongest--and the higher elevation you are the more probably it gets. However, initially there will be strong easterly flow that should keep the wesern side of the Sound snowfree. As the low moves east northerly flow will increase..resulting in upslope flow and potential snow immediately NE of the Olympics...like the Sequim area (the opposite of the normal rainshadow there). Then after midnight a puget sound convergence zone could form...providing light snow over central puget sound. We will get a better idea about the above threats as the higher resolution runs become available later this morning. On Saturday, strong northeasterly flow will be pouring through the Fraser River Valley into Bellingham and NW Washington (see second figure of near surface wind speeds). Very strong, cold, dry air.
The mountains will get snow...but less than the old storm track. Perhaps a foot in the pass. And this may not be enough to initiate downhill skiing.
No matter what, our region will switch to unusually cold, dry air. It will be like moving to Vermont or the upper midwest. Highs will only reach the low to mid 30s from Sunday to Tuesday....but it will be dry. Even sun. No seasonal affective disorder. But you need to protect pipes and plants.
how difficult this forecast problem is.... consider that the low doesn't even exist now...but will form shortly. That this low is forecast to amplify explosively. That a 100 mile error in its position can radically change the forecast. But as I will note, there is no doubt about cold air coming...the big issue is snow.So this is how I see it. Today w
ill be cloudy and dry. It better not rain...the weather radar is broken (I swear that hardware knows when challenging weather is coming.... similar to the fact the copy machines malfunction when you REALLY need them). The low will develop rapidly tomorrow, spreading rain over the area tomorrow, starting in the late morning . When the low was going north of us we didn't have to worry about snow, because there would be strong southerly and southwesterly flow. Now we have to worry.I think it will be too warm for snow over much of the lowlands initially...except for one place...southeast of the Olympics around the lower hood canal and the Kitsap. If you live there, better be prepared. Second, as the air gets colder later in the day there is the possibility of snow reaching the ground where showers are strongest--and the higher elevation you are the more probably it gets. However, initially there will be strong easterly flow that should keep the wesern side of the Sound snowfree. As the low moves east northerly flow will increase..resulting in upslope flow and potential snow immediately NE of the Olympics...like the Sequim area (the opposite of the normal rainshadow there). Then after midnight a puget sound convergence zone could form...providing light snow over central puget sound. We will get a better idea about the above threats as the higher resolution runs become available later this morning. On Saturday, strong northeasterly flow will be pouring through the Fraser River Valley into Bellingham and NW Washington (see second figure of near surface wind speeds). Very strong, cold, dry air.
The mountains will get snow...but less than the old storm track. Perhaps a foot in the pass. And this may not be enough to initiate downhill skiing.
No matter what, our region will switch to unusually cold, dry air. It will be like moving to Vermont or the upper midwest. Highs will only reach the low to mid 30s from Sunday to Tuesday....but it will be dry. Even sun. No seasonal affective disorder. But you need to protect pipes and plants.
Windstorm,snow in the Mountains, a chance of lowland snow, then cold and dry
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It is always fun to live through interesting times meteorologically..particularly after the boring few weeks we have just gone through (ok...some people like boring, benign weather). But what will happen Friday and Saturday will get your attention.
The models are slowly coming into agreement...but I have to stress that considerable uncertainty still exists in the details. This will be one of those periods that a wide variety of active weather will all occur together.
Today will be have considerable clouds and a few showers..particularly in the mountains. While tomorrow will be dry with some sun.
For Friday, the models are indicating the rapid development of a low pressure system that will pass over the north Olympics and then eastward. This system will produce strong winds over the coastal in the morning, with the winds increasing over Puget Sound during the afternoon. So step one: winds. Moderate rain associated with this low will spread over our area after 9 AM on Friday. Associated with this system there will be moderate to heavy snow over the Cascades, with at least 6 inches to a foot, maybe more. And they need it. As the low moves eastward, a strong westerly surge of powerful winds will move eastward through the strait of juan de fuca....with some gusts achieving 40-60 mph. The general rain will lessen after the low passes, but cold air will start streaming in. Now what about snow. Before the storm moves through the only lowland area that could get some will be the region to the SE of the Olympics....the lower Hood Canal/Kitsap area. After the low goes through a Puget Sound convergence zone may set up...and snow is quite possibile in it. But there is considerable uncertainty if that will happen....but it is a possibility.
There also could be some scattered snowshowers on Saturday at low levels...but nothing significant. During subsequent days cold air pushes southward through the region and we become cold and dry...and this could last for days. We are talking about HIGHS in the 30s and lows down in the 20s. Start thinking about protecting exposed pipes and vulnerable plants. Otherwise my plumber friends will be have a very good holiday.
The models are slowly coming into agreement...but I have to stress that considerable uncertainty still exists in the details. This will be one of those periods that a wide variety of active weather will all occur together.
Today will be have considerable clouds and a few showers..particularly in the mountains. While tomorrow will be dry with some sun.
For Friday, the models are indicating the rapid development of a low pressure system that will pass over the north Olympics and then eastward. This system will produce strong winds over the coastal in the morning, with the winds increasing over Puget Sound during the afternoon. So step one: winds. Moderate rain associated with this low will spread over our area after 9 AM on Friday. Associated with this system there will be moderate to heavy snow over the Cascades, with at least 6 inches to a foot, maybe more. And they need it. As the low moves eastward, a strong westerly surge of powerful winds will move eastward through the strait of juan de fuca....with some gusts achieving 40-60 mph. The general rain will lessen after the low passes, but cold air will start streaming in. Now what about snow. Before the storm moves through the only lowland area that could get some will be the region to the SE of the Olympics....the lower Hood Canal/Kitsap area. After the low goes through a Puget Sound convergence zone may set up...and snow is quite possibile in it. But there is considerable uncertainty if that will happen....but it is a possibility.
There also could be some scattered snowshowers on Saturday at low levels...but nothing significant. During subsequent days cold air pushes southward through the region and we become cold and dry...and this could last for days. We are talking about HIGHS in the 30s and lows down in the 20s. Start thinking about protecting exposed pipes and vulnerable plants. Otherwise my plumber friends will be have a very good holiday.
Today...warm front-cold front combo
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A warm front is approaching us this morning (see satellite picture) and the radar shows the advance of the associated rain (see image). Showers will develop over Puget Sound this morning, with most of the precipitation north of Centralia. Aloft the winds will strengthen from the SW and temps will warm a bit. The rain should lessen by dinner time and then pick up this evening with the passage of the associated cold front (the back line you see in the satellite picture).
Wednesday will bring some residual showers...particular in
the mountains and Thursday should be dry. The big issue is Friday and this weekend.There is still considerable uncertainty in the forecast for Friday--and particularly lower elevation snow. But it is clear that the weather will turn colder over the weekend and dry out.
The computer models have not locked on to a consistent solution for Friday...something I like to see to give confidence in the forecast. Most models bring precipitation in and the mountains will receive considerable snow. The latest run of the best local model produces a strong low that moves in later in the day...giving strong winds to the coast and southern Puget Sound and no general snowstorm. Just rain. The only wrinkle would be the chance of snow in a Puget Sound convergence zone that night and Saturday morning. We are going to have to wait at least until tomorrow to make a skillful forecast for this transition.
Finally, let me say that snow prediction is the most difficult type of prediction in the region. It is hard to snow here and the flow configuration has to be just right. Furthermore, the large scale atmosphere is going through a large reconfiguration...and skill is lessened during such periods. But that is why forecasting is fun!
A Radical Weather Shift on Friday
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Well, the big story is the major weather transition on Friday. I mean major. Today we have a residual Puget Sound convergence zone that is now dying with some weak showers in the mountains. This event produced a dusting at Snoqualmie Pass and several inches at Stevens. The snowpack right now is very poor, with the higher terrain only gaining about 20% of normal for this time of the year (see figure).
Tomorrow a warm front will bring showers for mainly the northern portion of the state...and some light snow to the N. Cascades about 3000 ft. This precipitation will continue on into Wednesday. Thursday will be generally dry. The big story in Friday. There will be a major reconfiguration of the large scale atmospheric pattern. The ridge over us will strengthen and move westward and we will be thrust into much colder northerly flow (see upper air chart for 7 PM on Friday night)--and a trough of lower pressure will move southward over region. We are pretty much guaranteed much, much colder air over us...and you should prepare for it. This kind of pattern makes plumbers very happy, as bursting pipes bring lots of business.
The mountains will get significant snow as the trough moves through. The question, of course, is lowland snow. I have studied this issue for a long time....and right now the flow situation is not ideal for much snow at low levels on Friday over Puget Sound. The threat is actually much higher to our south...Portland and the Willamette Valley. Anyway, no use speculating more on this until we have more confidence in the forecast...that will be Wednesday.
Major Changes Next Friday?
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I have been watching a major shift for late this week...but have not mentioned it before in this blog...because the models are not dependable out that far. But this morning's runs are continuing this solution...one that would bring much colder air to the Northwest, significant snows in the 
mountains, and the potential for snow in the lowlands. Specifically, on Friday a configuration close to the classic NW snow pattern develops...high amplitude ridge of high pressure offshore and a sharp upper trough moving southward over us. The models indicate a transition to MUCH 
colder air with it...which is getting to look more probable. The trick is to get snow in the lowlands...and I wont speculate on this right now. But we all need to watch this pattern...it if is still there on Tuesday...it will be pretty much a sure thing. The TV weathermongers should be ready..particularly my favorite..Jim Foreman of KING TV.
Today the weather is the worst of what has been an exceptional week. A weak front with cooler air is now passing south of us (see satellite picture). The steady rain is south of central Puget Sound and now post
frontal showers are moving in. Because the winds are westerly on the coast, the central Puget Sound region is being rainshadowed (see radar)--with showers in the mountains and on the coast. The freezing level has dropped enough so that the 
higher passes and elevation have had a few inches of snow. Compare the WSDOT cam images at Stevens pass (with snow) to Snoqualmie pass (rain). Just a thousand feet makes a big difference. A Puget Sound convergence zone will form over or north of Seattle today...so go north or south of it if you want dry weather. A ridge moves in tomorrow for generally dry weather..except for some showers in the mountains.
PS: Several of you have emailed me about the book...it looks like amazon and Barnes and Noble.com have temp sold out (more are being shipped to them). Many local book stores have supplies --except for Northgate B&N. UW bookstore had plenty last week and do online orders--as do many local bookstores.
mountains, and the potential for snow in the lowlands. Specifically, on Friday a configuration close to the classic NW snow pattern develops...high amplitude ridge of high pressure offshore and a sharp upper trough moving southward over us. The models indicate a transition to MUCH 
colder air with it...which is getting to look more probable. The trick is to get snow in the lowlands...and I wont speculate on this right now. But we all need to watch this pattern...it if is still there on Tuesday...it will be pretty much a sure thing. The TV weathermongers should be ready..particularly my favorite..Jim Foreman of KING TV.Today the weather is the worst of what has been an exceptional week. A weak front with cooler air is now passing south of us (see satellite picture). The steady rain is south of central Puget Sound and now post
frontal showers are moving in. Because the winds are westerly on the coast, the central Puget Sound region is being rainshadowed (see radar)--with showers in the mountains and on the coast. The freezing level has dropped enough so that the 
higher passes and elevation have had a few inches of snow. Compare the WSDOT cam images at Stevens pass (with snow) to Snoqualmie pass (rain). Just a thousand feet makes a big difference. A Puget Sound convergence zone will form over or north of Seattle today...so go north or south of it if you want dry weather. A ridge moves in tomorrow for generally dry weather..except for some showers in the mountains.PS: Several of you have emailed me about the book...it looks like amazon and Barnes and Noble.com have temp sold out (more are being shipped to them). Many local book stores have supplies --except for Northgate B&N. UW bookstore had plenty last week and do online orders--as do many local bookstores.
