the convergence zone has set up

You would almost think we know what we are doing.... the Puget Sound convergence zone has set up, having pushed southward during the last few hours...and as expected we are getting wet snow at higher elevations on the eastern side of the zone.... see the image... The surface map clearly shows the convergence zone, with northerly winds in the N. Sound converging with the southerly stream.

According to the profiler, it is still too warm for snow near sea level..(see image)..but that will change later.... If you look carefully, you can see the northerly winds associated with the convergence zone for the latest sounding (far left).Looking at the latest infrared satellite picture (attached) shows the front that moved though this morning, and an enhanced band off the coast (northern Vancouver Is)...that should move in later today and will rev up the mountain showers and the convergence zone. That is when the real action should occur. You see that the clouds are whiter there...that means they are higher and more active. So get ready, the main action is yet to come...
A reminder..sign up for the NW weather workshop if you are interested (we need to know how many refreshments to get, links at upper right). And next weekend and Monday, I will give public lectures on Bainbridge and Olympia (see links). UW Press likes to keep me busy. After that I will be taking a break.

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Complex situation

This is the kind of forecast where one can make big errors because there are so many degrees of freedom and things happening at once. So lets start with what we are sure about.

We are fairly certain that:

(1) a cold front is heading for us and will cross western Washington between 4 and 7 AM.
(2) some light precipitation will accompany the front
(3) that much colder air is behind the front the freezing level will plummet. The snow level will decline to only a few hundred meters above the surface very quickly and by the end of the day will reach sea level.
(4) that the mountains will get more heavy snow..at least a foot.
(5) the the freezing level is sufficiently low that the high eastern suburbs should get more snow than the lowlands near Puget Sound
(6) that the air will get colder on Sunday and will hold in until Tuesday
(7) that outflow will develop in Fraser River Valley, push into Bellingham, and give upslope snow on the ne side of the Olympics
(8) that there will be substantial rain/snow shadowing due to the Olympics
(9) that a Puget Sound convergence zone will form sometime tomorrow and produce moderate snow in the eastern suburbs and quite possibly down to sea level.
(10) that outside the convergence zone and the upslope on the mountains, precipitation will be generally absent or light after the front goes through in the central Puget Sound region.

You see, we know quite a lot. But there is plenty we don't know...when and to what degree will the convergence zone set up? Will it be cold enough for snow near sea level if the convergence zone sets up early. Those are the the million dollar questions. So you got to be ready for the white stuff. Or not.

My own take is that the convergence zone will set up by 9-11 AM over central Puget Sound and that there will be snow above 200-300 ft, with wet snow/rain down to sea level. The convergence zone will hand around for much of the day...although it could shift in position and intensity with time. Later in the day and Sunday AM, the convergence zone will shift north over Snohomish County. Anyway, the position and strength of the convergence zone is a hard one...so keep this uncertainty in mind. Watch the weather radar in the morning to see what happens in real time.

If anyone is interested, KCTS-channel 9 in Seattle-- will replay my weather program at 1 PM. And if you want to help a good cause, you might make a pledge to keep public TV going.

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Cold, Snow and Double Convergence Zone.

This morning I mentioned there was a double convergence zone..one that was obvious in the satellite and radar (see images). Why? Because there was convergence of air streams behind two barriers...the mountains of Vancouver Island and the Olympics.
Take a look at the surface observations this morning (image)--you can see the converging air streams behind both barriers in the winds.

The air was cold enough today that where there was substantial precipitation intensity, snow was able to reach the elevations down to a few hundred feet. And the mountains were hammered with a foot.

Better get used to it...more probably on the way.

Tomorrow will be splendid...sunny and dry...but things change on Saturday morning when a cold front moves through, with very cold air behind. There could be some rain and snow showers after frontal passage..but I suspect the real fun will be later on Saturday and on Sunday morning when another convergence zone sets up. So don't be surprised to see some light snow somewhere over the Puget Sound lowlands. And the mountains will get plenty more.

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Morning Convergence Zone

We do have a convergence zone now...as we often do after fronts...and the air is cold enough for snow above 500ft where precip intensity is great enough.

PS: Note there are TWO convergence lines (more on this later)

PSS: If any of you are interested in the NW weather workshop, please take a look at the link in the upper right and register if you want to go. The agenda is online. This is the meeting for hardcore local weather lovers.

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Update on cold and snow

Well, its pretty definite now...we are going to experience an unusually cold period for this time of the year...with a real threat of snow showers on Sunday.

Lets start with right now. A cold front is now approaching..and there are clouds and some light showers associated with it. But the flow is sufficiently westerly that central Puget Sound is being rain shadowed (see images). The showers will move through tomorrow am, with improving weather during the day.

On Friday, an upper ridge will move in and it will by dry and sunny. But the fun begins on Saturday as a major Pacific ridge shifts eastward and an upper trough moves southward down its eastern flanks (image). Behind the trough much colder air will flood the region on Saturday into Sunday. On Saturday, the associated showers will probably be rain...but on Sunday things get interesting. The winds will be westerly, so there will be rain shadowing, but the models are insistent about the creation of a Puget Sound convergence zone...and if they are right it will be cold enough for snow (see model snow forecast).
The cold air will hold in for several days...and there will be a substantial pressure difference across the Fraser River Valley...so Bellingham and NW Washington could be raked by strong NE winds and colder temps than anywhere else. This air is cold enough to allow temps to drop into the 20s at night...so there could well be a serious frost that has the potential to damage sensitive plants...particularly those that are budding and vulnerable...so get ready to protect them.
A positive part of the forecast is that the Cascades should enjoy plenty of snow tonight and over the weekend...with up to foot possible tonight and tomorrow.

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Cold and Snow?

It is March 3, and the weather maps for later this week and the weekend, are a real eye-opener--some the coldest air I have seen this late in the season for an extended period of time. And yes, there are snow chances for the lowlands. But keep in mind that we are working against the clock. Significant lowland snow after the first week of March is increasingly unlikely--although we did get an inch last April (the frigid spring from hell--or I should say the arctic).
During the next day or so, we will be in the typical spring shower regime. Right now a band is heading towards us (see satellite pic) and should get to Washington overnight (the precipitation from it is visible in the Portland radar).

But that is not the fun part.

A major upper-level ridge develops over the eastern Pacific on Wednesday and a trough moves southward over us on Thursday (see map). Such a flow pattern will bring colder air, certain snow in the mountains, and perhaps in some high elevations...but it is not ideal for much lowland snow..the trough is too far inland. But this pattern doesn't go away and another trough moves in on Sunday...and is much more threatening..colder and and more favorable trough location with greater upward motions. The WRF model in fact puts down some lowland snow...but this is so far out, I would not get too excited yet (image). My rule of thumb is I don't get psyched about snow until we are within 96hr of the event. But I would get those salt trucks ready. And the cold air holds in. Just amazing.

PS: the Northwest weather workshop will be on March 20-21st..the major annual meeting of local meteorologists and hard-core weather enthusiasts. If you want more info or to register, check out:

http://www.atmos.washington.edu/pnww/

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Warm Front

You see the increasing clouds aloft...these are associated with an approaching warm front aloft...one associated with a vigorous offshore system (see sat pic). But that system..and its strong winds will not make landfall in the NW and strong winds will not reach our interior.
With low pressure offshore and high pressure inland, strong offshore (easterly) flow has developed west of the Cascades. So I would expect breezy conditions as one approaches the passes today--on I90 east of North Bend. The Seattle profiler shows the easterlies aloft...and such flow often produces warm temperature over the lowlands...so I expect temps in Seattle to surge into the 50s today.
The precipitation should hold off until this evening...so today should be a fine one, expect for some high and middle clouds. Then tomorrow we will see considerable clouds and some showers...and mild temps on the south side of the warm front (50s).
The weather pattern this week is a familar one..with a major low/trough over the Pacific (see sample upper level chart on Sunday). Low centers will spin up the coast offshore and most of the precipitation will head into California..where they need it. A boring collection of clouds and showers for us through Wednesday, after which the models indicate the chance of a cool down again. But I will wait before talking about that...

PS: For those interesting, I will be on KCTS on Sunday at 7 PM, answering weather questions (see link at right). Also I wanted to note the NW weather workshop on March 20-21st for those interested...it is open to all, but you should register in advance--but this does include technical talks (see link to right).

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Good News

Some news:

(1) The Camano radar was fixed ...but unfortunately broke down again. Lets face it, this radar really doesn't break down very much..considering the constant rotation and movement of the antenna and the high-powered electronics.

(2) I had a nice talk with METRO technical and management people today. They promised that they are going to replace the servers of the bus track information system and this problem, which inconveniences hundreds or thousands of us unnecessarily.

(3) I learned yesterday, that partial support for a new coastal radar is in the 2009 Omnibus legislation (that has yet to pass). Thanks go out to Senator Maria Cantwell, who has spearheaded this. I have also heard from Senator Murray's office, which is also supportive. We aren't there yet, but we are making progress. So please keep letting your representatives know that this radar is needed. Today and yesterday convinced me more than ever of the importance of the coastal radar. Not having our own radar really made forecasting and understanding the weather difficult. I could not imagine being without it permanently...the current situation to our fellow citizens along the coast.

(4) The mountains have gotten a decent amount (roughly a foot) during the last week..which should make skiing far more palatable.

Tomorrow should be dry and the next weather feature will be a weak warm front late Saturday afternoon.

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Snow Blindness

It is really frustrating to be meteorologically blind--with the NWS radar covering western WA out of commission. It makes it hard to understand what is happening and to diagnose the situation--something those living on the coast have to deal with all the time.
There was quite a bit of snow yesterday and last night, depending on where you are, and the amounts were very variable. The two biggest snow dumps in the lowlands were near Bellingham and NE of the Olympics (Port Angeles to Sequim), where some locations received up to 10 inches or so. Bellingham has the Fraser outflow, with air accelerating SW as the trough of low pressure moved through yesterday. As air flowed around the low it rose up over the Fraser outflow giving snow. Later as the low moved south the Fraser outflow pushed southward toward the Olympic peninsula...rising on the terrain and causing snow on its NE flanks and adjacent areas (even the usual dry spot Sequim---see image for surface chart at 2AM).
There were some snow showers last night over Puget Sound, and they dropped very variable amounts of snow..something that is evident on the DOT cams. Some places have only a dusting, while others...like in central Puget Sound from Seattle to Bellevue...received 2-4 inches. I have three on the ground in my home in NE Seattle.
The KING-5 radar (which is running in degraded mode) shows some showers over Puget Sound producing a few light snow showers and the 6 AM observation revealed weak convergence over the south (northerly wind on north side, SW winds to the south) that is helping to maintain them. These showers should weaken over the next few hours and skies should begin to open up. The first decent visible satellite picture is now available (see attached)..and you can make out the clouds and shower over Puget Sound and clearing to the north and south. The coast is clear and sunny. Anyway, the worst (and for some the best) is over.


NOTE: Metro's Bus Tracker software AGAIN is overwhelmed and not functioning during a snow event. After everyone complained in December. Someone really needs to be relieved of duty in Metro's IT department and those in Metro that oversee this important application. When we most need to see where the buses are, the system fails. Just incompetence.

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Update

The worst is probably over now for most..particularly those living near Bellingham. The air is now cold enough for snow throughout the region (see temps from profiler over Seattle). The band I was worried about it my afternoon note has moved through central and northwest Washington and we have a few showers remaining...but nothing serious. The latest snow total forecast map ending 4 PM tomorrow is attached --indicating the rainshadowing (or snow shadowing of central Puget Sound), with SW and NW Washington getting most of the action. Fraser River outflow is still occurring, with cold air exiting the gap, and strong NE winds gusting to around 30 mph. The perfect place to send that Foreman-guy from KING TV...the one that is always in the big parka.
Anyway, there will be a few snowshower now, but no serious accumulation...and then things will dry out tomorrow.

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Snow in Bellingham and Elsewhere

The cold front has moved through and cooler air is now spreading over western Washington. Northeasterly winds have pushed through the Fraser River Valley and associated cooler, drier air has made its way into Bellingham and vicinity. Cold enough that snow is occurring at Bellingham Airport. (Look at the attached figure showing observations at Bellingham..time is in UTC (GMT). You can see the change from rain to snow and falling temps as the wind shifted to the NE.

Snow is also falling at Quillayute on the coast. Right now it is still to warm for snow over Puget Sound, but that will change by this evening. A big problem is that the NWS weather radar at Camano Island is down and won't be back up until tomorrow at the earliest...thus, we are somewhat blind to local precipitation details. The KING 5 radar is up and available on their web site.
The million dollar question is lowland snow. The temperatures will be cold enough for snow everywhere by this evening. The only question is moisture. The problem for snow lovers is the things will dry out tomorrow morning after the upper trough over us now noves through. The winds approaching the coast are now southwesterly...leaving much of the central sound rain shadowed right now, with the convergence zone over Whidbey Island into Bellingham (see Canadian radar image). So at this point the focus of snow will be north of Everett...and later as the trough and associated low moves south tomorrow the focus of the snow will be south of Olympia. There could be some snow showers around Seattle, but no more than an inch. And lots of snow in the mountains. The 24-h snow forecast from the high resolution model is attached.

I really wish I had a coastal radar now to see more into a band that is now making landfall.. perhaps in the future.

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Uncertain Snow in Seattle

Not an easy forecast. A cold front will move through tomorrow...bringing rain showers with its passage. Temperatures will cool behind it, and by later tomorrow evening the air mass will be cold enough for lowland snow, particularly where there is significant precipitation . The problem is that Puget Sound will be at least partially rain shadowed (or snow shadowed in this case). There doesn't seem to be much evidence of a convergence zone developing over the central Sound. Another issue is that there really won't be that much precipitation in the cold NW flow.Clearly, there will be far higher chances of snow showers south of Olympia and over NW Washington.
So to summarize...frontal passage tomorrow with some rain. Show showers later tomorrow evening and Thursday morning, not amounting to much over Puget Sound, but perhaps dropping an inch or two in some locations south of Olympia and north of Everett. Not a big deal, really. But we need to watch the model run tomorrow...if the flow was more westerly, allowing a convergence zone to form over the central Sound, it could be more interesting.

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More SNOW?!&%$

There has been some hyping of wind in some media outlets...it will get breezy as low pressure moves north of us this afternoon...perhaps 15-20 mph sustained for a few hours in well-exposed locations, but no windstorm. The showers we have been getting has produced significant snow in the mountains (see image), and this will continue the remainder of the week. FINALLY, we are starting to rebuild the snowpack...and I expected 1-2 feet snowfall at pass level and above by Friday. So grease your skis now.
But I did want to note the threat of snow showers in the lowlands on Thursday...something the National Weather Service hasn't mentioned yet. I cold front will move trough around dinner time on Wednesday, bringing in much colder air (see image, sea-level pressure--solid lines, colors are temperature, blue and purple are coldest). A upper trough will move through behind the cold front providing upward motion. A surface low associated with it, is heading towards the snow "sweet spot" off of SW Washington, and a Puget Sound convergence zone may for Thursday morning (graphic). There should be some cold air moving SW through the Fraser River Valley. Finally, this mornings high resolution run is showing snow reaching the surface Thursday morning (graphic--which shows 24-h snow ending 4 PM Thursday) . There is substantial uncertainty...and considering the time of the year and marginal temperatures, we are on the edge of this, but there is a significant chance (perhaps as high as 50-60%) that some snow showers with some accumulation could occur on Thursday AM. So I hope our friends in Metro and various DOTs are keeping a sharp eye on this!


Finally, let me note I will be at Town Hall tomorrow night (Wed) at 7:30 PM talking about the science of local weather prediction. And at the same time Knute Berger will be talking in another room at the same venue about his book "Pugetopolis"--which includes "weather wimps" in the title.

PS: There have been several snow events during the last few days of Feb, first week of March. But if we don't get it then, the probably drops precipitously the second week of the month.

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The Coastal Radar

The KIRO newspecial tonight hit the radar issue hard. It really is time we get this done. Virtually all sectors of the community agree..from the environmentalists, to the timber industry, to fishers, to the Port of Gray's harbor, to meteorologists, and almost everyone in between. The expense, although significant--4-10 million--is dwarfed by the costs of a single major storm or the savings--both in safety and economic--that the radar would allow. This is key infrastructure and it is shovel ready. NOAA is being given $600 million for infrastructure enhancements...surely this project deserves support from that. Senator Cantwell and Murry are supportive. Gary Locke, who will head the Dept of Commerce, surely knows why this hardwae is needed.
If you want to help, please contact our Senators and your local congressmperson....asking them to make this happen this year. Ted Buehner, the Warning Coordination Meteorologists at the Seattle NWS office, made the case better than I could on the KIRO show....this radar will save lives and property. It is outrageous that the wettest, most storm coastal area of the continental U.S. is the only location without a coastal radar. And for those of you who love weather...imagine being able to see the details of storms as they approach the coast!

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Coming in faster

The band of precipitation is moving through now...and should be through by dinner time for most of the lowlands. About 3-6h faster than the model's indicated yesterday. Such timing errors are not unusual, unfortunately. Lack of detailed observations offshore is a major contributor to these errors. Another reason why we need a coastal radar.

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