10 AM Update

Wet snow is still hanging on in central Puget Sound...but precip has switched to rain in parts of NW Washington (e.g., north Whidbey, Bellingham) and in the south sound near Tacoma. The profiler at Seattle Sand Point shows temps near 32F in the lower atmosphere...classic melting pattern (see figure, height is in meters, temp in C--really something called virtually temp which is .5 to 1 C above the actual temperature). Above 800 m I would not believe it. Times are in GMT--17 GMT is 9 AM.
A place that can remain snow and really get more accumulation is the Kitsap...so if you are in the lower hood canal area...be ready.
The character of the precipitaiton will change in next few hours from steady to more showery as the firs disturbance moves through. We will probably warm enough to make the showers rain below 500 ft...but if there intensity is enough snow can come back.

Snow Removal (if you don't like this stuff don't read it!)

Lots of you have commented about the lamentable snow removal in the city. Anyway, if I was the "snow czar" this is what I would do:

1. Acquire and be ready to use salt on the roads.
2. Triple the number of snowplows and use steel blades instead of the rubber ones. These units can be placed on city trucks. If necessary, contract with the private sector for more equipment, as they do in the eastern U.S. for snow emergencies.
3. Change the snow removal strategy to the immediate removal of snow off primary and secondary roads so we don't end up with thick, chunky ice we have today. Don't let it accumulate and freeze.

4. Work with Metro to establish a rational snow strategy. This would include moving buses to routes where they won't be endangered until the roads are cleared. Thus, you don't take so many buses off the roads or abandon them, but redirect them strategically before they get stuck. Have MORE buses on some routes (such as major routes in and out of downtown).

5. Make sure Metro's online bus tracker web pages are robust enough to handle the load. It is critical that the population knows where the buses in real time. We have the technology to do this--they just haven't sized their computer servers properly. And the bus tracker software should be made more prominent...not hidden as the current approach.

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On the edge

It is snowing now in much of the western interior, except for light rain around Tacoma, with rain on the coast. The temperatures aloft are right on the edge. Over Seattle, the temperature is 32 F for the first few thousand feet above the surface. In the business we call such a situation "isothermal" and that temperature is being dictated by the melting of snow falling from aloft.

You can see the incoming system in the satellite picture (image) and the precipitation in the radar picture to the right. The rainshadow(or in this case snowshadow) in the lee of the Olympics is clearly visible over Sequim and northern Whidbey Is. The lack of coastal and SW Olympic radar coverage are clear as well. Really frustrated we can't see what is coming in on the radar! The lack of a NWS coastal radar is similar to the city's lack of salt and snowplows...a reconsideration is needed.
The forecast from last night is still on track at this point...with snow for a few more hours and then change to rain as a stronger system comes in this afternoon. But the snow will be close...only a few thousand feet above us...and if our models and analyses are off....well, you know what could happen! In any case, the mountains will get large amounts of snow..which is good for our water supplies and those looking for some recreation over the holidays.

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Snow versus Rain

Tomorrow represents a classic problem for local meteorologists in winter...snow versus rain. Many winter events are on the margin around here because warm air from off the ocean is always close. Later tonight and tomorrow AM we will initially see snow.. in fact, take a look at the latest satellite and radar imagery....a disturbance is making landfall and associated snow showers are moving into the western Strait and Forks is reporting light snow. In fact, snow appears to be coming in a few hours early..and that is good. But after that the models suggest that by midday the lowland temperatures will be too warm (into the mid 30s) for snow below 300-500 m and we will see rain as a stronger disturbances (an occluded front) moves in. But before it does so, we could get 1-2 inches of snow. However, my colleagues at the National Weather Service have a different interpretation and their latest discussion suggests they believe it will be all snow tomorrow--with 2-4 inch totals. So it will be interesting to see what is going to happen.

Take a look at the model total snow forecast ending at 4 PM to check out your local area based on the latest model run. And clearly the mountains will be getting plenty of new snow.

Snow 101

Surface temperatures don't tell the entire story about snow...and snow can fall when surface temperatures are above freezing by a few degrees (although wet snow). It takes about 1000 ft of above-freezing temperatures to melt snow completely into rain. Thus, the snow level is about 1000 ft below the freezing level. And whether the temperatures will be cold enough can be difficult to determine. For example, if the air is relatively warm, but dry, then evaporation can cool the air down sufficiently to get snow....at least until the air becomes saturated. Another issue is precipitation rate. Precipitation around here almost always starts as snow if you go high enough. When the snow hits warmer air below, it melts and cools the air as it does so. (It takes energy to melt ice!). The heavier the precipitation the more melting and cooling...and if you have heavy precipitation, the snow level can be driven to the surface. So this makes the problem harder...you not only need to be able to predict the incoming air temperatures, but you have to get the humidities and precipitation rates right as well.
You can see why meteorologists need a happy hour once in a while.

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Stunning Pic and Snow

Last night didn't get quite as cold as expected because of the development of low clouds during the evening...but still cold enough to turn everything to ice and keep it that way. There is a stunning picture this morning, which I have attached. This is a high-resolution visible image from the NWS geostationary weather satellite at 35,000 km above the surface. According to aircraft reports this cloud has a base around 5000 ft and a top at 7000 ft. You can see the major mountains sticking throught it...like Rainier, Adams, and Baker....and this are clear shadows from the mountains on the cloud below. Would be wonderful to fly out and see this....assuming the plane was able to take off!
Other than roadway ice...not much happening today. The computer models are consistent on the approach of a Pacific system (see satellite picture)...which should bring snow to our region after midnight. There should be an inch or two by the end of the Wed. morning commute.
At this point it looks like temperatures will warm up enough by midday that that the snow might turn very wet or even to rain at the lowest elevations...but we are right on the edge. And then later in the day another system moves in--a stronger one associated with a Pacific occluded front. Now this storm will have lots of precipitation and if it were snow...then we would have a very major event. Right now, the models are suggesting the most of the precipitation from it will be rain at low elevations (below 500 ft)...but just barely. If the models are off or some of the model physics is error (like its tendency to mix out cold air too quickly) then we could have a major event. So right now...best estimate at lower elevations is snow starting midnight to 4 AM and continuing until midmorning...leaving a few inches. Then warming a bit and a let up in the precip, with the change to wet snow or rain miday. Then later in the afternoon the precip will pick up and probably turn to rain at low elevations and wet snow above roughly 500ft. But there is uncertainty in this. And knowing about uncertainty is in itself valuable information. Meteorologists like myself sometimes are very sure about the forecast, and other times we know there is substantial uncertainty...or a wide range of possible outcomes. A major challenge is learning how to quantify this uncertainty and then communicate to users like yourself....we have a major project to do this at the UW...including meteorologists, statisticians, psychologists, and others. The grant challenge in weather for the next ten years or so.
Getting back to the forecast.... on Thursday...another system... a tight, low pressure center moves southeastward....but the latest runs are suggesting that it will go far enough south to spare the Puget Sound region. Portand will not be so lucky. Will have to watch it. And on the weekend a warmer, wetter system is on tap.

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Update II

The more I look at the forecast models, the more snow I see. Well, at least those who like a white holiday won't be disappointed.

As I mentioned earlier, tomorrow morning will be icy...but no new accumulations. It was bad enough when I took the bus home from the UW---buses sprawled on roads, abandoned on the sides. One almost hit a pole while I watched. It will be worse in the morning at some locations. (I better watch myself..I will end up sounding like a TV reporter!)

A Pacific occluded front will approach the area on Wednesday morning. Snow will start after midnight and it will certainly be snowing during Wednesday commute time. But as the occluded front makes landfall it will bring warming aloft and increased onshore flow...the question is what that will do to precipitation type. My colleagues in the National Weather Service believe that precipitation will remain snow. I am not so sure. I think there is a good chance we will see a change to rain or VERY wet snow during the late morning and early afternoon. Cooler temperatures will follow and there will be a switch to snow later in the afternoon. Accumulations by the end of the day--1-2 inches at low levels near the Sound, 2-4 inches at higher elevations.

The fun doesn't stop there. A low center from the Gulf of Alaska moves in Thursday morning...hugging the coast. Having a low over SW WA is a classic major snow threat....it can draw down cool air over NW WA and the Sound...and drive moist air over it...occasionally with large snowfalls. Take a look at the forecast situation for Thursday at 4 AM (plot)...not a perfect position, but close. Several inches of new snow could easily occur over the lowlands...and maybe more.

If you want to want to get an idea of snow totals over the area...I have included below the 24-h predicted snowfall ending 4 PM Wednesday and Thursday.




More Snowplow Musings:

A number of you comments on my "editorial" regarding a lack of snowplows in Seattle. A few additional ideas:

1. Although we have less events than say Denver, Minneapolis, and NY, ours are more serious.
First, we have the hills, which GREATLY magnify the problem. Second, our snow often falls on relatively warm ground and starts out as slush, which then hardens later into very slippery ice. Third, our snow and ice are generally relatively warm (just below freezing) and thus are more slippery.

2. We have a major snowfall (like this year) every 5-8 years and significant snowfalls 4-8 inches every other year or so. Each year we generally have few 2-3 inch snows, but some years only get a dusting.

3. I checked around on Ebay...snowplow blades are availabe for trucks for around $2000. Ok, this is Seattle....lets make it $10,000. So we could get 50 blades for 500,000 dollars--half of what those fancy automated bathrooms cost.

4. I am no economist...but image if the city had 3x more snowplows and could keep the roads in far better shape. What is that worth? Tomorrow the UW is closing for a second day. Image the cost of that in lost productivity...certainly tens or hundreds of thousands of productivity lost. What about the loss of business to retail? Any reasonable analysis should reveal that better snow removal capabilities would be a extraordinary investment.

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Evening Update

I will be talking about Wednesday's potential storm later, but one thing is certain...there will be serious icing conditions in a few hours. Today temperatures got above freezing in most of the region and there was considerable sun. The unplowed roads became wet and slush and tonight many will freeze. We have clear skies that will promote good radiational cooling to space. Temperatures will drop into the lower 20s for most and into the teens in the normally cooler spots (away from water, in valleys or low areas). Snow really promotes nighttime cooling since snow is an excellent radiator in the infrared (that point and the fact that snow is a good reflector of solar radiation is why most record low temperatures occur when snow is on the ground).

So tomorrow morning may be a real problem with perhaps more troublesome conditions than this morning in some locations.

I am going to look at potential for snow from the upcoming storms...and it clear we have two shots at it...Wednesday and Thursday. But tomorrow, other than icy, should be a benign day with no new accumulations.

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Noon Update and Editorial

Well...it looks like more snow is on the way. I just got a look at the most high resolution forecasts available in our region (the 4-km WRF-GFS if you like to impress your friends!) and a collection of other forecast models used to give some idea of forecast uncertainty. As this point they are suggesting that another batch of snow will began in the early morning hours Wednesday, snow through 9-10 AM, turn to rain, and then turn back to snow later in the afternoon. This would be a slushy mess.

Right now, temperatures are getting above freezing...making things nice and slippery. Did you know that the colder ice is the less slippery it is? When ice is below freezing, there still is a layer of liquid water on its surface...that is why it is slippery. The colder it is, the thinner that liquid layer is and thus the ice becomes less slippery...particularly as the temperature drops below 25F.

Editorial

Seattle is really not ready for snow! You would think that instead of reducing the number of buses radically as they have done, they would reprogrammed cancelled routes using the buses for the streets they have cleared. No way. There appear to be less buses on key arterial routes. I have given "Snow Talks" at Sea-tac Airport for years and the staff there always brags they have more snow removal equipment than the entire city. I can believe it. The City claims they have 25-30 vehicles with plows. Well, if they do, it is certainly not enough...and major routes (such as Sand Point Way in NE Seattle) are completely unattended. It is true that having extra plows for city trucks are not free and that snow events like this are unusual. But the economic loss of allowing the city to be crippled by such modest snows is substantial...and major decisions (like the cancellation of schools last Wednesday when no snow fell) are made in the context of such poor snow removal. Buses are important when cars have problems and the bustracking web site of Metro should a key tool. Unfortunately, they didn't size their server well...so it was completely overwhelmed this morning. And they hide the bustracking software on their web site as well. Last week I was in NY and they had a minor snowstorm. Plows were everywhere almost immediately...including secondary and tertiary roads. Certainly, we can do better. Global warming will not be the answer to this problem...at least not for 50 years.

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The Break

Yesterday was a significant snow event for the region with the lowlands receiving 3-8 inches in general, on top of the considerable snows of the past week. The last week or so has turned into the most snowy, cold period since the great event of the last week of December 1996. Take a look at the temps at Sea-Tac compared to normal (graph). Our HIGH temps have been below the normal mins (blue line) for nine days now. However, 1996 made what we are going through look like child's play...many locations had nearly two feet on the ground after two major storms...my house at 23 inches on the ground on Dec 29th and earlier that week the worst ice storm in 50 years hit the southern Sound. The snow was followed intense warm rain that melted the snow causing flooding and landslides.

For the next two days we will be in a break from the action. This morning a few light snowshowers remain (see radar), mainly over SW Washington. These will lessen during the next few hours and the remainder of the day and Tuesday will be generally dry. The low center is now moving south of us and this will pull some cooler air back into the region (see plot of model pressure and temperature at 7 AM)
Another strong Pacific system will be moving towards us Wednesday, but temperatures will be warmer than the last go around...which will place us in the familar snow turning to rain, marginal temperature situation that local meteorologists love. I will look at the storm in more detail later in the morning.....

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5 and 9 PM Update

There has been 1-3 inches of additional snow this afternoon, with many large flakes. The origin of this afternoon's snow is a band rotating around an offshore low (see sat pic--you can see the clouds swirling around the low). As clear from the radar..this band is associated with light to moderate precipitation. The band is over western Washington right now and will be moving through by mid-evening. After that there will be a break, followed by additional snowshower bands overnight that will be swing around the low. Total new accumulation today could reach 4-6 inches in some locations.

Not everyone has been getting snow..there has been rain on the coast. Portland has had snow, but rain is falling to the south in Eugene.

Monday will be cool (highs in lower to mid 30s), but generally dry. We should stay with below normal temperatures for several more days. As a result, there is a good chance this will be a white Christmas (a white Chanukah is a sure thing....since it starts tonight!). By the way, a white Christmas only occurs 7% of the time.
...and did I mention there is the potential for more snow this week? In particular, there may be serious accumulations on Wednesday.

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More Precipitation Today

Lets examine what happened yesterday and then move to today's situation. Although the forecasts were not perfect, they did get a great deal correct. Looking at a range of reports (and I very much thank those of you who provided snowfall amounts), there was roughly 3.5 to 8 inches for the communities adjacent to central Puget Sound, while 6-15 inches occurred over Kitsap and neighboring westwide communities. Less snow--2 to 6 occurred over the east side. So the amounts in Seattle and immediately north and south were right on and the predicted east-west snow gradient was apparent, but was less than forecast (the Kitsap had less and the eastside had more than predicted). This is consistent with wind evolution as we will see.

Now lets talk about the winds. First, this was never going to be a general windstorm...from the first it a downslope wind event on the western slopes of the Cascades and a gap flow event over the Strait. The strong winds verified in the Strait and there were strong winds near the western foothills...sustained 30-40 mph, with gusts to 70. But the strong winds were not as extensive as our best local models suggested...even when we had a historic pressure difference across the mountains. That difference...17.3 millibars between Seattle and Yakima...was the highest I have seen in 30 years. The winds in Snoqualmie pass were fierce and closed down the pass. Anyway, the weaker easterly winds contributed to higher snowfall on the east side of Puget Sound and less snow on the western portion. I could go on about this...but my colleagues and I will try to understand this forecast error.

One issue I didn't mention was the freezing rain. During the event, warmer air was moving in aloft, while cold air was maintained at the surface. The temperatures several thousand feet up got above freezing, resulting in rain falling into the cold air below--particularly south of Snohomish County. The result was freezing rain as the rain was cooled as it fell into colder air below. Thus, there is a crust on the beautiful fluffy snow we had last night.

Several of you commented about the nature of the snow last night. Most of you are used to the large, dendritic crystals that fall when temperatures are near freezing...our usual situation. Last night you got to enjoy the type of snow they get in colder climates.

What about today? More precipitation is coming. Another system is now moving into our area (see satellite picture) and the radar shows the precipitation moving in from the north and northwest (see radar). Rain, occasionally heavy, has moved into the coast...and Shelton has reported snow and ice pellets.

I REALLY wish we had a coastal weather radar to see the details of this approaching system...it would very much help (see my link on the right about this issue). This afternoon and early evening, the precipitation will spread over us...and the big question is: will it be snow, freezing rain, or rain? The problem is that temperatures are now marginal for snow..in fact there are above freezing temperature above Puget Sound now. Temperatures will begin to cool aloft this afternoon and temperatures can be cooled by the melting of heavy precipitation. If the moisture falls as snow, we could have 3-4 more inches. The NWS is now angling towards snow and the computer models suggest a good chance of snow over Kitsap (which there will upslope on the Olympics) and light snow north of Sea Tac. But we are on the edge and there is considerable uncertainty. At this point, I would lean towards wet snow this afternoon north of Seattle-Tacoma, with a "wintry" mix to the south. But there is considerable uncertainty about this.

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Update

I will be giving a postmordem of this storm and today's expectations around 10-10:30 AM... its not over...cliff

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8:30 PM Update

There has been some "hot" comments about meteorologists hyping the weather....please be patient...it is too soon to throw in the towel on this event...although there are clearly deficiencies in the model's solutions. The winds have not accelerated as much as forecast...yet the pressure different across the mountains is extraordinary...nearly as high as I have ever seen it...nearly 16 millibars across the Cascades (Seattle-Yakima pressure difference). The highest I have seen occurred on Dec 24, 1983 (17.1 mb) ..the great Enumclaw windstorm of the century when winds exceeded 120 mph in the foothills. Winds have increased aloft (see plot from the profiler here at Seattle Sand Point,heights in meters, time increases from right to left and is GMT--21/03 is 7 PM) and Sea-Tac is reporting gusts 26 kts and one of the individuals commenting to this blog reported 45 mph. At northbend, WA a NWS spotter reported sustained 35 mph, gusting to 45. But this event is not over yet. I think one thing all of you have learned from following the weather is that timing errors are not unusual...particularly ones of 3-6 hr.
Regarding the snow, it is now picking up as the main warm frontal band comes through (see image)...then there will be a break and the snow will pick up with the cold front band. I have about an inch at my house now.

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5 PM Update

It is clear that the snow moved in in a few hours early...not an unusual timing error. A larger error is the easterly winds--which are substantially weaker than forecast by the high resolution models. They have picked up and will pick up further...but if they are weaker than expected that will increase the snow east of the Sound (since there will be less downsloping)...

6 PM...winds started to really increase aloft....and gusts increasing at surface sites...cliff

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A little early

Very light snow has made it into SW Washington already....the models often start the light snow 2-3h late..and this an example of it. So light snow is now falling from Shelton to the SW and should get to PS by 2-3 PM.....the easterly flow will slow it up a bit...also as of 3 PM the easterly flow really hasn't revved up yet...slower than the model's suggested....but the pressure difference across the mountains has increased substantially.

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The Storm tonight and Sunday

This is going to be a complex event and I am going to take some time to describe it...and Sunday may end up different than some of the media is describing. I think we can have substantial confidence what will happen through 4 AM tomorrow...after that there is more uncertainty.

Before first, I wanted to comment on the remarkable temperatures we are seeing in western Washington. This morning much of the area has had temperatures in the teens (16F at my house in north Seattle), with many getting into the single digits. One location Arlington got below zero (I can hardly believe it). Here are some examples:

Univ of Washington 19

Mountlake Terrace 13

Lake Forest Park 9

Woodinville 8

S Everett 8

S Whidbey Island 8

Marysville 3

Arlington AP -3

Look at the plot of Seattle temps against normal. Our high temps are less than the normal lows. This is certainly one of the most sustained cold periods in recent memory (please no comments on global warming!--not an issue with a short local situation like this).Another remarkable feature has been the extreme snow in eastern Washington...with records at Spokane and nearby sites.

Now to the forecast. As you can see in the infrared satellite picture at 9:30 AM, the cloud band of with approaching system has reached our coast. The computer models are all in agreement that snow showers will begin in the early afternoon on the coast and move inland, with snow reaching central Puget Sound between 4 and 7 PM. It will snow this evening around here...this is very certain. But before we talk about snow, how about wind?
The high resolution computer models are going for strong winds developing this afternoon on the western slopes of the Cascades, the Columbia Gorge, and the Strait of Juan de Fuca. I have attached some of this output for you to see (for 4 PM, 10 PM today, 4 AM tomorrow). The predicted easterly winds along the western Cascade foothills are some of the strongest I have seen, with sustained winds of 50-60 mph with gusts that could reach 70-80 mph. I suspect the model is overdoing this....excessive downslope winds is a frequent model error and looking at its predictions for right now...the observations are less. This will be a very major event...but I suspect sustained 35-45 mph and gusts to 60-70 mph will end up closer to the truth. Very strong easterly winds (sustained 40- 50 mph) will also occur in the Strait of Juan de Fuca. There will be power outages.

Next the snow. As noted above, there is little doubt this Pacific system will make landfall and snow will start in the Puget Sound lowlands sometime later in the afternoon or early evening. There is also little question there will be a large east-west snow gradient over lowlands with heavy snow in the Kitsap and eastern slopes of the Olympics (1-1.5 ft), moderate snow near the Sound (3-8 inches), and lighter amounts towards the western foothills (1-3 inches). As noted in yesterday's blog this difference is due to the easterly flow...the resulting downslope flow over the western Cascade foothills produces drying and upslope on the Olympics causing increased precip on its upstream side. Attached is the 24h snowfall ending 4 AM. You see this features and others...such as the heavy snow in the mountains...and substantial snow over the eastern Strait. There is also a rainshadow (or snowshadow) north of the Olympics. Since I think the easterly downslope flow is being overdone a bit...as is the drying effects, I suspect that the snow amounts over Seattle and the east side are being underdone in the model, and this could increase the snowfall by a few inches.
So here we are around 4 AM with lots of snow. The cold front associated with this system will move through in the morning and there will be increased flow from off the ocean...and as a result there will be some warming aloft. A secondary trough of low pressure moves through during the afternoon on Sunday with more showers. These will bring snow in the mountains, but what about the lowlands? That is where this gets complicated and more uncertain.
Looking at the temperature predictions it appears the central Puget Sound and NW Washington could stay as snow...albeit wet snow and we could end up with several more inches. The coast will switch to rain as will parts of SW Washington. I don't see a major freezing rain threat in the PS lowlands.
But let me be clear...I am less sure about the second half of the forecast than the first part.
Anyway, be prepared to see a notable weather show.

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