Wednesday, February 29, 2012

Wet Snow and the Mt. Rainier Convergence Zone

Many of you have noticed some wet snow mixed with the rain--even down to sea level.  However, the heaviest accumulations occurred where the models suggested:  southeast of the Olympic Mountains from Shelton to Silverdale to Quilcene.  The reason:  temperatures are marginal for snow and only places with heavy precipitation rates allow the snow level to fall to near sea level.  More precipitation means more melting, which cools the atmosphere--allowing the freezing and snow levels to descend (keep in mind the freezing level is typically about 1000 ft above the snow level (the level at which all the snow is melted)).

Here are a few nice pics of the snow:  one at Dale Ireland's home in Silverdale and the other one provded by Sarah Kirkegaard of Quilcene.

 And those of you at higher elevations (say above 1000 ft) saw some snow...here is a picture at Peter Benda's home at 1200 ft in Bellevue:


 Here is the 24-h snowfall ending about 7 AM this morning from the Cocorahs network (click to enlarge).  Some folks on the Kitsap Peninsula and eastern Jefferson county got 2-7 inches of snow.




Today there was a good example of something we don't see everyday...a Mt. Rainier convergence zone.  You know about the Puget Sound convergence zone....air passing around the Olympic barrier and converging on the eastern side...giving a line of clouds and precipitation.   Well, Mt. Rainier is big enough to do the same thing....and today the radar indicated a line of precipitation NE of Rainier from the downstream convergence.  The band stretches SE to NW and cross I90 between Snoqualmie Pass and Cle Elum.



Thanks to Colby Neuman of the National Weather Service for pointing this out.  Mt. Rainier produces a lot of its own weather...including a rain shadow.

Monday, February 27, 2012

Lowland Snow?, Thank You, and The Seattle Times Does it Again

We are now thoroughly stuck in a La Nina pattern, cold and occasionally wet.  The mountains are going to get several more feet this week...pretty much guaranteed...but there is also a possibility of some lowland areas....particularly southeast of the Olympics picking up some of the white stuff.  A front is approaching the coast right now and an associated low center will be off the Olympic Peninsula around dinnertime tomorrow (see graphic of sea level pressure and lower-atmospheric temperatures below).  Temperatures will be a bit too warm for snow in most of the lowlands, where rain showers will be observed, except for where the precipitation is heavy enough to push the snow level to the surface. This kind of pattern produces strong southeasterly flow approaching the Olympics, resulting in upslope flow strong enough to enhance precipitation rates and more upslope cooling...the result:  snow.

 Here is the 24 h snow totals ending 4 PM tomorrow (Tuesday) and 4 PM Wednesday from the UW high-res model.  LOTS of snow over the Olympics and its SE side, particularly the second day.  Big snow dumps over the Cascades.   Even the lowlands could see a few snow bursts during heavier precipitation bands....but it probably won't be much.  Eastern slopes of the Cascades will also get substantial amounts due to easterly upslope on that side of the mountains.


The problem with this situation is that we have very marginal air for snow (not really cold enough near sea level) on the western side, with good onshore flow.  No real push of cold air from southern BC.

And now the thank you.   I am extraordinarily thankful to a number of you have contributed to my research fund (link upper right in this blog).  I have used some of the contributions to maintain and develop the high resolution weather prediction that I show so often in this blog (including the new ultra-high 4/3 km resolution). A portion of the gifts are also being used as an undergraduate research scholarship, to aid some of our most promising undergraduates in  paying for tuition.  As undergraduate adviser I have sensitive to the increasing debt loan and multiple jobs many of the undergraduates are burdened with--particularly as tuition goes up 20% a year.    I have decided to award the first scholarship of $2000 to Steven Brey, shown below, a very promising junior in our program. Congratulations Stephen!  This scholarship could not have happened with the support of the readers of this blog.  Hopefully, I will be able to do this again.

 

 Finally, the depressing part of the blog.  The Seattle Times opinion and editorial staff have consistently provided misinformation to the public regarding public education issues and today was no different.  The main opinion headline in the Seattle Times was:

In this story they claimed that a 6-month old program to improve attendance (like offering prizes and pizza parties!) was working, causing public-school absentee rates to be nearly halved.  And they provide as proof a figure showing monthly absentee rates for this and  previous years:



This is entirely wacky!  The program started in Sept 2011.   You will notice that the absentee rates for this Sept through January are virtually the same as the last TWO years. For some reason, 2008-2009 was a bit higher--but that is not an issue here.  So other than this February there is ABSOLUTELY no evidence that the new program is doing anything.  Where in the world did they get that the rate was cut in half?    But it is worse than that.  Strangely, they show the absentee rate for February...a month that is not over yet...and that is their best month yet.  Is there a reason other than pizza parties and home checks that might explain this?  YOU BET!  As news headlines have attested, this is one of the quietest flu seasons on record.  A lot less kids are getting sick.  To illustrate this, here are the flu stats from King County:

Note that this year (2011-2012, red line) is by far the most benign flu year of all, and the difference with the other years is increasing.  I suspect that is the major contributor to less absenteeism.  Quite possibly, the next ST editorial will talk about how pizza and ice cream parties reduce flu outbreaks in the region.   

This would all be funny if it wasn't so embarrassing for our main local paper.  And this is not isolated incident.  Recently, the ST opinion page pushed charter schools, saying that 17% of them showed improved performance compared to regular schools.   What they didn't tell you was that 37% had WORSE performance than regular schools and the rest were no better.  Talking about deceiving with statistics. And of course there was their bogus front page headline and editorial about the UW rejecting great straight-A students to get a lot of out of state cash.  That was the one that got me kicked off of KUOW for daring to mention the true situation on-air. 

One wonders when the Blethen family, which controls the Seattle Times, will intervene to stop a disgraceful situation at this previously proud newspaper.

PS:  Last call if anyone wants to go to the NW Weather Workshop...see information on the right.

Saturday, February 25, 2012

Puget Sound Convergence Zone Snow (Updated)

We have a fairly strong convergence zone going on this morning, with a moderate precipitation rate, plus much colder air over us--the result has been some light snow, particularly places that have a little elevation.

Here is the latest radar (8:30 AM)....in fact, we have two convergence zones right now...one in the lee of the Olympics and the other in the lee of the mountains of Vancouver Island.


The latest Seattle Profiler data shows the decline of the freezing level to roughly 1500 ft, and thus the snow level to 500 ft (or even a bit lower in heavier precipitation.

This is virtual temperatures, subtract about 1 degree for regular temperature.
A few pictures;





 There are reports of 3-5 inches in Woodinville and Duvall.  This morning I saw a car with 2-3 inches on it, coming down from the north.

Little of this snow is sticking on highways since the road surface temps are pretty warm, but the air temperatures are falling to freezing where the precip intensities are large enough to drive the freezing level to the surface. 
Why does falling precipitation cool down the air below?  First, there is evaporation (like when you get out of the shower), but that ends quickly as the air layer below becomes saturated.  Then there is melting, which draws heat out of the air below and cools it.  More intensity of precipitation provides more melting and cooling. 

The effects of the precipitation cooling are  shown by the latest Seattle SNOWWATCH surface temperature map.  The square boxes show roadway temperatures (36 in bothel, 42 near southcenter).  No worries about travel.

The latest forecast model runs suggest less of a chance for significant lowland snow tomorrow.  However, the mountains are getting hit hard today.  About a foot since yesterday and there will be closures for avalanche work.

Reminder:  The NW Weather Workshop starts next Friday and it open to all.  See information and link on right hand panel.

Thursday, February 23, 2012

Lowland Snow Showers, Cold Air, and Strong Winds

 Extra:  If you would like to listen to my discussion of this weekend's weather on KPLU, check out:
http://www.kplu.org/post/snow-looking-likely-sunday-only-dusting-most

A lot of action coming up, including a good chance that some lowland folks will spot a few snowflakes. (Note to TV stations:  no big lowland snowstorms!!)

A strong Pacific front is approaching us now, behind which there is some cold air.   Here is the forecast for tomorrow afternoon of sea level pressure, near surface winds, and lower atmosphere temperatures---you can see a very nice windshift with the front.


This pattern will produce strong SE winds over NW Washington--something that often happens BEFORE the front passes through.

As the front moves through, not only does cold air follow (blues and whites), but an intense pressure gradient develops over the region. 


 The result will be a strong westerly surge through the Strait with sustained winds of 40 kts with higher gusts.   These winds are headed toward Everett and Mukilteo---yes, my favorite seafood restaurant...Ivar's Mukilteo Landing..is in the cross hairs.  THIS TIME THEY BETTER SCREW DOWN THE LATCH ON THAT HATCH! 

A convergence zone will then set up, but at this point the air is still a bit warm for surface snow....except if the zone really revs up and pushes the snow level to the surface.  Lots of snow in the mountains of course.   But then its get interesting...or I should say MORE interesting.  The models are taking a second trough southward over us and a surface low follows (see figures)



 This is getting awfully close to the canonical snow pattern and in fact the models are indicating some light lowland snow in places (see graphic of 24 h snow ending 4 PM Sunday).  NE flow will also push out of the Fraser on Sunday...so Bellingham will get quite cold.

We don't have much skill in getting the exact distributions of the snow in such a case and the temperatures are a bit marginal.  Considerable uncertainty in distribution and amounts over the lowlands.  But some of you will see the white stuff at or near sea level.  And protect delicate plants and animals on Monday morning...it will be chilly.

The Spada Lake Anomaly

There is a precipitation anomaly around here that is rarely discussed.
In many ways, it is the anti-Sequim, anti-rainshadow.
A place of extraordinary precipitation near Puget Sound.

I am talking about the Spada Lake anomaly.

Spada Lake
 Let us begin by talking about the mountain foothills, east and northeast of Everett, much of it in the Sultan River watershed.  On the map below,  Spada Lake is labeled and the red A is at Verlot.

Spada Lake is circled
During the 48 hrs ending Wednesday at 8 AM, Spada Lake got over TEN inches of rain (10.47 inches)--no other regional station was close.  On average, the surrounding Sultan River basin gets about 165 inches a year--almost identical to the Olympic Peninsula Hoh rain forest!  And consider the typical annual precipitation of nearby locations on the Mountain Loop Highway:

Verlot Ranger Station (elevation 980 ft):  135.5 inches
Big Four Ice Caves (elevation 1750 ft):  142.5 inches

Here are some gee-whiz numbers for Spada Lake precipitation:
Peak annual - 224 inches (1990-91)
Highest Month – 51 inches (November, 1990)
Wettest Day – 13 inches  (November 11, 1990)

Folks, this is a REALLY wet place.  In contrast, nearby Everett, gets only about 37 inches a year.  The city of Everett has a reservoir there and let me assure you, they don't have a problem of lack of water.  And will not have one under any imaginable circumstance.  Official precipitation maps (see below) suggest the effect (although this map has its issue).
A wet region extends from Spada Lake up through Verlot and beyond to Mt. Baker.  Why?  Take a look at the larger terrain map of the region (below)    You notice the Cascades takes a cant to the left from Everett northward.   Strong southerly to southwesterly flow, which is very prevalent around here in winter, moves up Puget Sound and then slams into this blocking terrain.   This forces the air to rise, which leads to clouds and precipitation.  Mount Baker enjoys some of this effect, and that explains why it holds the record for more annual snowfall of any location in the world.  As in real estate, location is everything.


 Although the winds were westerly and northwesterly at higher levels, southwesterly winds WERE observed during that period.   To illustrate this, here are the winds from the Seattle profiler during 24-h of the events:

 PS:  For the lowland snow lovers in the crowd, there appears to be an enhanced chance of some light snow in some lowland locations on Sunday.....more on that tomorrow.  No big storm though. And the long-term pattern is excellent for mountain snows... classic La Nina year late season snowfall!  Don't put your skis away!

Tuesday, February 21, 2012

Heavy Rain, Avalanches, and Reduced Threat of Lowland Snow

While central and western Puget Sound experienced a nearly rain-free day, very heavy rain has struck the western slopes of the Cascades.    Take a look at the current upper level pattern (see below)--one with a broad ridge over the eastern Pacific and you might think

that nothing much is happening, but such a ridge brings warmer temperatures and strong westerly/northwesterly winds the produce heavy precipitation as they rise on the western slopes of the Olympics and Cascades.  Many such windward locations have had 2-4 inches over the past day, with Spada Lake, northeast of Everett, receiving 5.9 inches in the 24h ending 4 PM today.  Here is the 48-h precipitation from the UW/Seattle Rainwatch system.  Huge amounts, over four inches along the slopes, while practically nothing fell to the SE of the Olympics.  This is a profound rainshadow...the one that usually is over Sequim during southwesterly flow.
Take a look at the precipitation for the last 24h.  A range from .01 inch near Hood Canal to 4.57 inches NW of Everett.  Precipitation was actually lighter over the Cascade crest and then declined to virtually nothing on the eastern slopes of the Cascades.


The snow level has risen to the passes and the effects of heavy rain on the huge snowfall of the past week has set off avalanches, producing EXTREME avalanche danger above 4000 ft.  I repeat extreme.  SR2 and I90 have periodically been closed due to this threat, and in fact Stevens is now closed for the evening.  Such heavy rainfall has resulted in the NWS putting out flood warnings for the Snoqualmie and Tolt Rivers draining the central Cascades, plus the Stillaguamish, Skykomish, and others.

The regional models have indicated this threat for a while; here is the 48h precipitation from a WRF run (our very highest, 1.3 km grid spacing) begun 4 AM on Monday.  Reds indicate over five inches!  And mamma mia...that is quite a rainshadow!

 During the next few days the mountains will get hammered with snow, with the central to northern Cascades getting many more feet.   But what about the lowland snow that folks have been talking about?

The truth is that it is getting less likely, the reason being that the trough over the Pacific is coming in from too westerly a position...not from the NW as associated with most lowland snowstorms in our area.  Here is the latest 72 h upper level forecast (500 hPa).  Not ideal.
It will get cold over the weekend, but a major lowland snow event does not look likely.  Of course, we should watch the situation....

Let me end with some good dog news...no my little dog Leah is still lost in Mountlake Terrace, Brier, and northern LF Park.  But a little beagle named Chunky has been found in the arboretum after being lost for two weeks, after a large effort by Chunky's owners, missingpetpartnership, and others.  We can only hope that someone will see Leah one day...
Chunky...back home again.
Leah--still alive and being spotted.
Remember:  The NW Weather Workshop in Seattle on March 2-3.   See information on the right panel.

Sunday, February 19, 2012

Chance of Lowland Snow Next Weekend?

I have gotten about a dozen emails the last few days asking about the potential for snow next weekend.  I am going to break my normal "120 hr rule" (don't talk about forecasts for more than 5 days out because uncertainty is so large).  Yes, the forecast patterns from a number of major modeling systems have produced configurations in the neighborhood of what might produce snow...but to get lowland snow you need to be more than in the neighborhood...details are everything.

First, lets consider climatology.  January is the the month with the greatest snowfall over the NW lowlands, but we still can get significant snow in February (like last year!).  The snow season really is over after the first in March...although we have gotten some light amounts that rapidly melted into April.   Here is the average and extreme snow amounts for Seattle-Tacoma Airport to illustrate.  There has been a few events the first week of March for some reason.  In two weeks, the chance are we can move on to other things...like killing moss in our lawns. 



The classic snow pattern is associated with a big ridge over the eastern Pacific and a sharp trough moving southeastward down the coast.  Here is an example:

Will this happen?

Lets start with the upper level charts from the gold standard of the long-range prediction models--the European Center (ECMWF) global model--for Sunday and Monday.  The left panels show the ensemble forecast means and the right the single high-res deterministic run (both at 500 hPa).  Remember, ensemble prediction is based on making many forecast simulations, with mean of the ensemble members tending to be more skillful than any particular forecast.


You see we are in the "neighborhood" but the color shading (which indicates the differences amount the model runs used in the ensembles) indicates considerable uncertainty.

Here is the UW WRF output for early Saturday (remember the UW model is driven by the National Weather Service GFS model).  Close, but not quite perfect (a little too much over the water).

Here is the average of the NWS GFS ensemble for 500 hPa and the variability amount the members (shading).  Lots of variability and thus uncertainty, but the general pattern is close enough to worry
 Another way of looking at the uncertainty is using "spaghetti" diagrams, in which we show two height lines from each ensemble member.  Here is the staring point of today's ensemble run:  the members are almost identical...but not quite!

 Here is the120 hour forecast.  Now you see why we call it a spaghetti diagram.  Lots of differences in the position and amplitude of that trough!


The bottom line:  there is a good chance we will get colder at the end of the week but we must wait a few days to have a good idea what will happen.  I expect the mountains to do well.   Lowland snow is a possibility, but far, far from certain.  Local DOTs should stock up on salt/deicer and make sure their drivers are well rested. Stay tuned.

And  a reminder that next Friday and Saturday is the NW Weather Workshop...you can still register.  See information on the right of this blog.  You will never see so many local meteorologists and weather fans in one room.  We would be one excited group if it were snowing outside during the meeting.

PS:  There has been 2-3 feet in the Cascades during the past day, with the heaviest snows downstream of the convergence zone last night. Here is the 48 hr precipitation from Rainwatch..multiply by ten to roughly get the snowfall totals (you can't believe the total over the mountains, but you get the idea)

 Major avalanche risk and several people have apparently died in avalanches today in backcountry areas.  Extreme caution is advised.

Friday, February 17, 2012

Big Winds in the Morning (updated)

A strong low pressure center is going to move across northern Washington tomorrow (Sat) morning and the winds will be very strong...there will certainly be some power outages.  In the infrared satellite this evening you can clearly see the swirl of clouds with this low:


 Here is the surface chart for 10 AM tomorrow--nice low center right in the sweet spot for Puget Sound winds.  Very like pressure gradient south and southwest of the low.  Gust over the water to 50-60 mph are quite possible.


And here is the 4-km WRF model wind predictions for 8 AM.   Very strong winds along the coast, and over the waters of NW Washington and Puget Sound.

This low is going to kick up strong waves and swell--reaching 25-30 ft.  Here is the latest WaveWatch III wave prediction from the NWS:

 Saturday morning would be a good one to watch the waves along the coast...assuming you aren't blown away by the very strong winds.

Here are the significant wave observations as of 9 AM Saturday morning for a buoy off the Olympic Peninsula coast....the forecast is verifying.