Saturday, November 22, 2014

When sun in Seattle is good sign for snow in the Cascades

Life has its seeming contradictions.

There was some nice sun in Seattle this afternoon and that was ironically a good sign for mountain snow lovers.   How could that be true?

First, the sun...here are a few cam shots Saturday afternoon..one looking at Seattle from Queen Anne and the other from the UW.



There were even blue skies, particularly over the Sound and the Kitsap Peninsula...a visible satellite image around the same time confirms this:

But at the same time, it was completely cloudy over the Cascades and the Olympics, with snow falling from roughly 3500 ft and above.  As proof, here are some cam shots at Crystal Mountain and Stevens.



Is there a connection between Seattle sun and Stevens/Crystal snow?  
You bet there is.

After the front went through Friday night the winds aloft turned from southerly and southwesterly to westerly and northwesterly.   I can show this change from the winds above Seattle-Tacoma Airport shown in the following image.  The winds are shown by the pennants and temperatures are in red. The vertical axis is pressure (850 hPa is about 5000 ft, 700 hPa about 10,000 ft.  The x-axis is time in UTC (22/06 is 10 PM Friday night). The front was associated with a wind shift and the rapid decline in temperatures aloft.


The Cascades are oriented roughly north-south and thus westerly winds (from the west) are forced to rise on  the mountains sharply since the winds are directly right up the height gradient.  That rising motion produces cooling and saturation, resulting in clouds and precipitation, and in this case snow! Southerly winds do not ascend the mountain much.

When air goes DOWN \terrain it warms, dries and clouds dissipate.  For westerly or northwesterly flow, like we had this afternoon, the air rises on the Olympics (producing clouds and precipitation on the western side of those mountains), but sinks on the eastern side of the Olympics, producing clearing skies west of and over the Sound.   The westerly flow then rises again on the Olympics giving snow.

You seen this happening in a recent weather radar image.  Dry over Puget Sound, but lots of precipitation on the western slopes and crest of the Cascades.


So Seattle's clearing is a good indication of strong westerly flow and thus good potential for snow in the Cascades  if the air is cold enough.

I know...you want to know how much snow will fall before Thanksgiving.  Here is the predicted total snow for the 72 h starting 4 AM today (Saturday). 1-2 feet in some locations of the central and northern Cascades.  I am pretty sure there won't be enough for Snoqualmie, but perhaps for Stevens, Baker, and Crystal.  But it will be close.

..........................................................
And if any of you would like to read about on snow in mountains, there is a very good book on mountain snow that has just come out:

Secrets of the Greatest Snow on Earth: Weather, Climate Change, and Finding Deep Powder in Utah's Wasatch Mountains and around the World




This is written by a colleague of mine (and a graduate of my department) Professor Jim Steenburgh of University of Utah.  This book not only explains why Utah's mountains enjoy such good snow, but describes the mechanisms of mountain snow, avalanches, and many other general snow topics. And there are lots of marvelous pictures.  Jim is an expert in mountain meteorology, is crazy about mountain snow, and has spent an extraordinary amount of time skiing.

Ordering information:

Barnes and Noble (paperback and nook): http://www.barnesandnoble.com/w/secrets-of-the-greatest-snow-on-earth-jim-steenburgh/1119400829?ean=9780874219500

Utah State University Press (paperback and e-book): http://www.usupress.com/book/_welcome_usup/9500

Amazon.com
http://www.amazon.com/Secrets-Greatest-Snow-Earth-Mountains/dp/0874219507/

Of course, there is another book that touches on these subjects, but at lesser depth.

Thursday, November 20, 2014

Normal Weather Returns

The past year has brought a lot of unusual weather here in the Northwest.  Fall 2013/ early winter 2014 was extremely dry, then the deluge of mid-Feb to mid March that contributed to the tragic Oso slide.   We had one of the warmest summers/early falls on record.  Then a deluge in late October, followed by a dry, cool pattern the first half of November.  The observed (red) and normal (blue) precipitation since October 1, 2013 at Seattle Tacoma Airport (see below) illustrates our swing between extremes.

Many of these gyrations were associated with amplified upper level wave patterns with ridging associated with dry conditions and a deep east Pacific trough with wet situations.
But the next week offers something different: a typical late November upper-level pattern with a strong jet stream barreling in on the Northwest   Rain and wind in the lowlands, snow in the mountains. Nature simply couldn't help itself in the climatologically most stormy/wet period of the year here in the Northwest.

Here is the jet stream forecast (300 hPa--around 30,000 ft, lines are heights, shading is wind speed)
for Friday at 7 PM and Monday at 4 PM.

Can you see the difference?  On Monday, we had a ridge of high pressure and weak winds aloft over us, while on Friday a strong jet stream--oriented almost east-west--comes right into the southern Oregon coast.   Think of the jet stream as the conduit of storms and rain.  The hose is directed at us.


Let me show you the forecast 24-h totals of precipitation for the next 3 days.  Lots of rain as a progression of systems comes in.   And it doesn't end there.




With the jet stream core south of us, the air will be cool enough to snow at least down to 4000 ft. 

Here is the 72 h snowfall map.  Several feet in the north WA Cascades and its extension up to Whistler.   Whistler will be able to offer decent skiing I suspect.  Snoqualmie will not be able to open.


The extended forecasts suggest a major precipitation event around Tuesday and dry conditions for Thanksgiving, but we can wait on that for a future blog.

My KPLU Radio Segment

I just wanted to remind everyone that I do a weekly weather segment on KPLU radio (88.5 for many of you) at 9 AM every Friday (like tomorrow).  It is also available on their web site (http://www.kplu.org/).   I generally give the weekend weather forecast and talk at depth on some topic.

Tuesday, November 18, 2014

Worst Air Quality in the Nation: Blame the Inversion

We can be proud (I guess) that the Northwest has some of the worst air quality in the nation--or so says the U.S. government's AirNow website:

And, in fact, Puget Sound Clean Air Agency has burn bans on right now in Snohomish and Pierce counties.

The region, strangely enough, is the push of warm air aloft.  The warming has been profound aloft during the past 48h, with the air warming 15-25F in layer starting a few thousand feet above the surface.   At Paradise on Mt. Rainier (5500ft) it has become nearly spring-like, with temps reaching near 50F.
With warming aloft, with cooler air stubbornly holding in at the surface, we have seen the development of a strong inversion (temp increasing with height).  To illustrate, here is the lower atmosphere temperature soundings on Monday morning from 1 AM to 8 AM.  Temperature increased 8C (14.5F)  in 500 meters (roughly 1600 ft) during that time period.
Inversions are very stable layers and tend to trap pollution near the surface.  Here are the particulate observations (PM2.5) for the last week for Seattle Duwamish, Tacoma, Lake Forest Park in N. Seattle, and Marysville in Snohomish County.  The trend is clearly upwards.


You notice that there is a big daily variation in air quality.  Better during the day and gets bad rapidly in the evening--worse around midnight.

A few things contribute to this diurnal (daily) variation.   First, folks come home around dinner time and crank up the heat...which pushes combustion products into the air.  Then around midnight the heat is turned off and air quality improves.  You will see a smaller secondary peak around 6 AM when the heat comes back on for some.   Another issue is meteorology.  Sun during the day warms the earth and causes some mixing in the vertical (like in your cereal pot).  This improves air quality.  At night, with nocturnal surface cooling, the inversion strengthens and air quality degrades.

We will have to deal with degraded air quality for a few days...later this week, the storms, rain, and wind return.

Sunday, November 16, 2014

Skiing this Thanksgiving. Is there any hope?

For Northwest residents thinking of skiing over Thanksgiving in the Cascades, you better be ready with other options. 

The Cascade Mountain snowpack right now is sparse, far worse than last year.  Yes, Thanksgiving downhill skiing is always iffy in our region, but usually there is enough for some cross country fun.   But this year is questionable.  Only places that can make snow (like Whistler) have a decent chance of opening soon.  But there is a glimmer of hope...


Not much snow at the top of Crystal Mountain


.
Paradise Visitor Center on Mt. Rainier.  One of the snowiest places on the planet.  Usually.

In October we had lots of precipitation, but we were also very warm, so that even higher elevations had rain.

Then during the past week we have been very cold, but also very dry except for a band of light snow in northern Oregon a few days ago.

Let's look at the latest snow depth analysis from NOAA.   Here is the snow depth analysis for today (Nov. 16th).    Very little in the Washington Cascades, but some light snow over the northern Oregon Cascades and northeastern Oregon.  Timberline Lodge at Mount Hood, which got a piece of this, only has 9 inches on the ground.  But there is one place that did well during this event:  Mt. Batchelor, with roughly 2 feet.

To give you some perspective on the current situation, here are the snow depth analysis for exactly the same date in 2013, 2012, and 2011.  A LOT MORE in the Washington Cascades.




 We are now close enough to Thanksgiving for our models to have some skill.  But first lets look at the Climate Prediction Center forecasts for the 6-10 day outlook.  Oh, oh...warmer than normal.


Virtually all our models and ensembles suggest a major shift for us.  The cold air is history.   In fact, the air above us has ALREADY warmed a great deal.  At around 5000 ft. it is about 15-20F warmer than yesterday.  Here is the proof--the temperatures at Paradise Mt. Rainier (5500ft) are approaching 40F...about 20 F warmer than yesterday.

Let's take a look at some of the latest model runs.

Here is the upper level map (500 hPa) for today.  Big ridge over the West Coast.  Dry.


By Tuesday at 4 PM, a modest trough undercuts the ridge, to bring clouds and precipitation to northern CA.  But the ridge holds over us.



The precipitation over the next 72h reflects this.  Those poor devils in California need all the precipitation they can get.



Then a series of weak weather disturbances break through later in the week...we get wet, but will be warm.  Not good for snow at ski areas or the passes.
So no snow through Friday.

The only hope is that some of the models are suggesting a major shift late next week, with the jet stream barreling in on us.  Here is the  500 hPa  upper level forecast (solid lines are heights)  for Saturday AM from the U.S. GFS model



and the European Model at 4 PM Saturday for the same level (ensemble forecast on left, high resolution on the right).  Similar idea.


With the jet stream (where the lines are crowded together) somewhat south of us, it would be cool enough to snow in our mountains.  Here is the snowfall prediction from the UW WRF model for the 72 h period ending 4 PM Saturday.   FINALLY, some snow in the Washington Cascades.

A start.

Mt. Batchelor conditions Monday AM.  The best around....

Friday, November 14, 2014

The Other Radar Gap: The Eastern Slopes of the Cascades

For over a decade, a group of Northwest meteorologists and weather-affected groups lobbied incessantly to fill a huge gap in the National Weather Service radar network over  the Washington coast and coastal waters.  With a lot of hard work, the strong support of Senator Cantwell and the rest of the Washington delegation, and the cooperation of the National Weather Service, a powerful radar was installed on September 2011 at Langley Hill, near Hoquiam.  And it has not disappointed, proving its worth on many occasions.


But although filling the coastal radar gap was the first order of business, we knew there was another important hole in National Weather Service radar coverage, on the eastern slopes of Cascades--extending from the crest down to the Okanagan, Wenatchee, Yakima, and Bend.

The NWS radar coverage map shows that western Washington is well covered at low levels, but that there is a distinct gap east of the Cascade crest.  Large gaps are found in eastern Oregon and along the central and southern Oregon coast.  I contacted the Oregon Congressional delegation and they were not interested in dealing with this.


There are two big issues here.  First, the Cascades block the view over the eastern slopes from the west-side radars (e.g., Camano Island, Portland, and Langley Hill).  Second, the east-side radars (Spokane, Pendleton) are too far away, with the radar beams far above the surface by the time they reach the eastern slopes....over 8,000 ft above sea level.


Why do we care about radar coverage east of the Cascade crest?   Here are some good reasons:

1.   There is little coverage of precipitation on the upper eastern slopes of the Cascades, which can be substantial.  This impedes hydrological prediction on eastern slope rivers like the Yakima.

2,  We can't use radars to track the beginning stages of thunderstorms along the eastern slopes.

3.  We can't use radar to get accurate precipitation amounts on the eastern slopes from thunderstorms, which is very important today, with so many unstable burn scar areas.

4.  We can't use the radar to track small to moderate fires (fire plumes do show in radar imagery)

5.  Folks in Yakima, Wenatchee, Winthrop and other eastern slope towns, and the varied agricultural interests in the region, don't have ability to do what we west-siders take for granted...the ability to know where it is raining and what will happen during the next hour.

6.  The Yakima Training Center, an important military facility, lacks radar coverage that would facilitate expensive maneuvers and weapon's testing.

Recently, a group of east-side folks have begun to discuss the eastern-slope radar gap under the leadership of Katherine Rowden and Ronald Miller of the National Weather Service Spokane office. I am hopeful that they and others can organize an effective effort to secure some additional radars to fill the gaps.

Yesterday was a good example of the problem.  A frontal band oriented east-west moved northward over Oregon.   Here is the visible satellite picture at 11:30 AM Thursday.


The 12-h precipitation totals ending about the same time showed precipitation on both sides of the Oregon Cascades (I suspect the larger east side amount of several inches are in error).  In any case, several locations got .5-1 inch on the eastern side of the Oregon Cascades.

Map covering the northern Oregon Cascades.  The Willamette Valley is on the left side.

The Portland radar "storm total" product shows plenty on the western slopes, but way less east of the Cascades...clearly less than observed on the ground.


The problem is even larger looking westward using the Pendleton radar.



I could give  you a dozen other examples of  poor eastern-slope weather radar coverage.  The solution is probably to secure 2 or 3 modest "C" band radars, each with a range of a few hundred km.  This will take substantial resources (perhaps as much as a million dollars ) and funds for maintenance and installation.  But I suspect the cost-benefit analysis for the region would be very favorable and the expenses could be shared by local, state, and Federal entities.   I wish the new group luck in their endeavor.