Sunday, January 22, 2017

Weather Conference Scares Away Bad Weather

The bad weather gods are running away in terror as thousands of meteorologists descend on Seattle.

From Monday through Thursday, the annual meeting of the American Meteorological Society will take place in Seattle and they will enjoy nearly perfect weather.  Dry and  temperatures reaching the upper 40s F each day.

It is fortunate that the meeting wasn't in San Francisco, Los Angeles, or California...locations that will continue to experience rain, wind, and mountain snows.

The infrared satellite image on Sunday night tells the story (below), with a deep low pressure area (swirling clouds) off of Oregon.  Cold instability showers are circling around into California.  During the next few days the low center will move southward, leaving a ridge of high pressure over our region.  Dry and relatively warm conditions will dominate.


Here is the upper level weather map for Thursday morning.   The ridge is evident, as is the trough of lower pressure over the hapless folks in California.


The precipitation forecast for the next 72hr indicates nothing over most of WA state, but substantial precipitation over northern CA.

And the forecasts provided by weather.com for Seattle indicate only a slight change of precipitation and temperatures reaching near 50F by the end of the week.  Add this weather to the later sunsets (after 5 PM!), will make it seem springlike in the city.


With warmer temperatures and dry conditions, little new snow is expected in the mountains.  There were a few inches of snow during the past 24h, which helps covers the ice layer produced by freezing rain this week in the lower passes.

Friday, January 20, 2017

California's Drought is Over

After a period of intense precipitation, with more on the way, it is clear that California's multi-year drought it over.

Let's begin with the percentage of normal precipitation for the last two months (below).  Nearly the entire state is above normal, with many of the mountain areas receiving 200-400% of normal.
Soil moisture measured by the GRACE satellite?   Above normal (blue colors)!

Streamflow?  Nearly all the state is above normal, with most of it much above normal.
Snowpack in the Sierra?  WAY above normal...nearly 200%

The famous Palmer Drought Index?  Most of the state is well above normal...extremely wet.


California reservoir levels?   Total reservoir storage is above normal....and remember California has multi-year storage capacity (see below)


Strangely enough, the official U.S. drought monitor (see below) suggests that half of the state is still in drought, with nearly quarter of the area in extreme drought.  Does not seem to fit the observations.


This drought monitor has a history of exaggerating drought or not dropping drought fast enough--so the current situation is not unusual.   A few small reservoirs in southern California are still low (like the Cachuma reservoir that supplies Santa Barbara).   And the water table in the Central Valley has been dropping for decades---but that is mainly from the "mining" of ancient water to irrigate the vast and expanded agriculture of the central valley of CA.

So by any reasonable measure (rainfall, snowpack, soil moisture, reservoir level), the CA drought of the past few years is over.  Furthermore, the latest model forecasts suggest ALL of California is going to be hammered with precipitation during the next three days (see 72h total below), with 3-10 inches along the coast and in the Sierra.


In fact, heavy rain has hit the last dry area of the state:  southern CA, resulting in flooding and mudslides.  The map below shows the amounts over the past 48h--some locations received more than 4 inches.


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Want some free weather fun on Sunday?  Go to the American Meteorological Society WeatherFest (see information here and below)



Wednesday, January 18, 2017

Major Freezing Rain Event Across the Region

Interstate 90 is now closed in both directions and will be closed at least until tomorrow.

Interstate I-84 is now closed both ways in the Gorge.

The reason?  A major regional ice storm in the Cascades Passes, the Columbia Gorge and in portions of the Columbia Basin.   

Freezing rain has resulted in several inches of ice on roadways, trees, and powerlines.  Some pictures  below show the story.  First, several around I-90 provided by the Washington State Department of Transportation.


 Scenes in the Columbia Gorge were equally dramatic (here is one taken by Patrick Oldright outside the Vista House in the Columbia Gorge)


The meteorological set-up was classic.

We started with a layer of subfreezing air east of the Cascade crest and an offshore directed pressure gradient (higher pressure to the east).  This pressure difference pushed cold air into the Cascade passes and through the Columbia Gorge.

Then a warm, wet Pacific frontal system approached, producing an above freezing layer aloft and rain that fell into the cold layer near the surface (see schematic).  Even when cooled below freezing the falling rain (comprised of supercooled water) did not freeze until it hit the ground.

Freezing rain also fell in the Columbia Basin today, as rain fell into the cold air that was trapped in the lower elevations of the Basin.

The Columbia Gorge and Portland are well known for freezing rain, which is sometimes called the "Silver Thaw".   Ditto for the Columbia Basin.
A map of the climatology of freezing rain over the U.S. below shows that eastern WA and the passes to its west experience freezing rain more frequently than any other region in the western U.S. (2-4 events a year on average).  Freezing rain is

even more frequent over the central and NE U.S., but the origin is very different: generally associated with warm fronts, with warm rain above the front  falling into cold air below.

With the atmosphere warming above and the reduction in the offshore flow as the cold air is mixed out to our east, the threat of freezing rain is rapidly diminishing in the passes.

Monday, January 16, 2017

Major Transition to Warmer and Wetter

It is about time.    A major transition in the atmospheric circulation is occurring over the eastern Pacific that will lead to much warmer and wetter conditions over the Northwest.

Eastern Washington will get out of the endless deep freeze.

Portland will finally warm up enough to rid itself of the icy roadways that have has made driving like a segment of Ice Road Truckers.

Western WA will lose the blue skies and bright sunshine that has been so pleasant for suffers of Seasonal Affective Disorder.

And tragically, Cascade skiers, particularly on the lower slopes, will give up powder conditions for the familiar Cascade Concrete.

Will the History Channel film a segment in Portland?

And there is a major threat tomorrow and in the Columbia Gorge:  an ice storm from freezing rain.

The origin of our unusual cold has been persistent high pressure east of the Cascades that has brought cool, dry easterly flow over much of the region.  A disturbance going south of that high gave Oregon the snow earlier this week.

To show you the changes, here are upper level (500 hPa) maps that illustrate the change.  In the first (for 4 AM Monday), an upper-level ridge is right over us, resulting in dry weather over the region.

In contrast, by 8 AM on Wednesday, the ridge is far east of us, a trough has developed over the eastern Pacific, and moist, warm southwesterly flow is over our region.
The map for 4 AM Friday is amazing...a nearly strait jet stream is directed towards southern California (remember, winds are parallel to the height lines and the wind speed is proportional to the gradient of the height lines).

A HUGE change is going to occur over eastern WA and Oregon, which has been locked in the freezer for weeks.  To illustrate, here are the temperatures at Pasco for the past four weeks (yellow lines), with the normal highs and lows indicated by the red and blue lines.  For virtually all of 2017, Pasco has been well below normal, with the highs on most days not even reaching the normal minima, and a number of hours below zero F.
Another way to see how extreme things have been..here is the deviation of the average minimum temperature from normal for the past month over our region.  From the Cascade crest eastward to the Rockies and beyond, some areas have had minimum temperature 15F below normal or more...virtually all  of that region is a least 9F below normal.  Stunning.


But all this is going to change... in fact, is changing.  Here are the predicted surface (2-m) air temperatures from the European Center model, valid for Hanford, Washington.  A major warming is predicted over the next two days.  Temperatures in the 30sF will feel like spring for the those chilled folks in the Columbia Basin.


What about Seattle and Portland?  The forecasts will warm your heart and your extremities.  Portland temperatures will climb into the forties on Tuesday, as will Seattle's.



Seattle is already in the mid-40s and it feels so mild.

And did I mention precipitation?   We are going to be very wet for the next few days, with the latest high-resolution WRF run suggesting that over the next 72 h as much as 5-10 inches of liquid precipitation will fall in the mountains--most of the that will be rain, except for the higher elevations of the Olympics and north Cascades.


And now we must talk about a problem:  a real threat of freezing rain in Portland on Tuesday during the transition.   It will take a day or two to scour all the cold air east of the Cascade crest and during the interim, some of which will move eastward into the Columbia Gorge towards Portland.  Warm rain from below will drop into this cold air and be chilled, resulting in freezing rain that will freeze on contact.    The NWS has an ice storm warning out for the Columbia Gorge region and Portland.

Over the next 7 days, the National GFS model forecasts suggest a LOT of precipitation along the West Coast (see below), with 5-10 inches being common over West Coast terrain.  As I will describe in a future blog, the West Coast drought is history.  Good for veggie prices next year.

The sun has been nice, but it is time to get back to normal for a while.

Saturday, January 14, 2017

Portland Fails To Clear Snow and Ice: Seattle SDOT Comes to the Rescue

After a major snow event earlier this week, with 6-15 inches over metropolitan Portland, primary and secondary roads are still in bad shape around Portland.  A few ODOT cam shots illustrate what I mean (click on them to expand):



It appears that the Portland road folks (PBOT), have followed the ineffective snow removal approach of Seattle's past mayor Greg Nickels, who lost his job because Seattle was unnecessarily crippled for over a week by impassable, rutted roads covered with ice.   Specifically, they did little pre-treatment before the storm and importantly did not use salt.   And Portland did not have enough equipment (only five decing trucks for example) and had to appeal to Seattle for help.

Seattle learned the hard way in 2008 that salt is really useful, particularly as a pre-treatment of roadway surfaces.  It can melt light snowfalls and prevents the development of a bonded ice layer for heavier snow...thus, making it easier to plow off.  If you want to view a very amusing analysis of the impacts of Seattle's reluctance to use salt and the positive effects of applying it, check out these videos by the "salt guru."



After the 2008 debacle, which probably cost Seattle tens or hundreds of millions of dollars in damage and lost economic productivity, a new mayor (McGinn) oversaw a radical change in Seattle snow practices,  using salt, aggressive pretreatment, acquisition of lots of equipment (e.g., plows, spreaders), changed removal practices (using metal tipped plows, pushing snow to the side of the road), putting in roadway temperature sensors, and working with the UW to build SnowWatch, the most advanced local snow/temperature guidance in the nation.   Mayor Murray has continued these investments.

The results of Seattle's new snow preparation approaches were dramatic, with subsequent snow events having far less impact.

During the past few days, Seattle has sent massive amounts of snow removal equipment to Portland (a dozen heavy salt-spreading trucks and plows, an aerial lift truck, a chainsaw crew and wood chipper truck, along with an additional four light duty salt and plow vehicles.)  Seattle residents can be proud of this assistance...but in some sense it was too late:  without sufficient pretreatment with salt or other deicers, the ice layer had bonded to the surface already, making it nearly impossible to remove.


This idea of regional assistance is a powerful one:   it is very, very unusual for BOTH Seattle and Portland to get major snowstorms at the same time.  Thus, it makes sense to have a regional pool of pretreatment vehicles and plows that could be moved around as needed.

Portland's Mayor Wheeler and his staff at SBOT need to understand Portland's meteorology:   the cold air gap flow coming out of the Columbia Gorge makes Portland particularly vulnerable to roadway icing from freezing rain and partially melted snow.  It is time for Portland to rethink is approach to dealing with roads and snow, or Wheeler might experience the unfortunate fate of Greg Nickels.

Scenes like this in Seattle in December 2008 show 
the costs of poor snow removal

Thursday, January 12, 2017

High Resolution Satellite Imagery of Washington/Oregon Snow

Today's high resolution imagery from the NASA MODIS satellite (below) shows a snowy region, since there are practically no clouds  to obscure the view over most of the domain.


A NOAA snow depth analysis is found below (which is not perfect, but useful).  Eastern Washington is completely snowed in and snow covers NE Oregon (except the immediate coast) and southwest Washington, as far north as Chehalis.

 

With some strong winds in Grant County on Tuesday/Wednesday, the snow drifted--in some locations up to eight feet high.  Here is an amazing image from the Grant County Sheriff's Office....more of a tunnel than a road.

With all the recent snow, the snowpack in Oregon is WAY above normal (see below), with much of the region with 130-140% percent of normal.  Some of the coastal mountains over NW Oregon are 3900% of normal.  Washington, other than the southern Cascades, is near normal.


Obviously, this healthy snow pack, coupled with excellent reservoir levels bodes well for water resources and reduced fire potential during next summer.

Wednesday, January 11, 2017

Major Snow Bust Around Portland

Although weather forecasts are immeasurably better today than even a decade ago, occasionally we still have major forecast failures (or "busts" as they are known in the field).  And no prediction is more difficult than lowland snow forecasts west of the Cascade crest.

Picture courtesy of Justin Sharp

On Tuesday, National Weather Service forecasts were consistent with model predictions, suggesting 1-4 inches in the Portland Metro area.    The reality, unfortunately, was very different:  as much as 12-14 inches in some locations.   The snow totals provided by the Portland Weather Service Office shows the story (see below), with a broad swath  of heavy snow from Salem, Oregon to Vancouver, Wa.  The eastern side of Portland got particularly hard hit.


The snow was associated with a low pressure system that crossed the southern Oregon coast and headed eastward VERY SLOWLY south of Portland.   To illustrate this, below is a short-term forecast map for 10 PM Wednesday, showing sea level pressure (solid lines), lower tropospheric temperatures (shading), and near surface winds (barbs).  With the low south of Portland, cold air moves into the northern Willamette Valley from the north and through the Columbia Gorge. Furthermore, there was a zone of confluent flow just north of the low (called a deformation zone), which produces a band of upward motion and precipitation.  It was a combination of cold and upward motion that produced the snow.


A radar image at 5:30 AM Wed. morning shows the modest precipitation with this low and the center of the circulation (curved radar echoes) between Salem and Portland.


Forecast models indicated snow, but nearly enough over Portland.  Here is the 24hr snow total forecast ending 4 PM Wednesday for the forecast started at 4 PM Monday. A few inches over Portland, but much more to its west and southeast.

Modest errors in the structure, position, and movement of the low pressure area and the associated deformation zone resulted in this forecast error.  

And even the ensemble forecasts (running the models many times) had difficulty with this prediction.  For example, the NWS SREF forecast initialized at 1 AM Tuesday for snow accumulation at Portland Airport (which got around 7 inches) showed a lot of uncertainty, with totals ranging from zero to 8 inches and an ensemble average of 1.5 inches. 


These ensemble forecasts indicated a possibility of heavy snow, but suggested it was improbable.

Can we do better in such a difficult event?   I believe so.  But a big issue is that the system came off the Pacific Ocean, where we have less near-surface information.   A coastal radar, such as the one recently placed on the Washington coast (the Langley Hill radar), would undoubtedly have helped the short-term forecast (0-12 hr), allowing folks more time to prepare.  Improvements in our models and how we use observations (data assimilation) could also have helped.

Folks in Oregon need to tell their political leadership that placing a powerful weather radar on the central Oregon coast is important and requires priority.  Quite honestly, it could pay for itself many times over in even one storm like this.

The Oregon Coast Needs One of These!

Northwest Weather Workshop

The Northwest Weather Workshop, the region's main gathering to discuss all aspects of Northwest weather, will take place on March 3-4, 2017 in Seattle at NOAA Sand Point.  There will be a special session of communicating forecast uncertainty during the first day.  More information on the meeting, as well as registration details, are  found at: https://www.atmos.washington.edu/pnww/

If you are interested in giving a talk at the meeting, please send me a title and short abstract by February 1.