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.


Tuesday, January 10, 2017

Make U.S. Numerical Weather Prediction Great (Again)

There are many folks in my community (climate and weather scientists) that are apprehensive about the upcoming Trump presidency.  They worry about Trump's unfounded suggestion that climate change is a "Chinese hoax" and his appointments to major office of folks that question the threat of increasing greenhouse gas.  They are concerned, like I am, that Trump might slash U.S. government support of climate change research, the importance of which I described in a previous blog.

Could a bull in a china shop be helpful?

But lets consider an intriguing possibility.   An unconventional Trump administration could choose to do something important and helpful:  restore U.S numerical weather prediction (NWP)  to its rightful place as the best in the world.   And in doing so, immeasurably foster the public safety and economic vitality of the U.S.   And don't forget:  better weather prediction science and technology leads to better climate forecasts.

Trump wants to make American great again.  Fine.  Let him start with a key technology in which the U.S. has unnecessarily fallen behind:  U.S. numerical weather prediction, the central tool for all weather forecasting.   As I will describe below, U.S. NWP development and operations needs a "disruptive" influence that might reorganize an ineffective bureaucratic structure and a bureaucracy that has been content to be second or third best.

Behind and not catching up

In a number of blogs I have documented the inadequacies of U.S. operational numerical weather prediction, with the NOAA/National Weather Service (NWS) having primary responsibility.  First, the U.S. is behind in global weather prediction--lagging both other nations (e.g., the European Center, the British UKMET office) and far behind the inherent capabilities of the U.S.  And with all the talk and investments of the last few years, the U.S. is not catching up (as documented below).

Let me demonstrate this to you with two graphics.  The first shows the skill over the past month of the global forecasts at 500 hPa (about 18,000 ft) for the 6-day forecast for several global modeling systems.  The quantity shown is the anomaly correlation, with 1 being perfect.  The European Center (ECM) is best (.857), followed by the British (UKMET) with .840, the U.S. NWS (.814), and trailed by the Canadians (CMC) and the US Navy (.756).

But here is another way the U.S. (NWS) global prediction is behind--the number of drop-outs, periods of much lower prediction skill.  This plot shows anomaly correlation for 500 hPa for the Northern Hemisphere (20-80N)  five-day forecast during the past year for  the U.S. (GFS model, red) and the European Center model (ECMWF, blue).  ECMWF is nearly always better and you see frequent downward excursions of the U.S. GFS model, sometimes down to very low skill levels.  These are the drop-outs and indicate major loss of skill.  Very bad.


I could have shown you a similar plot two years ago and the story would have been the same.  We are simply not catching up.

For seasonal forecasts (out to 9 months), the NWS is running a seasonal climate model (the CFS) , even though it has no demonstrable skill over statistical methods (I am doing research on this right now).  But there seems little impetus to pull the plug on this non-productive effort or make the radical changes necessary to make seasonal or subseasonal (weeks to a few months) better.

The U.S. is profoundly lagging in other areas of numerical weather prediction as well.  Numerous workshops, reports, and meetings have called for the National Weather Service to run a high-resolution ensemble (many forecasts) over the U.S. to aid forecasting of thunderstorms and smaller scale features. They have not done so, while the research community (NCAR) has an experimental operational system in place.  Nor has the NWS been effective in developing and applying improved model physics (such as the microphysics of clouds) and its statistical post-processing (improving the forecasts with statistics) is based on simple 1960s approaches.
The unphysical mottled appearance of NWS GFS model precipitation forecast over terrain is a sign of a serious error in model physics.  The European Center forecasts do not have this flaw.

There are many other examples of U.S. numerical weather prediction falling behind the inherent capabilities and needs of the nation, but the above examples suffice.   And keep in mind that the U.S. spends more on numerical prediction than anyone else and has the biggest weather research community in the world.

The questions you must be thinking is:  why is the U.S., the past leaders in numerical weather prediction, fallen behind, and how can this be fixed?   

And I will ask another question:

Could folks with a very different perspective and unafraid to break a few eggs (the Trump administration) make some acutely needed changes in U.S. NWP that could set it on a much better course?

The Real Reasons Why U.S. Numerical Weather Prediction (NWP) is Behind

I have studied this question for years, published peer-reviewed articles on the subject, and have served (and am now serving on) advisory committees to the U.S. government and other entities.  I believe I know where the skeletons in the closets are found.  And I am at the point in my career that I can afford to take some risks in the hope of promoting critically needed change.   So here it goes.


Reason Number 1:   Awkward and Ineffective Organization and Bureaucratic Structures

It would be hard to think of an organizational structure that is more problematic than the one used by NOAA/NWS/US government NWP development and research.  The byzantine organizational structure of NOAA and the NWS are found below for reference.


But first a lot of acronyms.  Operational numerical weather prediction (NWP) is found in the Environmental Modeling Center (EMC) of  the NCEP (National Centers for Environmental Prediction), which is part of the National Weather Service (NWS), which is part of the National Oceanographic and Atmospheric Administration (NOAA).

Amazingly, folks with the main responsibility for developing the models are NOT in the NWS, which is responsible for operational NWP, but in NOAA (at the ESRL and GFDL labs).  So the folks who run the weather forecasting models (NCEP EMC) don't have control of the scientists developing the models.

And this has led to a LOT of problems.  For example, the NOAA ESRL folks spent a lot of resources on models that never went operational, antagonism between the model developers and the operational people has been rampant (although better recently), and other issues.  

But it is worse than that.  The decisions on future model use is decided upon by ANOTHER group in the NWS outside of NCEP, called OSTP (Office of Science and Technology Policy).     And the development of the statistical post-processing of model is not done by the modelers or in the same organization doing operational NWP (NCEP's EMS), but another group in OSTP (called MDL).    It is surprising ANYTHING is accomplished in this crazy quilt bureaucracy.

But it is worse than that.  The U.S. Navy runs its own independent global and regional weather prediction effort at FNMOC (Fleet Numerical Meteorology and Oceanographic Center), based on science/technology developed by the Navy's own research arm (MRL Monterey).  A mainly duplicative effort, except for a greater emphasis on the oceans.  And all this is done, even though the Navy's global model's verification scores are consistently inferior to the National Weather Services (see above for proof, FNO is the Navy).   I am amazed Congress hasn't noticed this.

Can it get even worse and wasteful?  You bet.  The US Air Force runs ANOTHER NWP center and they decided to use a foreign model (the UKMET office unified model), rejecting the previous use of the NWS model (GFS) and aregional scale WRF model developed by the academic community (NCAR, the National Center for Atmospheric Research).   This decision was so silly, that anonymous researchers in the US Air Force (AFWA, Air Force Weather Agency, now Detachment 7), made a very funny video about it, suggesting that even Hitler would have been upset about the wacky decision.  So the US Air Force thought the NWS global model was so poor, they had to run a foreign model.  Just stunning.

http://www.captiongenerator.com/37268/Hitler-learns-the-USAF-is-changing-weather-models

In short, huge amounts of U.S. resources have been wasted in funding duplicate national weather prediction entities, with all being suboptimal for state-of-the-science weather prediction.  Combined and organized in a rational way, they could be the best in the world. Separated in this separate efforts, they are seriously lagging behind.

Reason Number 2:  Isolation of Governmental NWP Development from the U.S. Research Community

Numerical weather prediction is perhaps the most complicated technology of our species, with billion dollar satellites, international observing systems, the biggest supercomputers, and complex data assimilation and modeling software encompassing millions of lines of code.  It considers and models physical phenomena from the molecular to the planetary scales.  Only the organized and coherent efforts of the large U.S. research community can push the envelope to limits of our knowledge and technology.

As noted above, U.S. efforts have been divided among many efforts in the Federal government.  But the problem is far more serious than that.  The National Weather Service model development has been isolated from the vast U.S. academic community, and thus U.S. operational prediction has not fully benefited from the research sponsored by Federal Agencies and others. The inability to take advantage of the work of the U.S. research community is sometimes called the "Valley of Death."  A not invented here syndrome has been a major characteristic of NCEP's Environmental Modeling Center.


There are two good examples of NOAA/NWS isolation from the academic community. In the late 1990s, NCEP EMC realized it needed a new regional model to replace the deficient Eta model.  Instead of using the model developed at the National Center for Atmospheric Research (NCAR, an organization of US academic departments in atmospheric sciences) and used by thousands of researchers (WRF, Weather Research and Forecasting Model), they developed their own (NMM), a model that was not only inferior but never used by the academic community.

More recently, the NWS realized it needed to replace its aging GFS global model.  Instead of joining the academic community in using the new, but proven MPAS model developed by NCAR, they decided to acquire a model from a NOAA group (GFDL).  Thus, the isolation continues, with stark implications for U.S. operational prediction.  Only by joining with the academic community can the NWS hope to develop a state-of-science modeling system.

Reason Number 3:  Lack of Strategic Planning

NOAA/NWS numerical weather prediction efforts not only suffer from an inherently poor organizational structure for operations and research, but they have functioned without an actionable strategic plan and specifically one with clear/concrete goals and time tables.  They are working on one now, but I have been worried about its lack of detail.  The NWS has begun to fund extramural research on NWP to a greater degree, a very good thing for which NWS Director Louis Uccellini deserves a lot of credit.  But without strategic and implementation plans and a clear sense of priority, much of this funding is not being used wisely.

Reason Number 4:  Inadequate Computer Resources

Two years ago, the National Weather Service had 1/10th the computer power of the European Center, yet the NWS had far more responsibilities (both global and regional/local modeling) that the European Center.  After outside complaints, Congress and the administrator improved the situation, increasing computer resources to equity with the European Center.  But such computer resources are still woefully inadequate.  Based on my own analysis and that of several committees I have served on, the NWS need 30-50 times more computer power that it has today (total of 100-150 petaflops capacity) to forecast in a state-of-the-art manner, with a huge benefit for the nation.   The cost?  Roughly 100 million dollars, the price of a few fighter jets.  What do you think would benefit U.S. citizens more?  Dropping redundant or ineffective models, would also release computer power (but that is a drop in the bucket to what is needed).  And our local friends are CRAY computer are ready to provide the hardware.


Good People, Mediocre Results

Let me make something clear.  Many of the folks in NOAA/NWS are competent and interested in providing the U.S. with cutting edge numerical weather prediction capabilities.   I know personally many of those in leadership/management positions and most are highly motivated and have the required technical knowledge.  They want to make things better and are taking some steps.  For example, the NOAA/NWS have sponsored a number of reports (by the National Academy of Sciences and McKinsey consultants) and several advisory groups.  Things may get a little better, but the U.S. will still fall further behind because the fundamental issues, many noted above, that are not getting addressed.   Some NOAA management types complain that the real problem are NOAA/NWS unions, who they claim are dragging their feet on change.  As noted above, the real problems are elsewhere.

The U.S. Congress knows that U.S. weather forecasting is lagging, with several hearings on the topic.  In December, Congress came close to passing the Weather Forecasting Improvement and Innovations Act that would have invested hundreds of millions of dollars to fix the problems.   Whoever wrote it meant well, and addressed a few of the issues, but they didn't appreciate the fundamental organizational issues note above.

So What is Needed?

The only way U.S. NWP development and operations will be improved permanently is by a radical restructuring of the governmental forecast enterprise. No single agency or department head has the power to correct the structural and resource deficiencies.   Only the Congress and the Administration can fix it, and they need to be willing to make some tough choices.

Restructuring US NWP will require folks with an intimate knowledge of the relevant technologies, as well as representation of the entire U.S. weather prediction enterprise (government, academic, private sector, users).   If I was the President, I would establish a blue-ribbon committee with such representation to come up with an analysis and concrete plan.  It requires a willingness to prune an overgrown tree, so that the remaining branches can be flourish.  It will require the development of concrete strategic and implementation plans and bringing together of the vast U.S. weather research and development community.

Trump wants to make the U.S. great again....perhaps, such perhaps, his administration might take advantage of their outsider status to make the changes that are so acutely needed to make U.S. weather prediction great again.



_________________________________
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.


Sunday, January 8, 2017

Freezing Rain Hits Portland with a Threat to WA Passes

Temperatures are rapidly warming aloft as a Pacific weather system approaches.    Sounds good for cold-weary NW residents right?  But those located in or downstream of gaps in the Cascades or in particularly cold areas are experiencing something else:  freezing rain that produces surface icing, a real threat for aircraft and those driving.

As a result, Portland International Airport is essentially closed, with nearly all flights cancelled (see below)

A look at the flightware tracker website shows a lot of overflights but virtually none taking off or landing.

Aircraft are taking off and landing at Seattle Tacoma Airport and the time-height cross section of weather observations from aircraft indicate tremendous warming aloft, with temperatures above 8C in the lower atmosphere (heights in pressure, 850 is around 5000 ft, red is temperature in C)

Right now there is an absolutely HUGE difference in pressure across the Cascades, with high pressure to the east.   The value is nearly 16 hPa (mb).... believe me, that is unusual.  Such a pressure difference drives easterly flow... cold, dry easterly flow... at low levels through gaps and passes.  To show this to you, here is a short forecast (for 10 AM today) of sea level pressure, surface winds, and low-level temperatures (blue is cold).  You can see the tongues of colder temperatures and higher pressure extending into gaps and the large pressure gradient across the Cascades.


With cold, below-freezing air, at low levels and warmer air aloft, one gets a set up for freezing rain.   Precipitation starts as snow higher up and then falls into above-freezing air and melts into rain.  But then the rain falls into a below-freezing layer near the surface and cools below freezing, but remains liquid.  This is called supercooling of water.  Then when the supercooled rain hits the cold surface or an aircraft it freezes into ice....freezing rain.  Portland and the western Gorge is particularly susceptible to such freezing rain events because it is downstream of the Columbia Gorge...a near sea level conduit of cold air from eastern WA.

The latest observations at Portland Airport (KPDX) shows several hours of freezing rain.

My colleagues at the National Weather Service in Portland put out an ice storm warming last night (see below)....a good call.

The ice storm/freezing rain should weaken during the afternoon around Portland as the warm air reaches the surface and pressure differences relax,  Will hold on longer in the Columbia Gorge.

Here is a picture of an iced window looking out from the NWS office in Portland.


Further north, the big freezing rain threats are in the Cascade passes, which also supply a conduit of cold air from the east.  At this point, the NWS is mainly going for heavy snow in the Cascades, but I suspect that there is also a major freezing rain threat.

And did I mention winds?   With a huge pressure difference across the Cascades, winds in the Gorge are gusting to 30-50 mph, even higher in exposed location.   For example, Crown Point in the western Gorge, where gusts are exceeding 70 mph! (see below)


And to make things interesting, the Langley Hill weather radar is broken.  Not good.  Anyway, be careful if you around Portland, the Gorge, or the WA Cascade passes.