January 02, 2021

An Intense Front, Strong Winds, Heavy Precipitation, Flooding and Big Waves: The Northwest Will Be Hit By Everything

 Today will offer something for every meteorological taste, except for sunny and warm.

The front page of the National Weather Service's web page is lit up with almost every imaginable meteorological warning and advisory (see below).  High wind warnings, storm warnings, winter weather advisory, high surf advisory,  flood warnings, and more.

And the latest water vapor satellite image shows a very impressive plume of moisture poised to move into our region.  I mean THOUSANDS of miles long.


During the 36-h ending 4 AM Sunday, models are predicting up to 5 inches of liquid water equivalent in the mountains.


And by 4 PM Monday 5-10 inches of water will be widespread.

Considering that we are starting with rivers running quite high (see figure below), some flooding is inevitable.   The blue dots indicate river measuring sites where the flow is ALREADY much above normal.

For example, the Tolt River, draining off the central WA Cascades, is predicted to surge to moderate flood level.


But for me, the big excitement is a very intense cold front that will approach our shores later this afternoon.   This winter we have had several of them, including the one that brought the snow a few weeks ago.  The exciting thing for me is that our models have been capable of realistically simulating and forecasting these amazingly intense features.

To illustrate, here is the super high-resolution forecast by the UW model for 7 PM tonight, showing surface wind gusts (color shading) and surface winds (the wind barbs) along the WA coast.  Look closely and you will see an extraordinary sharp and dramatic wind shift from southwesterly (from the SW) to northwesterly winds.   THAT is the front.


This sharp wind shift is associated with tremendous convergence of air at the surface, forcing intense upward motion and heavy rain, something that the model is simulating (see the simulated radar image below for the same time).  

You see the undulating orange line on the coast?  THAT is the intense rainfall associated with a strong narrow cold frontal rainband, stretches northeastward to north of Everett.

Trust me.  You do NOT want to be outside when that hits.


And let's not forget about wind.  A strong pressure gradient (wind difference over distance) will precede and accompany the front, and many of you will experience winds gusting to 40-50 mph.  The latest NOAA HRRR model forecast of surface gusts at 11 AM this morning shows gusts as high as 50-60 mph
along the coast and over NW Washington, with lesser, but still strong, winds over Puget Sound.
Now let me show you a high-tech wind product we make available to Seattle City Light from the Seattle WindWatch website. (They use the skillful wind forecasts to deal with power outages).  This guidance shows the high-resolution forecasts, the ensemble of many (slightly lower resolution) prediction, and new guidance making use of machine learning for max wind gust over Seattle.  Time is on the x-axis and predicted gust is the y-axis.

The winds will increase during the day and hit a peak during the late afternoon and early evening, plummeting after the front moves through.  Quite a bit of uncertainty, with the highest winds around 50 mph.  Machine learning is knocking the winds down to 30-40 mph, while the high-resolution models going 40-50 mph.
The application of machine learning is a new technology for weather model calibration and we have a lot to "learn" about applying this approach.   With saturated soils, I expect there will be scattered power outages.   In the future, perhaps, we will use machine learning to directly predict the power outages based on preceding and forecast conditions.

Enjoy the active weather.






17 comments:

  1. Thanks, Cliff. I wish everyone well, but this is going to be exciting.

    ReplyDelete
  2. For those who want to follow along with this front, and other winter weather, you can do so using an app called LuckGrib, available for the Mac, iPhone and iPad. LuckGrib provides access to: HRRR, NAM, RAP, NBM, GFS, GEFS, and many more GRIB models. The app allows you to view the data as images, or as a meteogram (along with many other features for sailors.) Cliff, it would be interesting to see your high resolution models in LuckGrib. Are they publicly available?

    ReplyDelete
  3. Thinking about heading out to the coast to drop a couple probes to sample the front with 1-min intervals! Maybe Westport. I also don’t want to miss any strong winds here in Puget Sound however. Tough choices....

    ReplyDelete
  4. I’m glad not to be flying today and tomorrow. Along with the winds, there will be icing in the clouds over the Cascades. Probably going to see a lot of turbulence reports from aircraft coming and going here in the Puget Sound. Bumpy rides!

    ReplyDelete
  5. Just -- "WOW" and "Thanks for the warnings!" Forecasts really matter. Much appreciated.

    ReplyDelete
  6. Suppose to have 20 to 30 mph winds right now, and yet our max gust in the past hour is 7mph.

    I've yet to see a predicted wind storm actually happen here in east auburn/lea hill area. We are at 500ft, on top of a ridge. Should expect some kind of wind? I can see mt rainer, cascade foothills, and olympmic mountains, so defintely up on a ridge, yet no wind...ever, in any of these predicted events.

    We always have our highest winds on days where there's no prediction. This entire year has been like this.

    ReplyDelete
    Replies
    1. Now at 2:30pm we have a high gust of 18mph, still well below the 30 to 40+ we should have. 18mph is the same max we had yesterday...same we have most days that never have a wind storm predicted.

      Quite frustrating that the predicted wind events never materialize for this area. Maybe the ability to predict for the SE king county area needs attention?

      Delete
    2. In most cases the forecast windspeed only occurs in big open fields and it takes high tech instruments to accurately measure it. I live in Renton and my highest wind gust was 11mph but the nearby Sea Tac airport measured a 36 mph gust and I could see the trees swaying alot so I suspect my anemometer doesn't have good exposure. If my yard didn't have any trees or I mounted the anemometer on top of a tree I'd get much higher wind gusts.

      Delete
    3. Proof of my earlier complain is right now. During those Jan 2nd high 30 to 50mph wind predictions, we had a max speed of 18mph.

      Today, with basically no major wind prediction in the forecasts, we had a max wind gust of 19mph already.

      I get that the readings are generally taken in wide open areas at about 30ft above ground level. My issue is the forecast predictions on wind events are literally almost always exact opposite of reality for SE king county area at least. In the past 9 years of me living here, I can't remember a single predicted wind event that actually happened. Every single big wind event (or even minor, like today's 19mph gust) happened on days where there was no wind predicted.

      It makes reading the wind forecasts 100% pointless.

      Delete
  7. Great job Cliff. I think I will skip my trip to Moclips.

    ReplyDelete
  8. I see on the radar that line of the cold front starting to arrive. There's some structure around aberdeen flowing SE to NE (the line), but that might not be 'the line' quite yet. I'm glued to the radar hoping to see it form this evening.

    ReplyDelete
  9. I guess that extreme line of the cold front must be skirting by S. Everett...at nearly 7pm, no unusual gusts of wind--maybe a few in the 25mph range--and rain is just sporadic, and not torrential...another "ho-hum" system for this area!

    ReplyDelete
  10. so much for that computer forecast.. I am a fan of yours :)

    ReplyDelete
  11. 1.9 inches already today (as of 8:45pm) here on the hill above Kingston and still raining heavily. Wow.

    ReplyDelete
  12. Yep..another rainy night in snohomish county.

    ReplyDelete
  13. OLM station measured a top gust of 37 mph, once, during the whole event. Not 40 - 50 mph, and certainly not worthy of the wind advisory. Olympia - Lacey gets routine gusts 30 - 35 mph during these "breezy" storms.

    So that 30 - 40 mph was more accurate.

    ReplyDelete
  14. Wacky snow levels out there for January. Dropped to 2000ft briefly along I90 this morning before bouncing up to 4600ft with rain on snow causing tremendous runoff from the mountains and wet loose avalanche conditions more like spring than winter. I thought El Nino was supposed to be wet and cool not just wet?

    ReplyDelete

Colder Air and Limited Lowland Snow Ahead

Our region will soon experience colder temperatures and substantial snowfall in the mountains.  The snow level will fall and virtually every...