Tropical Air over Seattle

Breath deeply this morning. 

A few days earlier the air was over the tropics.  Moist, warm and soothing to our wind and cold whipped skin.  And we just broke a major low temperature record.  This morning, our low temperature (56F) was the HIGHEST low temperature ever recorded in November at Seattle Tacoma Airport.  That is a big record to break.

Yesterday, Bellingham broke their daily high temperature record (60F) and today all sorts of daily high temperature records will be broken around the region.  



To certify the tropical origins of our air, I used the NOAA Hysplit trajectory model to trace the origin of the air above us at 500 meters (blue), 1500 meters (red), and 3000 meters (green) for the past 150 hours.  Our low level air, came from just east of Hawaii.  The 1500 meter air from the deep tropics.  No wonder many of us are fighting the urge to grab a Mai Tai today.


A plot of the winds and temperatures above Seattle for the past day (below), shows a freezing level of 10,000 feet, with strong southwesterly winds aloft--a sign of a potent atmospheric river event.

Over the past 24 hr (ending 5 AM), portions of the SW slopes of the Olympics received over 6 inches of rain, with the north Cascades getting as much as 3-5 inches.



But perhaps more impressive than the rain on the windward sides of the mountains, is the profound rain shadowing in the lee of the Olympics, where some locations only received 1-2 hundredths of an inch (see below).  Just amazing.


However, the wacky weather award yesterday had to go to Bellingham, Washington, where in less than an hour (around 4 PM Tuesday),  the winds turned southerly and surged to over 40 knots, and the temperature rose from 46 to 60F (see report below).


The temperature trace there shows the story and the fact the temperatures are EVEN WARMER right now--62F (and there are strong winds at Bellingham currently as well).
Perhaps just as unusual was the existence of sea fog (a.k.a., warm advection fog) over Lake Washington  this morning (see below).  The air was so humid and warm (dew point at Seattle-Tacoma Airport was 57F at 7 AM), that the cooler waters of Lake Washington (51F according to the Lake WA buoy) was able to bring the air to saturation.



The temperatures today will delight you.  A plot of temperatures during the past two weeks at Seattle shows that our current morning temperatures are WAY higher than the normal highs (purple line below).
 And the UW high resolution model forecast for surface air temperature at 2 PM  today shows 60s all over western Washington.  Some locations in the upper 60s.


 So pull out a short-sleeve shirt and breath in the tropical air.  Today, will not feel like normal Seattle weather fare of November.



Giving Thanks for the NCAR Ensemble

For nearly three years, the National Center for Atmospheric Research (NCAR) has produced a daily, 10-member, cloud permitting ensemble at 3-km grid spacing known as the "NCAR Ensemble". 

For those of us in the western U.S., the NCAR Ensemble forecasts, available from web sites hosted by NCAR and the University of Utah, attempted to do something that no current operational forecast system could three years ago — capture the extreme spatial contrasts and quantify the inherent uncertainty of precipitation over the western United States. 

Last night's forecast, for example, shows the major deluge expected to affect the Pacific Northwest through Thanksgiving.  At 3-km grid spacing, the NCAR ensemble accounts for many regional and local topographic influences and, with 10-members, one can derive statistics related to the range of possible forecast outcomes and the likelihood of precipitation above certain thresholds (our standard 1" and 2" thresholds work well for the Wasatch, but not the Cascades!). 
Plume diagrams allow one to examine precipitation at various locations, including Mt. Baker Ski Area below.  Such a pity that nearly all of that water will fall in the form of rain.

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Recently, NCAR announced that the NCAR Ensemble will sunset at the end of the calendar year.  More information is below. 


Although I'm sad to see it go, I believe this move makes sense.  NCAR is a research lab, not an operational center.  They need to be unshackled from routine forecasting and free to explore creative ideas and pursue modeling breakthroughs.  The NCAR Ensemble did this for three years.  It has allowed us to learn a great deal about cloud-permitting ensembles.  For example, we have a paper examining the performance of the NCAR Ensemble that may be the subject of a future post.   

Given that tomorrow is Thanksgiving, it seems fitting to toast the NCAR Ensemble team that includes Kate Fossell, Glen Romine, Craig Schwartz, and Ryan Sobash.  Thanks so much! We look forward to a few more weeks of NCAR Ensemble forecasts, and hope that Mother Nature shifts this damn pattern so that we can actually use them for powder hunting in Utah!