Extreme Morning Heat Wave Hits the Puget Sound Region

Major, long-term, temperature records are being broken this morning, with amazingly high temperatures around Puget Sound.  Stunning records.

I knew something was up when I walked my dog this morning around 6:15 AM.... it felt amazingly warm.   Then I checked and was floored.

Temperatures at 6 AM were in the mid-60s from Seattle to Tacoma (see graphic, click to expand).  50s over north Seattle.  Normal lows this time of the year are around 38-39F.

Sea-Tac Airport was 63F at 6 AM, with an overnight minimum of 62F.    The previous minimum temperature temperature record for the date was 50F--but temperatures will fall today....so we will have to see if we beat it.

We are talking about a stunning record low temperature.  The plot of temperature at Seattle illustrates this (normal highs and low temps plotted with purple and cyan color lines).  The low this morning was roughly 10F higher than our normal high temperatures.

According to my colleagues at the National Weather Service, the 5 AM PDT temperature at Renton, Washington (at 66 F) was the 2nd warmest spot in the lower 48 states....just behind Palm Springs, California (69 F). 
So what is going on?   A very strong easterly wind event with powerful downslope winds.   In fact, there is windstorm going on right now in the Cascades foothills, particularly around Enumclaw.   And strong downslope winds cause powerful compressional heating of the air, like in your bicycle pump.  Thus, the extreme temperatures.

Here are the temperatures and winds around Puget Sound.  Look closely (click on image to expand) and you will see that the warmest places have easterly winds.

The pressure gradient across the Cascades is very large now (7.5 hPa across the mountains, higher to the east) and the winds above Sea-Tac Airport (see below) shows a deep layer of easterly flow...and easterly flow that is very strong at low levels. ( the figure shows temperatures in red and wind barbs, time is on the x-axis and height in pressure on the y-axis, 850 is roughly 5000 ft).

The turbulent easterly flow is mixing down to the surface, working against any nighttime cooling by the emission of infrared radiation to space.  The strong easterly winds have gusted to 52 mph in Enumclaw and 30-40 mph as far west as the Sound and as far north as Issaquah.

Why are there strong winds and warmth between Seattle and Tacoma?  Because of a "weakness" in the Cascades to the east....what meteorologists call "Stampede Gap"---- see the terrain map below.

The winds and high temperatures will fade today....but those of you living between Seattle and Tacoma are experiencing an unusual event today.

Record Highs Today over Western Washington State and a Very Wet California

As promised, temperatures surged into record territory today (Monday), with many locations getting into the lower to mid-70s.   Here are the high temps over the region today.   Lower to mid 70s from Bellingham to Medford, Oregon.
With 70s even along the coast (made possible by warm offshore winds).  Warmer in Seattle than in the Tri-Cities.

Several locations beat daily records ( Sea-Tac, Olympia, Quillayture, Hoquiam, Bellingham)...and some by a large margin ( Seattle beat the old record by 5F!, Bellingham by 6F)

The 73F today at Sea Tac is the warmest at that location since late last September,  as shown by this plot.  And 20F above normal.

Getting to 73F at Sea-Tac early in March is quite unusual.  It is the earliest day on record that the temperature has risen above 70F at the airport.  Now that should impress someone.  It impresses me.

The temperature spiked today for a reason: the air was relatively warm due to southerly flow aloft and then we had strong easterly (from the east) flow that supercharged the temperatures by adding strong compressional warming as the air sank down the western slopes of the Cascades and coastal mountains.  Plus, few clouds to get into the way.

Here is a plot of wind direction at Sea-Tac Airport for the last 12-h....easterly flow dominated, and some of the winds were quite strong (15-25 mph gusts)

Easterly flow is a relatively unusual direction in central Puget Sound, as shown the the wind rose for March at Sea-Tac airport (see below).  To construct this chart one needs a database of March wind speeds and directions at the location.  The plot is a polar plot showing direction (with north at the top, south at the bottom, etc.)  The frequency of winds from any direction is indicated by the length of the "rose petals."    And the relative frequency of various wind speed ranges is shown by the colors.   So winds from the south to southwest are the most probable based on the climatology at Sea-Tac.  Easterlies are rare.

The easterlies were associated with a strong offshore pressure gradient (higher pressure inland and lower pressure offshore), connected with a very slow-moving front offshore.

The warm temperatures in our area were well timed, considering today was National Nap Day (I kid you not).   But rain and cooler temperatures will move into tomorrow.

But something else unusual is about to happen.   California is going to be inundated with heavy precipitation, much more that is typical of March.  Here is the latest model prediction (NWS GFS model)  of accumulated precipitation for the next 10 days.  The entire state will get plenty of precipitation, with up to 10 inches in the Sierra Nevada.

What about the  vaunted European Center model for the same period?  Up to 9 inches of precipitable water in the Sierra, and 2-4 inches over much of the northern part of the State.

 Accumulated snowfall...  3-4 feet over a large area of the Sierra Nevada.

The operators of CA reservoirs and dams will have to watch the water levels...they are going to rise substantially during the next week or so.  And perhaps this event will quiet the drought talk for CA this summer.