April 26, 2014

April Heat Wave!

Get your shorts out.  Stock up on sun tan lotion.  Make sure you have ice and cold drinks.   Because some of the warmest April/early May weather we have seen in over a decade looks increasingly probable for Wednesday and Thursday of the upcoming week.  Maybe even reaching the big EIGHT-OH!

At this point most of the leading models are going for this warm forecast, so I feel pretty confident telling you about it.

Let me show you the 12-km UW WRF model forecasts for this week.    First, we have to get through a some rain tonight and showers on Sunday...sorry folks.  April showers are required.  But then on Monday and Tuesday, upper level ridging  (high pressure) start building over the eastern Pacific.  Here is the upper level (500 hPa, around 18,000 ft) maps  for 5 PM Monday and 5 PM Wednesday.  The will be  a huge ridge developing over the West Coast with very large north-south extent.

 This ridge will warm us up in two ways, first it is associated with general warming of the atmosphere and lots of sun.  But it will also bring increasing offshore flow, which really revs up the heat, as warm, continental air east of the Cascades sinks and is warmed further by compression as it descends into the western lowlands.

Let's follow the 2-m (surface) air temperature and near surface (10-m) winds  that is forecast by the UW model.   First,  at 5 PM Monday:  56-60F over western Washington and a bit warmer near Portland and the Columbia Basin.

Tuesday afternoon, a notch warmer,with 60s over western WA and 70s to the east.

 Wednesday brings real warming. Widespread 70s in western Washington as easterly flow really cranks up, with some areas in SW Washington and the Willamette Valley hitting 80F.  Portland will be warm.

And then Thursday at 5 PM.  What can I say?  We haven't seen April temperatures like this in a decade.  A number of folks away from the water could get to 80+F that day.  I suspect that a 24-h virus may be rampant that day.

 Friday is the transition day, as onshore flow develops, with temperatures remaining warm from Seattle northward, and eastern Washington really surging in the torrid zone as the ridge moves inland.

At this point in time, the official outlets are going conservative, as they should.  The National Weather Service is predicting 79F for Wednesday and 81F for Thursday. Very reasonable.

The Weather Channel is slightly cooler than the NWS:

For those of you those like weather statistics, my colleagues at the National Weather Service have noted that the average first day getting to 80F in Seattle is May 23rd....we will do much better that that this year!   And let me provide an important warning.  Just because we are going to have a few summer-like days, don't think you can put those tomatoes outside yet:  cool weather will come back next weekend! 


  1. Gross. Way too early for crappy weather like this.

  2. I am very excited for the warm weather this week. However, I wanted to note that here in Northwest Oregon (on the coast even, believe it or not, thanks to offshore flow) we had two days of 82 and 85 degrees on May 4th/5th of last year at Astoria, for example. So it has occurred not only in the last decade but just last year. Seattle and Portland both also had two or three days in a row of temperatures in the mid 80s around May 4th/5th, 2013. Bring on the warmth!It seems to be a common theme in late April/early May to have at least of a couple of days with much above average temperatures.

  3. And along with this unusual heat-wave occurs May-day, and all that has come to mean in (downtown) Seattle. Has there been a proper study done of temperature on the probability of population unrest?


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