May 01, 2018

A Dry, Warming Period Ahead for the Pacific Northwest

After a cool several days, with lots of low clouds, we finally cleared out today, bringing some real sun for change.

The reason is clear, a modest ridge of high pressure has begun to build northward over the eastern Pacific (see below for 11 PM tonight) and this configuration should stick around for several days.  Ironically, a trough is over southern CA, bringing showers and clouds to portions of the southwest--which is good because they needed the precipitation.

The next few days look dry, with a warming trend.  As expert forecasters, of course you want to look at the ensemble forecasts to secure some idea of the uncertainty in the forecasts.  Here is the U.S./Canadian ensemble output (from NAEFS) for the next two weeks for Seattle.  There are about 50 members in this ensemble, with the median value shown by the horizontal lines, the range by the "whiskers", and the inner 50% of values by the yellow boxes. 

Temperature slowly increases to about 20C (68F).  Little or no precipitation.  Few clouds tomorrow, but increasing clouds on Friday.

 So forget the "May Gloom" this week.

What about the April precipitation, did Sea-Tac Airport beat the record?  Sadly no.  With drying during the second half of the month, we ended up with 5.69 inches, 2.98 inches above normal for the month.  The puts us in third place for the wettest April on record.  Respectable but no cigar.  The record is 6.53 inches, which fell in 1991.

A downside of the warmer weather will be increased pollen levels, and thus suffering for those with allergies.

The values in Seattle for the past 30 days show ups and downs, with ups often associated with warmer/drier weather.

And with warming the next few days, predicts increasing levels this week. How good are these predictions?  I haven't verified them and they don't show uncertainty information.  I do see cars being caked by there has been plenty of it floating in the air.


  1. Some of the models are hinting at a very wet period just before mid month.An atmospheric river in May? It seems rather implausible,but we better enjoy the upcoming nice weather while it lasts....

  2. I've lived in the Seattle region all my life and have never experienced allergies as I have this last month. Nose, throat and lungs. Yes, the yellow pollen from pine and other trees is a culprit, but there are likely other sources too. Glad to hear we'll be getting some drying out and good riddance to the pollen season. It's been terrible!

  3. I'm looking forward to the warmth. But I really hope we don't have another fire season like last year!

  4. Wondering with the fact that high clouds will be in the area, will that create any discomfort in the form of extra humidity between Sunday and Tuesday?


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