May 14, 2018

Some Record Minimum Temperatures This Morning and Dry May

Walking outside early this morning it was evident that something was up.   It felt really warm.

In fact, the minimum temperatures at locations around the region were warm with upper 50s at several locations, with some stations only dropping to the mid-60s.    Sea-Tac Airport had their record high low temperature for the date (58F).  In fact, it was the highest low for any date during the first half of May.

What was the reason for this morning warmth?    Well, we started out with near record warm air aloft for the date because of a ridge of high pressure overhead.  To show this, here are the climatological temperatures in the lower atmosphere (925 hPa pressure, about 3000 ft) at Quillayute, on the WA coast, with today's observation at 5 AM shown by the silver circle.  The red line shows the record for each date.  The temps aloft were near record levels.

But warm temperatures aloft are not enough since infrared cooling to space from the surface will cause low-level temperatures to fall, working against any record.

But there was another factor that worked against this nighttime cooling:  lots of water vapor in the lower atmosphere.   A good measure of water vapor content is the dew point temperature, with higher dew points indicating more water vapor.  So  here is the climatology of surface dew point at Quillayute, with the circle indicating today's values--quite high...nearly at record levels.

Water vapor is a very active absorber and emitter in the infrared and helps to keep the temperatures up at night.  That is why very dry deserts often get chilly at night even when the temperatures are extremely warm during the day.  So with lots of water vapor, the normal nighttime cooling was lessened.

One factor that helped with keeping the moisture high was the lack of offshore-directed, easterly winds.  Nothing dries out the air like strong downslope, easterly flow.  Only when downslope, easterly flow is very, very strong can it produce record high temperatures.

One more thing....this has been an extraordinarily dry May so far.   Seattle has only received .08 inches as of today...and we are halfway through the month.    The rest of the month looks fairly dry, with the forecast through May 28th never showing more than a 20% probability of rain for any day.  The driest May on record at Sea-Tac only received .12 inches.   So perhaps we have a chance to beat the record.

Ironically, the morning high resolution WRF model simulation showed the greatest rain action over northern CA and southern Oregon, which is unusual this time of the year.  Good for topping off the reservoirs in northern CA.


  1. So I know that we could have the driest May on record, but are we on track for the WARMEST May on record?

    Also what does this do to our water supply?

  2. No.... not on track to be the warmest. And we have plenty of water....reservoirs are in excellent shape from a wet spring and normal winter....

  3. Any idea how much more population greater Puget Sound can absorb and still supply fresh water to with our current sources?

    1. Connected with your question, here's an interesting paper in the journal for professional civil engineers. I expect it has been subject to critical scrutiny in the 7 years since it was published, and of course engineers come at this from an engineering angle, but it looks at things through the perspective of three different models.

  4. Cue the Greek Chorus that's soon to follow screaming about Climate Change. Funny, they don't call it Global Warming antmore, since that message proved ineffective. Orwell knew the manipulation of semantics all too well.

    1. This isn't semantics:

  5. I have already begun my outdoor swimming program: Over half a mile in two different lakes yesterday and today- Silver Lake (Everett) was comfortably warm yesterday. I always consider it a bonus if I can start in May.

  6. Sunday evening was very warm. It was a sheer delight to have a nice family campfire, for Mother's day. Come to think of it usually by the time evenings warm up, our perennial summer burn ban is on. So a warm evening and a campfire was a real treat.

    It has been perfect farming weather this May, March and April, were a real setback with so much cool cloudy and damp weather we had.

    I don't want to hear any whinning about a little nice weather, just think, you will be able to eat Washington grown produce soon. Save the planet, by not eating foods imported from California and beyond. (Lots of hydrocarbons used to ship them to Washington...)


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