Saturday, July 20, 2019

Humidity Storm Hits the Northeast While the Northwest Has the Best Weather in the Nation

For those of you living in the Northwest, this is weather payoff time.   Warm, but not too warm.  Generally dry, but with a few showers next week to keep things moist enough to keep down the fires.

But the situation back east is different:  in several places the humidity will be debilitating, with effective temperatures getting well above 100F.

As I talked about this week, the dew point temperature is a good measure of moisture in the atmosphere, and when summer dew points get into the mid-60s, it starts feeling "sticky" and unpleasant.  Dew points in the 70s start getting really irritating and upper 70s, really bad.   The National Weather Service dew point analysis at 8 AM EDT today  show the national moisture divide.  The eastern half of the nation is steamy, with dew points approaching 80F that extends into the New York area.    In contrast, low dew points over the West.


Why the difference?  The east coast air is coming off the warm Gulf of Mexico and south Atlantic, while West Coast air originates over the cool Pacific Ocean.  In addition, the high terrain of  West extends into drier layers aloft.

The latest surface dew points for the New York area are amazing, with a number in the mid to upper 70s.   Some hit 80F!


These dew point, coupled with temperatures rising into the middle 90s, is resulting in effective  or apparent temperatures as high as 110F in the New York area and some locations in the Midwest.

Apparent temperatures take in consideration the decline in effectiveness of evaporation from our skin as humidity rises, and give the "dry temperature" equivalence of the current temperature and humidity.


It is interesting to consider that human beings are exquisitely designed to function in hot temperatures--more so than almost any animal on the planet.  When we have sufficient water, sweating from our bare skin can cool effectively.   But heat coupled with high humidity can undermine our prodigious capabilities for evaporative cooling.

The dew points over the Eastern U.S. are quite unusual.  Here is a plot of the climatology of surface dew point at Islip, Long Island, with the red line being the record for each date.  The circle gives the observation this morning.  Today's value was a new record for the date and one of the highest values for any date.  I want to grab a cold drink just thinking about it.

Getting back to the Northwest,  weather should be as close to perfect as imaginable over western Washington today with highs in the upper 70s in western Washington and lower to mid 80s in the Willlamette Valley.   Not too hot in eastern WA.


Sunday will be warmer, particularly east of the Cascade crest, but nothing extreme.   But dew points will be low-- in the 40s!!!----so skin evaporation should work well.  Just drink plenty of water.  Or whatever.

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I will be giving a talk "The Great Storms of the Pacific Coast" in Ocean Shores at 6:30 PM on September 7th at the Shilo Inn as part of the Coastal Interpretative Center's summer lecture series.  More information is found here: https://www.interpretivecenter.org/.   Shilo Inn is offering special room  rates for those wishing to stay overnight, as well as a special buffet.