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.


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.   


  1. My daughter who grew up here in the NW moved to Raleigh, NC about 10 months ago. This is her first summer in the South. She called yesterday to tell me it was insanely uncomfortable compared to Seattle! She commented that parts of her clothes were soaked in less then 2 minutes outside in the sun going from her car to work and this was a daily issue. I cannot imagine 2-3 months of that! And how did society cope 75 years ago before widespread household A/C. Hate to think about it... With all the clouds of late, I will remain grateful for our near perfect summer climate. ;)

  2. I was just commenting to a friend that I don’t think I’ve ever felt 100 degree heat in my entire life. It can get up to 105 or so sometimes in Eastern Washington but our dew points are so low, it actually feels colder than it really is. Accuweather calls it realfeel and I’ve never seen their measurement over a 100.

  3. question and a segue related to humidity.... from my basic understanding of atmospheric science, atmospheric water vapor leads to clouds as moisture in the air rises to high altitudes and cools/condenses. Would you have any insight into why in the coming decades, warmer weather would not be leading to increase in cloud coverage with a corresponding cooler weather? This where my basic understanding atmospheric science goes astray with future warming. Being an engineer, I have a hard time full supporting something until I can understand the basics of what drives it. Thanks

    1. When high atmospheric pressure in the upper levels of the troposphere dominates, air tends to sink rather than rise. In such conditions, a given parcel of sinking air will tend to increase in pressure and, thus, temperature according to the ideal gas law. Of course the relevant physical parameters acting on such a parcel preclude the condensation of water vapor and the formation of clouds. Imagine that the emission of GHGs leads to global warming due to an increase in upper atmospheric high pressure systems which produce sinking and, thus warming air like we've seen in the Pacific Northwest the past several summers. Regarding atmospheric conditions conducive to cloud formation, yes, this tends to suppress maximum daytime temperatures but, conversely, inhibits nighttime cooling - just as we've increasingly observed in the Pacific Northwest. It's very easy to imagine average annual temperatures increasing due to a combination of the preceding atmospheric dynamics. For what it's worth, I'm not an alarmist and I believe the jury is still out regarding the ultimate effects of anthropogenic GHG emissions. However, the instrumental temperature record certainly indicates a warming Earth and it certainly does make sense that a cause, at least in part, of this warming is the very well understood and elucidated mechanism by which certain molecules of gases containing 3 or more constituent atoms absorb and emit infrared radiation in the wavelength emitted by Earth. The atmospheric-oceanic system is vastly complex and no one knows for sure what will happen but it's not unreasonable to bet on what's simplest/staring you right in the face. Also, not only is water vapor a GHG, it's the primary GHG in our atmosphere.

  4. Weekend spent in Leavenworth .. picture perfect!!!!

  5. Max temp in NW Bellingham today was 88F. By far the warmest day of the month, as well as the warmest day of the year, so far, and the only day this month to reach 80F or above at my location. Yesterday's min temp of 48F was the coolest temp of the month so far and the only day to drop below 50F. Today's min relative humidity, at 33%, was the lowest of the month, however, the today's max dew point of 66F was the highest of the month so far.

  6. 83 with a 55 dew point at Renton as of now. SeaTac is slightly warmer but with a 42 dew point. Why the difference in mugginess levels ?


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

Lightning Returns to the Pacific Northwest

 Lots of thunderstorms, some approaching severe levels, have hit eastern Oregon and Washington during the past day.....and there are severe ...