Northeast Heat Was Less Intense Than 2010, ’11 & ’12, Warm SST’s & Wet Ground Explain Why!

Written by on July 21, 2013 in United States of America with 0 Comments

The Mid-Atlantic and Northeast has finally seen an end to the heatwave which produced the most consecutive 90s in New York City since August 2002 according to AccuWeather. That was the summer I was in New Jersey interestingly. While there was no 100s that summer from Philly up to Boston, it sure was hot and humid with 96 one day I was walking around Manhattan and another it hit 98 the day I was leaving out of Philadelphia for home.

The highest temperature of this year’s heatwave was 98 in New York’s Central Park with 3 days at 96+. 98 was the top temperature in Philadelphia while it was a cooler than expected 97 in both Baltimore and Washington DC but higher humidity down towards Chesapeake Bay meant higher real feels.

The noteworthy aspect to this heatwave was the night time lows. Central Park endured 3 straight nights of 80 with one night holding at a steamy 83. Despite hitting 100 last July, no night’s stayed above 80. Why? The air was likely less humid compared to this year. Like New York, Philadelphia, Baltimore and DC ALL failed to hit 100 this time around, likely due to unusually warm waters offshore and wet soils holding dew points up more. A significant contributor to the increase in humidity, especially over the Mid-Atlantic region is the wet soils over the Southeast.

article-2350736-1A9161B2000005DC-111_634x286The flow around the Bermuda high travels over this saturated ground and drives it up the coast, making the heat particularly around DC and Baltimore worse. Bad but slightly less up into Philly and less again for New York and Boston. Interestingly Boston, even Burlington, VT saw a hotter reading than DC… Was this because there’s far less rain fell here than further south or it’s much further away from the swampy Southeast and so there’s less humidity which means the air is heated easier? Probably!

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The most striking of the warm night’s and none extreme daytime highs is probably DC which topped only 97 which isn’t bad by DC standards. What’s impressive is the lack of cooling overnight with 5 straight nights not dipping below 80. The warmest night being 81. Last July saw 7 days above 100 with 4 straight 100s and a peak of 105.

Had the air been less humidity, Central Park, Philly and DC would likely have hit 100 and that would have been a 4th summer in a row with 100 in DC, Baltimore, Philly and New York, however it probably wouldn’t have held in the 80s at night. Drier air heats easier by day by also cools more by night.

Interestingly, back during the heatwave of July 2011, Central Park hit 100 2 days in a row with a peak of 104. Nights DID stay exceptionally warm, in fact there was two nights at 83 and 84 respectively. Warm waters offshore, stronger ridge a likely contributor.

1013953_10151615498308052_1055747126_nWhy Did It Hit 100 From DC To Boston 3 July’s In A Row But Not This Year?

Most summer’s top 100 in DC but for Philly northwards there was a long gap between 2001 and 2010 in 100 degree days in Philly, NYC and Boston but then we saw a string of 3 straight summer’s with 100+ with 2010 and 2011 seeing consecutive days of 100+. The lack of 100s up until 2010 was likely due to wetter soils in the East and less warm waters offshore. Why the return of 100s? I believe the drought conditions in the Southeast helped produce hotter than normal conditions to the south and with the clockwise flow around the Bermuda high, this heat was lifted north up the coast.

The drier conditions in the South which extended through the Carolinas and into Virginia and adjacent areas likely also helped pull the Bermuda high further west. Drought commenced proper in the Southeast back in 2007 and likely peaked in the summer of 2012 when many regional cities saw their hottest day on record.

The Northeast’s extreme heat peaked around the same time the drought did in the South and let’s not forget the influence of drought further west too.

Check these charts out..

2007-2012

southeast-drought-e1336716664924

2013

southeast_dm

The warm phase of the AMO has been particularly strong in the last 3 years and this helps force warmer water right up against the North American coast which intensifies drought in the South. All these factors coincide with the 3 summer’s of 100+ from DC to Boston. The big change this summer was record rains and the end of drought in the Southeast. Exceptional rains in the Midwest too has helped increase humidity and rainfall throughout the East and thus there’s a lot more of the sun’s energy goes into evaporation rather than heating the air. In other words drought is replaced by wet ground and thus this year hasn’t seen the same level of heat as the last 3 years.

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