The three H’s! Hazy, Hot, and Humid! Thunderstorms too

by Steven DiMartino on June 22nd, 2010 Comment

The heat and humidity is here as advertised, complete with excessive heat warnings for the Philadelphia metropolitan area and all of the Delaware River Valley.  The rest of the week is not going to be much better with a continuation of the hot and humid weather conditions into this coming weekend.

However, another threat will be making headlines later this afternoon and evening.  A strong disturbance over the Ohio Valley will move east this afternoon and move through the New York City and Philadelphia metropolitan area this evening.  This disturbance will increase lifting and some wind shear over the northern Mid Atlantic this evening and create a line of strong to severe thunderstorms along and ahead of the warm front.

The overall development of these thunderstorms in this air mass suggest that synoptic scale lifting will be needed to produce the thunderstorms.  The reason for this is that the air mass is so warm up to 500 MB, that there is really not much in the way of instability or thermal lapse rate with this atmosphere.  A cooler air mass aloft must be introduced to create instability, which is where the upper level disturbance to the west comes in.  I expect a line of thunderstorms to develop this afternoon and move east through the region in the evening and overnight hours.  I do not expect a wide spread threat here given the weakening upper level support as the surface boundary moves east.  However, given the increase shear and plenty of low level moisture, there will be a threat for a few severe thunderstorms with the primary threats being heavy downpours, wind gusts over 55 mph, frequent lightning, and small hail.

A very hot, hazy, and humid air mass will be established over the northern Mid Atlantic through the rest of the week with temperatures peaking in the mid 90's over the Delaware River Valley Wednesday and Thursday.  A decrease in humidity is expected by Sunday night into Monday in the form of a strong cold front with the threat of showers and thunderstorms.

However, the hot and humid weather conditions will return by the middle of next week as the summer pattern returns quickly.

For details on your location, visit the NY NJ PA Weather Local Seven Day Forecast.