NY NJ PA Weather Forecasts

Dry this afternoon, thunderstorms return tonight

10:41 AM

High pressure continues to move to the east of the forecast area this morning towards the New England coast while a strong cold front approaches from the Ohio Valley.

Before typing up this forecast discussion, I wanted to take a real good look at the upper level dynamics of this cold front.  As we all know, the them this season is for the upper low over the Great Lakes to sling shot these cold fronts through the Ohio Valley and then lose influence on the cold front as they progress eastward.  As a result, the thunderstorms lose some support approaching the region and the cold front slows to a halt.  However, in this case the trough axis is still in a state of transition and further to the east compared to previous set ups.  This will allow the cold front to move slightly faster and with more energy than previous cold fronts this summer.  Note that the trough this morning is in a slight negative tilt towards the eastern Ohio Valley and the cold front this morning is moving at a progressive clip through western Pennsylvania.  To me, these signs point to a more robust 850 MB and 500 MB mesoscale jet maximums over the region, which would give the thunderstorms the potential to produce strong wind gusts and heavy downpours well after the sun sets this evening.  While I don’t think this set up would lead to wide spread severe thunderstorms, I think the potential is there for some thunderstorms to push to that level as the cold front moves through.

Of course, the speed of the cold front is also a positive as by Sunday morning, the cold front is well off the coast and much of the day on Sunday is high and dry.

Through next week, the Northeast and Great Lakes will continue to be under the influence of a large scale trough while two upper level lows migrate into and out of Ontario and Quebec.  I think this is a tricky forecast in term of detailing the when and where of showers and thunderstorms each day throughout the Northeast let alone the forecast area.  The question is really what is the timing of these upper lows and associated upper level disturbances.  Currently, the threat for showers and thunderstorms will be present on Monday, Tuesday, Thursday, and Friday while high pressure will take hold for Wednesday.  However, this forecast is all based on the position and speed of mid level and upper level disturbances which at times can move faster or slower than guidance suggest.  As a result, I think the best course of action is for this forecast period is to expect sun and clouds each day with a risk of a passing shower or thunderstorm.  I think this perfectly describes the pattern overall and frankly has been the case since mid May.  As for temperatures, the influence of the trough over the East will continue to promote slightly below normal to near normal temperatures through the period.

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