Aug 31: Rain and Thunderstorms Approaching!

Jonathan Carr
By Jonathan Carr August 31, 2014 11:15

Aug 31: Rain and Thunderstorms Approaching!

Hopefully everyone is having a great weekend so far! By now you should feel the humidity across the region thanks to our dominant SW flow. All the ingredients are on the table for showers and thunderstorms (some severe) to form this afternoon-evening. Exact timing is hard to gauge since the axis of the storms runs NE to SW. Therefore NWNJ could get hit as early as 5-6PM and SENJ as late as midnight. As always (9 times out of 10) these storms should weaken as they cross the state and meet the Atlantic Ocean’s marine influence.

Let’s look at some guidance. Here’s the short-range 4km NAM showing expected precipitation at 9PM tonight. As you can see, NWNJ has already felt impacts while SENJ has yet to see any. Again, this is because the axis of storms and their west to east movement. By ~midnight, SENJ “should” experience weakened versions of whatever EPA and NWNJ experience before and during sunset:

NAM model 4km short-range shows thunderstorms approaching new jersey this evening

If the sun is allowed to heat the surface through the afternoon today then instability will aid the storms in producing higher clouds and frequent lightning. Here’s the expected surface-based CAPE (Convective Available Potential Energy) at noon today. As you can see values are well above 2000 j/kg (joules per kilogram). Higher (MLCAPE) is also supportive of decent thundercell development:

convective available potential energy (CAPE) will increase today with diurnal surface heating

As far as wind shear goes, we’re looking at 30-35knots of bulk effective shear which is enough to trigger and sustain severe thunderstorms. All it takes is a few up and down-drafts to bring the stronger winds aloft to the surface. Rainfall amounts should range between .25-.50 of an inch depending on where the heavier downpours set up.

In English: Expect a warm and muggy day before showers and thunderstorms move into the region later this afternoon through evening (NWNJ first-as early as 5PM…then NENJ/CNJ/SWNJ…and lastly coastal/SENJ-as late as midnight). Some storms could produce strong winds, heavy downpours, and frequent lightning. You know I’ll be tracking on radar! As far as tomorrow goes, the Labor Day Weekend Outlook stands as called. Please be safe! JC

Model images reproduced with permission from WeatherBell Analytics.

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Jonathan Carr
By Jonathan Carr August 31, 2014 11:15

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