Doug Simonian

What caused the tornado warnings in New Jersey on Tuesday?

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RAP 850mb Analysis for 00z Wednesday, September 5th or 8pm EDT Tuesday, September 4th 2012.

“Tornado Warning” has always been an ominous phrase. When you hear those words, things generally tend to get a little more serious. On Tuesday, there were more than three Tornado Warnings issued throughout the state of New Jersey, beginning in the afternoon and continuing into the evening hours. Although the area did not see much in the way of severe weather reports in a quantitative sense, there were several reports of low-level mesocyclones, funnel clouds, and even tornadoes in the general extreme Eastern PA and NJ areas. In hindsight, this was actually a pretty good setup for low-level mesocyclones and tornadoes, and I’ll explain why.

Synoptically, we had a surface low that slowly deepened to around 1006mb located in Western Upstate New York, along with a closed 850mb low located in the same area. This placed our area in a pressure trough, and also resulted in a warm front that moved to the north across our region. Warm fronts are generally a better lifting mechanism for rotating thunderstorms than cold fronts. This closed 850mb low helped to provide a nice low-level jet, as 850mb winds were around 30 knots in most locations.

Additionally, there was some helicity as well, which is an indicator of rotation in the low levels of the atmosphere. What is also interesting to note is the light SE surface winds, and the importance of that will be explained in a bit. Click “Read More” below to read the full article..

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John Homenuk

Periods of rain likely through mid-week

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A warm front draped over the forecast area will serve as a focal point for the development of showers and embedded thunderstorms through Tuesday and continuing into Wednesday. With plenty of moisture in the atmosphere and an unsettled

NAM Model showing the potential for total accumulated rain amounts of over 1.5″ in some spots by Thursday morning.

weather pattern in place, showers are expected to develop along the front beginning early on Tuesday. Forecast models show the coverage of the showers and rain becoming more wingspread by later Tuesday, with most of the area experiencing a period of steady rain Tuesday afternoon. A weak area of low pressure developing along the warm front, in association with the remnants of Hurricane Isaac, won’t help the situation much…as the forcing from that weak low pressure should touch off the development of more showers. The most steady rain is expected Tuesday afternoon and evening, with the showers then becoming more spotty once again early Wednesday.

By later Wednesday, forecast models show a weak cold frontal zone or wind shift near the area with the potential for more showers and storms in the afternoon. Later this week, the showers are expected to become less numerous but will remain a chance in the forecast each day. You can check out the day-by-day details of the forecast in our Forecast Briefing, which is updated every morning.

John Homenuk

Weather turns cooler during Labor Day weekend

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Although 90 degree weather has dominated the first half of Labor-day weekend, the weather pattern is undergoing a change which is fitting for the first few days of

NAM Model forecasting high temperatures in the low to mid 70’s around the area on Monday afternoon.

meteorological Fall, which officially began this September 1st. A cold front moving through the area will usher out the 90 degree warmth, and unfortunately usher in some cloudy and cooler weather. The clouds will begin to enter the area on Sunday, which will probably still fair decently well with highs in the 80’s. But as a backdoor cold front sneaks in from Atlantic and New England on Monday, showers/drizzle and clouds will keep highs in the 70’s and the weather will turn more dreary.

Things don’t look to improve much towards the beginning of the first week of September (after Labor Day), as the much-weakened remnant moisture of Isaac finally slips east and interacts with the front…potentially producing more showers and clouds. Things should eventually clear out during the week at some point, but the cloudy and dreary weather will, at the very least, serve as a shock to the system after a warm summer and the recent 90 degree weather.