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John Homenuk

Warm, unsettled weather continues Wednesday

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Strong thunderstorms powered through the area on Tuesday afternoon and evening, as an energetic trough moved through the Great Lakes and Ohio Valley. Thunderstorms maintained themselves through much of New Jersey on the leading edge of stronger forcing from the mid and upper level trough. As they shifted eastward, weakening occurred due to lesser instability in our area. Still, gust fronts on the edge of the pre-frontal trough mixed down stronger winds aloft, leading to branch and tree damage in many areas. Figure 1, below, shows the storm reports from Tuesday via the Storm Prediction Center. Needless to say — it was a significant severe weather event in the Northeast US.

Figure 1 (NWS/SPC)

Figure 1 (NWS/SPC)

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John Homenuk

Strong, severe storms possible this afternoon west of NYC

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Hazy, hot and humid air has settled into the region this afternoon as southerly winds pump in the warmth thanks to mid level ridging. Back to our west-northwest, an energetic disturbance is ejecting northeastward through the Ohio Valley. Increased lift and forcing is helping to force the development of thunderstorms within an unstable environment, leading to the threat of widespread severe weather over Pennsylvania and New York State. The Storm Prediction Center has issued a Moderate Risk for severe weather in those areas through this evening.

Why is this threat developing? 

There are many pieces at play, but the main culprits are most definitely the Western Atlantic Ridge (actually centered near Bermuda at this point) and the incoming energetic trough. The combination of the two is leading to increased instability, strong forcing for thunderstorms, and sufficient wind shear for storm organization. Figure 1 (below) shows a four panel model image from this afternoons 12z NAM model. On the top left, the model is producing precipitation along elongated height falls from the system to our northwest. On the top right, very warm air at 850mb has advanced into the region with temperatures over 18 C. Finally, the bottom two panels show the energetic pattern at 500 and 300 mb.

Figure 1. (NYMetroWeather models)

Figure 1. (NYMetroWeather models)

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Update: Slight Risk of severe storms from SPC

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The Storm Prediction Center has placed parts of Northern New Jersey, Southeast New York ,Connecticut, and the New York City Metro Area in a “Slight Risk” for severe thunderstorms Wednesday afternoon and evening. The “Slight Risk” category is triggered by probabilities of severe weather within 25 miles of a point — and in this case the SPC indicates a 15%-30% chance of severe storms within 25 miles of any point in that area.

Scattered thunderstorms are expected to develop over Pennsylvania and New York later this afternoon before moving into Western New England and Southeast New York. The storms may then eventually drop south and east towards Northern NJ and New York City. However, confidence is higher in the potential for storms to the north of our area. Here, better shear and instability parameters are juxtaposed to support organized severe thunderstorm potential. One forecast model, run for the Storm Prediction Center, suggests the storms may move farther south — into Northern NJ and NYC ( see below ).

SPC-WRF model, forecasting strong thunderstorms impacting the NYC Area Wednesday evening.

SPC-WRF model, forecasting strong thunderstorms impacting the NYC Area Wednesday evening.

After a warm front passed the area this morning, southwesterly winds ushered in a much warmer and more humid airmass. So, the potential exists for the strong storms to move into the NYC Area later this evening despite the fact that the better support for severe weather remains to the north.

Stay tuned for updates on potential watches and warnings from the National Weather Service through the afternoon (this post will be updated).

Damp Tuesday, but big warmup en route

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Warm fronts can be pretty deceiving. Depending on the positioning of the front at the surface, and the amount of warm air that looms behind the front, conditions can seem fairly raw and damp near and ahead it. Much of the same is true in our area today, as east winds ahead of a surface warm front to our south along with a weak low pressure system riding along the front itself will provide cooler conditions and periods of rain.

Waiting behind the front, which will pass the area early Wednesday, is a surge of warm air. Temperatures at the 850mb level will rise from around 8-9 C Tuesday morning, to 15-16 C by Wednesday — and even warmer on Thursday. At the surface, highs in the 60’s on Tuesday with clouds will rapidly rise into the upper 80’s and lower 90’s later this week. In addition, a westerly wind component should help the warmth get all the way to the coast — and limit the inland extent of the seabreeze.

Showers and storms, however, will linger through Wednesday before the heat arrives. In fact, the Storm Prediction Center suggests a small chance (5-15%) of a severe thunderstorm in the area as the warm front passes on Wednesday. Stay tuned for further updates. Their probabilistic outlook, shown below, suggests the best chance for severe thunderstorms will be farther north — where the warm front will be Wednesday afternoon. A slight chance of storms capable of producing gusty winds exists as far south as New Jersey.

Storm Prediction Center Day 2 Outlook, valid for May 29th, 2013. The probability of any severe weather within 25 miles of a point is shown. A 15% probability (yellow) triggers a "Slight Risk" of severe weather.

Storm Prediction Center Day 2 Outlook, valid for May 29th, 2013. The probability of any severe weather within 25 miles of a point is shown. A 15% probability (yellow) triggers a “Slight Risk” of severe weather.

Stay tuned for further updates on not only the potential for storms, but the impending warmup and warm frontal passage on Wednesday. You can follow our social media accounts on Facebook and Twitter for more frequent updates and posts throughout each day.