Posts

John Homenuk

Despite lowering humidity, more heat looms

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The past few weeks have featured high humidity values and warmer than normal temperatures — with an uncomfortable airmass lingering throughout the area. Over the next few days, a bit of a break in that airmass is likely as a cold front nears the area and brings in not only some clouds, but slightly cooler air. The front won’t make much progress past our area, though, as it runs into a strong Western Atlantic Ridge. The weakening disturbance associated with the cold front will eventually become absorbed in the mid – level atmospheric flow, and the forecast models suggest that the West Atlantic ridge will win the battle.

As the front stalls and dissipates, a building ridge over the Central United States will make its way east. The end result? A brief break — but then a return to the heat. Forecast models, in fact, have hinted at the potential for temperatures at the 850mb level to approach or exceed 20 C next week, a benchmark for “Hot” weather in our area.

GFS model forecasts of height and vorticity at 500mb. Valid Thursday 7/11/2013 (left) and Monday 7/15/2013 (right).

GFS model forecasts of height and vorticity at 500mb. Valid Thursday 7/11/2013 (left) and Monday 7/15/2013 (right).

Pictured above, the GFS model shows the forecast heights and vorticity at 500mb (mid levels of the atmosphere) valid both Thursday (left) and Monday (right). The important features are highlighted, with the Western Atlantic Ridge and Central US Ridge in yellow on the left side. The vorticity (red) in our area associated with the cold front has created clouds and showers today. However, by Monday, the ridge has completely taken over the pattern and “domed” over the Central and Eastern United States.

As a result, despite the break in the heat and humidity over the next few days, it appears that next week should be highlighted by a return to heat — with temperatures approaching the mid 90’s by the middle part of the week. Stay tuned for any potential heat related watches or warnings– and prepare to stay cool!

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.