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Strong storms possible with big cold front Thursday

A significant cold front moving through the Central United States will approach the region late on Thursday evening, bringing a wind shift and drop in temperatures both aloft and at the surface. The cold front is associated with a major mid level disturbance, which will shift from the North Central US into Southeastern Canada. As the front shifts through our region, moderate instability and favorable wind fields could support the development of strong/severe thunderstorms.

The Storm Prediction Center has placed parts of the area in a Slight Risk for severe thunderstorms on Thursday afternoon and evening, citing a risk for strong winds. In addition to the winds, unseasonably high precipitable water could support heavy rain and flooding in any storms that shift through the area Thursday evening. But the severe weather threat isn’t as straightforward as it may seem.

The main concern with the development and organization of any severe thunderstorms on Thursday is the degree of instability which develops in the atmosphere. This will ultimately depend on a few things; including the timing of the front itself, the amount of clouds which hang around in the area on Thursday morning and afternoon, and the wind direction/resulting surface temperatures as well. Forecast models, as you may imagine, are up in arms in regards to the degree of destabilization.

One thing that most models agree on is the fact that instability will be quite limited east of New York City. What is the reason for this, you ask? The answer lies in the southerly winds which will develop Thursday morning. This pulls marine air in off the Western Atlantic in to areas East of NYC (specifically Long Island). While this time of year, the waters are warmer and the stabilizing effect not as dramatic, the general idea still stays the same — instability will be greater and more supportive of storms the farther west/southwest you are of New York City.

NAM model showing CAPE (instability) developing Thursday afternoon, mainly west of NYC.

NAM model showing CAPE (instability) developing Thursday afternoon, mainly west of NYC.

Accordingly, the severe weather threat seems likely to manifest itself mostly west of the city. The timing of the front, sliding through during the mid-evening hours, won’t help to force the development of any storms either — the best forcing shift past New Jersey until instability will already have been maximized. So, the general idea is that strong to severe storms are possible, but are likely to be weakening on their approach to New York City by Thursday evening.

Farther west and south of the city, across New Jersey and parts of Pennsylvania, strong to severe thunderstorms capable of producing a few strong wind gusts are likely. We’ll have a live thread up tomorrow afternoon as the storms rumble through. Behind the front, much cooler autumn-like air is expected…with a pleasant weekend on the way.

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