Severe WX Threat: Instability is Wildcard
By Quincy Vagell on September 17, 2012, 2:15pm
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Severe weather is possible tomorrow night, but marginal instability will be the wildcard in determining the threat across Connecticut.
Setup:
A vigorous disturbance with very strong winds aloft will move through the Northeast tomorrow night. If the atmosphere can destabilize, severe weather could be widespread. At this point, it looks like there will only be marginal instability, meaning that severe weather may be isolated.
Forecast:
A few scattered showers and isolated thunderstorms are possible during the day tomorrow. Winds will pick up, into the range of 15 to 25 MPH across the area by evening. A line of thunderstorms may weaken as it approaches the area, sometime around or shortly after midnight. At that time, winds may gust over 40 MPH across the higher terrain and immediate shoreline. Right now, the main concern is that a few thunderstorms may cause damaging wind gusts.
Analysis:
The dynamics are in place and an anomalously strong low-level jet will swing through the area. Winds may reach 70kts at 850mb across our area. There is a strong signal of winds mixing down to near the surface. Dew-points will climb through the 60s and could reach the lower 70s in spots, mainly along the I-95 corridor, due to relatively warm sea-surface temperatures. 
Daytime heating is expected to be marginal. This means that instability parameters will not be terribly impressive. The concern is if more sunshine breaks through the clouds, then there could be further destabilization. If this occurs, isolated supercell thunderstorms may develop ahead of the cold front.
Since the cold front will not make it through the area until after midnight, heating will be lost and widespread severe storms are not expected. However, the line of storms may still pack a punch with damaging winds, mainly across the higher terrain of western Connecticut.
Who gets the worst?
It's a bit of a complex setup. Wind parameters indicate that there could be a few isolated tornadoes, although that zone will likely setup west or southwest of Connecticut. The higher terrain may see strong winds without any convective activity, due to their proximity to the higher winds aloft. The shoreline may also get some strong winds ahead of the cold front, as models indicate winds over 30 MPH sustained for a time.
Stay tuned to WXedge.com for all the latest details.
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