Severe T-Storm Outlook for Friday

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By Quincy Vagell on April 17, 2013, 5:00pm Last modified: April 18, 2013, 3:26pm

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There is a risk of severe thunderstorm activity in the Northeast on Friday.

I first highlighted this risk yesterday and little has changed with my forecast. A strong cold front approaches the Appalachians Friday afternoon and evening. Along that cold front, a squall line with thunderstorms is currently expected is develop.

(Marginal threat)
Middle Appalachians into Pennsylvania, northwestern New Jersey and interior New York: 
Daytime heating is expected to push temperatures into the low to mid-70's in the valley locations with mid to upper 60's in the higher elevations. Low and mid-level clouds will likely limit just how unstable the atmosphere can get. As a result, relatively low SBCAPE below 500 J/KG combined with near-zero or marginally negative Lifted Index values are expected. Despite strong winds aloft and effective bulk shear values increasing to 35 to 50kts along a cold front, the lack of instability will likely minimize the threat of severe weather. In addition, dew-points are forecast to stay in the 50's, perhaps coming close to 60° in Maryland and eastern Pennsylvania.
However, a few isolated strong thunderstorms could develop Friday afternoon ahead of a cold front. There is a marginal threat of a few damaging wind gusts associated with a squall line along the cold front Friday afternoon into Friday night. 

(Low threat)
Interior Virginia, east of the Appalachians:
The atmosphere is likely to become slightly more unstable further south. SBCAPE values of 500 to 750 J/KG are forecast based off of SREF guidance. Lifted Index values as low as -3 combined with dew-points in the 60's and higher helicity values would support more strong to severe thunderstorm activity.
Based off of this, there is a low threat of severe thunderstorms with damaging winds and large hail in this area. Some isolated thunderstorm cells are possible Friday afternoon, but locally severe storms could develop along a squall line Friday night as the cold front approaches.
There is a marginal threat for an isolated tornado or two, but confidence in this potential is not particularly high at this point.

(No appreciable severe weather threat)
Connecticut (southern new England), NYC, Long Island and coastal plain of NJ/DE:
With more of a marine influence allowing for less daytime heating, there is no appreciable threat of severe weather in these areas. Also, with the cold front not expected to move through until after midnight Friday (into early Saturday), this further implies that the severe weather threat is virtually non-existent.
With that said, some locally strong wind gusts are possible as a decaying squall line and associated cold front moves through late Friday night into early Saturday morning. 

As the spring season goes forward, I will be making more severe weather outlooks. Any feedback is appreciated and I am still working on the outlook/threat scale. I would like to compare forecasts to verification in the future, so some thought will be needed to address just how best to do so.

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Quincy Vagell

Town: Marlborough, CT  

Reporting for WXedge since January 2012.

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