Overnight Severe Weather Outlook for Tuesday, July 7, 2009...

Overnight D1 SWO July 7, 2009 will feature a Slight Risk for severe storms over parts of E and SE NY/W CT/W MA/SW VT. Slight Risk includes the following counties…

Connecticut: Fairfield, Hartford, Litchfield, New Haven.

Massachusetts: Berkshire, Franklin, Hampden, Hampshire.

New York: Albany, Columbia, Dutchess, Fulton, Greene, Montgomery, Orange, Putnam, Renssalaer, Rockland, Saratoga, Schenectady, Schoharie, Ulster, Washington, West Chester.

Vermont: Bennington, Windham.

Discussion...As of 1:42AM 7/7/09

SWO for Today is one of below normal confidence than usual heading into D1. Of biggest concern will be the amount of instability that is realized from Late Morning into the Evening hours in what otherwise is an environment of decent negative lift and sufficient shear to support organized thunderstorm activity, some of which could become severe. Again, this will depend on the amount of CAPE that is realized as to whether or not this potential is maximized to its fullest extent.

As of now, degree of destabilization is modeled around 750-1500 J/KG. Should the upward part of this range be realized or exceeded, potential will be in place for an area of favorable for large hail/damaging winds, and perhaps a tornado or two given ample bulk shear values aoa 40 kts and supportive low level helicity values across much of the Slight Risk area. ATTM, best window of opportunity for severe appears to be Late Morning into mid-Afternoon, which makes the amount of instability even more important.

Given unusually high uncertainty surrounding the forecast, outlook will almost certainly need to be fine tuned and adjusted accordingly later this morning once 12z NAM/RUC analysis is complete.

..EGAN..