Updated Severe Weather Outlook for This Afternoon/Evening, August 4, 2009...

Updated Discussion... as of 12:45PM 08/04/2009
Still some uncertainties regarding severe potential this Afternoon/Evening. All in all, not going to change much at all from previous outlook, and whatever happens I’ll live with.

Currently 2 MCS systems on-going. The first was on-going over parts of eastern KY/southern WV, and getting set to move into southwestern VA. Activity has shown a gradual weakening trend over the past several hours as activity encounters a less supportive environment, with no warnings/reports to show for in the past few hours.

A second, more potent MCS was located upstream near the IL/IN border as of this writing. Severe weather is occurring all along this line, with widespread wind damage reports thru central IL. Current SPC meso-analysis shows a much more stable environment near the IN/OH border out ahead of this line. Both the WRF/NAM show this MCS losing it’s punch and weakening across IN, before reaching the far western portion of the area. Hence, continue to think best chance for severe weather will have to come from storm development out of ahead of the front later this Afternoon/Evening as organized convection upstream weakens and slips south/west of the area.

This Mornings NAM12/RUC13 simulated reflectivity continue to hint at storms firing from southern Ontario to northern WV by mid-Afternoon, and moving east into western NY/PA by Evening hours. Here the environment has been untouched by previous convective remnants from the Overnight thru this Morning, so convective parameters should be somewhat supportive for severe, with the best window of opportunity from 4PM-9PM. However, a second line of convection is shown to originate over southern Ontario, and move in off Lake Erie from roughly KCLE to KROC by 11PM. Not out of the question, depending on how previous convective schemes play out later this Afternoon/Evening, that some severe could linger across the Slight Risk area up until the end of the outlook period, or 12AM Wednesday.

Previous Discussion below...

..EGAN.. 08/04/2009

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Discussion... as of 2:30AM 08/04/2009
Overall conditions will be favorable for general thunderstorms along and west of line from approximately Caribou ME- Portland ME- Hartford CT. A Slight risk will be in affect across parts of NY/PA/WV/MD.

Rather complex outlook is in store for Today. 00z WRF shows a rather potent MCS developing Tonight over Southern IN and continuing Southeast toward the western edge of the forecast area. The bulk of the action looks to stay west of the area, primarily from Southern IN/Central KY, and points south and west.

Despite favorable SBCAPE and Negative LI across much of the western areas, best low level shear values will remain north of the border in Canada and northern MI for the most part. 00z WRF depicts a noticeable split in the action between the aforementioned MCS and the area of thunderstorm development later this Morning/Early Afternoon.

If this ends up being the case, best chances for severe weather appear to be along the Ohio River from OH/WV border and points north/east from 3 PM onward. Overall storm mode looks to favor a more linear assortment and multi-cellular clusters, however, there is a chance for a couple supercells. Hence, an equal 15% hail probability, and minimal 2% tornado probability will also be included. All in all, there is certainly a chance that things will need adjustment later this Morning.

..EGAN.. 08/04/2009