7/22/06 FCST: VA/MD/PA/DE

There is a possibility of tornadic supercells Saturday in the Mid-Atlantic. There is an approaching trough with an unstable airmass across the area. Dewpoints will be in the 70’s. At the 500mb level, there will be 30 to 40 winds from the SW in northern Virginia and Maryland. A low is predicted to move across West Virginia into Pennsylvania. Backed winds ahead of the low should produce sufficient shear for tornadic storms. The 12Z GFS for 00Z July 23 shows the low in northeast Penn while earlier at 18Z, the low is in Northeast West Virginia. In this scenario, the backed winds should be best in northeastern Maryland, southeast Penn. The 12Z run Eta has the low a bit farther south and I would expect the backed winds to be in Eastern Maryland, close to the Virginia border (near Washington D.C.) over to Delaware. I like this solution better and would pick Annapolis as a theoretical target. Negatives include slightly less forecast CAPE than than ideal (approx 1000).

A decision to chase will be made Saturday morning when I can get a better handle on the position of the low and area of backed winds in relation to the 500 mb wind max. The though of chasing across the Washington D.C. area doesn’t excite me. There is major construction on the WW bridge (495 crossing the Potomac near Alexandria) and there are often summer delays on the bridge over the Chesapeake by Annapolis. I also have to decide whether to blow off my wife’s friends who will be staying as houseguests Saturday afternoon to Sunday.

Bill Hark
 
Hey Bill the WW bridge should be better I think the new section just open last week which is four lanes in and out...Might not be that bad around there...Se Ya
 
It's best just to pretend the Potomac is a wall. On days like tomorrow in this area, it's best just to pick a target either east or west of the river and not plan on ever seeing the other side. The new span is open, but delays remain.
 
I think there is still a potential for tornadic storms provided there is enough clearing during the mid day after AM convection. On the AM satellite lop, there is an area of clearing in central MD that is moving eastward. Upper level support is sufficient. At the 500 mb level, 40 winds from the SW will overspread the mid Atlantic during the day. CAPE was forecast to be marginal but the 12Z RUC model init is more favorable with forecast CAPE of 2000 to 2500 in SE PA and most of NJ at 1800 Z. This area decreases slighlty by 0000Z July 23 with the main focus in central DE. Surface dewpoints are already in the mid 70's. In areas with backed winds, there should be sufficient low level shear for tornadic storms. The forecast position of the low is more morthward than I had hoped yesterday evening.

I am shifting my target to the north and east. I would like Wilmington, DE. The area of New Castle in the southern part of Wilmington is close to the most southerly crossing of the Delaware river on 295. There is the possibility of shifting the target further to the north and the east due to the position of the low and the thought of driving around to the east side of Philadelphia is not exciting. Central Delaware and the surrounding part of Maryland would be better chase territory and a possible alternative but I don't think the surface winds will be backed this afternoon.

With the driving time from Richmond, VA, traffic congestion, water barriers including the Delaware River, Delaware Bay, and northern parts of the Chesapeake Bay along with having to blow off my wife's friends who will be house guests, I will sit this one out. For those who live closer to that area, especially if they have XM and are familiar with the local road conditions, I definitely would suggest chasing this set-up. Opportunities in the east are very few.

Bill Hark
 
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