4/22/06 FCST: VA/MD/DE

Bill Hark

Jan 13, 2004
Richmond Virginia
Possible severe storms including tornadic supercells across Virginia, Maryland and possibly DE, NC.

A cold front is predicted to pass through the Mid-Atlantic by early Sunday (April 23) morning. According to the GFS (init 00Z 21 April), a surface low will move across Kentucky, northeastward along the eastern portion of Ohio and northward into Michigan on April 22-23. This leads to backed surface winds across eastern Virginia, Maryland and Delaware. The Eta shows only a hint of a low, but still backed winds across the area. A wide area of dewpoints 60-65 pushes northward along central/eastern Virginia to southern Maryland. (mainly 60 per Eta) The Eta also shows SRH to about 150, much higher north of Maryland. In the upper levels, there is a jet streak at the 500 mb level of winds from the 40 to 50 from the southwest across VA and MD. With 850 level winds also from the southwest at 20 to 30 and the surface winds from the SE, there should be significant low level shear. I expect storms to form ahead of the cold front and along the warm front that will move northward from northern Virginia, D.C. and through Maryland. My main concerns are lack of decent CAPE (forecasts approx 500), and movement of the low too far north with resulting northward shift of backing winds toward DE and NJ, away from better moisture and worse chase territory. Selecting a target now is difficult, but I’d like to be somewhere between Washington D.C. and La Plata, MD., assuming I can get off from work. I may be stuck cyber chasing in my own area!
Any thoughts on this possible eastern tornadic situation.
I'll be chasing Saturday, plan to leave Goldsboro around 8am and head somehwere west or southwest of Richmond for around noon, with the target shifting to northeast of Richmond around the Potomac by late afternoon/early evening. I have the same concerns for tomorrow's setup, would be nice to have the surface low/wave track farther south into the higher instability say along the NC/VA border during the afternoon instead of up through the Delmarva. Also the forecasted SSWly flow at 850-500mb, parallel to the cold front, will probably be quick force any convection into lines or line segments. Looking at 700 and 500mb UVVs, surface convergence, and precip output for 12Z, I'm thinking there will be an existing line coming out of West Virginia and western VA/western NC moving eastward during the morning hours. Unless any discrete convection forms ahead of the main line, I'll probably just target tail end charlies within the segments. At least storm speed shouldn't be outrageous, but ~40mph to the NNE. One positive for Saturday looks to be low temp-dewpoint depressions, with temps forecated to max out in the mid 70s and dews not too far behind in the 62-65 degree range.
Update: 12Z ETA now seems to suggest the surface low will move through a bit more quickly than last night's run, with it in northern VA at 18Z and then moving northeast to the Jersey area by 00Z. If this verifies, I'll target the Potomac river area, maybe La Plata, earlier in the day. New numbers still look good for low level shear, with SSE surface winds at 15-20kts under SSW 850MB winds of 30-35 kts. CAPE looks like it'll be relatively marginal, between 500-1000 J/kg, but the strong BL shear and moderate deep layer unidirectional shear should help compensate for that, as well all forcing from the upper jet max.
Hopefully northeast VA can get at least at little sunlight to peek through by afternoon, but clouds will probably be widespread well east of the approaching line. I'll be using the hourly surface obs display on Wxworx to try and pinpoint a target/storm just east of the surface low. Without that wave, tomorrow's tornado threat would be close to zero, but with it I think there could end up being a half dozen or so Tor reports before the day is over.
Not much change on my analysis except as Brody mentioned, the slightly increased speed of the surface low, which will shift my target more to the east and the north. I like the shear but am worried about cloudcover/instability and decreasing area of backed winds. For now, I am still thinking about the La Plata area. I'd rather not chase if I get pulled too far toward DE with the increase traffic/poor road network. Unfortunately, I have to make a decision this afternoon whether to "suddenly get sick" and not be able to work tomorrow. I am supposed to go on a short business trip Saturday.

Bill Hark
Two things I'm liking right now. Dewpoint readings of 63 currently in extreme southern VA, and the meso-low moving northeast out of the MS/AL region. Im not quite sure of the timing of this meso low though. I looked at a 5 hr infrared loop and measured the center of it on the fist and last frames, and then doubled that distance following the line northeast. From that estimated the mesolow to be somewhere in far south central VA, or slightly west of there, by 8AM and in the MD/DE region by 2pm. That track would also place the meso low close to the forecasted track of the primary surface low, not sure what effect that may have other that increasing the southern extent of backed winds into southern and southeast VA during the early afternoon. I still want to be in the Richmond area by late morning - I still think the best chance for any tornadic activity will be in northeast VA and southern MD. Hopefully the 00Z NAM run will give a better clue to the timing of iniation and strengthening of existing convection. I'm currently thinking 1-4pm from Richmond to the Potomac.

Edit: Ok the NAM is back to where it was last night on the timing, with the surface low in western VA at 18Z and central MD by 00Z. If that verifies then Danville to Richmond look good at 18Z and then Richmond to Washington and points east by 00Z. More daylight to keep up with the low and have backed surface winds, I'd be happy with that.
11AM and I'm still in Goldsboro. Looks like the only event today, if any, will be from the clusters from yesterdays activity in AL moving out of SC into central eastern NC/VA. Appears there will be no sunlight, but dewpoints in eastern NC are in the mid to upper 60s and approaching mid 60s in SE VA. Not much turn from surface to 850mb winds, maybe 30-40 degrees, and winds are backing with each surface update. So I think the Severe watch put out by the SPC was the right one to pick.
Guess it's a now event from here on, will keep my eye on the clusters as they approach, have noticed a couple mesos already on some of the cells, even though radar signatures are more 'Florida-ish', with 45-55 dbs returns.