4/20/09 FCST: MD/DE/VA/NC/SC

[Bill Hark]

Severe storms are likely across the Mid-Atlantic Monday evening with possible tornadic supercells. An approaching trough becoming a closed low over the Great Lakes area will give 40-50kt sw winds at the 500 mb level across the Mid-Atlantic according to the 00Z WRF. A surface low over Michigan will produce SE surface winds from central and eastern Virginia northward by 1800Z. These SE suface winds winds will shift a bit farther north away from the area by 00Z Tuesday. The WRF indicates an area of 1000 CAPE through eastern Virginia into Maryland by 00Z Tuesday with SRH of about 200 also for eastern Virginia. Dewpoints will be around 60. Unfortunately, the 850 mb winds are only from the SE in Maryland, PA, and Delaware and not in Virginia where they are predicted to be from the SW. I am also worried about cloud cover limiting heating. The 00Z Monday GFS is fairly in agreement though the surface low is slightly more to the south earlier in the day on Monday. I'd prefer some more backing of the surface winds farther to the south in central and SE Virginia to better use moisture. Right now, I am thinking near Williamsburg, Virginia. Another option would be along the warm front that is predicted to be through Maryland by later in the day. The east side of Baltimore would be the target for that option but I have concerns about CAPE and that area has terrible traffic. I will check data Monday morning to decide on whether to keep my current Williamsburg target. I have to work until noon and that will limit my range.

Bill Hark

 

[Jason Foster]

For you Bill, and possibly myself (basing out of DC), I'm considering an area south of Richmond, into North Carolina. This area is likely to see the sunshine first, and the lower level shear appears it will be better south or Richmond as are the LIs. Seems much, other than the cape is cut short around Baltimore, and in this area, I'm not happy when there's clouds and grunge even with better numbers. I'm sure there will be very little time between unique supercells before the system forms a line of storms with bows (as the 06z Day1 SPC says too).

Chasing wise, north of Richmond is very poor if you don't expect initiation further west than the I-95 corridor. Plus, should you need to cross the Potomac, there are few options, and even fewer options to cross the Chesapeake Bay. I will be up early checking on the latest SPC Day 1 at 9am EDT, and the latest model runs before deciding if I go however.

 

[Dan Robinson]

With setups in these regions, I tend to employ a heavier terrain/road bias in targeting as long as some potential exists in the more chaseable areas. As Bill mentioned, the Baltimore and DC metros would likely be chase-enders if the day took you through there. That said, the 4km WRF (which has been performing very well recently) suggests at least a broken line of strong convection south of I-64 into eastern NC. Winds look more unidirectional there, but CAPE and low-level shear still look sufficient. This area is modestly chaseable, with flat terrain and a good number of open fields. I can't chase this, but my starting point would be just east of Emporia, VA - I would prefer to use US 58 to catch any breaks in the line as they move ENE across the state line.

 

[David Dildine]

I'll be setting up shop in lower southern Maryland hoping for something along the warm front. At least up this way, if any updrafts work their way across the Potomac they'll in a highly sheared environment. I was just in SE VA yesterday and am not willing to do the I-95, I-64 double whammy again. It is very tempting though when considering what I missed out on last year on April 28.

 

[Jason Foster]

I'll be setting up shop in lower southern Maryland hoping for something along the warm front. At least up this way, if any updrafts work their way across the Potomac they'll in a highly sheared environment. I was just in SE VA yesterday and am not willing to do the I-95, I-64 double whammy again. It is very tempting though when considering what I missed out on last year on April 28.

Yeah, I-95 is going to be a b***h, but I'm still liking the areas to the south (for instability reason in combo with roads). I should be able to hit the US 301 bridge across the river pretty fast if I set up in S. VA. Using the east side Richmond beltway avoids a bit of traffic.

 

[Bill Hark]

I am in Richmond checking data from work. I am surprised the SPC upgraded to a 10% tornado risk for most of central Virginia as I was expecting a continuation of their 5%. I really like the SE surface winds to the south and dewpoints shifting to the low to mid 60. The RUC is picking up on the meso low in SW Virginia that is expected to move to the northeast. My main concern is instability as there is still extensive cloud cover in this area though there is clearing in SE and SW Virginia. The 15Z is only showing a forecast CAPE of about 500 for eastern Virginia. At this point, I will probably wait outside of Richmond with easy access to I-64 and I-95. The warm front is just north of Richmond and I’ll have to decide whether to follow it northward or wait on the east side of Richmond.

Bill Hark

 

[David Dildine]

Visible is showing clearing near the NC/VA border but not enough into central VA to get me out into lower Southern MD. The warm front is reluctant to head north and temps here are still in the mid 50s. I like the area east of Richmond into Hampton Roads though, Bill.

 

[Chris Hovanic]

Watching this one as well, as I grew up in Orange County...just outside of Charlottesville, VA.

As of 18z, surface mesolow was located between Roanoke and Martinsville. Warm front extended E-NE from near Roanoke to just south of Lynchburg, to Dillwyn, to near Ashland. As David noted above, warm front is moving slower than model projections...thinking the warm front will extend from just south of Charlottesville to near Fredericksburg by 20-21z.

I think that the storms currently initiating in vicinity of the mesolow near Roanoke should intensify and become more organized as they move into higher moisture/instability to the east/northeast, as well as moving into the heart of the upper-diffluent axis. Deep-layer shear also improves as one moves northeast.

Hodographs in vicinity of the warm front look reasonable for Mid-Atlantic standards, with a "short-sickle" shape evident...low-level storm relative inflow is very close to normal with the 0-0.5km shear vector, suggestive of tornadic potential (Giuliano/Estherheld - see link - http://www.ejssm.org/ojs/index.php/ejssm/article/view/33), especially given ambient moisture content and associated low LCLs.

Fredericksburg, VA 21z Hodograph:

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=009&STATIONID=KEZF