5/11/2006 FCST: NC/VA

Based on the 051006 12Z NAM run, right now I have a preliminary 18Z target within a 50-mile radius of Statesville, NC and 00Z target centered around Chase City, VA. Forecast consensus is for a mid level cyclone centered over the lower Great Lakes region to deepen and and move slowly east-southeast. Deep surface low, initially east of the mid/upper level low center, is forecast to become more vertically stacked during the afternoon. Current SPC thinking is for convective mode to generally in the form of a low topped squall with embedded (mini) supercells and bows/lewps possiblle. Looking at NAM Skew-T forecasts, I am thinking the same for convective mode, but plan on chasing this one nevertheless. 051006 12Z NAM sounding forecasts for NC/VA stations show rather warm temps from 700-500mb, especially at 550mb, reducing overall CAPE values to under 1500 J/kg. However, forecast soundings for points in target region of west-central NC to south central VA suggest a relativelly steep plume of low level lapse rates will move into the region by mid afternoon, increasing low level CAPE vales to aoa 300 J/kg. Forecasted helicity indices, though not great, do appear adquate for possible short lived tornadoes with the stronger storms, especially just north and east of the weak surface low progged to move from southwestern VA to northeast VA during the afternoon and evening. GFS has a similar solution but moves the system east more quickly Thursday than the NAM. Right now I'm going with the NAM on the timing, with convection firing/intensifying in the eastern NC/VA foothills/western piedmont early afternoon and moving northeast to the western coastal plains of east-central NC/VA (around the I-85 corridor) by 00Z. GFS basically has everything off the coast by 8pm - right now I just don't see things prpgressing that quickly. A compromise between the two models would have convection somewhere near or just east the I-95 corridor in eastern VA/NC by 00Z, a solution I would not write off either atm.
My two primary concerns right now have to do with instability and storm mode, as deep layer and low level shear both look to be moderate to strong by late afternoon, at least the speed components of them. Directional shear gets better north of the NC/VA border, nearer the surface low. My first concern is the amount of sunlight and corresponding surface temps that will be reached during the afternoon. Current indication is that a mid level dry slot will punch in behind the retreating morning convection and help to clear things out, allowing temps to reach the low 70s in western VA to near 80 around the NC/SC border south of Charlotte by mid afternoon. This idea seems reasonable, fairly common occurence with deep mature cyclones. Storm mode - even a quick glance at the dynamics of the system, and it's closed, stacked nature, suggest squall line. My questions are, will storms develop out ahead of the main line/cold front, a bit farther east into the higher low level helicities? Or will convection simply enter from the west as a line and remain in that form as it moves east to the coast by late evening. Hard to tell right now, but I'm concerened there is a good chance for the latter, which would put a big damper on any chasable tornado opportunity tomorrow. I plan on taking the gamble anyways, and will leave for western NC by 8am tomorrow.
 
Possible severe storms for east-central Virginia and North Carolina on Thursday, May 11. There is an approaching cold front and low over the Great Lakes region. A warm front will lift northward. According to the latest NAM, the 500 mb level winds will be from 40 to 60 (SW) while surface winds will be backed. (the GFS shows most of VA with SE winds) Dewpoints will be 65 across Virginia. Helicities will be 150 to 200 across eastern Virginia (better to the NE). Negatives include CAPE that is only forecast to be 500 in central and eastern Virginia. If there can be more clearing, I suspect a severe weather event is possible especially for areas east and northeast of Richmond, Virginia. For right now, my target area is between Richmond and Fredricksburg, VA. Supercells and isolated tornadoes are possible if the CAPE becomes higher than the current forecast.

I will be stuck at work until 5PM, thus the storms may already be fireing and merging into a squall line by the time I can chase. I will be prepared for a quck getaway just in case!

Bill Hark
http://www.harkphoto.com
 
Several NCSU folks are going to be chasing E NC/SE VA today. Certainly a possibility of a few isolated tornadoes assuming we can get mesocyclogenesis along the cf to back the low level flow, which would be juxtaposed on very low LCL heights (AOB 800m). Will post an update once we get out of the city in the next hour.

Funny that today was SUPPOSED to be the start of our Midwest chasing vacation ;)
 
Sitting in a wifi plethora in Wilson, NC E of RAH along I-95. Spotty clearing here and areas both to the N and S. Looks like CU going up along cf and lee trough. Don't think we are going to have a discrete storm mode, but even if it's linear, I could go in for some thunder, lightning and small hail :)

Maybe a cell trying to develop in Hartnett Co to our SW. Otherwise, looks like convection going up in S VA, moving at the speed of sound! :) Hopefully Dr. Bill will catch something up there.

We are gonna hang tight or drift NE.
 
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