4/03/06 FCST: NC/VA

As the models have been consistently indicating moderate instability co-located with 50-60kt deep layer shear and favorable low level storm relative helicities over parts of North Carolina and Virginia on Monday, and since there are a handful of chasers besides myself that live in/near the region, I decided to go ahead start a forecast thread for the area for April 3. Upper trough and associated surface cold front will race quickly eastward thru the Carolinas and Virginia during the afternoon and early evening Monday, encountering an increasingly unstable airmass farther east as the afternoon wears on. Although the primary storm mode Monday will likely to be broken bows/lewps, my current thinking is that there will be a relatively small area tomorrow that has a chance of discrete supercells, with locally enchanced 0-3km directional shear (speed shear doesn't look to be an issue anywhere ahead of the front.) Right now, I am especially liking an area along and east of I-95 south/east Richmond, VA and north/east of Rocky Mount, NC sometime during the last 3 hours of daylight Monday. If I had to pick a target city now, I'd say Murfreesboro, NC at the intersections of Hwy 158/258 along the NC/VA border. Areas north of there are likely to be under a rain sheild and/or thick clouds throughout most of the afternoon, and any convection to the north is likely to be strongly forced into one or more lines, whereas areas south and southwest of the target also look to be much more linearly forced with nearly unidirectional shear from 0-6km agl.

My reasoning behind this target: 4/2/06 12Z NAM, as well as previous runs, is showing a strong dry punch at 700mb from western South Carolina ENE across southeastern NC, with this dry air nosing into northeastern NC to just south/SW of the target area by 00Z. The dry punch should focus surface convergence north of it, while at the same time helping to clear out any non-anvil WAA-related low/mid level clouds that may exist over the TA during the early afternoon hours. The NAM indicates a secondary surface low (meso low?) will develop along the triple point across northeast WV during the late afternoon and move east into northern VA by early evening, as the primary surface low continues to track NE near Ontraio, Canada. This secondary low should help back the winds in the TA so that they have at least some eastlerly component to them. I'm not sure if I agree with the pure southeast (135 degree) winds the NAM has forecasted for most of the TA, but I do feel that at least SSE surface winds are not out of the question in the area. Forecasted storm motions range from 265-280 degrees from north to south across the TA, so even southerly surface winds would allow for 70-80 degrees of 0-6km directional shear. However, with nearly unidirectional flow from 850mb - 500mb likely, southerly or SSE surface winds would also mean 70-80 degree of directional shear from the surface to 850, leading to 0-1km storm relative helicities from 150-250 m^2/s^2 from south to north across the TA.

My primary concern for tomorrow is storm mode, but I'm thinking there is a chance for discrete supercells in the target area. Although the western edge of the temperature axis is forecasted to be oriented SW to NE across the region, the western 60 degree isodrosotherm is forecasted to be lined up generally south to north, even taking on a 'negative' tilt over far northeastern NC at 00Z, likely due to the strong dry punch at 700mb to the south. West-southwesterly 500mb flow would cross the western edge of the dewpoint axis at nearly 90 degrees in this area, increasing the likelihood of discrete convection.

To sum it all up, severe storms are likely across southeastern VA and northeastern NC on Monday, although the development of discrete supercells and tornadic activity will strongly depend of the development and timing/position of the secondary surface low late Monday afternoon/early evening.
 
Possible severe storms across eastern Virginia, North Carolina


According to the 00Z Eta, there is an approaching 500 MB trough, though the best winds (40 knots or greater) shift to SE Virginia and southward by 00Z. A cold front is approaching from the west and a surface low will be moving across eastern Michigan. This will produce backed winds across eastern Virginia, North Carolina and Maryland. 60 degree dewpoints should cover eastern Virginia with a brief period of time by 18 Z of 65 degree dewpoints to the VA/NC border. There is a predicted narrow area of CAPE up to 3000 that pushes northward to about the town of Winton by 18Z. Helicities should increase from 100 at 18Z to 200 by 0Z across Se Va/Ne NC. Supposedly, a secondary surface low will develop over central and eastern Virginia per the SPC but I don’t see it. I am currently targeting the Emporia to Roanoke Rapids area (maximizing instability, upper level support and hopefully backing of winds) but I’ll have to look at more data in the A.M. Hopefully I can get out of work early enough.

Bill Hark
 
We'll see if we can actually keep the flow backed here in E NC...and if we can keep storms isolated for long enough. NC Stater's planning to go out tomorrow to chase..err...get run over by slow moving..err...speed of sound moving supercells that are isolated..err..part of a larger convective cluster/MCS. :) In all seriousness, would be a good test run before we track out to the Midwest in Mid-May.

4.5 km WRF NMM develops convection W of Winston Salem, NC as early as 16 UTC, then roars a massive squally squall through the Triangle and out to the big pond. More isolated convection develops behind the initial MCS closer to 00 UTC, and as much as I'd like to believe discrete cells will be roaming around here tomorrow, I realize the only ones will be in my dreams. Certainly a damaging wind/hail threat.

http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/

Will post in the morning before we decide on a location to chase, err get run over :)
 
Cirrocast from west looks troublesome per visible. Thoughts? I have to get at leaaast a couple more hours of sleep if I'm going to make the best of a moderate day in VA. I'm ready 2006: let's see whachu got!
 
Ya David that is what gets me to today but maybe the deck will clear later giving us some daytime heating. For all that will be out in the Midatlantic I and Jesse Bass will be out there. Bill H I need to follow you, you have the Virginia tornado record...lol.

Good Luck to all stay safe..
 
Getting ready to see my last patient, then I am out the door. I am still hopeful about today. Surface winds are still backed across most of E VA and NC. Approaching 500 trough. Predicted CAPE (via RUC) not as high, maybe 1000 in SE VA and E NC. Helicities should be around 200 at 0Z. Thereis nice clearing and already some active Cu near Raleigh. I hope the airmass can recover. I will blast out of Richmond by approx 2:30PM, initally targetting RockyMount NC. There is a good east option. Unfortunately, I like the better predicted helicities near Wilmington but I can't make it intime.

Good luck to those chasing. There may be a nice shot at isolated tornadic cells before they "line out".

Bill Hark
 
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