Mid-Atlantic Discussion – Aug 21, 2011

It seems like I jinx our severe weather every time I make a post about it. We’ve been faring a lot better with the pulse-type storms than with any sort of organized system this summer, but unfortunately you can’t really chase pulsers since they almost always weaken before you can get to them… not to mention the fact that they almost never produce tornadoes.

Anyway, getting to tomorrow’s threat, we see a cold front and upper-level trough moving through the region, with the best dynamics to our north in PA/NJ/NY up through parts of New England. I’m not particularly thrilled with the setup locally, though it does raise an eyebrow. Most of the concern comes with how the mesoscale features pan out, which the models have had a hard time dealing with since the upper-level energy isn’t that organized. The complicated and convoluted upper-levels, along with weak low-level winds, has been our biggest downfall this summer. Stronger, more highly concentrated features would help improve not only lift but the mid-level lapse rates as well, which is another key to getting well-organized and sustained storms (at least in our region).

Tomorrow looks a bit better than previous setups this summer (mostly due to the better looking lapse rates and possibility of a low-level “jet”) as a cold front and upper-level jet streak move into the region. Lapse rates are good up to 650mb, but the 650mb-300mb lapse rates are fairly poor. A low-level jet could develop tomorrow across the eastern parts of the region, which would help boost storm formation and organization. Another issue is timing, with the storms expected to form before peak heating in most of the region. Pre-frontal rain/clouds are also a concern, thought not so much as they have been in previous setups.

Chase-wise, I would pick eastern PA/NJ or even the Delmarva Peninsula as possible targets unless good storms can get going early in MD/NoVA/central PA. I may have to sit this one out as I am working the overnight tonight, and sleep will weigh into the decision.

SPC’s thoughts:

…NEW ENGLAND/ERN NY/MID-ATLANTIC/CNTRL APPALACHIANS…
A LARGE UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS THE GREAT LAKES AND
OH VALLEY SUNDAY AS A 60 TO 75 KT MID-LEVEL JET ROUNDS THE BASE OF
THE TROUGH. AHEAD OF THE UPPER-LEVEL TROUGH….MODEL FORECASTS
INITIATE NUMEROUS THUNDERSTORMS ALONG AN AXIS OF MODERATE
INSTABILITY FROM WRN NEW ENGLAND SSWWD INTO THE MID-ATLANTIC BY
EARLY SUNDAY AFTERNOON. FORECAST SOUNDINGS ALONG THIS CORRIDOR AT
21Z SHOW MLCAPE VALUES IN THE 1200 TO 2000 J/KG RANGE WITH MODERATE
DEEP LAYER SHEAR AND SOME DIRECTIONAL SHEAR IN THE LOW-LEVELS. AS
THE NOSE OF THE MID-LEVEL JET MOVES INTO THE NERN STATES SUNDAY
AFTERNOON…DEEP LAYER SHEAR WILL INCREASE MAKING CONDITIONS
FAVORABLE FOR SEVERE STORMS ALONG THE INSTABILITY AXIS. IN
ADDITION…MODEL FORECASTS INTENSIFY A LOW-LEVEL JET ACROSS THE
SLIGHT RISK AREA IN THE LATE AFTERNOON SUGGESTING WIND DAMAGE COULD
BE THE GREATEST THREAT. CONSIDERING 500 MB TEMPS SHOULD BE IN THE
-10 C TO -12 C RANGE…HAIL WILL ALSO BE POSSIBLE IN AREAS WHERE
INSTABILITY AND SHEAR ARE MAXIMIZED. ALTHOUGH MORE CONDITIONAL…AN
ISOLATED TORNADO THREAT COULD ALSO DEVELOP NEAR THE CENTER OF THE
LOW-LEVEL JET IN THE MID-ATLANTIC WHERE THE STRONGEST INSTABILITY IS
FORECAST AND SFC DEWPOINTS SHOULD BE IN THE MID TO UPPER 60S F.


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