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Saturday, Sept 8, 2012 Severe Event


Kmlwx

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Pros: Good wind shear, potent vort max, right-entrance region of a jet streak, good surface wind convergence along the cold front.

Cons: Best shear and dynamics are further north up into PA, instability will be a concern (750-1500 J/kg), mid-level lapse rates are poor everywhere, and pre-frontal clouds and rain could muck stuff up a bit. Also, GFS low-level winds aren't as backed as the NAM, which raises concerns as the GFS tends to be more correct in that regard in our region.

Conclusion: A strong to severe line of storms along the cold front with damaging winds is the biggest concern. Hail is a low risk, and a couple of tornadoes are possible, but that risk is more to our north. I would be more excited about this setup if I were up in PA and/or if the instability improves. Chase potential is questionable... might be best just to chill at home and find a good view.

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I'm not the trough is wicked

It's a good trough, but what surprised me was the vort max being as far south and as strong as it is. I never really took a good look at it recently but I recall thinking the energy was going to be too far north to do us much good aside from "just a line of regular storms" along the cold front. One of the few times we've gotten a nice vort max to dig down in just the right spot for us this year, though it is just a little bit north of ideal placement.

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Just for posterity

...ERN PORTIONS OF OH VALLEY...MID ATLANTIC THROUGH NERN STATES...

A PRE-FRONTAL SQUALL LINE WILL LIKELY BE IN PROGRESS SATURDAY

MORNING FROM THE OH VALLEY SWWD INTO THE TN VALLEY. RICH GULF

MOISTURE /UPPER 60S TO 70F DEWPOINTS/ NOW RESIDING OVER THE MID

ATLANTIC AND SRN PORTIONS OF NERN STATES WILL ADVECT THROUGH

REMAINDER OF THE WARM SECTOR SATURDAY AS SLY LLJ STRENGTHENS IN

ASSOCIATION WITH EJECTING SHORTWAVE TROUGH AND DEEPENING SFC LOW.

WEAK MID LEVEL LAPSE RATES AND AREAS OF CLOUDS WILL MITIGATE

INSTABILITY SOMEWHAT. HOWEVER...BREAKS IN CLOUDS SHOULD ALLOW FOR

SOME DIABATIC WARMING OF THE MOIST BOUNDARY LAYER...CONTRIBUTING TO

MLCAPE FROM 500-1000 J/KG. STORMS ARE EXPECTED TO INTENSIFY ALONG

AND AHEAD OF PRE-EXISTING PROGRESSIVE OUTFLOW BOUNDARY AS WARM

SECTOR DESTABILIZES. DEEP LAYER WINDS WILL INCREASE IN ASSOCIATION

WITH THE SHORTWAVE TROUGH AND ITS ATTENDANT SFC LOW WITH LARGE

HODOGRAPHS AND 40+ KT 0-6 KM SHEAR. ORGANIZED STORMS INCLUDING

LEWP/BOWING STRUCTURES AND EMBEDDED SUPERCELLS WILL BE POSSIBLE AS

ACTIVITY DEVELOPS EWD. DAMAGING WIND AND MAYBE A FEW TORNADOES WILL

BE THE PRIMARY THREATS.

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It's a good trough, but what surprised me was the vort max being as far south and as strong as it is. I never really took a good look at it recently but I recall thinking the energy was going to be too far north to do us much good aside from "just a line of regular storms" along the cold front. One of the few times we've gotten a nice vort max to dig down in just the right spot for us this year, though it is just a little bit north of ideal placement.

I'm not sure there'll be a big tornado threat -- or at least not one worth trying for. A nice line seems more likely. But around here usually good dynamics is more important than anything.

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I'm not sure there'll be a big tornado threat -- or at least not one worth trying for. A nice line seems more likely. But around here usually good dynamics is more important than anything.

Agreed on all points. The mid-level lapse rates are sketching me out big time, but I imagine the dynamics are strong enough to create a good line of storms regardless.

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LWX in their morning disco did state that they expect them to steepen some more in later model runs

I would agree to a point... should see that better further north than in DC/MD specifically (just from looking at the gradient in the height falls). Even then, you're taking the mid-level lapse rates from "bad" to "not as bad but still not good," so while it's notable it's not necessarily going to lead to a significant change (though given the delicate balance of features it could).

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