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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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Just now, 09-10 analogy said:

The remnant surface is in SW PA now and what to Dc’s south look like it’s going wide to the right? So I guess I shouldn’t plan on much local excitement, not that expectations were that high anyway. 

There is likely to be renewed activity. Where exactly that impacts remains to be seen. 

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23 minutes ago, Kmlwx said:

Still not really much development going on to the south of that line. Nice storm for HGR though it seems. 

      A few cells popping up in western Montgomery and near Culpepper.     HRRR shows a strong line (or line with embedded supercells?) moving through DC  and points north after dinner time.

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11 minutes ago, mappy said:

WBAL at noon was honking on big time severe this evening. Was a surprise to me.

Sterling's updated short term AFD is...interesting:

Quote
.NEAR TERM /THROUGH TONIGHT/...
A LIGHT SOUTH TO SOUTHWEST FLOW THROUGH THE LOW-LEVELS WILL 
CONTINUE AROUND THE HIGH OVER THE ATLANTIC AND AHEAD OF THE 
APPROACHING COLD FRONT, AND THIS WILL CAUSE MORE HOT AND HUMID 
CONDITIONS THIS AFTERNOON WITH MAX TEMPS IN THE LOWER TO MIDDLE 
90S FOR MOST AREAS WITH HEAT INDICES IN THE UPPER 90S TO LOWER 
100S. CONFIDENCE IS TOO LOW FOR A HEAT ADVISORY SINCE DEWPOINTS 
MAY MIX DOWN JUST A BIT AROUND PEAK HEATING, AND THERE WILL BE 
MORE SHOWERS AND THUNDERSTORMS DURING PEAK HEATING AS WELL.

A POTENT SHORTWAVE WILL SLOWLY MOVE EAST, PASSING THROUGH OUR
AREA THIS AFTERNOON AND EVENING. AT THE SAME TIME, A PRESSURE 
TROUGH WILL BE OVER OUR AREA, AND IT MAY BE ENHANCED SOMEWHAT BY
THE SHORTWAVE. A LIGHT FLOW THAT MEANS MORE BOUNDARIES FROM 
TERRAIN CIRCULATION AND THE BAY/POTOMAC BREEZES ARE EXPECTED AS 
WELL. 

STRONG TO EXTREME INSTABILITY IS EXPECTED THIS AFTERNOON AND
EVENING WITH 1000-2000 J/KG MLCAPE ALREADY PRESENT NEAR AND EAST
OF THE BLUE RIDGE AS OF 12Z PER MESOANALYSIS. MID-LEVEL LAPSE
RATES ARE MODEST 6 C/KM IN THE 12Z RAOB IAD AS IS TO BE EXPECTED
IN A MOIST LATE SUMMER ENVIRONMENT AND MAY ACTUALLY DECREASE
SOMEWHAT THROUGH MIDDAY BEFORE STEEPENING SLIGHTLY AGAIN LATE
THIS AFTERNOON. EVEN SO, DEW POINTS NEAR OR IN EXCESS OF 70
DEGREES AND PWS EXCEEDING 2 INCHES SHOULD RESULT IN AMPLE MLCAPE
OF 2500-3500 J/KG EAST OF I-81. A WEAK SHORTWAVE PERTURBATION
OVER EASTERN WV THIS MORNING WILL DRIFT EASTWARD THROUGH THE
DAY, RESULTING IN A SHARPENING LEE PRESSURE TROUGH WHICH SHOULD
IGNITE NUMEROUS THUNDERSTORMS THIS AFTERNOON. DESPITE WEAK FLOW
OF 15 KTS IN THE MID-LEVELS, THE COMBINATION OF STRONG
CONVERGENCE ALONG THE LEE TROUGH COUPLE WITH ADDED CONVERGENCE,
LIFT AND MODEST LOW LEVEL DIRECTIONAL SHEAR ACROSS BAY/RIVER
BREEZE CIRCULATIONS SHOULD BE ENOUGH TO LOOSELY ORGANIZE CELLS
INTO CLUSTERS CAPABLE OF PRODUCING SCATTERED WIND DAMAGE; A
COUPLE OF CONSIDERABLE MICROBURSTS CAN'T BE COMPLETELY RULED OUT
GIVE A SLIGHT ENHANCEMENT OF ABOUT 20 KTS AT 700 MB AROUND THE
NORTHERN PERIPHERY OF RIDGING OFF THE CAROLINAS AND DCAPE 
AROUND 1000 J/KG. LARGE HAIL CANNOT BE RULED OUT EITHER GIVEN 
THE STRONG TO EXTREME INSTABILITY. IN ADDITION, THE ABUNDANT 
CAPE IN THE HAIL GROWTH ZONE WITH DEEP MOIST PROFILES MAY RESULT
IN PROLIFIC LIGHTNING PRODUCING STORMS THIS AFTERNOON AND 
EVENING. HREF PROBABILITIES OF UPDRAFTS SPEEDS >20 M/S OF 
50-70% SUPPORT THE NOTION OF SCATTERED SEVERE THUNDERSTORM 
COVERAGE THIS AFTERNOON AND EVENING. 

A FLASH FLOOD WATCH IS IN EFFECT FOR NORTHEASTERN MD AS WELL AS
THE BALTIMORE AND WASHINGTON METRO AREAS. THUNDERSTORMS ARE MOST
LIKELY ACROSS THESE AREAS, AND THIS OVERLAYS WHERE THE BEST 
MOISTURE IS. ALSO, AS THE SHORTWAVE PASSES THROUGH, IT DOES 
APPEAR THAT IT WILL BE STRONG ENOUGH FOR LOW PRESSURE TO 
DEVELOP. MOST GUIDANCE CLOSES OFF AN 850MB LOW OVER NORTHEASTERN
MD. THIS WILL ENHANCE FORCING LATE THIS AFTERNOON THROUGH THIS 
EVENING, CAUSING A BETTER CHANCE FOR TRAINING CONVECTION ACROSS 
THE BALTIMORE METRO AREA INTO NORTHEASTERN MD. FARTHER 
SOUTHWEST, CONVECTION MAY BE A LITTLE MORE PROGRESSIVE ACROSS 
THE DC AREA, BUT THERE MAY BE A COUPLE ROUNDS, AND VERY HEAVY 
RAINFALL RATES MAY STILL CAUSE ISSUES WITH FLASH FLOODING IN 
URBAN AREAS EVEN IF IT IS SOMEWHAT PROGRESSIVE. THAT'S WHY THE 
WATCH WAS ISSUED FOR THIS AREA. AN EXPANSION OF THE WATCH MAY BE
NEEDED IN AREA TO THE NORTHWEST INTO NORTH-CENTRAL MD, OR EVEN 
ACROSS PORTIONS OF SOUTHERN MD. WILL CONTINUE TO MONITOR THIS 
POSSIBILITY THROUGHOUT THE DAY. WHILE THE BEST CHANCE FOR 
NUMEROUS THUNDERSTORMS WILL BE LATE THIS AFTERNOON AND EVENING, 
AN EARLIER INITIATION IS POSSIBLE ALONG THE BAY/POTOMAC BREEZES
SINCE THERE MAY BE A LITTLE MORE CONVERGENCE (SOUTHEAST WIND 
INTO SOUTH OR SOUTHWEST WIND). THAT'S WHY THE WATCH STARTS 
EARLIER THIS AFTERNOON. 

THE SHORTWAVE WILL MOVE OFF TO THE EAST LATER THIS EVENING AND
OVERNIGHT. CONVECTION SHOULD DISSIPATE THIS EVENING FOR MOST
AREAS, BUT IT MAY HANG AROUND FOR A BIT ACROSS NORTHEASTERN MD
BEFORE DISSIPATING OVERNIGHT. AREAS OF FOG AND LOW CLOUDS ARE
POSSIBLE OVERNIGHT.

 

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