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7/27 Severe Threat Discussion and Obs


Kmlwx

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You have to look at more than instability parameters. Location of the low level jet and best upper divergence occurs in Ohio and WV. Look at the upward vertical velocity and relative vorticity at 850, 700, and 500 mb.. It all comes together aloft over the moderate risk area. 

 

MDT area looks fine, meant the 30% going more north into PA. 

 

Either way, should be interesting. 

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LWX going all in... disco good and warns people to keep tabs on weather

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
308 PM EDT SAT JUL 26 2014

.SYNOPSIS...
HIGH PRESSURE IS MOVING OFFSHORE. LOW PRESSURE IS EXPECTED TO
TRACK ACROSS PENNSYLVANIA SUNDAY NIGHT WITH AN ASSOCIATED COLD
FRONT MOVING INTO THE MID ATLANTIC. A REINFORCING FRONT WILL CROSS THE
REGION MONDAY. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT BRINGING
COOLER AND DRIER CONDITIONS DURING MIDWEEK.


&&

.NEAR TERM /THROUGH SUNDAY/...
HIGH PRESSURE HAS MOVED FURTHER OFF THE COAST THIS AFTERNOON WHILE A
SFC TROUGH HAS DEVELOPED ACROSS THE MID-ATLANTIC. A TIGHT DEWPT
GRADIENT PERSISTS NEAR THE BLUE RIDGE. A SHORTWAVE TROUGH HAS
MOVED OFF THE EAST COAST EARLY THIS AFTERNOON. A LINE OF SHOWERS AND
THUNDERSTORMS FORMED ON AN OUTFLOW BOUNDARY FROM MORNING SHOWERS TODAY.
THESE SHOWERS HAVE INTENSIFIED AS THEY ENTERED AN AREA OF HIGHER
INSTABILITY AND MOVED ACROSS WARM WATERS. SUBSIDENCE BEHIND THE
DEPARTING SHORTWAVE HAS LEFT THE REMAINING LOOKOUT AREA MOSTLY
SUNNY WITH TEMPS REACHING THE MID TO UPPER 80S.

WARM AIR ADVECTION WILL INCREASE THIS EVENING AS A WARM FRONT
APPROACHES THE REGION. THIS WILL BE THE BEGINNING OF DETERIORATING
CONDITIONS ACROSS THE MID-ATLANTIC AS WINDS ALOFT INCREASE. SCT
SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS THE HIGHLANDS LATE
TONIGHT AS WAA MOVES INTO THE REGION. REMNANTS OF SEVERE
THUNDERSTORMS WILL CONGEAL INTO A MCS ACROSS THE OHIO VALLEY LATE
TONIGHT. THIS ACTIVITY WILL BE AHEAD OF A COLD FRONT AND
ASSOCIATED SFC LOW AND IS HARD TO PINPOINT THE EVOLUTION. THERE ARE
DIFFERENT SOLUTIONS FOR THE TRACK AND SPEED OF THIS MCS AT THIS
TIME BUT ALL SOLUTIONS SHOW A FEATURE TRACKING ACROSS THE OHIO
VALLEY AND REACHING THE MID ATLANTIC LATE TONIGHT AND INTO SUNDAY
MORNING. HEAVY RAIN AND THUNDERSTORMS ARE EXPECTED TO MOVE INTO
THE POTOMAC HIGHLANDS EARLY SUNDAY MORNING AND TRACK EASTWARD.
INSTABILITY WILL LOW SUNDAY MORNING BUT SHEAR WILL BE INCREASING
AND AT THIS TIME THUNDERSTORMS ARE EXPECTED TO BE SUB-SEVERE. THIS
MCS/SHORTWAVE TROUGH SHOULD MOVE ACROSS THE REGION BY SUNDAY
AFTERNOON AND SUBSIDENCE BEHIND IT WILL LEAD TO SOME BREAKS IN THE
CLOUDS. DESTABILIZATION ON SUNDAY WILL DEPEND ON THE TRACK AND
SPEED OF THIS MCS. OVERALL...INSTABILITY IS PROJECTED TO INCREASE
TO AROUND 2K J/KG SUNDAY AFTERNOON. AT THIS TIME...SHEAR PROFILES
WILL HAVE ALSO INCREASED WITH 40-50KTS OF 0-6 KM SHEAR ACROSS THE
REGION WITH A MAJORITY OF THAT BETWEEN 0-1KM.


THE COLD FRONT IS EXPECTED TO PRODUCE DISCRETE STRONG TO SEVERE
CELLS ACROSS THE OHIO VALLEY SUNDAY AFTERNOON. THIS ACTIVITY WILL
TRACK EASTWARD AND REACH THE POTOMAC HIGHLANDS SUN LATE AFTERNOON
REACHING THE INTERSTATE 95 CORRIDOR AFTER 8 PM. AHEAD OF THE FRONT
THUNDERSTORMS ARE EXPECTED ALONG OUTFLOW/DIFFERENTIAL HEATING
BOUNDARIES FROM DEPARTING MCS. THE ATM WILL BE CONDUCIVE FOR SEVERE
THUNDERSTORMS CAPABLE OF SUPERCELLS. CURVED HODOGRAPHS WITH 50KTS OF
SHEAR WILL LIKELY CAUSE DMG WINDS...LARGE HAIL AND TORNADOES.
SUPERCELLS WILL BE CAPABLE OF SPAWNING A COUPLE TORNADOES. THESE
SIGNALS ARE STRONGER THAN THE MID-ATLANTIC USUALLY WITNESSES.
PLEASE USE CAUTION SUNDAY AND SUNDAY NIGHT AND MAKE SURE YOU ARE
NEAR AN OUTLET TO RECEIVE UP TO DATE WEATHER INFORMATION.
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MDT area looks fine, meant the 30% going more north into PA.

Either way, should be interesting.

I would assume that's the warm frontal zone? Haven't been on a computer much last day or two to examine.
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Well... night time tors are never fun... ~300 1km m2/s2 at 2am per 06z sounding at KIAD with 1500 SBCAPE and 1800 MLCAPE

It almost looks like the 18z NAM just backed up a few hours with our threat IMO

Good luck with that. ;)

Just hope the nam is wrong. :P

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Latest SREF again has best parameters south of the area. 

That map above looks pretty bad for DC lol

Tracking severe threats for this area is fun and all, but most of the time the actual outcome is a notch above garden variety. Thats always fine with me, as by mid to late summer my goal is to get rain frequently enough to keep me from having to reseed half my lawn in the fall.

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15% slight risk in the morning when we wake up? ;)

Wooooo mehstorms

Pattern recognition still says it's worth an extra eye but the GFS has a huge cape hole over us thru much of the day. I dunno.
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