Mesoscale Discussion 2001

Issued

Sep 27, 2012, 8:57 PM EDT (00:57 UTC)

Expired

Sep 27, 2012, 10:00 PM EDT

In force

63 min

Issued by

the Storm Prediction Center

The Sterling radar (KLWX), 53 km from the middle of the area, began a volume at 00:59 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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036 
ACUS11 KWNS 280058
SWOMCD
SPC MCD 280057
MDZ000-VAZ000-DCZ000-280200-

MESOSCALE DISCUSSION 2001
NWS STORM PREDICTION CENTER NORMAN OK
0757 PM CDT THU SEP 27 2012

AREAS AFFECTED...NRN VA INTO PARTS OF CENTRAL AND SRN MD INCLUDING
THE WASHINGTON DC METRO

CONCERNING...SEVERE THUNDERSTORM WATCH 654...

VALID 280057Z - 280200Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 654
CONTINUES.

SUMMARY...THREAT FOR DAMAGING WINDS AND HAIL REMAIN POSSIBLE ACROSS
MUCH OF WW 654 THIS EVENING.  A CLUSTER OF STORMS...CURRENTLY
LOCATED IN FAR NRN VA /GENERALLY IN AN AREA FROM 25 W OF DCA TO 50
AND 65 WSW OF DCA/...PER REGIONAL RADAR IMAGERY WILL PROGRESS EWD
WITH THE LEADING PART OF THIS ACTIVITY MOVING ACROSS THE WASHINGTON
DC AREA BETWEEN 01-02Z.  A TORNADO THREAT CANNOT BE RULED OUT GIVEN
VERTICALLY VEERING WINDS COMBINED WITH A STORM MOTION TO THE ESE AT
20-25 KT.  COUNTIES IN THE WAKE OF THE MAIN TSTM CLUSTER SHOULD
CONTINUE TO HAVE A DIMINISHED SVR WEATHER THREAT AND CAN BE LOCALLY
CANCELLED FROM THIS WATCH.

PW VALUES OF 1-1.5 INCH AND A SOMEWHAT SLOWER STORM MOTION SUGGEST
HEAVY RAINFALL RATES WILL BE POSSIBLE WITH THE STORMS MOVING FROM
NRN VA INTO THE WASHINGTON DC METRO AND EVENTUALLY PARTS OF
CENTRAL/SRN MD.

DISCUSSION...A PROGRESSIVE CLUSTER OF STORMS LOCATED TO THE WSW OF
DCA IS LOCATED WITHIN A ZONE OF DEEP LAYER ASCENT ASSOCIATED WITH
DIVERGENCE IN THE EXIT REGION OF A 60-65 KT WLY UPPER LEVEL JET
EXTENDING FROM SRN WV INTO VA.  LOW LEVEL CONVERGENCE MAY BE
ENHANCED IN NRN VA ATTENDANT TO A MESOLOW WITHIN THE SRN LOBE OF
VORTICITY EXTENDING SWD FROM THE MORE VIGOROUS MIDLEVEL IMPULSE
ADVANCING EWD ACROSS SWRN-SOUTH CENTRAL PA TO NRN WV.  DESPITE WEAK
MIDLEVEL LAPSE RATES...A RELATIVELY MOIST AIR MASS WITH PW VALUES
EXCEEDING 1-1.5 INCH CONTINUE TO CONTRIBUTE TO MLCAPE OF 500-1000
J/KG. THIS COMBINED WITH EFFECTIVE BULK SHEAR OF 30-35 KT IS
SUFFICIENT FOR STORM ORGANIZATION.

ALTHOUGH STRONG WIND GUSTS AND HAIL SHOULD BE THE PRIMARY THREATS...
VERTICALLY VEERING WINDS IN THE LOWER TROPOSPHERE AND STORM MOTIONS
TO THE ESE AT 20-25 KT RESULT IN LOW LEVEL SRH VALUES /0-3 KM NEAR
400 M2 PER S2/ SUPPORTING LOW LEVEL STORM ROTATION AND A LOW
PROBABILITY FOR A TORNADO.

..PETERS.. 09/28/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...PHI...AKQ...LWX...

LAT...LON   37907624 38127672 38197725 37977767 38167832 38367803
            38637831 38767816 38847781 39117763 39237740 39367710
            39317677 39207649 39047634 38537617 37887606 37907624

Mesoscale Discussions in Virginia, 2012Mesoscale Discussions in Maryland, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.