Mesoscale Discussion 1239

Issued

Jun 22, 2012, 12:18 PM EDT (16:18 UTC)

Expired

Jun 22, 2012, 2:45 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Chance of a watch

60%

The Philadelphia radar (KDIX), 71 km from the middle of the area, began a volume at 16:19 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Severe Thunderstorm Watch 417Jun 22, 1:45 PM EDT
• Severe Thunderstorm Watch 418Jun 22, 2:15 PM EDT

620 
ACUS11 KWNS 221619
SWOMCD
SPC MCD 221618
NYZ000-CTZ000-MAZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-221845-

MESOSCALE DISCUSSION 1239
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CDT FRI JUN 22 2012

AREAS AFFECTED...PORTIONS NRN/ERN  VA...CENTRAL/ERN PA...SWRN NEW
ENGLAND...SRN NY...DE...MD...NJ...DC.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 221618Z - 221845Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...SVR THREAT FCST TO INCREASE FROM MULTICELLULAR
CONVECTION...OF DISCRETE...CLUSTERED AND QUASI-LINEAR
CHARACTER...DEVELOPING THROUGH MID-AFTERNOON AND MOVING OVER THIS
AREA.  MAIN CONCERN IS DAMAGING GUSTS.

DISCUSSION...TSTMS ARE FCST TO DEVELOP IN AT LEAST TWO PRIMARY
SWATHS OR BANDS...
1. NEAR AND E OF DIFFERENTIAL HEATING ZONE...ASSOCIATED WITH
LOW-MIDDLE LEVEL CLOUD BAND NOW EVIDENT ON VIS IMAGERY FROM ERN PA
SWWD ACROSS VA/WV BORDER REGION.  ANY SUCH TSTMS WILL POSE EARLIEST
SVR RISK FROM TIDEWATER AREA NEWD OVER COASTAL MID-ATLC AND SRN NEW
ENGLAND.
2. ALONG/AHEAD OF SFC COLD FRONT...INITIALLY OVER HIGHER TERRAIN OF
CENTRAL PA INTO NRN WV.  FRONT PRECEDES POSITIVELY TILTED MID-UPPER
TROUGH BY ABOUT 100-150 NM USING MOISTURE CHANNEL IMAGERY...BUT WITH
SOME LARGE-SCALE ASCENT EVIDENT OVER FRONTAL ZONE.  THESE FEATURES
WILL SHIFT EWD OVER MID-ATLC REGION THIS AFTERNOON.

16Z SFC ANALYSIS SHOWED COLD FRONT FROM NRN NY SWWD ACROSS
CENTRAL/SWRN PA AND WRN WV.  SFC TROUGH WITH WEAK EMBEDDED LOWS WAS
EVIDENT PARALLEL TO COLD FRONT AND FARTHER E...EXTENDING FROM SERN
VA NNEWD OVER SRN CHESAPEAKE BAY AND ERN NJ TO RI AND ERN
MA...INTERSECTING WARM FRONT JUST OFFSHORE NH.  WARM FRONT EXTENDED
NNEWD FROM THERE OVER MAINE.  TROUGH APPEARS COLLOCATED WITH SEA
BREEZE BOUNDARY OVER ERN NJ...AND A COUPLE OF TSTMS ALREADY HAVE
DEVELOPED THERE.

MODIFIED IAD/APG/WAL/OKX RAOBS SUGGEST PREFRONTAL BOUNDARY LAYER
SHOULD MIX VIGOROUSLY ACROSS MUCH OF NEAR-COASTAL CORRIDOR IN
RESPONSE TO CONTINUED STG SFC DIABATIC HEATING.  SIMILAR PROCESS
SHOULD OCCUR BEHIND AFOREMENTIONED PREFRONTAL CLOUD BAND.  RESULT
WOULD BE POCKETS OF REDUCED SFC DEW POINTS...AT BASE OF INVERTED-V
THERMODYNAMIC PROFILE FEATURING NEARLY DRY-ADIABATIC LOW-LEVEL LAPSE
RATES.  YET MOISTURE WILL REMAIN SUFFICIENT EVEN IN THOSE RELATIVELY
DRY AREAS TO OFFSET MODEST MIDLEVEL LAPSE RATES AND KEEP AT LEAST
MRGL BUOYANCY OVER REGION.  GIVEN HORIZONTALLY INHOMOGENEOUS NATURE
OF EXPECTED MIXING/MOISTURE FIELDS...MLCAPE WILL VARY GREATLY WITH
VALUES RANGING FROM 500-2500 J/KG...TRENDING INVERSELY WITH STRENGTH
OF VERTICAL MIXING.  30-35 KT EFFECTIVE SHEAR MAGNITUDES SUPPORT
SOME ORGANIZATION TO MULTICELL MODES...AND POTENTIAL FOR SMALL BOWS
WITH LOCALLY ENHANCED COLD-POOL FORCING.

..EDWARDS/WEISS.. 06/22/2012

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

ATTN...WFO...BOX...OKX...ALY...PHI...BGM...AKQ...CTP...LWX...

LAT...LON   40577881 43297415 41777296 41317279 40647311 40567396
            40587407 40487425 40417399 39797408 39447430 39217462
            38977484 38947498 38737510 38347509 37947531 37837545
            37537632 37627736 38077913 40577881

Mesoscale Discussions in Virginia, 2012Mesoscale Discussions in Pennsylvania, 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.