Alert archive / Maryland / Mesoscale Discussions in 2012

Mesoscale Discussion 1933

September 8, 20126 states

The Storm Prediction Center issued this mesoscale discussion at Sep 8, 2012, 2:12 PM EDT for 6 states. It was in force for 93 min.

The area

The outline as issued.

The facts

Issued
Sep 8, 2012, 2:12 PM EDT (18:12 UTC)
Expired
Sep 8, 2012, 3:45 PM EDT
In force
93 min
Issued by
the Storm Prediction Center
All 58 counties

Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Talbot County, MD, Burlington County, NJ, Camden County, NJ, Cumberland County, NJ, Essex County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Morris County, NJ, Salem County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Richmond County, NY, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Delaware County, PA, Lancaster County, PA, Lehigh County, PA, Monroe County, PA, Montgomery County, PA, Northampton County, PA, Philadelphia County, PA, York County, PA, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Manassas, VA, City of Manassas Park, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Loudoun County, VA, Prince William County, VA, Rappahannock County, VA, Stafford County, VA, Warren County, VA

The radar

The Dover AFB radar (KDOX), 125 km from the middle of the area, began a volume at 18:16 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.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 6.2 hours before the alert went out and 125 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Washington/Dulle, VA at 12:00Z on 2012-09-08Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 252 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 12:00Z on 2012-09-08The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 150 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
252 J/kg
Mixed-layer CIN
-81 J/kg
Mixed-layer LCL
638 m above ground
0-6 km bulk shear
39 kt
0-1 km storm-relative helicity
150 m²/s²
0-3 km storm-relative helicity
140 m²/s²
Significant tornado parameter
0.1
Supercell composite
1.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

694 
ACUS11 KWNS 081813
SWOMCD
SPC MCD 081812
NJZ000-NYZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-081945-

MESOSCALE DISCUSSION 1933
NWS STORM PREDICTION CENTER NORMAN OK
0112 PM CDT SAT SEP 08 2012

AREAS AFFECTED...ERN PA...NJ...MD...NRN VA/DE...DC

CONCERNING...SEVERE THUNDERSTORM WATCH 636...

VALID 081812Z - 081945Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 636
CONTINUES.

SUMMARY...DAMAGING WIND THREAT INCREASING AS COLD FRONT MERGES WITH
PRE-FRONTAL CONVECTIVE BAND. EMBEDDED LEWPS/BOWING STRUCTURES WILL
BE CAPABLE OF ENHANCED/SIGNIFICANT WIND DAMAGE WITH COVERAGE LIKELY
INCREASING SUBSTANTIALLY.

DISCUSSION...COLD FRONT FROM BRADFORD COUNTY PA TO HIGHLAND COUNTY
VA AS OF 18Z. THIS FRONT IS ABOUT TO MERGE WITH PRE-FRONTAL
CONVECTION THAT HAS DEVELOPED ALONG A DIFFERENTIAL HEATING ZONE. AS
THIS PROCESS OCCURS AMIDST A DOWNSTREAM AIR MASS CHARACTERIZED BY
SURFACE TEMPERATURES IN THE 80S TO LOWER 90S...THIS QLCS SHOULD
INTENSIFY. DEEP-LAYER SHEAR WILL BE FAVORABLE FOR BOWING/LEWP
STRUCTURES CAPABLE OF POTENTIALLY SIGNIFICANT/NUMEROUS REPORTS OF
WIND DAMAGE. A BRIEF TORNADO OR TWO IS ALSO POSSIBLE PARTICULARLY
ACROSS THE NRN PORTION OF WW 636 ON THE FRINGE OF STRONGER LOW-LEVEL
SWLYS.

..GRAMS.. 09/08/2012

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

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

LAT...LON   38917828 39427728 40307636 40937599 41237557 41267516
            41147453 40687408 40067421 39137508 38387641 38367722
            38397802 38577844 38917828

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 8, 12:15 PM EDTSevere Thunderstorm WatchSPCKent, New Castle, Sussex9 hr
Sep 8, 4:22 PM EDTMesoscale DiscussionSPCKent, New Castle, Sussex53 min
Sep 8, 5:00 AM EDTMesoscale DiscussionSPCAllegany, Garrett60 min
Sep 8, 11:38 AM EDTMesoscale DiscussionSPCAllegany, Baltimore, Carroll, Frederick, Howard, Montgomery and 2 more97 min
Sep 8, 1:48 PM EDTSevere Thunderstorm WatchSPCDorchester, Somerset, Wicomico, Worcester7 hr
Sep 8, 3:25 PM EDTMesoscale DiscussionSPCSaint Mary's, Somerset65 min
Sep 8, 10:39 AM EDTMesoscale DiscussionSPCBergen, Hudson, Passaic2 hr
Sep 8, 11:18 AM EDTTornado WatchSPCBergen, Essex, Hudson, Passaic, Union10 hr
Sep 8, 1:30 PM EDTMesoscale DiscussionSPCBergen, Hudson60 min
Sep 8, 12:57 AM EDTMesoscale DiscussionSPCChautauqua2 hr
Sep 8, 8:42 AM EDTMesoscale DiscussionSPCBroome, Cayuga, Chemung, Chenango, Cortland, Herkimer and 13 more93 min
Sep 8, 10:03 AM EDTSevere Thunderstorm WatchSPCAllegany, Cattaraugus, Cayuga, Chemung, Franklin, Genesee and 16 more5 hr
Sep 8, 12:40 PM EDTTornado WatchSPCAlbany, Broome, Chenango, Clinton, Columbia, Cortland and 22 more7 hr
Sep 8, 2:46 PM EDTMesoscale DiscussionSPCAlbany, Clinton, Columbia, Delaware, Dutchess, Essex and 14 more59 min
Sep 8, 3:55 PM EDTMesoscale DiscussionSPCColumbia, Rensselaer, Washington65 min
Sep 8, 6:17 PM EDTMesoscale DiscussionSPCSuffolk58 min
Sep 8, 12:20 PM EDTMesoscale DiscussionSPCAmherst, Appomattox, Bedford, Botetourt, Buckingham, Campbell and 22 more115 min
Sep 8, 7:10 PM EDTMesoscale DiscussionSPCGreensville, Isle of Wight, Prince George, Southampton, Surry, Sussex and 3 more65 min

Nearby

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

Sources

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.