Alert archive / Virginia / Mesoscale Discussions in 2013

Mesoscale Discussion 2113

December 22, 20136 counties in Maryland; 39 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Dec 22, 2013, 10:00 AM EST for 6 counties in Maryland; 39 counties in Virginia. It was in force for 60 min.

The area

The outline as issued.

The facts

Issued: Dec 22, 2013, 10:00 AM EST (15:00 UTC)
Expired: Dec 22, 2013, 11:00 AM EST
In force: 60 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 45 counties

Calvert County, MD, Charles County, MD, Dorchester County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Amelia County, VA, Brunswick County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Colonial Heights, VA, City of Hopewell, VA, City of Petersburg, VA, City of Richmond, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Gloucester County, VA, Goochland County, VA, Hanover County, VA, Henrico County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Lunenburg County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Richmond County, VA, Spotsylvania County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 83 km from the middle of the area, began a volume at 15:02 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, 3.0 hours before the alert went out and 139 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 0 m above ground
0-6 km bulk shear: 72 kt
0-1 km storm-relative helicity: 470 m²/s²
0-3 km storm-relative helicity: 486 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

903 
ACUS11 KWNS 221500
SWOMCD
SPC MCD 221500 
VAZ000-MDZ000-221600-

MESOSCALE DISCUSSION 2113
NWS STORM PREDICTION CENTER NORMAN OK
0900 AM CST SUN DEC 22 2013

AREAS AFFECTED...CNTRL AND SERN VA INTO SRN/SERN MD

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 221500Z - 221600Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THE THREAT FOR LOCALLY DAMAGING WINDS AND PERHAPS A BRIEF
TORNADO MAY INCREASE THIS MORNING AND CONVECTIVE TRENDS ARE BEING
MONITORED FOR A POSSIBLE WW.

DISCUSSION...RECENT TRENDS IN RADAR DATA SHOW A GRADUAL DEEPENING OF
PRE-FRONTAL CONVECTION FROM ROCKINGHAM COUNTY NC TO CHARLOTTE COUNTY
VA AS OF 1445Z.  ANOTHER AREA OF CONVECTIVE INTENSIFICATION WAS
NOTED OVER PRINCE GEORGE COUNTY MD TO SPOTSYLVANIA AND STAFFORD
COUNTIES VA.  THE FORMER ACTIVITY APPEARS TO BE COINCIDENT WITH A
LOW-LEVEL CONFLUENCE ZONE...POSSIBLY AIDED BY TERRAIN. 
MEANWHILE...THE LATTER IS ASSOCIATED WITH A RESIDUAL COLD POOL
ATTENDANT TO A RECENTLY DECAYED NOCTURNAL QLCS.  

VISIBLE SATELLITE IMAGERY INDICATES BREAKS IN CLOUDS WHICH SHOULD
ALLOW FOR SOME HEATING OF THE BOUNDARY LAYER.  AND BASED ON THE 12Z
RNK SOUNDING...IT APPEARS THAT AS TEMPERATURES CONTINUE TO WARM INTO
THE 70S...SUFFICIENT BUOYANCY WILL EXIST TO SUPPORT MLCAPE OF
500-750 J/KG.  WHEN COUPLED WITH THE STRONG SWLY WIND FIELD...THE
POTENTIAL WILL EXIST FOR BOWING CONVECTIVE ELEMENTS WITH A RISK FOR
LOCALLY DAMAGING WINDS AND PERHAPS A BRIEF TORNADO.

THE PRIMARY UNCERTAINTY TO THIS SCENARIO IS WHETHER THE EXPANSIVE
COLD POOL ASSOCIATED WITH A RECENTLY DECAYED NOCTURNAL QLCS WILL
UNDERCUT THE DEVELOPING STORMS AS THEY TRY TO MATURE.  SHOULD
FURTHER STORM INTENSIFICATION OCCUR...A WATCH MAY NEED TO BE
CONSIDERED.

..MEAD.. 12/22/2013

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

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

LAT...LON   36817907 38147775 38817663 38927617 38727587 38177570
            37227635 36797744 36637844 36817907

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 22, 1:36 AM EST	Severe Thunderstorm Watch	SPC	Garrett	3 hr
Dec 22, 3:37 AM EST	Severe Thunderstorm Watch	SPC	Allegany, Anne Arundel, Baltimore, Carroll, Charles, Frederick and 6 more	5 hr
Dec 22, 6:14 AM EST	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Carroll, Frederick, Howard, Montgomery and 3 more	61 min
Dec 21, 11:38 PM EST	Severe Thunderstorm Watch	SPC	Lee	6 hr

Nearby

Mesoscale Discussions in Virginia, 2013 Mesoscale Discussions in Maryland, 2013 Every mesoscale discussion in 2013

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.