Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 38

January 21, 201224 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Jan 21, 2012, 4:20 AM EST for 24 counties in Virginia. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued
Jan 21, 2012, 4:20 AM EST (09:20 UTC)
Expired
Jan 21, 2012, 8:15 AM EST
In force
4 hr
Issued by
the Storm Prediction Center
All 24 counties

Albemarle County, VA, Arlington County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Greene County, VA, Highland County, VA, Louisa County, VA, Madison County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Spotsylvania County, VA, Stafford County, VA

The radar

The Sterling radar (KLWX), 93 km from the middle of the area, began a volume at 09:22 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 00:00Z, 9.3 hours before the alert went out and 97 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 00:00Z on 2012-01-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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 00:00Z on 2012-01-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 150 square meters per square second.1939587897117Sfc1 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1689 m above ground
0-6 km bulk shear
65 kt
0-1 km storm-relative helicity
150 m²/s²
0-3 km storm-relative helicity
131 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.

219 
ACUS11 KWNS 210920
SWOMCD
SPC MCD 210920 
MDZ000-DCZ000-VAZ000-WVZ000-211315-

MESOSCALE DISCUSSION 0038
NWS STORM PREDICTION CENTER NORMAN OK
0320 AM CST SAT JAN 21 2012

AREAS AFFECTED...PORTIONS ERN WV...CENTRAL/NRN VA...DC AND ADJACENT
MD.

CONCERNING...FREEZING RAIN 

VALID 210920Z - 211315Z

BAND OF PRECIP...NOW MOVING ENEWD 45-55 KT ACROSS ERN KY AND SRN
WV...IS EXPECTED TO MOVE OVER SHALLOW LAYER OF SUBFREEZING AIR NEAR
SFC FROM HSP-CHO CORRIDOR ENEWD TO AT LEAST PORTIONS DC METRO. 
ALTHOUGH LIGHT SNOW/SLEET MAY OCCUR INITIALLY...ESPECIALLY OVER ERN
PORTIONS OF DISCUSSION AREA...MAIN THREAT WILL COME FROM FREEZING
RAIN RATES .10-.25 INCH/HOUR IN PRIMARY PRECIP PLUME. 
LOCALLY/BRIEFLY HIGHER RATES ALSO MAY OCCUR WITH EMBEDDED HEAVIER
SHOWERS AND ISOLATED TSTMS.  MAIN PRECIP PLUME SHOULD REACH CHO AREA
IN 10-1030Z TIME FRAME...AND LOWER POTOMAC AREA BETWEEN 11Z-12Z.

ACTIVITY WILL BE SUPPORTED BY ENEWD TRANSLATION/EXPANSION OF
ELEVATED/LOW-LEVEL PLUME OF WAA AND MOISTURE TRANSPORT...CURRENTLY
CHARACTERIZING NRN PORTIONS OF 40-50 KT LLJ.  ACCORDINGLY MODIFIED
RUC/ETA-KF FCST SOUNDINGS REASONABLY INDICATE STRENGTHENING IN PW
ABOVE BOUNDARY LAYER...AS WELL AS INCREASE IN BOTH MAGNITUDE AND
DEPTH OF SUPERFREEZING LAYER ALOFT.  HIGHEST COLUMNAR THETAE WILL BE
LOCATED NEAR 800 MB...ABOVE WHICH MUCAPE UP TO 50 J/KG IS POSSIBLE
IN SUPPORT OF EMBEDDED CONVECTIVE POTENTIAL.  DEPTH OF SUPERFREEZING
LAYER WILL BE FROM 6-9 KFT...MORE THAN SUFFICIENT TO MELT ANY PRECIP
GENERATED ABOVE THAT.  FREEZING RAIN THREAT WILL END FROM S-N ACROSS
DISCUSSION AREA DURING MID-LATE MORNING LOCAL TIME AS NEAR-SFC
STABLE LAYER ERODES...AND SFC TEMPS WARM ABOVE 32 F.

..EDWARDS.. 01/21/2012

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

ATTN...WFO...AKQ...LWX...RNK...RLX...

LAT...LON   38437721 37917803 38067873 38317888 38117971 38467999
            38737915 39047732 38947690 38437721

Nearby

Mesoscale 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.