Alert archive / West Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 2091

October 29, 2012Garrett County, Maryland; Buchanan County, Virginia; 12 counties in West Virginia

The Storm Prediction Center issued this mesoscale discussion at Oct 29, 2012, 2:51 PM EDT for Garrett County, Maryland; Buchanan County, Virginia; 12 counties in West Virginia. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Oct 29, 2012, 2:51 PM EDT (18:51 UTC)
Expired: Oct 29, 2012, 8:45 PM EDT
In force: 6 hr
Issued by: the Storm Prediction Center

Counties Garrett County, MD, Buchanan County, VA, Fayette County, WV, Greenbrier County, WV, McDowell County, WV, Mercer County, WV, Nicholas County, WV, Pocahontas County, WV, Raleigh County, WV, Randolph County, WV, Summers County, WV, Tucker County, WV, Webster County, WV, Wyoming County, WV

The radar

The Charleston,WV radar (KRLX), 104 km from the middle of the area, began a volume at 18:53 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

Roanoke, VA (KRNK), launched 12:00Z, 6.9 hours before the alert went out and 151 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: 643 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 182 m²/s²
0-3 km storm-relative helicity: 278 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.

629 
ACUS11 KWNS 291852
SWOMCD
SPC MCD 291851
WVZ000-MDZ000-VAZ000-300045-

MESOSCALE DISCUSSION 2091
NWS STORM PREDICTION CENTER NORMAN OK
0151 PM CDT MON OCT 29 2012

AREAS AFFECTED...APPALACHIAN MOUNTAINS OF FAR WRN MD...WV...AND
PARTS OF WRN VA

CONCERNING...BLIZZARD

VALID 291851Z - 300045Z

SUMMARY...BLIZZARD CONDITIONS WILL DEVELOP AFTER 21Z WITH SNOWFALL
RATES INCREASING TO 1-2 IN/HR...AND LOCALLY HIGHER RATES ARE
ANTICIPATED. THESE CONDITIONS WILL CONTINUE THROUGH THE EVENING
HOURS...WITH THE HIGHEST SNOWFALL RATES AND STRONGEST WINDS
ANTICIPATED FOR ELEVATIONS AOA 2000 FT.

DISCUSSION...OBSERVATIONS INDICATE A MIX OF RAIN AND SNOW ONGOING AS
OF MID AFTERNOON OWING TO THE UPSLOPE FLOW REGIME -- I.E. 20-30 KT
OF NWLY FLOW SAMPLED BY THE CHARLESTON WV VWP WITHIN THE 0.5-1-KM
LAYER. INTENSE LARGE-SCALE ASCENT ASSOCIATED WITH THE INTERACTION
BETWEEN HURRICANE SANDY AND A MID-LEVEL VORT MAX OVER THE CAROLINAS
WILL YIELD A MARKED INCREASE IN PRECIPITATION RATES LATE THIS
AFTERNOON AND ESPECIALLY INTO THIS EVENING. ASSOCIATED ADIABATIC
COOLING WILL ALLOW SNOW LEVELS TO LOWER...WITH SNOWFALL RATES
INCREASING TO 1 IN/HR FOR ELEVATIONS AOA 2000 FT AFTER 21Z. HIGHER
RATES TO 2 IN/HR /LOCALLY HIGHER/ WILL DEVELOP AFTER 00Z. THIS WILL
OCCUR AS ASCENT IS AUGMENTED BY WAA AND STRONG FRONTOGENESIS OVER
THE FRINGES OF THE WARM CORE ACCOMPANYING BECOMING-POST-TROPICAL
CYCLONE SANDY...AND NOCTURNAL BOUNDARY-LAYER COOLING TAKES PLACE.
NAM/RAPID-REFRESH FORECAST SOUNDINGS INDICATE A NEARLY 100-MB DEEP
DENDRITIC GROWTH ZONE DEVELOPING WITHIN THE MID-LEVELS...ATOP -2C TO
-4C ISOTHERMAL LAYERS IN THE LOWER LEVELS...SUPPORTING THESE HEAVY
SNOW RATES.

AS THE LOW-LEVEL PRESSURE GRADIENT INCREASES IN RESPONSE TO THE
APPROACH OF SANDY...0-1-KM MEAN FLOW WILL INCREASE TO 45-50 KT AFTER
21Z. AS SUCH...SUSTAINED NWLY/WNWLY WINDS OF 35-40 MPH WITH GUSTS
REACHING 60 MPH ARE EXPECTED...STRONGEST OVER RIDGE TOPS.
VISIBILITIES WILL BE REDUCED TO BELOW 1/4 MILE WITH BLOWING
SNOW...RESULTING IN BLIZZARD CONDITIONS. THESE CONDITIONS WILL
CONTINUE THROUGH THE EVENING HOURS.

..COHEN.. 10/29/2012

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

ATTN...WFO...LWX...RNK...PBZ...RLX...MRX...

LAT...LON   39197918 38827931 38517956 38118004 37718061 37358114
            37218156 36938216 37018233 37178235 37538190 37908140
            38208099 38398074 38638036 39077993 39587959 39687933
            39547908 39197918

Nearby

Mesoscale Discussions in West Virginia, 2012 Mesoscale Discussions in Maryland, 2012 Mesoscale Discussions in Virginia, 2012 Every 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.