Alert archive / Pennsylvania / Mesoscale Discussions in 2019

Mesoscale Discussion 113

February 20, 20194 states

The Storm Prediction Center issued this mesoscale discussion at Feb 20, 2019, 5:55 AM EST for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Feb 20, 2019, 5:55 AM EST (10:55 UTC)
Expired: Feb 20, 2019, 12:00 PM EST
In force: 6 hr
Issued by: the Storm Prediction Center

All 32 counties

Allegany County, MD, Frederick County, MD, Garrett County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Blair County, PA, Cambria County, PA, Cumberland County, PA, Fayette County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Mifflin County, PA, Perry County, PA, Somerset County, PA, City of Winchester, VA, Clarke County, VA, Frederick County, VA, Loudoun County, VA, Shenandoah County, VA, Warren County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Preston County, WV, Tucker County, WV

The radar

The Sterling radar (KLWX), 98 km from the middle of the area, began a volume at 10:57 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, 10.9 hours before the alert went out and 105 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: 2365 m above ground
0-6 km bulk shear: 89 kt
0-1 km storm-relative helicity: -51 m²/s²
0-3 km storm-relative helicity: 82 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

092 
ACUS11 KWNS 201056
SWOMCD
SPC MCD 201055 
PAZ000-MDZ000-VAZ000-WVZ000-201700-

Mesoscale Discussion 0113
NWS Storm Prediction Center Norman OK
0455 AM CST Wed Feb 20 2019

Areas affected...Northern Virginia and West Virginia...western
Maryland...much of south-central Pennsylvania

Concerning...Heavy snow 

Valid 201055Z - 201700Z

SUMMARY...Snow rates are expected to increase into the 1-2"/hr range
through mid-morning with an eventual changeover to sleet from south
to north.

DISCUSSION...Southwesterly flow aloft continues to moisten profiles
this morning with a broad area of lift and precipitation extending
from the OH Valley to the East Coast. Most of the precipitation is
snow across the MCD area, but rain exists across central WV where
warm advection in the 850-700 mb layer is strongest. Snow should
remain the dominant precipitation type across the MCD area due to a
surface ridge and cooler temperatures, but a warm nose aloft will
eventually lead to snow changing to sleet from south to north later
today. Until then, snow rates are expected to increase to over
1"/hr, possibly up to 2"/hr at times from far northern VA/WV into
south-central PA.

..Jewell.. 02/20/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CTP...LWX...PBZ...RLX...

LAT...LON   38877746 38747790 38657847 38697950 38847974 39187967
            39407993 39797979 40367942 40737853 40837759 40627705
            40207684 39797700 39237723 38877746

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 20, 6:32 PM EST	Mesoscale Discussion	SPC	Allegany, Baltimore, Carroll, Cecil, Frederick, Harford and 4 more	4 hr
Feb 20, 3:25 AM EST	Mesoscale Discussion	SPC	Beaver	6 hr
Feb 20, 12:26 AM EST	Mesoscale Discussion	SPC	Alleghany, Amherst, Augusta, Bath, Bedford, Bland and 23 more	4 hr

Nearby

Mesoscale Discussions in Pennsylvania, 2019 Mesoscale Discussions in West Virginia, 2019 Mesoscale Discussions in Virginia, 2019 Every mesoscale discussion in 2019

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.