Alert archive / Virginia / Mesoscale Discussions in 2021

Mesoscale Discussion 115

February 18, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Feb 18, 2021, 4:28 AM EST for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Feb 18, 2021, 4:28 AM EST (09:28 UTC)
Expired: Feb 18, 2021, 10:30 AM EST
In force: 6 hr
Issued by: the Storm Prediction Center
Concerning: Freezing rain

All 86 counties

Charles County, MD, Alleghany County, NC, Ashe County, NC, Caswell County, NC, Person County, NC, Rockingham County, NC, Stokes County, NC, Surry County, NC, Albemarle County, VA, Alleghany County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Augusta County, VA, Bedford County, VA, Bland County, VA, Botetourt County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Carroll County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Covington, VA, City of Danville, VA, City of Fredericksburg, VA, City of Galax, VA, City of Hopewell, VA, City of Lexington, VA, City of Lynchburg, VA, City of Martinsville, VA, City of Petersburg, VA, City of Radford, VA, City of Richmond, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Waynesboro, VA, Craig County, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Giles County, VA, Goochland County, VA, Grayson County, VA, Greene County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Henry County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mecklenburg County, VA, Montgomery County, VA, Nelson County, VA, New Kent County, VA, Nottoway County, VA, Orange County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Pulaski County, VA, Richmond County, VA, Roanoke County, VA, Rockbridge County, VA, Spotsylvania County, VA, Stafford County, VA, Sussex County, VA, Westmoreland County, VA, Wythe County, VA, Monroe County, WV

The radar

The Roanoke radar (KFCX), 123 km from the middle of the area, began a volume at 09:29 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 00:00Z, 9.5 hours before the alert went out and 56 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: 1200 m above ground
0-6 km bulk shear: 98 kt
0-1 km storm-relative helicity: 180 m²/s²
0-3 km storm-relative helicity: 326 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

966 
ACUS11 KWNS 180929
SWOMCD
SPC MCD 180928 
VAZ000-MDZ000-NCZ000-WVZ000-181530-

Mesoscale Discussion 0115
NWS Storm Prediction Center Norman OK
0328 AM CST Thu Feb 18 2021

Areas affected...southern and central VA

Concerning...Freezing rain 

Valid 180928Z - 181530Z

SUMMARY...Freezing rain rates 0.05-0.15 inch per 3 hours are
expected to develop through 10am EST.

DISCUSSION...Radar mosaic shows an expanding precipitation plume
over the Carolina Piedmont within a zone of strong low-level warm
air advection atop a cool surface layer.  Surface observations show
temperatures ranging from the lower 30s in western NC northeastward
into parts of southeast VA with upper 20s farther northwest over
southwest/central VA.  

The 1am EST Blacksburg, VA raob showed a profile primarily
supporting sleet/snow with a layer of temperatures near freezing or
slightly below freezing between 800-600 mb.  However, forecast
soundings show the profile has likely warmed to 2-4 deg C around 750
mb---supporting freezing rain as the primary precipitation type. 
Short-term model guidance indicates precipitation will increase in
coverage/intensity during the morning hours with rates reaching
0.05-0.15 per 3 hours.  Weak elevated instability may support
convection with accompanying localized heavier bursts of
precipitation, especially during the 7-10am EST period.

..Smith.. 02/18/2021

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

ATTN...WFO...AKQ...LWX...RAH...RNK...MRX...

LAT...LON   37957992 37478085 36708166 36348146 36327861 36837727
            37917661 38557676 38677778 38447881 37957992

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 18, 10:23 AM EST	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 11 more	3 hr
Feb 17, 8:44 PM EST	Mesoscale Discussion	SPC	Wayne	5 hr

Nearby

Mesoscale Discussions in Virginia, 2021 Mesoscale Discussions in North Carolina, 2021 Mesoscale Discussions in Maryland, 2021 Every mesoscale discussion in 2021

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.