Alert archive / Virginia / Mesoscale Discussions in 2017

Mesoscale Discussion 211

February 25, 20174 states

The Storm Prediction Center issued this mesoscale discussion at Feb 25, 2017, 12:24 PM EST for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Feb 25, 2017, 12:24 PM EST (17:24 UTC)
Expired: Feb 25, 2017, 2:30 PM EST
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 95 counties

Kent County, DE, Sussex County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Wicomico County, MD, Worcester County, MD, Warren County, NC, Accomack County, VA, Amelia County, VA, Appomattox County, VA, Arlington County, VA, Brunswick County, VA, Buckingham County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Colonial Heights, VA, City of Emporia, VA, City of Fairfax, VA, City of Falls Church, VA, City of Franklin, VA, City of Fredericksburg, VA, City of Hampton, VA, City of Hopewell, VA, City of Manassas, VA, City of Manassas Park, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Richmond, VA, City of Suffolk, VA, City of Williamsburg, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Gloucester County, VA, Goochland County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Prince William County, VA, Richmond County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 112 km from the middle of the area, began a volume at 17:24 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 39Feb 25, 1:30 PM EST

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 5.4 hours before the alert went out and 114 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: 235 J/kg
Mixed-layer CIN: -194 J/kg
Mixed-layer LCL: 676 m above ground
0-6 km bulk shear: 46 kt
0-1 km storm-relative helicity: 164 m²/s²
0-3 km storm-relative helicity: 143 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

963 
ACUS11 KWNS 251725
SWOMCD
SPC MCD 251724 
MDZ000-DEZ000-VAZ000-PAZ000-NCZ000-DCZ000-251930-

Mesoscale Discussion 0211
NWS Storm Prediction Center Norman OK
1124 AM CST Sat Feb 25 2017

Areas affected...Maryland...central and eastern Virginia and
northern North Carolina

Concerning...Severe potential...Watch possible 

Valid 251724Z - 251930Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms are expected to increase in coverage and
intensity this afternoon ahead of a cold front. Locally damaging
winds are possible, along with hail in the strongest cells. A watch
may be needed if it is clear storms will become severe.

DISCUSSION...Rapid surface heating continues across the region ahead
of the cold front which extended from northwestern VA into western
NC as of 17Z. Dewpoints were holding in the mid to upper 50s
suggesting a well-mixed and unstable boundary layer with MUCAPE to
around 1000 J/kg.

Satellite and radar show a few weak thunderstorms already forming
over the higher terrain near the front, and a general upward trend
is expected through the afternoon as it progresses east. By 18-19Z,
some storms may be severe. Wind profiles will continue to
strengthen, especially in the mid to upper levels, with long
hodographs favoring long-lived storms. Damaging winds appear to be
the main threat with a broken line of cells or small bows. The cold
air in the mid to upper levels would support the formation of hail.
However, a relatively warm layer exists above 700 mb, and updrafts
may struggle. As a result of this warm layer, storms may be slow to
become severe, but with time, long-acting shear may overcome this,
especially over eastern VA into MD, and northeastern NC later this
afternoon.

The tornado threat is low, but not zero. Although storms could
remain cellular, and low-level shear is in the sufficient category
with 0-1 SRH near 100 m2/s2, strong boundary layer mixing will be a
detriment, as will be the warm layer aloft hampering vertical
updraft accelerations in the lower parts of the storm.

..Jewell/Hart.. 02/25/2017

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

ATTN...WFO...PHI...AKQ...CTP...LWX...RAH...RNK...

LAT...LON   37997518 37457556 37037585 36707636 36497718 36377824
            36457905 36887910 37257891 37657868 38207835 38657805
            39117772 39627728 39737666 39627590 39267550 38877524
            38427508 37997518

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 25, 12:16 PM EST	Mesoscale Discussion	SPC	New Castle	89 min
Feb 25, 1:30 PM EST	Severe Thunderstorm Watch	SPC	Kent, New Castle, Sussex	6 hr
Feb 25, 4:26 PM EST	Mesoscale Discussion	SPC	Kent, New Castle, Sussex	94 min

Nearby

Mesoscale Discussions in Virginia, 2017 Mesoscale Discussions in Maryland, 2017 Mesoscale Discussions in Delaware, 2017 Every mesoscale discussion in 2017

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.