Alert archive / Virginia / Mesoscale Discussions in 2017

Mesoscale Discussion 657

May 5, 20175 states

The Storm Prediction Center issued this mesoscale discussion at May 5, 2017, 6:15 PM EDT for 5 states. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued
May 5, 2017, 6:15 PM EDT (22:15 UTC)
Expired
May 5, 2017, 7:45 PM EDT
In force
90 min
Issued by
the Storm Prediction Center
Chance of a watch
20%
All 51 counties

Frederick County, MD, Montgomery County, MD, Washington County, MD, Halifax County, NC, Hertford County, NC, Northampton County, NC, Franklin County, PA, Amelia County, VA, Brunswick County, VA, Caroline County, VA, Charles City County, VA, Chesterfield County, 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 Hopewell, VA, City of Manassas, VA, City of Manassas Park, VA, City of Petersburg, VA, City of Richmond, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Fairfax County, VA, Fauquier County, VA, Goochland County, VA, Greensville County, VA, Hanover County, VA, Henrico County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Nottoway County, VA, Orange County, VA, Powhatan County, VA, Prince George County, VA, Prince William County, VA, Rappahannock County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Sussex County, VA, Warren County, VA, Berkeley County, WV, Jefferson County, WV

The radar

The Sterling radar (KLWX), 110 km from the middle of the area, began a volume at 22:17 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 12:00Z, 10.3 hours before the alert went out and 108 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 12:00Z on 2017-05-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 8 joules per kilogram.LCLLFCEL10008507005003002001001 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 12:00Z on 2017-05-05The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 407 square meters per square second.1939587897Sfc1 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
8 J/kg
Mixed-layer CIN
-15 J/kg
Mixed-layer LCL
473 m above ground
0-6 km bulk shear
53 kt
0-1 km storm-relative helicity
407 m²/s²
0-3 km storm-relative helicity
508 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

413 
ACUS11 KWNS 052216
SWOMCD
SPC MCD 052215 
VAZ000-NCZ000-MDZ000-PAZ000-WVZ000-052345-

Mesoscale Discussion 0657
NWS Storm Prediction Center Norman OK
0515 PM CDT Fri May 05 2017

Areas affected...Portions of the Middle Atlantic

Concerning...Severe potential...Watch unlikely 

Valid 052215Z - 052345Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated strong storms may linger for a few hours across
portions of the Middle Atlantic.  Marginally severe hail and gusty
winds are the primary threats.

DISCUSSION...Early-day convection that spread across the Middle
Atlantic region has reinforced cooler boundary-layer conditions from
northeast NC northward into southeast PA.  Along the western fringe
of this air mass, strong sunshine has steepened surface-3km lapse
rates such that surface-based convection has evolved along weakly
convergent wind shift.  This activity is concentrated within a 50mi
corridor extending from Halifax County NC to Cumberland County PA. 
Deep-layer shear is more than adequate for sustained rotating
updrafts but weak low-level shear and only modest buoyancy, 500-1000
J/kg MLCAPE, suggest ongoing activity may struggle to attain
organized severe threshold.  For these reasons it appears the
strongest storms may generate marginally severe hail or gusty winds.
 WW is probabilistically unlikely.

..Darrow/Edwards.. 05/05/2017

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

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

LAT...LON   36127770 37277829 39037826 40057792 40217734 39597714
            38127713 37127698 36237680 36127770

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 4, 8:49 PM EDTTornado WatchSPCBladen, Brunswick, Carteret, Columbus, Craven, Cumberland and 13 more6 hr
May 4, 11:24 PM EDTMesoscale DiscussionSPCBladen, Brunswick, Columbus, Duplin, Greene, Jones and 7 more66 min
May 5, 2:28 AM EDTMesoscale DiscussionSPCAlamance, Beaufort, Bertie, Bladen, Camden, Caswell and 43 more92 min
May 5, 3:09 AM EDTTornado WatchSPCAlamance, Anson, Bladen, Brunswick, Carteret, Chatham and 37 more6 hr
May 5, 5:56 AM EDTMesoscale DiscussionSPCBeaufort, Bertie, Camden, Chowan, Currituck, Dare and 12 more94 min
May 5, 6:25 AM EDTTornado WatchSPCBeaufort, Bertie, Camden, Chowan, Currituck, Dare and 9 more5 hr
May 5, 8:27 AM EDTMesoscale DiscussionSPCBeaufort, Bertie, Camden, Carteret, Chowan, Craven and 9 more93 min
May 5, 4:07 PM EDTMesoscale DiscussionSPCAllegheny, Armstrong, Butler, Clarion, Fayette, Greene and 3 more113 min

Nearby

Mesoscale Discussions in Virginia, 2017Mesoscale Discussions in Maryland, 2017Mesoscale Discussions in North Carolina, 2017Every 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.