Alert archive / Virginia / Mesoscale Discussions in 2021

Mesoscale Discussion 537

May 4, 202124 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at May 4, 2021, 5:52 PM EDT for 24 counties in Virginia. It was in force for 53 min.

The area

The outline as issued.

The facts

Issued: May 4, 2021, 5:52 PM EDT (21:52 UTC)
Expired: May 4, 2021, 6:45 PM EDT
In force: 53 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 148

All 24 counties

Charles City County, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Emporia, VA, City of Franklin, VA, City of Hampton, VA, City of Hopewell, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Gloucester County, VA, Greensville County, VA, Isle of Wight County, VA, James City County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 34 km from the middle of the area, began a volume at 21:54 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

Wallops Is Stn, VA (KWAL), launched 12:00Z, 9.9 hours before the alert went out and 164 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: 60 J/kg
Mixed-layer CIN: -270 J/kg
Mixed-layer LCL: 1140 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: 46 m²/s²
0-3 km storm-relative helicity: 96 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

503 
ACUS11 KWNS 042152
SWOMCD
SPC MCD 042152 
VAZ000-NCZ000-042245-

Mesoscale Discussion 0537
NWS Storm Prediction Center Norman OK
0452 PM CDT Tue May 04 2021

Areas affected...southeastern Virginia and extreme northern North
Carolina.

Concerning...Severe Thunderstorm Watch 148...

Valid 042152Z - 042245Z

The severe weather threat for Severe Thunderstorm Watch 148
continues.

SUMMARY...Strong thunderstorms have become increasingly organized
over the last half hour suggesting an increased potential for severe
weather. WW148 may need to be locally extended.

DISCUSSION...2130z radar shows some consolidation of updrafts and a
merging of outflow with ongoing storms to the north occurring with
the scattered convection along and west of the I-95 corridor through
southern Virginia. Hi-res model guidance and observation trends
suggest this will likely continue as storms move into an
increasingly unstable and moderately sheared environment. A local
maximum (1500-2000 J/kg) of MLCAPE near the eastern coast will
likely continue to support robust updraft development over the next
1 to 2 hours. Storm organization in the form of clusters and short
line segments from 20-30 kts of effective shear will continue to
pose a risk for damaging wind gusts before storms move offshore
around 23-00z. A local extension of WW148 southward may be needed to
cover the evolving severe threat.

..Lyons/Thompson.. 05/04/2021

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

ATTN...WFO...AKQ...

LAT...LON   36467592 36447649 36457715 36507741 36597764 36967764
            37247749 37407724 37537691 37367623 37097584 36847575
            36597574 36467592

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 4, 1:04 PM EDT	Mesoscale Discussion	SPC	Albemarle, Alleghany, Amelia, Amherst, Appomattox, Augusta and 92 more	56 min
May 4, 1:51 PM EDT	Severe Thunderstorm Watch	SPC	Albemarle, Alleghany, Amelia, Amherst, Appomattox, Arlington and 98 more	6 hr
May 4, 3:50 PM EDT	Mesoscale Discussion	SPC	Albemarle, Amelia, Amherst, Appomattox, Arlington, Buckingham and 52 more	115 min

Nearby

Mesoscale Discussions in Virginia, 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.