Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1431
The Storm Prediction Center issued this mesoscale discussion at Aug 7, 2021, 1:32 PM EDT for 19 counties in North Carolina; 20 counties in Virginia. It was in force for 88 min.
The area
The outline as issued.
The facts
- Issued
- Aug 7, 2021, 1:32 PM EDT (17:32 UTC)
- Expired
- Aug 7, 2021, 3:00 PM EDT
- In force
- 88 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 39 counties
Beaufort County, NC, Bertie County, NC, Camden County, NC, Chowan County, NC, Currituck County, NC, Edgecombe County, NC, Gates County, NC, Greene County, NC, Halifax County, NC, Hertford County, NC, Martin County, NC, Nash County, NC, Northampton County, NC, Pasquotank County, NC, Perquimans County, NC, Pitt County, NC, Tyrrell County, NC, Washington County, NC, Wilson County, NC, City of Chesapeake, VA, City of Emporia, VA, City of Franklin, VA, City of Hampton, VA, City of Newport News, VA, City of Norfolk, 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, Isle of Wight County, VA, James City County, VA, Mathews County, VA, Northampton County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA
The radar
The Norfolk radar (KAKQ), 80 km from the middle of the area, began a volume at 17:34 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
Newport, NC (KMHX), launched 12:00Z, 5.5 hours before the alert went out and 168 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.
- Mixed-layer CAPE
- 1428 J/kg
- Mixed-layer CIN
- -9 J/kg
- Mixed-layer LCL
- 758 m above ground
- 0-6 km bulk shear
- 19 kt
- 0-1 km storm-relative helicity
- 73 m²/s²
- 0-3 km storm-relative helicity
- 116 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 2.5
The text
As transmitted.
674
ACUS11 KWNS 071733
SWOMCD
SPC MCD 071732
NCZ000-VAZ000-071900-
Mesoscale Discussion 1431
NWS Storm Prediction Center Norman OK
1232 PM CDT Sat Aug 07 2021
Areas affected...Northeast North Carolina and southeast Virginia
Concerning...Severe potential...Watch unlikely
Valid 071732Z - 071900Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated damaging winds and potentially a tornado are
possible over the next 2 to 3 hours.
DISCUSSION...A line of convection along a surface front has slowly
moved east across northern North Carolina with occasional lightning.
Cloud cover ahead of this line has limited overall instability, but
surface dewpoints in the low to mid 70s have provided sufficient
low-level moisture for MLCAPE around 500 to 1000 J/kg. Overall this
line of storms has been mostly unorganized, likely due to the
relatively weak wind profile sampled by the KAKQ VWP. However,
despite this weak shear, a more organized segment of the line has
developed across Northampton county. with a comma-head signature
developing. Within this a broad, yet somewhat strong, area of
rotation has been persistent for the past hour. The aforementioned
weak shear should be a limiting factor for a greater tornado threat,
but internal processes within this organized section of the line
could provide an environment favorable for a brief tornado or two as
this section of the line moves into southeast Virginia. Due to the
isolated threat area, no watch is anticipated.
..Bentley/Thompson.. 08/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...MHX...RAH...
LAT...LON 36497772 37187712 37557635 37497589 36917555 36397550
35987564 35547614 35307682 35327744 35427786 35697820
36497772Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in North Carolina, 2021Every 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.