Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1554
The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2021, 2:38 PM EDT for 7 counties in North Carolina; 26 counties in Virginia. It was in force for 97 min.
The area
The outline as issued.
The facts
- Issued
- Aug 18, 2021, 2:38 PM EDT (18:38 UTC)
- Expired
- Aug 18, 2021, 4:15 PM EDT
- In force
- 97 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 33 counties
Bertie County, NC, Camden County, NC, Chowan County, NC, Gates County, NC, Hertford County, NC, Pasquotank County, NC, Perquimans County, NC, Charles City County, VA, City of Chesapeake, 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, King and Queen County, VA, Lancaster County, VA, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA
The radar
The Norfolk radar (KAKQ), 38 km from the middle of the area, began a volume at 18:37 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, 6.6 hours before the alert went out and 160 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
- 770 J/kg
- Mixed-layer CIN
- -21 J/kg
- Mixed-layer LCL
- 834 m above ground
- 0-6 km bulk shear
- 18 kt
- 0-1 km storm-relative helicity
- 43 m²/s²
- 0-3 km storm-relative helicity
- 69 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
618
ACUS11 KWNS 181838
SWOMCD
SPC MCD 181838
VAZ000-NCZ000-182015-
Mesoscale Discussion 1554
NWS Storm Prediction Center Norman OK
0138 PM CDT Wed Aug 18 2021
Areas affected...Tidewater Region
Concerning...Severe potential...Watch unlikely
Valid 181838Z - 182015Z
Probability of Watch Issuance...20 percent
SUMMARY...Storms capable of locally damaging wind and perhaps a
brief tornado are possible this afternoon.
DISCUSSION...At 1830Z, convection is gradually increasing across
northeast NC and southeast VA within a warm and very moist
environment, with MLCAPE in excess of 2000 J/kg per recent
mesoanalyses. While the strongest low/midlevel flow associated with
post-tropical cyclone Fred is lifting northward away from the
region, flow remains sufficient to support 20-25 kt of effective
shear, with some weak curvature persisting in low-level hodographs.
Loosely organized cells and clusters capable of locally damaging
wind gusts should be the primary threat this afternoon, though a
brief tornado cannot be ruled out, especially in areas across
southeast VA where low-level winds remain locally backed. The
magnitude and coverage of the severe threat is expected to remain
too limited for watch issuance.
..Dean/Dial.. 08/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...MHX...RAH...
LAT...LON 36527739 37287723 37917701 37917643 37807598 37477592
36647592 36207601 36007629 35957646 36117724 36527739SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 17, 10:04 PM EDT | Mesoscale Discussion | SPC | Alexander, Alleghany, Ashe, Cabarrus, Caldwell, Catawba and 20 more | 116 min |
| Aug 18, 8:46 AM EDT | Mesoscale Discussion | SPC | Clarke, Fauquier, Loudoun, Prince William, City of Manassas, City of Manassas Park | 119 min |
| Aug 18, 10:58 AM EDT | Mesoscale Discussion | SPC | Arlington, Clarke, Culpeper, Fairfax, Fauquier, Frederick and 15 more | 92 min |
| Aug 18, 11:37 AM EDT | Tornado Watch | SPC | Arlington, Clarke, Culpeper, Fairfax, Fauquier, Frederick and 14 more | 11 hr |
| Aug 18, 3:29 PM EDT | Mesoscale Discussion | SPC | Arlington, Clarke, Fairfax, Frederick, Loudoun, City of Fairfax and 3 more | 91 min |
| Aug 18, 4:57 PM EDT | Mesoscale Discussion | SPC | Arlington, Fairfax, Loudoun, City of Alexandria, City of Fairfax, City of Falls Church | 93 min |
Nearby
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.