Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 403
The Storm Prediction Center issued this mesoscale discussion at Apr 21, 2021, 12:22 PM EDT for 4 states. It was in force for 113 min.
The area
The outline as issued.
The facts
- Issued
- Apr 21, 2021, 12:22 PM EDT (16:22 UTC)
- Expired
- Apr 21, 2021, 2:15 PM EDT
- In force
- 113 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 59 counties
Kent County, DE, New Castle County, DE, Sussex County, DE, Anne Arundel County, MD, Calvert County, MD, Caroline County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, MD, Harford County, MD, Kent 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, Cape May County, NJ, Cumberland County, NJ, Salem County, NJ, Accomack County, VA, Brunswick County, VA, Caroline County, VA, Charles City County, VA, Chesterfield County, VA, City of Colonial Heights, 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 Richmond, VA, City of Williamsburg, VA, Dinwiddie County, VA, Essex County, VA, Gloucester 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, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Prince George County, VA, Richmond County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA
The radar
The Dover AFB radar (KDOX), 86 km from the middle of the area, began a volume at 16:25 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.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 4.4 hours before the alert went out and 98 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
- 8 J/kg
- Mixed-layer CIN
- -277 J/kg
- Mixed-layer LCL
- 1577 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- 128 m²/s²
- 0-3 km storm-relative helicity
- 109 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
279
ACUS11 KWNS 211623
SWOMCD
SPC MCD 211622
NJZ000-MDZ000-DEZ000-PAZ000-VAZ000-DCZ000-211815-
Mesoscale Discussion 0403
NWS Storm Prediction Center Norman OK
1122 AM CDT Wed Apr 21 2021
Areas affected...Far Southern NJ...Delmarva...Southeast VA
Concerning...Severe potential...Watch possible
Valid 211622Z - 211815Z
Probability of Watch Issuance...40 percent
SUMMARY...Damaging wind gusts are possible as storm develop along
the front this afternoon.
DISCUSSION...Recent surface analysis places a cold front from far
eastern PA southwestward through south-central VA. Temperatures are
in the low 70s across southern NJ, increasing into the mid 70s
across south-central/southeast VA. Dewpoints follow a similar trend,
increasing from the upper 40s across southern NJ into the mid 50s
across southeast VA. Steep low and mid-level lapse rates are
fostering destabilization, despite this relatively modest low-level
moisture. This destabilization is evidenced by an increase in
cumulus across southeast VA as well as the deepening convection
along the front from northeast into south-central VA.
Surface winds are veering ahead of the front, limiting convergence
along this boundary but at least scattered storm coverage is still
possible. The presence of steep low-level lapse rates will augment
downdrafts, resulting in the potential for damaging wind gusts.
Overall coverage of these stronger gusts is in question, largely as
a result of uncertainty regarding overall coverage of storms.
Convective trends will be monitored closely and a Severe
Thunderstorm Watch may eventually be needed.
..Mosier/Guyer.. 04/21/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...CTP...LWX...
LAT...LON 38807709 39697635 39897563 39337450 36817582 36737815
38807709SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 21, 12:28 PM EDT | Severe Thunderstorm Watch | SPC | Kent, New Castle, Sussex | 5 hr |
| Apr 21, 11:49 AM EDT | Mesoscale Discussion | SPC | Bergen, Burlington, Camden, Essex, Hudson, Hunterdon and 10 more | 2 hr |
Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in Maryland, 2021Mesoscale Discussions in Delaware, 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.