Alert archive / Maryland / Mesoscale Discussions in 2021

Mesoscale Discussion 1779

September 22, 2021Kent County, Sussex County, Delaware; 15 counties in Maryland; 5 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Sep 22, 2021, 6:14 PM EDT for Kent County, Sussex County, Delaware; 15 counties in Maryland; 5 counties in Virginia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 22, 2021, 6:14 PM EDT (22:14 UTC)
Expired: Sep 22, 2021, 8:15 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

All 22 counties

Kent County, DE, Sussex County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Cecil 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, Lancaster County, VA, Middlesex County, VA, Northumberland County, VA, Richmond County, VA, Westmoreland County, VA

The radar

The Dover AFB radar (KDOX), 76 km from the middle of the area, began a volume at 22:15 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, 10.2 hours before the alert went out and 100 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: 127 J/kg
Mixed-layer CIN: -10 J/kg
Mixed-layer LCL: 759 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 72 m²/s²
0-3 km storm-relative helicity: 90 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

288 
ACUS11 KWNS 222215
SWOMCD
SPC MCD 222214 
MDZ000-DEZ000-VAZ000-PAZ000-DCZ000-230015-

Mesoscale Discussion 1779
NWS Storm Prediction Center Norman OK
0514 PM CDT Wed Sep 22 2021

Areas affected...Delmarva region

Concerning...Severe potential...Watch unlikely 

Valid 222214Z - 230015Z

Probability of Watch Issuance...5 percent

SUMMARY...Sporadic wind damage is possible over the next couple of
hours as storm segments move across far eastern Virginia, central
Maryland, and Delaware. This threat will remain isolated in nature,
and a watch is not expected.

DISCUSSION...A few wind damage reports have been noted over the past
hour associated with a short line segment moving through the
Washington D.C. area. Despite a modest shear environment, VWP
observations from KLWX show 40-45 knot winds within the lowest 1 km.
Convective downdrafts mixing this stronger flow downward is likely
responsible for the wind damage reports. This flow regime will
persist for the near-term, and a combination of modest bulk shear
oriented orthogonal to the line and sufficient downstream
instability (approximately 500-1000 J/kg MLCAPE) should support
storm maintenance for the next 1-2 hours. As such, additional
sporadic wind damage will continue to be possible with this line, as
well as with a developing cluster of storms across south-central MD.
This threat will remain localized in nature, so no watch is
expected.

..Moore/Grams.. 09/22/2021

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

ATTN...WFO...PHI...AKQ...CTP...LWX...

LAT...LON   37707675 38537696 38997702 39427682 39777650 39767596
            39387554 38937535 38577532 38107561 37797593 37517627
            37467650 37707675

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 22, 2:44 PM EDT	Mesoscale Discussion	SPC	Alleghany, Amherst, Appomattox, Bath, Bedford, Botetourt and 28 more	3 hr

Nearby

Mesoscale Discussions in Maryland, 2021 Mesoscale Discussions in Virginia, 2021 Mesoscale Discussions in Delaware, 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.