Alert archive / Maryland / Mesoscale Discussions in 2021
Mesoscale Discussion 1324
The Storm Prediction Center issued this mesoscale discussion at Jul 21, 2021, 2:39 PM EDT for 7 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 21, 2021, 2:39 PM EDT (18:39 UTC)
- Expired
- Jul 21, 2021, 4:45 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 385
All 39 counties
Kent County, DE, New Castle County, DE, Sussex County, DE, Barnstable County, MA, Bristol County, MA, Dukes County, MA, Nantucket County, MA, Plymouth County, MA, Calvert County, MD, Caroline County, MD, Cecil County, MD, Dorchester County, MD, Kent County, MD, Queen Anne's County, MD, Somerset County, MD, Talbot County, MD, Wicomico County, MD, Worcester County, MD, Atlantic County, NJ, Burlington County, NJ, Camden County, NJ, Cape May County, NJ, Cumberland County, NJ, Gloucester County, NJ, Mercer County, NJ, Monmouth County, NJ, Ocean County, NJ, Salem County, NJ, Chester County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA, Bristol County, RI, Kent County, RI, Newport County, RI, Providence County, RI, Washington County, RI, Accomack County, VA, Northampton County, VA
The radar
The Philadelphia radar (KDIX), 86 km from the middle of the area, began a volume at 18:38 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
Brookhaven, NY (KOKX), launched 12:00Z, 6.7 hours before the alert went out and 120 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
- 130 J/kg
- Mixed-layer CIN
- -165 J/kg
- Mixed-layer LCL
- 1495 m above ground
- 0-6 km bulk shear
- 35 kt
- 0-1 km storm-relative helicity
- 22 m²/s²
- 0-3 km storm-relative helicity
- 48 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.0
The text
As transmitted.
070
ACUS11 KWNS 211840
SWOMCD
SPC MCD 211839
MAZ000-RIZ000-CTZ000-NJZ000-PAZ000-MDZ000-DEZ000-VAZ000-212045-
Mesoscale Discussion 1324
NWS Storm Prediction Center Norman OK
0139 PM CDT Wed Jul 21 2021
Areas affected...Parts of eastern Maryland...Delaware...southeastern
Pennsylvania...southern New Jersey...Rhode Island...southeastern
Massachusetts
Concerning...Severe Thunderstorm Watch 385...
Valid 211839Z - 212045Z
The severe weather threat for Severe Thunderstorm Watch 385
continues.
SUMMARY...Strong thunderstorm development may still impact parts of
southeastern New England, southern New Jersey and the Delmarva
Peninsula, posing a risk for marginally severe hail and locally
damaging wind gusts through 4-6 PM EDT, while becoming more isolated
in nature elsewhere.
DISCUSSION...The eastward progression of the mid-level trough, slow
southeastward advancement of the cold front and influence of
convective outflow associated with early thunderstorm development
have increasingly confined stronger boundary-layer instability to
the Delmarva Peninsula, southern New Jersey and portions of
southeastern New England. This is generally focused south of the
the cold front into pre-frontal surface troughing, where stronger
thunderstorm development is expected to continue to increase and
tend to consolidate through 4-6 PM EDT.
Beneath cool mid-level temperatures, residual moisture may maintain
sufficient instability to support a continuing risk for additional
thunderstorm development across the remainder of the watch area to
the west and north, but this probably will be much more isolated in
nature.
..Kerr.. 07/21/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BOX...OKX...PHI...AKQ...CTP...LWX...
LAT...LON 39317638 39847607 40297525 40367428 40517320 40757202
41277154 41647208 42337058 41776958 40707023 39677034
38847134 37927433 37477525 37187586 38497670 39317638SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 21, 10:32 AM EDT | Mesoscale Discussion | SPC | Kent, New Castle | 58 min |
| Jul 21, 11:56 AM EDT | Severe Thunderstorm Watch | SPC | Kent, New Castle, Sussex | 7 hr |
| Jul 20, 10:01 PM EDT | Mesoscale Discussion | SPC | Berkshire, Franklin, Hampden, Hampshire, Worcester | 59 min |
Nearby
Mesoscale Discussions in Maryland, 2021Mesoscale Discussions in New Jersey, 2021Mesoscale Discussions in Massachusetts, 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.