Mesoscale Discussion 1048

Issued

Jun 21, 2021, 1:51 PM EDT (17:51 UTC)

Expired

Jun 21, 2021, 3:45 PM EDT

In force

114 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...severe thunderstorm watch likely

Chance of a watch

80%

The State College radar (KCCX), 125 km from the middle of the area, began a volume at 17:54 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.

• Severe Thunderstorm Watch 302Jun 21, 2:20 PM EDT
• Severe Thunderstorm Watch 303Jun 21, 3:45 PM EDT
• Severe Thunderstorm Watch 304Jun 21, 4:30 PM EDT

612 
ACUS11 KWNS 211752
SWOMCD
SPC MCD 211751 
NJZ000-NYZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-211945-

Mesoscale Discussion 1048
NWS Storm Prediction Center Norman OK
1251 PM CDT Mon Jun 21 2021

Areas affected...northern VA...much of MD...northern
DE...central-eastern PA...western NJ

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 211751Z - 211945Z

Probability of Watch Issuance...80 percent

SUMMARY...Clusters of strong to severe thunderstorms capable
primarily of isolated to widely scattered damaging gusts, are
possible this afternoon into the early evening.  A severe
thunderstorm watch will likely be needed over most of the discussion
area by mid afternoon.

DISCUSSION...Visible-satellite imagery shows a cluster of strong to
locally severe thunderstorms over WV moving eastward.  This
thunderstorm cluster will approach the eastern panhandle of WV and
far western MD (to the east of severe thunderstorm watch #299)
during the next few hours.  A cumulus field has developed over the
remainder of the discussion area from VA north to the NY/PA border. 
It seems possible convective initiation occurs over central PA near
State College over the next hour.

Surface analysis indicates the airmass has destabilized early this
afternoon with temperatures generally in the upper 80s deg F with
upper 60s to lower 70s dewpoints.  Modifying the the Pittsburgh, PA
8am raob for current conditions over central PA yields around 2000
J/kg MLCAPE.  The Dulles, VA 8am raob was noticeably less unstable
this morning compared to the Pittsburgh, PA raob.  However, strong
heating and moistening of the boundary layer east of the higher
terrain has resulted in moderate buoyancy over this area too.  

The strong heating across this broad region has steepened low-level
lapse rates.  As storms move into the region from the west, the
lapse rate profiles will support the potential for strong downdrafts
with the heavier water-loaded cores or small bow-shaped segments
that may evolve.  Peak gusts ranging from 50-70 mph are possible
with the strongest storms.  

It is uncertain whether isolated storms will develop over eastern PA
during the afternoon or whether the thunderstorm risk will be
delayed until storms arrive from the west.  This uncertainty is due
in part to large-scale subsidence likely suppressing activity on the
northwest periphery of Tropical Storm Claudette.

..Smith/Hart.. 06/21/2021

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

ATTN...WFO...PHI...BGM...AKQ...CTP...LWX...RNK...PBZ...RLX...

LAT...LON   41967569 41977758 39627938 38167972 37727908 37857820
            39317564 40657447 41497491 41967569

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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.