Mesoscale Discussion 787

Issued

May 28, 2021, 3:56 PM EDT (19:56 UTC)

Expired

May 28, 2021, 6:00 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Norfolk radar (KAKQ), 117 km from the middle of the area, began a volume at 19:57 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.

419 
ACUS11 KWNS 281957
SWOMCD
SPC MCD 281956 
VAZ000-MDZ000-WVZ000-282200-

Mesoscale Discussion 0787
NWS Storm Prediction Center Norman OK
0256 PM CDT Fri May 28 2021

Areas affected...eastern Virginia

Concerning...Severe potential...Watch unlikely 

Valid 281956Z - 282200Z

Probability of Watch Issuance...20 percent

SUMMARY...Ongoing thunderstorms across eastern Virginia will
continue to pose a threat for gusty winds and hail before crossing
the Chesapeake. Additional thunderstorms may develop later this
afternoon farther west posing an additional threat for wind as they
move east. A watch is currently not expected, but trends will be
monitored.

DISCUSSION...A relatively strong coastal front remains draped across
the Chesapeake Bay area, with easterly flow off the cooler Atlantic
waters to the north and warm southerly flow to the south. To the
south of this front, isolated thunderstorms developed earlier this
afternoon within a zone of strong surface heating (surface
temperatures greater than 90F) and modest low-level warm-air
advection. The warm, moist low levels have contributed to
most-unstable CAPE values around 2000-3000 J/kg across a small
corridor of eastern Virginia despite weak mid-level lapse rates (on
the order of 5-6 C/km). Gusty thunderstorm outflow winds will remain
possible with the stronger updrafts, although a brief tornado
potential will exist with any thunderstorm moving across the coastal
front where backed surface winds may support enhanced low-level
helical flow.

High-resolution convection permitting models, such as the HRRR and
experimental WoFS guidance, continue to suggest additional
thunderstorms may develop across central Virginia this afternoon as
increased ascent from an approaching mid-level trough encounters the
aforementioned unstable environment. These thunderstorms will also
pose a threat for gusty thunderstorm winds as they move east,
although a brief tornado cannot be ruled out with any thunderstorm
that interacts with the backed low-level flow in and near the
aforementioned coastal front.

At this time thunderstorm coverage is anticipated to remain sparse
enough to preclude the need for a watch, but conditions will
continue to be monitored.

..Marsh/Hart.. 05/28/2021

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

ATTN...WFO...AKQ...LWX...RNK...

LAT...LON   36788051 38017989 38907887 38877755 38397632 37487584
            36877611 36667693 36627876 36788051

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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.