Mesoscale Discussion 1265
NWS Storm Prediction Center Norman OK
1232 PM CDT Mon Jul 12 2021
Areas affected...Portions of the Northeast
Concerning...Severe potential...Watch possible=20
Valid 121732Z - 121900Z
Probability of Watch Issuance...60 percent
SUMMARY...A few multicell clusters of storms should emerge by mid to
late afternoon, posing a threat for damaging winds. Trends will
continue to be monitored for a possible severe thunderstorm watch.
DISCUSSION...Visible satellite shows morning clearing over the
region has allowed surface temperatures to warm into the mid to
upper 80s F amid dew point temperatures in the low 70s F. This has
led to somewhat rapid destabilization, with moderate instability
(MLCAPE 2000-2500 J/kg) being analyzed on surface mesoanalysis.
Scattered convection is already developing across portions of
southern Pennsylvania, western Maryland, and northern Virginia, as
convective temperatures are being eclipsed amid a weak cap. Despite
these thermodynamic indices, mid-level lapse rates and deep-layer
shear remains rather weak (20-25 kt effective bulk shear). Thus,
storms may struggle to organize in the short-term.
Additional storms should develop across the region as
isolation/destabilization continues. This should lead to the
development of a few multicell clusters of storms this afternoon.
Should this occur, strong low-level lapse rates should support a
damaging wind potential. Thus, convective trends will continue to be
monitored for possible watch issuance this afternoon.
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