SPC day 2 convective outlook puts us at a slight risk tomorrow
SPC AC 210600
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Tue Jul 21 2020
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
Strong to severe thunderstorms capable of producing mainly damaging
winds may occur Wednesday across parts of the Northeast,
Mid-Atlantic, Ohio Valley, and vicinity. Other isolated severe
storms appear possible across parts of the central Plains.
...Ohio Valley into the Mid-Atlantic and Northeast...
A convectively augmented shortwave trough should move northeastward
across the OH Valley into the Mid-Atlantic and Northeast on
Wednesday. At least isolated storms may be ongoing Wednesday morning
across parts of the OH Valley in association with this shortwave
trough. Current expectations are for rather robust diurnal heating
to occur along/east of the Appalachians in the Mid-Atlantic.
Low-level moisture should also increase across this region through
the day. Most guidance suggests that moderate to locally strong
instability should develop by peak afternoon heating from central
PA/northern VA eastward to the Atlantic Coast. Although mid-level
flow should not be overly strong, around 20-35 kt at 500 mb will
probably be enough to foster some storm organization.
Bowing line segments and clusters should be the dominant storm mode
given marginal deep-layer shear, although a supercell or two cannot
be ruled out along a northward-advancing warm front in southern
NY/northern PA vicinity, where effective bulk shear will be slightly
stronger. With steepened low-level lapse rates, storms that move
east-southeastward across the warm sector may produce strong to
locally damaging downdraft winds. There is enough signal in both
convection-allowing and global guidance of a more favorable corridor
for scattered, linear convection to include 15% wind probabilities
across parts of the Mid-Atlantic. Farther southwest, mid-level flow
and associated shear should be even weaker, but loosely organized
storms capable of producing isolated wind damage may still occur
through Wednesday evening.
A small cluster of storms may be present Wednesday morning
along/near the NE/KS border, perhaps posing an isolated hail/wind
threat before weakening. Even though mid-level heights are forecast
to rise over the central Plains through the day, additional
convective development appears possible along a trailing outflow
boundary. Low-level flow will remain modest until Wednesday evening,
when a southerly low-level jet should strengthen. There is enough
signal in guidance for isolated storm development to include 5%
probabilities for both large hail and severe wind gusts, given the
forecast combination of strong instability with marginal shear.