SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0247 PM CDT Fri Jul 08 2022
Valid 082000Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
MONTANA INTO THE WESTERN DAKOTAS...AND OVER PARTS OF THE OHIO VALLEY
CENTERED OVER KENTUCKY...
...SUMMARY...
Isolated very large hail and significant outflow gusts are possible
late this afternoon into early tonight across Montana, and
occasional damaging winds will be possible this afternoon across
Kentucky and vicinity.
No changes were required to the outlook at 20Z.
..Jewell.. 07/08/2022
.PREV DISCUSSION... /ISSUED 1126 AM CDT Fri Jul 08 2022/
...OH Valley into the Southeast this afternoon/evening...
An expansive midlevel ridge will dominate the Southwest and southern
Plains through the period, with mostly weak west-northwesterly flow
over the upper MS and OH Valleys. Weak convectively-enhanced
perturbations in the west-northwest flow, with associated convective
clusters, will continue to move east-southeastward through the
afternoon from southern IN into KY. These storm clusters will move
along the southern fringe of the 30 kt midlevel flow, and along a
baroclinic zone coincident with the northern edge of the warmest
boundary layer, where dewpoints will range from the low to mid 70s.
Though midlevel lapse rates will not be steep, the warm/moist
boundary layer will drive MLCAPE values in the 2000-3000 J/kg range,
which will help maintain the ongoing clusters, and support
additional storm development to the southwest along the trailing
outflow near the confluence of the MS/OH Rivers. The modest
midlevel flow and steepening low-level lapse rates during the
afternoon will support occasional strong/damaging outflow gusts as
the main threat across KY and vicinity.
Scattered diurnal thunderstorms are expected in the weak northwest
flow regime into the Carolinas/GA this afternoon, with storm
development focused along diffuse boundaries/differential heating
zones. The weak flow and poor midlevel lapse rates suggest that
pulse storm downbursts with outflow winds near or above 50 kt will
be sparse.
...MT area later this afternoon into western ND tonight...
Clusters of high-based thunderstorms are expected to form from
southwest into central/north central MT later this
afternoon/evening, in association with surface heating/deep mixing
and embedded speed maxima moving around the northwest periphery of
the Southwest/southern Plains ridge aloft. Steep midlevel lapse
rates will be replenished from the southwest during the day, and
surface heating will boost MLCAPE to 2000-3000 J/kg. Long
hodographs with effective shear in excess of 40 kt, in combination
with the steep lapse rates and strong buoyancy will support clusters
with embedded supercells and bowing segments, capable of producing
isolated very large hail (2 to 2.5 inches in diameter) and isolated
significant outflow gusts up to 75 mph.
...High Plains area this afternoon/evening...
Isolated to widely scattered thunderstorms are expected this
afternoon/evening east of the high terrain from eastern WY into
northeast CO. Forcing for ascent will be weak, but terrain
circulations and weak upslope low-level flow should support storm
development. Deep-layer, northwesterly vertical shear/hodograph
length will be sufficient for supercells and small clusters capable
of producing isolated strong-severe outflow gusts and hail late this
afternoon through late evening.
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