SPC Jun 13, 2025 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1126 AM CDT Fri Jun 13 2025

Valid 131630Z - 141200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR PARTS OF CENTRAL AND SOUTHERN MONTANA...

...SUMMARY...
Scattered severe thunderstorms are expected this afternoon and
evening across parts of Montana, extending southward across portions
of the central/southern High Plains. The greatest concentration of
severe thunderstorms should occur across central/southern Montana,
where large to very large hail, severe winds, and a couple tornadoes
will be possible.

...Central/southern MT this afternoon/evening...
Embedded speed maxima will progress east-northeastward over the
northern Rockies, with associated bands of ascent denoted by weak
convection now over ID.  Surface heating along and southwest of a
baroclinic zone oriented from north central into southeast MT, and
arrival of the bands of ascent from ID will contribute to
thunderstorm development by early afternoon over the higher terrain
of southwest MT.  Storms will then spread eastward through the
afternoon/evening, in an environment supportive of supercells on the
northeast edge of the steeper midlevel lapse rates, in a corridor
with long hodographs/effective bulk shear in excess of 50 kt.  The
strong deep-layer shear and moderate buoyancy (MLCAPE near 1500
J/kg) will favor large hail production, some greater than 2 inch
diameter with the supercells, as well as damaging outflow gusts that
could reach or exceed 75 mph.  A couple of tornadoes will also be
possible, though relatively deep mixing and relatively straight
hodographs cast some doubt on the tornado threat.

...High Plains this afternoon into early tonight...
Despite being near the crest of the midlevel ridge, sufficiently
moist, low-level upslope flow and steep midlevel lapse rates will
support thunderstorm development near and east of the lee trough
from eastern WY to eastern CO/western KS and the northern TX
Panhandle later this afternoon/evening.  Deep mixing, steep lapse
rates, and relatively weak vertical shear all support initial storms
growing upscale into clusters through outflow interactions, and the
clusters will spread southeastward into tonight.  Isolated large
hail will be possible with the stronger embedded storms, while
severe outflow gusts will become the main concern with storm
clusters this evening into early tonight.

...MS/AL to KY this afternoon...
East of a weak midlevel trough from east TX to MO, modest
enhancement of midlevel flow (to roughly 30-35 kt) and daytime
heating of a moist air mass will contribute to scattered
thunderstorm development through the afternoon from southeast LA/MS
across northwest AL, TN and KY.  MLCAPE of 1500-2500 J/kg and the
aforementioned enhancement to midlevel flow will support storm
clusters/line segments with some potential for isolated wind damage
this afternoon.

...Mid-Atlantic this afternoon...
Strong surface heating is underway to the south of a slow-moving
front from DE into northern MD, which will steepen low-level lapse
rates and boost MLCAPE to 1000-1500 J/kg this afternoon.  Scattered
thunderstorm development is possible along the front and the Blue
Ridge, and storms will spread eastward through late
afternoon/evening.  The moderate buoyancy, steep low-level lapse
rates and modest deep-layer vertical shear (effective bulk shear of
25-30 kt) will support some storm/cluster organization and the
potential for isolated wind damage.

..Thompson/Barnes.. 06/13/2025

StormPrep