SPC Jun 21, 2025 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1149 AM CDT Sat Jun 21 2025

Valid 211630Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER NORTHERN
PORTIONS OF NEW YORK AND VERMONT...

CORRECTED FOR SPELLING IN SUMMARY

...SUMMARY...
Thunderstorms associated with severe wind gusts and hail will be
possible tonight across New York and New England. Isolated severe
storms will also be possible across portions of the Great Lakes, the
northern High Plains and Middle Missouri Valley.

...Great Lakes...
Strong/intermittently severe thunderstorms continue across the
northern Lower Peninsula of Michigan this morning, associated with
the long-lived severe MCS that moved across the northern
Plains/upper Midwest Friday afternoon and night. Although the
immediate downstream environment is only slowly warming due to the
presence of mid/high-level clouds, some slow destabilization is
occurring.  This will maintain at least some continued risk for a
strong/severe storm through early afternoon across northern Lower MI
and adjacent waters of Lake Huron.

Across the MI Upper Peninsula, a warm front is expected to sharpen
across this area, along with rising heights in the wake of the
convectively-augmented vorticity maximum now moving through southern
Ontario. Heating of a very moist boundary layer will result in
strong to extreme instability (MLCAPE in excess of 3000 J/kg),
however the presence of a pronounced cap should suppress storms
during the afternoon. As a modest low-level jet strengthens this
evening, isolated elevated severe storms will be possible on the
immediate cool side of the front, within an environment supportive
of organized storms including supercells. Large hail and damaging
winds will be possible. 

...NY into Western New England...
Thunderstorms moving across Lake Huron/southwestern Ontario at 16z
will continue east, and most morning CAM guidance suggests storms
will remain west of western NY. Of greater concern will be the
potential for storms to move into northern NY/western New England
late tonight ahead of a southeast-moving cold front, where modest
destabilization and strong deep-layer shear will support storm
organization. Morning hi-res guidance supports a loosely organized
linear structure, and perhaps supercells with an attendant risk for
strong winds and severe hail late tonight. The Level 2/Slight Risk
has been expanded east into northern VT based on this expectation.

...Eastern MT into Western ND...
Isolated thunderstorms have weakened over eastern MT this morning,
with additional isolated redevelopment possible this afternoon and
tonight as ascent associated with minor perturbations within
southwest mid-level flow moves across the area. Modest instability
and strong deep-layer shear will support updraft organization and a
risk for severe hail and/or damaging gusts.

...Central NE/SD/ND into the Upper Midwest...
Surface low currently over central SD is expected to move little
this afternoon, with low-level moisture advection throughout the
warm sector east of this low. Air mass recovery/modification
following the overnight MCS is expected, and this will contribute to
a sharpening warm-frontal zone. Strong to extreme buoyancy (i.e.
MLCAPE greater from 3000 to 5000 J/kg) is expected by this evening
along this warm front from the ND/SD border vicinity eastward
through central MN into northern WI. Some low-level convergence is
anticipated in this region, but height rises will occur within the
large-scale environment. Additionally, warm mid-level temperatures
(16 to 17 deg C at 700 mb) are expected, capping the airmass to deep
convection this afternoon. Isolated thunderstorm development will be
possible mainly this evening as a low-level jet strengthens, with a
risk for severe wind and isolated hail.

..Bunting.. 06/21/2025

StormPrep