SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0254 PM CDT Fri Jun 20 2025
Valid 202000Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM FAR
EASTERN MONTANA...ACROSS MUCH OF NORTH DAKOTA TO NORTHERN
MINNESOTA...
...SUMMARY...
Severe thunderstorms are likely late this afternoon into tonight
from far eastern Montana eastward across the northern Plains and
into the upper Mississippi Valley. Tornadoes, winds greater than 75
mph, and hailstones greater than 2 inches in diameter will all be
possible.
...20z Update Northern Plains...
Confidence in the overall convective evolution of storms expected
today and tonight remains low. Recent observations and CAM guidance
show potential for isolated supercell development within a focused
low-level upslope regime across far eastern MT and southwestern ND.
Current expectations are that isolated storms may develop late this
afternoon and track eastward along the stationary front in eastern
MT and southern ND with a risk for all hazards. Given this
potential, the Slight Risk has been expanded southwestward toward
the MT/WY/SD border where strong heating and low-level convergence
are being maximized near the surface low.
Farther east across ND and western MN, confidence in surface-based
storm initiation remains quite low owing to warm 700 mb temperatures
(13-16 C) and mid-level ridging. However, very strong heating and
mixing (max sfc temps near/exceeding 100 F to the south) may provide
enough ascent for isolated high-based storm development in the early
evening. Should they remain surface-based, they will mature within
an extremely buoyant, and very strongly sheared air mass supportive
of significant severe weather including; very large hail and
tornadoes.
A perhaps more plausible scenario is for scattered storm initiation
from strong low-level warm advection, courtesy of a 40-60 kt
low-level jet, later tonight across central/eastern ND. Likely
elevated, these supercells would pose a risk for large to very large
hail and damaging gusts before growing upscale along the front into
the western Great Lakes overnight. Should this occur, one or more
organized bows with significant damaging winds and a couple
tornadoes is possible. Given the conditional risk and resulting
uncertainties, the outlook remains largely unchanged.
...Florida...
Scattered thunderstorms have developed along typical sea breeze
boundaries across the FL Space Coast to near Tampa Bay. Moderate to
large CAPE (2000-3000 J/kg of MLCAPE) will continue to support
strong pulse updrafts through this evening. Some of these storms
could produce an isolated damaging gust or small hail However, very
weak mid and upper level flow suggests storm organization is
unlikely and the threat will likely remain below 5%.
..Lyons.. 06/20/2025
.PREV DISCUSSION... /ISSUED 1125 AM CDT Fri Jun 20 2025/
...Eastern MT/ND/MN/WI/Upper MI...
No significant changes have been made to the ongoing outlook. Water
vapor imagery shows a deepening upper trough over the northern
Rockies, with a pronounced shortwave trough entering western MT.
Strong lift associated with this trough will overspread eastern MT
and western ND this evening, leading to the development of scattered
supercell thunderstorms in a region of backed/upslope flow to the
north of the surface low. These storms will track eastward through
the evening across ND and eventually grow upscale. Very large hail
and tornadoes will be possible for the first few hours of this
scenario, with an increasing risk of damaging winds with time. An
upgrade to MDT risk was considered, but will maintain ENH due to
diversity of solutions in various model guidance and uncertainty of
corridor of greatest threat.
Farther east, an increasingly strong nocturnal low-level jet will
help rapid thunderstorm development from eastern ND into MN this
evening. Parameters in this area are very favorable for supercells
capable of all severe hazards, including very large hail and
tornadoes. However, late initiation of storms, warm temperatures in
the 850-700mb layer, and rapid storm interactions lend uncertainty
regarding the evolution of this activity. Some 12z guidance
suggests one or more bowing structures evolve out of this cluster,
tracking eastward overnight across MN into WI and Upper MI.
...Western MT...
As the aforementioned shortwave trough moves eastward, scattered
thunderstorms are forecast to develop off the mountains of western
MT. Widespread cloud cover will limit heating/destabilization, but
favorable deep-layer shear may support a few rotating thunderstorms.
Hail could occur in the strongest storms.
...Southeast Lower MI...
A convectively-aided shortwave trough is moving across Lake MI and
western Lower MI. This feature may encourage the development of
scattered thunderstorms this afternoon over southeast Lower MI and
western Lake Erie. These storms could produce gusty winds and hail.
...High Plains...
Full sunshine will lead to steep low-level lapse rates and moderate
CAPE values this afternoon from southwest NE into eastern NM. Deep
mixing will likely result in widely scattered afternoon and evening
thunderstorms. This high-based activity will be capable of locally
damaging wind gusts.
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