SPC Jun 20, 2025 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1125 AM CDT Fri Jun 20 2025

Valid 201630Z - 211200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS EVENING
AND TONIGHT FROM EASTERN MONTANA...ACROSS MUCH OF NORTH
DAKOTA...INTO NORTHERN MINNESOTA....

...SUMMARY...
Severe thunderstorms are likely 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.

...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.

..Hart/Squitieri.. 06/20/2025

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