SPC Jun 20, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Fri Jun 20 2025

Valid 201300Z - 211200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...

...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.

...Northern Plains/Upper Mississippi Valley...
Showers and thunderstorms have persisted throughout much of the
night into early this morning across central/southern MN, much of IA
and central WI. This activity was supported by a persistent and
moderately strong low-level jet. Expectation is for this cluster to
persist for the next few hours while gradually losing strength amid
a weakening low-level jet.

A very moist airmass exists to the west of this cluster across the
Great Plains. Recent surface analysis places mid 60s dewpoints
through eastern NE, with low 60s reaching into south-central ND.
Surface analysis also places a low near the central SD/NE border
vicinity, with a warm front arcing southeastward from this low
across northeastern NE and western IA before becoming oriented more
north-to-south over western MO. Expectation throughout the day is
for this warm front to become better defined as the current surface
low fills and another develops over western SD. This evolution will
be supported as the shortwave trough currently located over the
Great Basin progresses quickly northeastward towards the northern
Plains.

By the mid to late afternoon, a deep surface low will likely be over
western SD with a sharp warm front extending eastward from the low
roughly along the ND/SD border through central MN. Upper 60s to low
70s dewpoints are anticipated along this frontal zone by the late
afternoon, with surface temperatures in the upper 80s to low 90s.
These surface conditions beneath steep mid-level lapse rates will
result in strong to extreme buoyancy, with HREF mean SBCAPE ranging
from 2000 J/kg across western ND to over 4500 J/kg from northeastern
SD into central MN. Thunderstorm development is expected across
eastern MT as the approaching shortwave trough interacts with this
buoyant airmass during the late afternoon. Additionally, surface
convergence could lead to thunderstorm development along the front
farther east from ND into northern MN around the same time. Given
the environment, storms in both of these areas should quickly become
severe, with large to very large hail and tornadoes as the primary
risk. The storms over eastern MT will likely grow upscale into an
organized convective line, although their is still uncertainty
regarding how quickly this occurs. Environmental conditions support
the development of a forward-progressing convective line capable of
strong to severe wind gusts. Some gust over 75 mph are possible. The
potential for line-embedded tornadoes exists as well. The threat for
damaging gusts with this line should continue into Upper Great Lakes
region early Saturday morning.

...Southern/Central High Plains...
Isolated high-based thunderstorms are possible across the region
amid increasing mid-level moisture and glancing ascent from a
shortwave trough farther north. A few strong gusts are possible as
these storms move into the lower elevations this evening.

..Mosier/Leitman.. 06/20/2025

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