SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Sun Jun 22 2025
Valid 221300Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE PLAINS...UPPER MISSISSIPPI VALLEY...AND THE NORTHEAST...
...SUMMARY...
Isolated to scattered thunderstorms are expected to develop today
across the northern Plains and Upper Mississippi Valley, some of
which could produce large hail, damaging wind gusts and tornadoes.
Storms associated with severe gusts and hail may also develop across
parts of the Northeast, and in the southern and central Plains.
...Northern/Central Plains into the Upper Midwest...
Widely scattered elevated thunderstorms are currently moving
northeastward across the eastern Dakotas. A few stronger storms are
embedded within these clusters and overall trends suggest increasing
storm coverage is possible as these storms move into more of eastern
ND and northwest/west-central MN. The airmass here is characterized
by very steep mid-level lapse rates (around 8 to 8.5 deg C per km
from 700 to 500 mb per recent mesoanalysis) and moderate deep-layer
vertical shear. These environmental conditions support the potential
for large hail within any more organized updrafts throughout the
morning. See MCD #1400 for additional details.
The strength and extent of these early day storms could impact
thunderstorm chances later. However, the general expectation
supported by all the guidance is that the airmass should easily
recover as the surface low currently over the western SD/NE border
vicinity shifts northeastward across SD and moderate/strong
southerly surface winds persist through the warm sector. By 21Z, the
surface low will likely be over northeast SD with a cold front
extending north-northeastward to a secondary low over northern MN.
Warm mid-level temperatures will cap the airmass until after 21Z,
when isolated development appears possible across northern MN.
Another scenario is for early afternoon initiation behind the front
across ND, supported by a weak vorticity maximum moving out of
western SD. These storms could then gradually move northeastward
into the more unstable airmass farther east. In either case, any
warm-sector development would likely be supercellular and capable of
all severe hazards, including very large hail up to 2" in diameter,
gusts to 75 mph, and tornadoes. The warm front is currently expected
to be just north of the international border, keeping the best
tornado environment in Canada. Upscale growth into a
forward-progressing MCS is possible, but there is currently low
confidence in the overall storm evolution.
Additional development is also possible farther south from
central/eastern NE into eastern SD this evening. This activity
should initially be elevated with hail as the primary risk. A
general northeastward motion is anticipated and there is some chance
for this activity to begin interacting with the frontal zone. If
that occurs, some strong gusts are also possible throughout the
evening.
Lastly, late afternoon thunderstorm development appears probable
across far eastern WY, the NE Panhandle, and southwest SD. High
storm bases coupled with modest buoyancy, deep mixing, and steep
low-level lapse rates will support the potential for strong outflow
with this activity.
...Central/Southern High Plains...
Low-level moisture advection and related airmass destabilization
coupled with low-level convergence along the lee trough is expected
to result in widespread convective initiation from eastern
CO/western KS through eastern NM and into far west TX. Vertical
shear will be modest, likely resulting in a predominantly
outflow-dominant storm structure and the potential for damaging wind
gusts. Some isolated hail is possible as well.
...Northeast...
Remnants of an overnight MCS currently cover much of the Northeast,
with the strongest storms confined to just north of the outflow
along its western periphery. Given the extensive precipitation
ongoing, this outflow will likely shift gradually
south-southwestward throughout the morning. Warm-air advection along
this boundary will weaken throughout the day as upper ridging builds
northward into the region. Even so, low-level convergence along this
boundary will likely continue, and there is some chance for
thunderstorms to persist along this boundary as well. Steepening
mid-level lapse rates and resulting strong buoyancy will support a
conditional risk for severe thunderstorms during the
afternoon/evening in the vicinity of this boundary. Large hail and
damaging gusts are the primary risk with any storms that do develop.
..Mosier/Dean.. 06/22/2025
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