SPC Jun 20, 2025 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0800 PM CDT Thu Jun 19 2025

Valid 200100Z - 201200Z

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

...SUMMARY...
Scattered severe thunderstorms with large to very large hail and
damaging wind gusts are expected across the northern Plains and
upper Mississippi Valley this evening into tonight. Isolated severe
gusts will also be possible from central and eastern North Carolina
north-northeastward to New England.

...Northern and Central Plains/Upper Mississippi Valley...
Latest water vapor imagery at mid-levels shows a ridge over the High
Plains, with west-northwesterly flow over much of the central and
northern Plains. At the surface, a 1002 mb low is located over
north-central South Dakota, with a trough extending
south-southwestward into northwest Kansas. An axis of low-level
moisture is analyzed from central Plains northward to near the
surface low and northwestward into western North Dakota. Along this
corridor, the RAP has MLCAPE mostly in the 2000 to 3000 J/kg range.
A severe storm is currently ongoing near the instability max in
southwest North Dakota, with additional isolated severe storms
located in north-central Nebraska and northwest Kansas.

Moderate deep-layer shear is present across much of the central and
northern Plains, which will contribute to an environment supportive
of supercells this evening. A severe threat with more longevity is
expected in the northern Plains. The Bismarck 00Z sounding has a 0-6
km shear around 40 knots, with nearly dry adiabatic low to mid-level
lapse rates. This will support supercells with large to very large
hail, possibly greater than 2 inches in diameter. This, combined
with surface dewpoints in the lower 60s F and substantial
directional shear from the surface to 700 mb, will also support an
isolated tornado threat. 

Concerning future convective development, the latest HRRR maintains
a widely spaced coverage for much of the early to mid evening, but
then begins to increases thunderstorm coverage over eastern parts of
the northern Plains late this evening. As the nose of a low-level
jet moves into the eastern Dakotas, a cluster of severe storms is
expected to develop and move eastward into the upper Mississippi
Valley tonight. Supercells with large hail will be possible with
cells than remain discrete. However, linear mode should become
favored, which will likely support an increase in the potential for
severe gusts.

...Eastern States...
A mid-level trough is currently evident on water vapor imagery over
the southern and central Appalachians. Ahead of the trough, a moist
airmass is present from the Carolinas north-northeastward into New
England. The RAP suggests that instability is weak along and ahead
of the surface trough. Short-term model forecasts suggest that
scattered convective coverage will continue over the next few hours.
00Z soundings across the region show moderate deep-layer shear and
have steep lapse rates around 850 mb. This should support an
isolated severe threat over the next couple of hours as low-level
flow gradually increases. Severe wind gusts will be the primary
threat, associated with short bowing line segments.

..Broyles.. 06/20/2025

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