SPC Jun 26, 2025 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1226 PM CDT Thu Jun 26 2025

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE FRIDAY INTO
FRIDAY NIGHT ACROSS MUCH OF NORTH AND SOUTH DAKOTA INTO PARTS OF
WESTERN MINNESOTA AND NORTH CENTRAL NEBRASKA...

...SUMMARY...
Scattered strong thunderstorms, and perhaps one or two small
organizing clusters, may impact parts of the northern Great Plains
late Friday afternoon into Friday night, accompanied by a risk for
severe hail and wind.

...Discussion...
Although a mid to upper low is likely to linger across parts of the
Southeast, perhaps migrating slowly northward across the northern
Florida into Georgia vicinity, modest subtropical ridging at
mid-levels will generally prevail across much of the central and
southern tier of the U.S. through this period.  Models indicate that
modest mid-level westerlies will remain confined to the northern
tier, with one embedded short wave trough forecast to slowly
progress across the Great Lakes region.  A couple of, perhaps, more
subtle perturbations within a broader cyclonic regime are forecast
to progress east-northeastward near and north of the Montana/North
Dakota international border vicinity.

In lower levels, a surface cold front, in the wake of a digging
short wave trough well offshore of the northern Atlantic coast, may
make further southward progress through portions of the northern Mid
Atlantic states, before retreating northeastward late Friday through
Friday night.  Upstream, another cold front, likely into the upper
Great Lakes vicinity and through much of the northern Great Plains
by 12Z Friday, is forecast to continue to advance eastward across
the Great Lakes through the remainder of the period, while the cool
air gradually modifies from west to east across the Dakotas.  In
between and south of these boundaries, seasonably moist conditions,
including upper 60s to 70+ F dew points, appear likely to persist
across most areas east of the high plains.

...Northern Great Plains...
Models indicate that low-level warming and moistening across the
western into central Dakotas may contribute to strong potential
instability by Friday afternoon, beneath warm elevated mixed-layer
air advecting east of the northern Rockies, ahead of the broad
approaching upstream mid-level troughing.  This destabilization will
become focused east of the modestly deep lee surface trough axis,
along a developing warm frontal zone aided by strengthening
differential surface heating.  

The northern periphery of the warmer and more strongly capping
elevated mixed-layer air is forecast to nose across western through
central South Dakota by early Friday evening. 
Lower/mid-tropospheric warm advection on the edge of this air mass
may provide the focus for an upscale growing cluster of storms
across north central South Dakota, or perhaps south central North
Dakota, aided by a modestly strengthening low-level jet Friday
evening.  This would likely tend to propagate east-southeastward
overnight, beneath  strengthening westerly mid/upper flow (including
30-40+ kt at 500 mb). 

Otherwise, widely scattered strong to severe thunderstorms,
including a couple of supercells, may initiate near/east of the lee
trough during the late afternoon into evening across the western
Dakotas, and perhaps parts of north central Nebraska into
northeastern Colorado, though this is a bit more uncertain due to
potentially stronger mid-level inhibition.

...Lower Great Lakes Vicinity...
Latest model output indicates that strengthening thunderstorm
development is possible in a narrow pre-frontal corridor across
parts of southwestern Ontario and southeastern Lower Michigan into
northwestern Indiana and northwestern Ohio, near or after 28/00Z. 
Although this is after peak diurnal heating, moderately large
residual CAPE, in the presence of southwesterly deep-layer mean flow
strengthening to 20-30 kt, might become supportive of convection
capable of producing a few locally strong to severe wind gusts,
before storms weaken late Friday evening.

...Appalachians into Southeast...
In the presence of relatively weak mid-level inhibition, forcing for
ascent aided by orography and inland advancing sea breezes may
support considerable diurnal thunderstorm development, as insolation
within a seasonably moist boundary-layer contributes to moderate
potential instability.  Stronger convection will probably pose a
risk for locally damaging downbursts, before activity weakens early
Friday evening.

..Kerr.. 06/26/2025

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