598
ACUS01 KWNS 172003
SWODY1
SPC AC 172001

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0301 PM CDT Sun Aug 17 2025

Valid 172000Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MIDDLE MISSOURI VALLEY VICINITY...

...SUMMARY...
One or two clusters of thunderstorms may develop and gradually pose
a risk for damaging wind gusts from the northern High Plains into
the Midwest this afternoon and tonight. Damaging thunderstorm wind
gusts may also occur across parts of the northern Mid Atlantic into
southern New England late this afternoon and evening.

...20Z Update...
Preceding a remnant MCV tracking northeastward across parts of
southeastern SD, an elevated cluster of thunderstorms is spreading
northeastward from east-central SD into southwest MN. Ahead of this
activity, earlier stable/billow clouds have eroded along/north of a
surface boundary draped across southwestern MN, where diurnal
heating amid lower 70s dewpoints is contributing to gradual air mass
recovery/destabilization. Given this continued destabilization, the
Slight Risk was expanded slightly northward, and was also trimmed on
the western edge in the wake of the MCV.

Farther east, the Marginal Risk was expanded slightly westward into
northeastern WV -- ahead of an ongoing cluster of thunderstorms with
a history of wind damage. See MCD 1975 for more details. For details
on the near-term severe threat over the Black Hills vicinity,
reference MCD 1976.

..Weinman.. 08/17/2025

.PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Aug 17 2025/

...Northern/Central Plains into Upper Midwest...
The combination of close proximity to the upper ridge that covers
much of the central/southern CONUS, lack of more defined synoptic
features, and ample low-level moisture and buoyancy yields a complex
and uncertain forecast from the northern/central Plains into the
Midwest today and tonight. Recent satellite and radar imagery
depicts two MCVs across the region, one over central SD and the
other across central NE. Surface analysis also shows a low over the
central SD/NE border, along the northern periphery of the NE MCV. A
mix of convective outflow, cloud cover, and a formally more defined
surface boundary has resulted in a warm-front-like feature extending
southeastward from this surface low through central IA. All of these
features will likely play a role in thunderstorm development today.

The general expectation is for mesoscale ascent attendant to the
surface low and MCV to yield increasing thunderstorm development
across southeast SD and northeast NE over the next few hours. A
sharpening warm front will likely shift northward, providing a
favored corridor for storm progression, with the ongoing storms
continuing downstream along this corridor into southwest MN and
northwest/north-central IA. Damaging gusts will be the primary risk,
with severe coverage expected to become high enough to merit
introducing 15% wind probabilities. A more stable airmass to the
north/northeast of the boundary should limit the severe risk over
central MN and central WI.

Much of the guidance also shows evening thunderstorm development
beginning in eastern WY/southwest SD/NE Panhandle region before then
spreading eastward/southeastward with time. This activity appears to
be initially associated with low-level convergence along the lee
troughing, with its progression southeastward likely tied to an
increasing low-level jet. Isolated hail is possible initially with a
few stronger gusts then possible overnight.

...Northern Rockies/northern High Plains...
Scattered high-based thunderstorms are expected this afternoon and
evening as ascent attendant the shortwave trough currently moving
through eastern OR spreads into the region. Combination of moderate
mid-level southwesterly flow, steep low-level lapse rates, and high
cloud bases could contribute to isolated strong to severe gusts
within these storms as they gradually move from southwest MT into
central/southeastern MT.

...Mid Atlantic into southern New England...
Recent surface analysis places a cold front from northern ME
southwestward through western NY and northwest PA in northern OH.
Mid-level lapse rates are weak, and the relatively warm profiles
will likely limit buoyancy, despite dewpoints in the mid to upper
60s. However, strong heating into the 80s and 90s F and steep
low-level lapse rates combined with modest westerly flow aloft and
frontal forcing may be sufficient for isolated strong storms capable
of locally gusty/damaging winds this afternoon. Locally higher
probability for damaging gusts appears to exist across southern ME,
where greater deep-layer shear is presence, and over the northern
Mid-Atlantic where dewpoints and buoyancy will be highest.

$$