861
ACUS01 KWNS 190537
SWODY1
SPC AC 190535

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1235 AM CDT Tue Aug 19 2025

Valid 191200Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
AND EVENING ACROSS PARTS OF THE CENTRAL GREAT PLAINS AND OZARK
PLATEAU INTO OHIO VALLEY...AND THIS EVENING INTO THE OVERNIGHT HOURS
ACROSS PARTS OF WESTERN MONTANA...

...SUMMARY...
Scattered strong thunderstorm activity may impact a corridor from
the central Great Plains into the Ohio Valley this afternoon and
evening, accompanied by locally strong to severe wind gusts.  A
cluster of thunderstorms may also develop across and northeast of
the mountains of western Montana accompanied by strong to severe
wind gusts this evening into the overnight hours.

...Discussion...
Models indicate that a prominent mid/upper high centered near/east
of the Four Corners will be maintained through this period.  To the
north of this circulation, heights are forecast to build through the
day along a broad axis extending north-northeastward into the
eastern Canadian Prairies, ahead of a fairly vigorous low and
south-southwestward trailing troughing migrating inland of the
British Columbia/Pacific Northwest coast.

Downstream, to the south of the stronger westerlies, it appears that
weak mid-level troughing will dig across and southeast of the Great
Lakes region, perhaps suppressing mid-level heights across parts of
the northern Mid Atlantic into southern Appalachians by 12Z
Wednesday, to the northwest of Hurricane Erin as it continues a slow
north-northwestward migration to the east/northeast of the Bahamas.
On the trailing, southwestern flank of this troughing, a remnant
convectively enhanced perturbation initially across Kansas may
slowly dig southward toward the southern Great Plains Red River
vicinity.

In lower levels, a weak surface low is forecast to slowly progress
across southern portions of the Great Lakes region, with a weak
trailing surface front, reinforced in segments by convective
outflow, advancing southward into the Ohio Valley, Mid South and Red
River Valley by late tonight.

...Central Great Plains into Ohio Valley...
Seasonably high boundary-layer moisture content along/ahead of the
southward advancing front is forecast to contribute to the
development of moderate to strong potential instability with daytime
heating, beneath a residual plume of relatively steep
lower/mid-tropospheric lapse rates, particularly across parts of the
central Great Plains into Ozark Plateau.  Coincident with and
subsequent to peak boundary-layer destabilization, weak mid-level
height falls may contribute to considerable upscale growing
thunderstorm development during the mid to late afternoon and
evening.  Although rather weak deep-layer mean wind fields and shear
are likely to limit the risk for organized severe convection,
thermodynamic profiles may still be conducive to localized
downbursts in stronger storms, and gusty winds occasionally
approaching severe limits along consolidating and strengthening
southward propagating cold pools into this evening.

...Northern Rockies...
Although the time of arrival of mid-level height falls/forcing for
ascent downstream of the inland progressing mid-level troughing may
be sometime this evening, it appears that this will be preceded by
sufficient moistening in the presence of steep lapse rates to
support thunderstorm development.  Models suggest that convection
will initiate across the mountains of western Montana this evening,
before consolidating and spreading in a cluster east of the higher
terrain through north central Montana overnight.  Given
west-southwesterly mean flow strengthening to 30-40+ kt in the
cloud-bearing layer, and a residual deep sub-cloud mixed-layer,
there may be sufficient downward mixing of momentum to contribute to
a few strong to severe surface gusts.

..Kerr/Lyons.. 08/19/2025

$$