463
ACUS01 KWNS 170552
SWODY1
SPC AC 170550

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1250 AM CDT Thu Jul 17 2025

Valid 171200Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN NORTHERN PARTS
OF THE GREAT PLAINS AND NEW ENGLAND...

...SUMMARY...
A confined corridor of large hail and severe gusts may occur from
north-central Montana to southwest North Dakota this evening.
Scattered damaging winds and a brief tornado are possible across
northern New England this afternoon. Isolated/sporadic damaging
winds are also possible across a broad swath of the
Northeast/Mid-Atlantic to the southern High Plains.

...Northern Great Plains...
A confined corridor of supercell potential is evident across
north-central MT to southwest ND this evening. A positive-tilt
shortwave trough over the southern Canadian Rockies will progress
east along the international border with MT/ND. 00Z HREF guidance is
consistent in indicating mid-afternoon storm development over
southwest AB. A confined plume of weak buoyancy initially ahead of
this activity should temper intensity as it spreads east-southeast
into north-central MT by late afternoon. But favorably timed
strengthening of a 500-mb westerly jetlet will aid in hodograph
elongation. This could support a long-lived/long-track supercell
during the evening, impinging on the nose of moderate MLCAPE across
southeast MT. Modest mid-level lapse rates and a cooler-than-normal
boundary layer should be the primary limiting factor to greater
hail/wind magnitudes. But enough signal exists to warrant a narrow
level 2-SLGT risk for hail. Low-probability hail/wind threats may
persist along the ND/SD border area overnight.

...New England/Northeast...
A large MCV over Lower MI will become further absorbed into a
shortwave trough that will progress from the Upper Great Lakes to
the ON/QC border area by early evening. This will help broaden a
swath of enhanced 850-700 mb west-southwesterlies from PA/NJ north.
But further weakening of already marginal mid-level lapse rates,
owing to the influence of the MCV, should yield a pocket of 500-mb
temperatures warming to -4 C in the Hudson Valley vicinity by late
afternoon. This will likely limit convective coverage across the
Northeast to southern New England vicinity. Scattered, mainly
discrete, convection is anticipated along the QC border across
northern New England. A few weak supercells are probable, capable of
mainly damaging winds and a brief tornado.

...Lower Mid-Atlantic to the southern High Plains...
Scattered to widespread thunderstorms are expected west of the
Appalachians along a large-scale west/east-oriented convective
outflow, augmented by a surface cold front stalling in the southern
High Plains. Ample buoyancy south of the outflow/front will support
sporadic wet microbursts. Modest deep-layer shear and warm 500-mb
temperatures should modulate overall organization/coverage. Isolated
damaging winds are also expected east of the central Appalachians,
where storm coverage should be reduced but downbursts are possible.

..Grams/Thornton.. 07/17/2025

$$