ACUS01 KWNS 171232
SWODY1
SPC AC 171231

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0731 AM CDT Fri Jul 17 2026

Valid 171300Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHERN ROCKIES AND HIGH PLAINS...UPPER GREAT LAKES...AND OHIO
VALLEY INTO THE SOUTHEAST...

...SUMMARY...
Strong to potentially severe storms are possible today across parts
of western Montana and northern Idaho, and also across parts of the
Upper Midwest and northern Great Lakes. More isolated strong to
severe storms with damaging gusts are possible over parts of the
Ohio Valley into parts of the Southeast.

...Northern Rockies and adjacent High Plains...
To the east of an upper low near the WA/Vancouver vicinity, an upper
ridge with a plume of monsoonal moisture will extend northward from
the Great Basin into the northern Rockies and adjacent High Plains. 
Orographic lift and heating will promote the development of
scattered thunderstorms this afternoon.  Steepened low-level lapse
rates will potentially yield storms capable of isolated severe gusts
beginning this afternoon and continuing into the mid-late evening. 
Isolated large hail may occur with the stronger thunderstorm cores,
especially over northwest MT where 0-6 km shear will be 25-35 kt.

...Upper Midwest and northern Great Lakes...
A cluster of weak thunderstorms over the MN Arrowhead will likely
move southeast this morning ahead of an amplifying upper trough
forecast to move from northern SK to the Upper Peninsula of MI
during the period.  A cold front associated with the upper wave will
push southeastward across the Upper Midwest and provide a focus for
thunderstorms later this afternoon and evening.  

A warm frontal zone draped across the northern Great Lakes will
advance northeastward as a low over western ON moves eastward into
central ON by early evening.  Forecast model guidance shows moderate
buoyancy developing today within a belt of 25-40 kt
west-northwesterly 500-mb flow.  As a result, a few of the stronger
thunderstorms will probably evolve into supercells and organized
multicell clusters.  Isolated large hail and damaging gusts are the
primary hazards, although a brief tornado risk may also develop in
the areas surrounding Lake Superior.  One or more clusters of strong
to severe storms may persist into the overnight along the warm
front.  However, confidence in this scenario is lower owing to the
prior convection and uncertainties of diurnal development along the
cold front.  Still, a strengthening wind field and ample moisture
could support a risk for damaging winds into northern Lower MI
overnight.

...OH Valley to the southern Appalachians and FL...
A moist and diurnally destabilizing airmass will support scattered
to numerous storms developing by the mid afternoon.  Some of the
stronger water-loaded downdrafts will potentially be capable of
50-60 mph gusts and isolated wind damage.  

...West-central TX...
A weak mid- to upper-level low over west TX will move little during
the day while a warm/moist conveyor persists across southern into
central parts of TX.  An ongoing thunderstorm cluster will likely
continue across the Concho Valley aided in part by a convectively
augmented zone of low-level warm-air advection.  Despite very moist
low levels and some enlargement of the low-level hodograph per KSJT
and KDFX VAD data, weak flow in the mid levels will likely promote
enough convective outflow to limit storm organization (i.e.,
transient storm-scale cyclonic shear) and favor a heavy rain threat.

..Smith.. 07/17/2026

$$
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