SPC AC 170547

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1247 AM CDT Thu Sep 17 2026

   Valid 171200Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE INTERMOUNTAIN WEST AND IN THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Thunderstorms with isolated severe wind gusts and hail will be
   possible in parts of the Intermountain West late this afternoon and
   early this evening. A few strong gusts may also occur in parts of
   the central High Plains.

   ...Intermountain West...
   An upper-level low will move inland into the Intermountain West
   today, as southwest flow remains at mid-levels over much of the
   region. At the surface, a trough will deepen from southern Idaho
   into western Utah. To the east of the trough, dewpoints in the 50s
   F, will contribute to weak instability by afternoon. As surface
   temperatures warm, thunderstorms will develop in the higher terrain.
   RAP forecast soundings to the east of the trough at 00Z have 0-6 km
   shear in the 30 to 40 knot range. In addition, low to mid-level
   lapse rates are forecast to be in the 6.5 to 7.5 C/km range. This
   environment will likely support an isolated threat for severe gusts
   and hail. The threat should be concentrated during the late
   afternoon and early evening, as cell coverage maximizes near the
   instability axis.

   ...Central High Plains...
   An upper-level ridge will move eastward today across the
   north-central U.S, as a shortwave trough embedded in the ridge moves
   through the central High Plains. At the surface, a warm front is
   forecast to move slowly northward across southern and western
   Nebraska this afternoon. An axis of moisture, with surface dewpoints
   in the 60s and 70s F, will be oriented north of the front from the
   mid Missouri Valley west-northwestward into the central High Plains.
   During the late afternoon, scattered thunderstorms are expected to
   develop near the shortwave trough, with storms moving gradually
   northeastward across the central High Plains. Forecast soundings
   near the area of greatest expected convective coverage have moderate
   deep-layer shear suggesting an isolated severe threat will be
   possible. However, lapse rates are forecast to be poor, which should
   keep any severe threat marginal. If storms near the front can remain
   nearly surface-based, then an isolated wind-damage threat could
   develop, mainly during the early to mid evening, as low-level flow
   increases.

   ..Broyles/Thornton.. 09/17/2026

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