SPC AC 170600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Tue Sep 17 2024

   Valid 171200Z - 181200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Thunderstorms capable of severe wind gusts and isolated large hail
   will be possible this afternoon and evening across parts of the
   central and northern High Plains. Wind gusts greater than 70 mph are
   likely in parts of northeast Colorado, far northwest Kansas and
   western Nebraska. A marginal potential for severe wind gusts is also
   expected to develop in parts of the southern and central Rockies,
   and in parts of eastern Florida.

   ...High Plains/Central and Southern Rockies...
   A mid-level low will move across the Intermountain West today, as an
   associated upper-level trough becomes negatively tilted. A 50 to 65
   knot mid-level jet in the base of the trough will move into the
   central Rockies. Ahead of the system, a lee trough will deepen
   across the central and northern High Plains. The western edge of a
   moist airmass will be located just to the east of the surface trough
   from eastern Colorado into the western Dakotas and eastern Montana.
   During the day, thunderstorms are expected to develop ahead of the
   mid-level trough across the central and northern Rockies, with these
   storms moving east-northeasteastward across the central and northern
   High Plains during the afternoon and evening.  A severe threat will
   likely accompany many of the stronger storms.

   Ahead of the approaching trough, partial clearing will result in
   strong surface heating this afternoon over the central High Plains.
   MLCAPE is expected to peak near 1500 J/kg from eastern Colorado
   northward into western Nebraska. A slab of strong large-scale
   ascent, and an associated mid-level jet will move into the central
   Plains late this afternoon. This will coincide with strengthening
   low-level flow and maximized instability, which will make severe
   storms likely along parts of a convective line moving across the
   central High Plains. The greatest combination of instability, lift
   and deep-layer shear is forecast across western Nebraska and
   northeast Colorado, suggesting an enhanced threat for severe wind
   gusts. Gusts above 70 mph will be possible ahead of an organized
   line segment that is expected to move across the central High Plains
   during the early evening. The potential for severe wind gusts will
   extend southward and westward into the southern and central Rockies,
   but the threat will be more isolated in areas where instability
   remains weak.

   ...Northern High Plains...
   A mid-level low will move across the Intermoutain West. Ahead of the
   low, divergent south to south-southeasterly flow will be in place
   across the northern Rockies and northern Plains. During the
   afternoon, thunderstorms will develop in the north-central Rockies
   and move north to northeastward across the northern High Plains. An
   axis of moderate instability is forecast by afternoon from the
   Dakotas northwestward into northeast Montana. As large-scale ascent
   and moderate deep-layer shear overspread the northern High Plains
   late this afternoon and evening, organized storms will be possible.
   Severe wind gusts and isolated large hail will be the primary
   threats.

   ...Eastern Florida...
   A mid-level trough will move across the eastern Gulf of Mexico
   today, as an associated surface trough moves across the Florida
   Peninsula. Surface dewpoints in the lower to mid 70s F, along with
   surface heating will contribute to moderate instability by
   afternoon. As surface temperatures warm today, scattered
   thunderstorms are expected to develop along and ahead of the surface
   trough. RAP forecast soundings at 21Z in eastern Florida have MLCAPE
   in the 2000 to 3000 J/kg range, with 0-6 km shear around 20 knots.
   This, combined with steep low-level lapse rates could be enough for
   a marginal threat for severe wind gusts.

   ..Broyles/Weinman.. 09/17/2024

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