SPC AC 272000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sat Jun 27 2026

   Valid 272000Z - 281200Z

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

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   TENNESSEE VALLEY TO THE CAROLINAS...

   ...SUMMARY...
   Severe thunderstorms are likely today across the northern High
   Plains including northeast Wyoming and eastern Montana into the
   western Dakotas, with storms capable of very large hail, very strong
   outflow winds (80+ mph), and tornadoes late this afternoon into
   tonight.

   ...20Z Update...
   The previous forecast remains on track, and only minor adjustments
   were made with this update. The ENH risk was expanded slightly
   southwestward in northeastern WY, where several discrete supercell
   have evolved off the Bighorn Mountains -- posing a risk of large to
   very large hail. 

   In western ND, the CIG1 tornado area was extended slightly
   northward. Continued diurnal heating amid upper 60s dewpoints will
   yield moderate-strong surface-based buoyancy and minimal inhibition.
   Backed surface winds beneath strengthening flow aloft will
   contribute to favorably curved hodographs. Any storms that can form
   or move into this environment will conditionally support a strong
   tornado.  

   Farther east, the SLGT risk was expanded northward in the lower OH
   Valley. Here, diurnal heating/destabilization of a very moist air
   mass (upper 70s dewpoints) will continue to support loosely
   organized thunderstorm clusters capable of producing widely
   scattered damaging winds this afternoon.

   ..Weinman.. 06/27/2026

   .PREV DISCUSSION... /ISSUED 1142 AM CDT Sat Jun 27 2026/

   ...Northern High Plains this afternoon into tonight...
   A rather active severe-weather scenario is anticipated regionally
   later today, including the potential for intense/locally significant
   severe storms. A lead shortwave trough/speed max will continue to
   approach through late today, with the exit region of a strong
   upper-level jet overspreading the region including 50+ kt
   southwesterlies above 5km AGL. Boundary-layer dewpoints in the 60s F
   will continue to spread northward regionally, to the east of a
   deepening surface low across northeast Wyoming toward the far
   western Dakotas, and a sharpening lee trough/dryline across a more
   prevalent north/south extent of the High Plains. This low-level
   moistening will occur beneath a plume of steep mid-level lapse rates
   emanating from the Great Basin and north-central Rockies.  

   Initial surface-based development is expected near the surface
   low/trough near the Big Horn Mountains toward the
   Wyoming/Montana/North Dakota border vicinity. The maturing stronger
   initial storms will almost certainly be supercellular owing to
   moderate to large CAPE and a strong wind field. The risk for large
   to very large hail (2-3 inches in diameter) is greatest near this
   aforementioned border region where supercells are forecast early in
   the convective life cycle, although additional/somewhat more
   discrete development will also likely occur a bit later farther
   southeastward across northwest South Dakota. 

   A few tornadoes are also possible particularly in the more
   moisture-rich environment near the surface triple point, but
   relatively large temperature-dewpoint spreads and a transition to
   upscale growth may temper the tornado threat, particularly with
   northward extent either side of the Montana/North Dakota border
   vicinity.  As more storms develop leading to storm mergers and
   coalescing outflow, a linear cluster will likely develop into a
   maturing/accelerating bow echo into western North Dakota this
   evening, with significant/intense thunderstorm winds (80+ mph)
   possible. 

   Severe storms will likely develop eastward tonight across the
   Dakotas, and prior to that, diurnally enhanced, but more isolated
   intense, development is plausible as far south as western Nebraska
   with large hail and damaging winds. 

   ...Northern Intermountain West including northern UT/western WY...
   Influenced by a lead shortwave trough/speed max associated with the
   prominent upper-level trough centered over the Pacific Northwest,
   strong to locally severe thunderstorm potential will probably exist
   early today. The prolifically strong wind field and modest
   destabilization will tend to focus today across northern Utah,
   southeast Idaho into western Wyoming, including the Star Valley
   vicinity. Severe-caliber wind gusts and some hail may occur.

   ...Mid-South/Tennessee/southern Kentucky to North Carolina...
   Multiple MCVs, including across far south-central Missouri and
   southeast Kansas at midday, will influence the region as they
   progress east-southward generally toward Kentucky and Tennessee.
   Related flow enhancement is evident in regional WSR-88d VWP data,
   and particularly in the 12z Lamont, OK observed sounding (40+ kt
   4-9km AGL). See Mesoscale Discussion 1346 for additional short-term
   details. 

   These MCVs will influence and semi-focus thunderstorm development
   within a moist and increasingly unstable boundary layer from the
   southeast Missouri/northeast Arkansas border vicinity into Kentucky
   and Tennessee. This includes the possibility of some supercells and
   well-organized clusters in the presence of 35-40 kt effective shear.
   Pockets of wind damage will be the most common risk, but some
   tornado potential will exist as well. Additional severe storms
   capable of wind damage are also expected farther eastward into the
   Carolinas this afternoon through around mid-evening.

   ...Texas Panhandle/West Texas late this afternoon/evening...
   Though forcing for ascent will be weak at best this far south,
   strong surface heating/mixing along the lee trough/dryline could
   support high-based thunderstorm development late this afternoon. 
   Inverted-V profiles will favor the potential for isolated severe
   outflow gusts of 60-75 mph.

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