SPC AC 180601

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0101 AM CDT Tue Jul 18 2023

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE MID-MISSOURI VALLEY INTO THE LOWER OHIO VALLEY AND THE
   DAKOTAS....

   ...SUMMARY...
   Thunderstorms associated with large hail and damaging wind gusts
   will be possible this morning/afternoon through Missouri and again
   overnight across parts of the mid Mississippi/Lower-Missouri Valley.
   Other strong to severe storms will also be possible in various parts
   of the US from the Great Basin and Southwest and from the Plains to
   the Midwest and East Coast.

   ...Synopsis...
   A mid-level ridge across the western CONUS will flatten this morning
   as a trough crosses Montana. Another somewhat convectively enhanced
   mid-level shortwave trough across the central Plains this morning
   will move southeast into the Tennessee Valley tonight. A broad
   mid-level trough across the Great Lakes into the Northeast will
   shift slowly east through the day. The surface pattern is more
   nebulous with a diffuse surface front extending from the Northeast
   across the southern Great Lakes and into the Plains. Across the
   Plains, a warm front will become better defined as a surface low
   develops across Kansas. An additional cold front, currently across
   eastern Montana, will move east across the northern Plains and
   become more defined through the day.

   ...Lower Missouri Valley to the Lower Ohio Valley...
   Current convective trends and surface analysis suggests a line of
   elevated storms across central Nebraska currently will likely
   intensify as it moves into greater instability across southeast
   Nebraska/northeast Kansas. Several members of the 00Z HREF support
   this evolution with several showing the potential for a
   well-developed bow echo moving across Missouri this morning and
   potentially through the afternoon into the Mid-Mississippi/Tennessee
   Valley region. Even if a mature bow echo can develop, the longevity
   may remain questionable due to downstream destabilization as a large
   cloud mass could inhibit heating downstream and perhaps limit the
   threat for a more significant severe wind threat. 

   Late tonight and into Wednesday morning, elevated thunderstorms are
   expected to develop along a northwest-southeast oriented frontal
   zone in the vicinity of southeast Missouri. The location of this
   convection remains uncertain as the location of the frontal zone
   will augmented by the intensity/location of convection from the
   thunderstorms this morning. Nonetheless, wherever this boundary
   aligns, supercells will pose a threat for large hail given strong
   elevated instability and strong deep layer shear. Eventually, some
   upscale growth will be possible and a severe wind threat may develop
   across the Mid-Mississippi Valley closer to 12Z Wednesday.  

   ...Northern Plains...
   A combination of low-level moisture advection and surface heating
   will lead to moderate to strong instability across central North
   Dakota and South Dakota by this afternoon. This instability,
   combined with convergence from a sharpening cold front and an
   approaching mid-level shortwave trough should be sufficient for
   storm development along the cold front this afternoon. 45 to 55
   knots of mid-level flow will result in supercell wind profiles and a
   threat for large hail, some potentially 2+ inches. 

   ...Mid-Atlantic to the Northeast...
   Weak, broad ascent across an uncapped and moderately unstable warm
   sector across the Mid-Atlantic and Northeast may result in isolated
   to widely scattered thunderstorms. Some stronger flow, particularly
   from New York northeastward will promote more storm organization and
   the potential for rotating updrafts. These longer-lived updrafts may
   pose some threat for isolated large hail and damaging wind gusts.

   ...Central High Plains...
   A few thunderstorms are possible late this afternoon as low-level
   flow veers from northeasterly to easterly and becomes more upslope
   with low-level moisture advection on the northern periphery of the
   surface cyclone. The favorable period may be relatively short-lived
   since moisture arrives late, but a favorable environment may develop
   with 2000+ J/kg MLCAPE and a supercell wind profile. 

   ...Great Basin...
   A deeply mixed airmass is expected today across the Great Basin with
   ample instability for scattered thunderstorms across much of the
   region. A belt of stronger mid-level flow around 30 knots will exist
   from east-central Nevada and across north-central Utah. This may
   support some storm organization with the potential for isolated
   severe wind gusts given the deeply mixed sub-cloud layer.

   ...Southern Arizona...
   Weak to moderate instability is expected to develop across southeast
   Arizona today with a LCL around 3000m. Shear will be weak in the
   region with less than 10 knots of flow through the troposphere,
   which will limit storm organization. However, this instability, 
   coupled with sub-cloud evaporative cooling in the well mixed airmass
   may support some strong to severe wind gusts this afternoon/evening.

   ..Bentley/Wendt.. 07/18/2023

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