SPC AC 061251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Wed Jul 06 2022

   Valid 061300Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   NORTHERN HIGH PLAINS/ROCKIES REGION...CENTRAL PLAINS...AND PARTS OF
   THE OHIO VALLEY TO CAROLINAS...

   ...SUMMARY...
   Severe-thunderstorm potential (mainly gusts and hail) appears most
   concentrated today over parts of the northern High Plains/Rockies
   region, central Plains, and parts of the Ohio Valley to Carolinas.

   ...Synopsis...
   The mid/upper-level pattern will be dominated by troughing offshore
   from the West Coast, with a cyclone offshore from the Pacific
   Northwest, mean ridging from the Gulf Coast states across the
   central/northern Rockies, and belt of west-northwesterly to
   northwesterly flow from the mid/upper Mississippi Valley to the
   coastal Carolinas and Tidewater regions.  The following shortwave
   troughs influencing convective potential were evident in moisture-
   channel imagery.
   1.  Western/central NV, forecast to move northeastward to eastern ID
   and western MT by 00Z, through the mean ridge position, then
   pivoting eastward to eastern MT with some convective reinforcement
   overnight.
   2.  Western parts of CO/NM, forecast to pivot northeastward and
   eastward, also through the mean ridge, then across the central
   Plains by 12Z tomorrow.
   3.  Southern Lower MI, northwestern IN and IL, convectively
   reinforced by the previous day's severe MCS, with an MCV apparent
   near the southern end of Lake Michigan.  This feature should move
   southeastward to WV by 00Z, the over parts of VA and the Carolinas
   by 12Z.

   At the surface, 11Z analysis showed a wavy, slow-moving cold front,
   with several weak lows attached, from southeastern NY across
   northern portions of OH/IN/IL to central/southwestern KS.  Most of
   the front east of the Mississippi River should sag southward through
   the period, while a low initially near DDC moves slowly toward
   central KS along the boundary.  Several outflow boundaries from
   earlier MCS activity also exist south of the front over the Ohio
   Valley States.

   ...Northern High Plains/Rockies region...
   Widely scattered thunderstorms are expected to develop initially
   over higher terrain of western/southern MT and northeastern WY this
   afternoon, where diabatic heating and orographic lift will weaken
   and overcome MLCINH first, beneath increasing large-scale ascent
   related to the approaching perturbation.  Resulting convection
   should move east-northeastward to eastward over the nearby northern
   High Plains this afternoon and evening, offering occasional severe
   hail and gusts, with isolated significant severe possible.

   A roughly zonal corridor of relatively maximized moisture/theta-e
   will be in place over eastern and central MT into western SD, with
   dewpoints commonly in the 50s over western areas to mid 60s in the
   east by around 00Z.  In tandem with diurnal surface heating and
   steep low/middle-level lapse rates, corridor of MLCAPE around
   1500-2000 J/kg should develop.  Strong veering of flow with height
   will offset modest low/midlevel wind speeds enough to yield
   effective-shear magnitudes commonly in the 35-45-kt range,
   supporting both supercells and organized multicells (including
   bowing structures).  Some clustering and related, localized
   cold-pool growth may occur for a few hours to support wind potential
   into the evening.  The severe threat should diminish with time
   tonight as both ambient/antecedent MLCINH from the EML base, and
   nocturnal surface cooling, become increasingly hostile to convective
   growth.

   ...Central Plains...
   Widely scattered to scattered thunderstorms should develop from
   midday into this afternoon over the foothills, Cheyenne Ridge and
   Palmer Divide, then move eastward over the adjoining High Plains. 
   Severe hail and gusts are possible.  Some of this activity may
   coalesce into a forward-propagational thunderstorm cluster this
   evening into tonight.  Strong diurnal surface heating of the higher
   elevations will erode MLCINH quickly today, amidst favorable
   moisture (with surface dew points commonly in the 50s to low 60s F
   and areas of 1.25-1.5-inch PW).  Being removed from the stronger
   mid/upper winds aloft, deep shear will be limited, though strong
   veering with height of weak low-level flow will exist to support
   30-40 kt effective-shear magnitudes.  Peak/preconvective MLCAPE
   should range from around 1000 J/kg near the foothills to around 2000
   J/kg near the latitude of the eastern border of CO.  Well-mixed
   subcloud layers will support gust potential.

   ...Parts of the Ohio Valley to Carolinas...
   Widely scattered to scattered thunderstorms are expected to develop
   through this afternoon along any of several plausible foci:  higher
   terrain in the Appalachians, the prefrontal/lee-side surface trough,
   sea breezes, and outflow/differential-heating boundaries from
   antecedent/ongoing convection.  This includes boundaries related to
   non-severe convection now crossing portions of WV and OH. 
   Thunderstorm coverage should increase through the afternoon, with a
   few clusters potentially aggregating upscale and offering
   concentrations of damaging winds.  Isolated large hail also is
   possible.

   The air mass along and south of the composite front/outflow boundary
   will remain richly moist, with lower-elevation dewpoints commonly in
   the upper 60s to mid-70s F, and strong diurnal heating.  These
   factors should offset modest midlevel lapse rates enough to
   contribute to MLCAPE in the 1000-2000 J/kg range over most of the
   area, with 2000-3000 J/kg possible over parts of the Ohio Valley
   region not substantially altered by prior convection.  With the area
   displaced south of strong mid/upper-level winds, vertical shear
   generally will be weak, with small hodographs and effective-shear
   magnitudes.  As such, the dominant mode should be multicellular and
   clustered, with activity moving generally southeastward amidst
   difluent/northwesterly mid/upper-level winds.

   ..Edwards/Goss.. 07/06/2022

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