SPC AC 121736

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1236 PM CDT Sun Jul 12 2020

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN
   NEBRASKA AND FAR NORTHEASTERN COLORADO...

   ...SUMMARY...
   Severe storms are possible across portions of the central Plains
   into the eastern Dakotas, western Minnesota and Iowa on Monday
   afternoon into Monday night. Additional isolated strong storms are
   possible near the Gulf Coast region and from the eastern Carolinas
   into Southern New England Monday afternoon.

   ...Synopsis...
   A longwave trough over western Canada/northwestern CONUS will
   continue to amplify slightly, spreading height falls as south as
   Utah and Colorado during the day.  Meanwhile, a substantial
   shortwave trough will migrate through the base of the broader trough
   and impact the Dakotas and Minnesota through the latter half of the
   forecast period.  Meanwhile, a mid-level ridge centered over New
   Mexico/west Texas will weaken slightly, while another long-wave
   trough along the East Coast shifts slowly eastward throughout the
   period.

   At the surface, lee troughing will extend from the central Dakotas
   southward through eastern New Mexico/Texas Panhandle initially and
   gradually strengthen/deepen throughout the day.  The northern
   portion of this trough (across the Dakotas) will shift eastward
   toward western Minnesota through the afternoon.  Another weak
   surface trough will extend from New England southwestward to the
   Carolinas, with a trailing boundary extending westward toward south
   Louisiana.  The position of this boundary may be augmented by
   ongoing convection during the D1 period, which may impact subsequent
   afternoon development of thunderstorms in Louisiana during the
   forecast period.

   ...Nebraska southward through northeastern New Mexico...
   Models suggest that convective development will begin in earnest
   across the higher terrain of the central Rockies during the early
   afternoon within a deeply mixed boundary layer environment and weak
   low-level shear.  These storms will likely evolve into clusters and
   loosely organized linear segments that propagate eastward into
   gradually deeper boundary layer moisture through the afternoon and
   early evening.  The greatest concentration of storms is currently
   expected from western through northeastern Nebraska, where enough of
   a concentration of severe wind/hail producing convection will exist
   to justify a categorical upgrade to Enhanced driven by 30% hail and
   30% wind probabilities.  Storms in this environment will tend to be
   outflow dominant, although steep tropospheric lapse rates, upper 50s
   to low 60s F dewpoints, and afternoon temperatures nearing 100 F
   will maintain 3000 J/kg MUCAPE, while 40-45 kt deep shear will aid
   in modest organization into linear segments.  An isolated tornado
   cannot be ruled out - especially in Nebraska.  Farther south,
   somewhat weaker deep shear will exist in eastern Colorado, New
   Mexico, and vicinity, although enough flow aloft will exist to
   encourage forward-propagating clusters and linear segments that
   could reach western Kansas and the Texas/Oklahoma Panhandles late in
   the day.  Large hail and damaging wind gusts are possible with this
   activity.

   ...Eastern Dakotas through western Wisconsin...
   The aforementioned shortwave will advance upon western portions of
   the warm sector in that area and encourage robust convective
   development beginning in eastern North Dakota/northwestern Minnesota
   during the afternoon.  Initial development will likely be
   supercellular - enough mid-level inhibition will exist to keep
   storms isolated within an environment characterized by appreciable
   low-level sear (200-300 m2/s2 SRH) and 2000-2500 J/kg MLCAPE. 
   Significant hail and a few tornadoes are possible - especially near
   discrete updrafts.  

   Over time, models suggest that these storms will congeal into one or
   two linear complexes that will migrate eastward across much of
   northern and central Minnesota through the evening.  All severe
   hazards will be possible through the evening before storms gradually
   become elevated due to nocturnal boundary layer cooling. 
   Nevertheless, steep lapse rates aloft and appreciable mid-level flow
   will promote a hail/wind risk even after dark as far east as western
   Wisconsin.  Additional convection migrating northeastward from
   Nebraska into eastern South Dakota will also be capable of hail and
   damaging wind gusts.

   ...Louisiana, far southeast Texas, and coastal Mississippi...
   Though forcing for ascent is modest at best, a weak surface
   boundary/remnant outflow boundary will exist across the region and
   may promote isolated thunderstorm development during the afternoon. 
   Dry air aloft, steep mid-level lapse rates, and near 80F
   dewpoints/90s F surface temperatures will promote very strong
   instability and downdraft potential within any convection that can
   materialize.  5% hail/wind probabilities were address to address
   this primarily diurnally driven threat.

   ...New England southward through the Carolinas...
   Though mid-level lapse rates will generally be weaker compared to
   areas west, the combination of surface heating and ascent with the
   longwave trough over the region will foster scattered to numerous
   band of convection throughout the entire region in the afternoon and
   early evening.  Enough mid-level flow will exist for loose
   organization into clusters and linear segments, which will promote
   potential for isolated damaging wind gusts in a few areas.  This
   threat will also be diurnally driven and wane after sunset.

   ..Cook.. 07/12/2020

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