SPC AC 111728

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1228 PM CDT Sat Jul 11 2020

   Valid 121200Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS
   SOUTHEASTERN COLORADO...NORTHEASTERN NEW MEXICO...EXTREME
   NORTHWESTERN TEXAS PANHANDLE...AND THE WESTERN OKLAHOMA PANHANDLE...

   ...SUMMARY...
   Isolated severe thunderstorms will be possible on Sunday across
   portions of the southern U.S. into the Ohio Valley and central
   Appalachians vicinity, as well as across parts of the central and
   southern High Plains. Locally damaging winds and hail will be the
   main hazards.

   ...Synopsis...
   Over the course of the forecast period, a longwave trough will make
   slow eastward progress and extend from the Great Lakes southward
   through the Lower Mississippi Valley and vicinity.  Farther
   southwest, a mid/upper ridge centered over Arizona/New Mexico will
   gradually weaken with time as a shortwave trough traverses Colorado
   and the central High Plains late Sunday through Sunday evening. 
   Farther north, another mid-level wave will amplify across the
   Pacific Northwest and northern Rockies.

   At the surface, a weak low and cold front over the Ohio Valley will
   shift eastward throughout the day.  The trailing front will
   transition to a stationary boundary/wind shift farther west across
   Arkansas and Oklahoma while promoting low-level easterly flow and
   low-level moist advection toward portions of the Colorado/New Mexico
   Plains.  A weak surface trough will also persist from eastern
   Montana southward through northeastern New Mexico, and a weak
   surface low will also develop during the day across far southwest
   Oklahoma and vicinity.

   ...Ohio Valley southwestward into the Lower Mississippi Valley...
   Most models indicate the presence of bands of convection left over
   from D1/Sat across portions of Arkansas into western Kentucky.  The
   specific location of these bands of convection will play a
   significant role in later-day convection and severity.  The overall
   consensus from model guidance is that forward-propagating convection
   will migrate west to east across Kentucky and adjacent areas, while
   likely re-intensifying during peak heating hours as storms approach
   eastern portions of the state and West Virginia.  Mid-level lapse
   rates are relatively poor, though forcing for ascent associated with
   the mid-level wave, surface heating, and appreciable deep shear will
   foster an isolated wind-damage threat with linear segments across
   the region.  This threat should be largely diurnally driven.

   Farther to the southwest (northern Louisiana to western Alabama),
   models are less focused with late afternoon convection, which should
   redevelop late afternoon along differential heating zones/left-over
   boundaries from morning convection.  Lapse rates/instability will be
   substantially greater - especially across Mississippi where MLCAPE
   values will likely exceed 3000 J/kg where stronger insolation will
   exist.  CAMS/HREF and coarser-grid models suggest southward-moving
   complex(es) of storms during the afternoon that will likely pose a
   damaging-wind threat, although isolated hail cannot be completely
   ruled out in tandem with favorable (cellular) storm mode.  Portions
   of this region may need an upgrade to Slight risk for damaging wind
   gusts - especially if focused corridors of greater convective
   potential emerge and surface instability materializes as expected.

   ...Central/Southern Plains...
   Low-level upslope flow and solar insolation should be sufficient for
   development of several hail/wind-producing thunderstorms after about
   19Z or so - initially across higher terrain of Colorado/New Mexico
   before migrating eastward through lower elevations/High Plains
   during the afternoon and evening.  Though low-level wind fields are
   modest, low-level easterlies veering and strengthening to westerly
   with height along with steep lapse rates should foster a mix of
   linear and cellular modes with occasional updraft rotation.  An
   approaching shortwave trough will also encourage storm development. 
   There appears to be enough of a concentration of storms across
   southeastern Colorado and northeastern New Mexico to introduce a
   small Slight risk - primarily for afternoon and evening storms.  Any
   linear complex that can organize will likely ride along and just
   north of the aforementioned stationary boundary into portions of the
   Oklahoma/Texas Panhandles, southwest Kansas, and vicinity overnight
   with an attendant hail/wind threat.

   ...Oklahoma...
   A couple of potential scenarios for storm development will exist
   across the state.  Indications are that abundant surface heating
   will occur along a surface boundary that will extend from west to
   east across the center of the state and/or along convective outflows
   remaining from early morning convection that should migrate
   southward/southeastward from eastern Oklahoma into Arkansas.  A
   pronounced moist axis will exist along and north of the remnant
   boundary, while models indicate potential for convective
   temperatures to be reached in a few areas along and south of the
   boundary in the afternoon/early evening.  Should one or two storms
   develop in this environment, steep tropospheric lapse rates and 35
   knots of shear will support large hail and damaging wind gusts. 
   Forcing for ascent aloft will likely remain negligible throughout
   the day however, and any development will likely be tied to weak
   convergence along the front and surface heating to remove and/or
   overcome any inhibition.

   Later in the evening, a modest low-level jet increase (indicated by
   the models across the southern Texas Panhandle and south Texas
   Plains) will support some risk for elevated convection overnight. 
   Also, any lasting MCS across the Texas Panhandle may persist into
   western or even central Oklahoma, though this potential is also
   uncertain. Any storm will be capable of hail given steep lapse rates
   aloft.  If an MCS can persist overnight while migrating eastward
   into the region, damaging wind gusts would be more of a risk as
   well.

   ...North Dakota...
   After dark, height falls associated with the amplifying mid-level
   trough over the northern Rockies will foster increasing convective
   development along and east of a surface trough across the region. 
   Thermodynamics aren't as impressive in these areas, although
   abundant shear in the cloud-bearing layer and 7-8 C/km mid-level
   lapse rates may promote hail in the stronger cells.  Marginal hail
   probabilities may be needed in a later update pending overall
   convective coverage, which is in question at this time.

   ..Cook.. 07/11/2020

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