Current SPC Activity Chart

Current Severe US Wx Maps

SPC Activity Chart
Hazard Sat (01/18) Sun (01/19) Mon (01/20) Tue (01/21) Wed (01/22) Thu (01/23) Fri (01/24) Sat (01/25)
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Forecast Discussion - Convective Outlook

   SPC AC 181246

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0646 AM CST Sat Jan 18 2020

   Valid 181300Z - 191200Z


   Isolated thunderstorms are possible from south Texas across the
   central Gulf Coast States.  Organized severe weather is not

   The dominant upper-air feature for this period will be a pronounced
   synoptic-scale trough, now evident in moisture-channel imagery from
   a weak mid/upper low over MN to eastern OK.  An initially separate,
   strong shortwave trough -- currently located from southern SK across
   western ND and central SD -- will phase with the synoptic trough
   during the day, as the MN low crosses portions of Lake Superior. 
   Meanwhile, a basal shortwave trough -- now over western MO and
   northeastern OK, will eject northeastward and weaken.  By 12Z, the
   shortwave-reconfigured synoptic trough should extend from southern
   QC across Lower MI to IL.

   At the surface, an occluded cyclone was analyzed over the upper
   Mississippi Valley at 11Z.  Two cold fronts were drawn emanating
   from its southern sector -- the first across southeastern IL to the
   Arklatex region, becoming quasistationary near a TXK-AUS-LRD line. 
   The trailing/reinforcing front extended across northwestern IL,
   southwestern MO, south-central OK, and far west TX.  A marine/warm
   front was analyzed from between EYW and MUHA (Havana) northwestward
   across the eastern Gulf to southeastern LA.

   By 00Z, the low should move to Lake Huron, with the cold fronts
   combining and reaching middle TN, central portions of MS/LA, the TX
   Gulf shelf waters, to near BRO.  By 12Z, the front should reach the
   Carolinas, southern GA, and the central/southwestern Gulf.  The
   warm/marine front is expected to move slowly east-northeastward
   across the central Gulf Coast and adjacent waters, reaching the
   western/central FL Panhandle this evening before being overtaken by
   the cold front.

   ...Gulf Coast region...
   Isolated to widely scattered thunderstorms may develop near the
   front today and tonight.  Organized severe is not expected, given
   the lack of upper-air support and modest flow/middle-level flow, 
   with the basal shortwave trough weakening and increasingly distant
   from the region.  Still, a few strong cells may develop, most
   notably over deep south TX an near the warm front across the
   northern Gulf near the MS/AL/western FL Panhandle coasts.

   Over the lowest part of the Rio Grande Valley and Laguna Madre/Padre
   Island region of deep south TX, strong diurnal heating is possible
   just ahead of the front.  The prefrontal boundary layer will remain
   characterized by rich moisture, with surface dew points upper 60s to
   low 70s F, and near-record PW around 1.75-2 inches.  These
   conditions will offset modest mid/upper-level lapse rates enough to
   generate around 1500 J/kg deep MLCAPE, locally/briefly near 2000
   J/kg.  Gusts approaching severe limits may occur in the most
   intense/water-loaded downdrafts, regardless of the weak low-level
   winds/shear.  However, severe potential appears too isolated,
   conditional and uncertain for a categorical area.  The more-
   important threat should be locally heavy rain, per the marginal risk
   of excessive rainfall in the WPC outlook.

   Another area of interest is the coastal region from near the
   Mississippi River mouth northeastward toward the western FL
   Panhandle.  Locally enlarged low-level hodographs, juxtaposed with
   surface-based buoyancy, may occur in a narrow corridor corresponding
   to the warm-frontal zone and related backed surface winds.  However,
   low/middle-level lapse rates, convective-scale forcing and frontal
   convergence all appear weak, casting doubt on thunderstorm strength
   and maintenance.  Brief storm-scale rotation is possible in any
   cells in this environment, but the tornado potential remains too
   uncertain and low to assign unconditional/categorical-level

   ..Edwards.. 01/18/2020