SPC AC 120548

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1148 PM CST Tue Dec 11 2018

   Valid 131200Z - 141200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY
   AFTERNOON INTO THURSDAY NIGHT ACROSS PARTS OF THE ARK-LA-TEX REGION
   INTO THE LOWER MISSISSIPPI VALLEY AND NORTH CENTRAL GULF COAST
   VICINITY...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Ark-La-Tex region into
   the lower Mississippi Valley and north central Gulf coast vicinity
   Thursday into Thursday night, accompanied by at least some risk for
   severe weather.

   ...Synopsis...
   Models continue to indicate further amplification within split
   westerlies emanating from the mid-latitude Pacific through this
   period.  Troughing and ridging within these belts across the eastern
   Pacific into western North America may become increasingly in phase.
   However, the vigorous southern portion of a splitting tough across
   and east of the Rockies is forecast to continue digging sharply into
   the southern Plains, where a significant embedded lower/mid
   tropospheric cyclone may evolve, while it gradually turns eastward
   toward the lower Mississippi Valley.

   Models generally indicate that this will be accompanied by a
   modestly deep and occluding surface low migrating eastward near or
   just south of the southern Plains Red River.  Secondary surface wave
   development still appears possible near/east of the southeast
   Louisiana Gulf coast by late Thursday evening.

   Large-scale forcing for ascent associated with this evolving regime
   is expected to support considerable precipitation and embedded
   thunderstorm activity across the southeastern Plains and upper Texas
   coastal areas, into the western Gulf of Mexico, through much of the
   lower Mississippi Valley and remainder of the Gulf of Mexico.  This
   probably will include at least some risk for severe thunderstorms. 
   However, with the Gulf boundary layer only beginning to modify in
   the wake of recent cooling/drying, it still appears that severe
   weather potential, in general, will be mitigated over inland areas
   by weak warm sector boundary layer destabilization.

   ...Ark-La-Tex/lower Mississippi Valley/Gulf coast...
   Broad brush 5 percent severe probabilities have been maintained
   across the region with some adjustment based on current expectations
   of the evolving warm sector.  However, any developing severe weather
   potential during this period may ultimately become focused in a
   couple of distinct areas.

   Cloud cover/precipitation accompanying an initial band or cluster of
   convection (largely aided by forcing associated with an initial
   perturbation within the subtropical westerlies) probably will
   inhibit destabilization through much of the inland developing warm
   sector, as it spreads into and east of the lower Mississippi Valley.
   However, in the wake of this activity, a developing dry slot may
   allow for sufficient insolation to contribute to mixed layer CAPE on
   the order of 500 J/kg, beneath cold mid-level air near the Sabine
   Valley into the Ark-La-Tex by late Thursday afternoon.  

   It appears possible that the exit region of a 90-100 kt 500 mb jet
   may overspread this instability axis before the onset of diurnal
   cooling, supporting discrete storm development across the Ark-La-Tex
   vicinity, and perhaps southward through western/central Louisiana. 
   Given the strong deep layer shear, this may include a couple of
   supercells.  It remains unclear whether low-level hodographs will
   become large enough to support an appreciable risk for tornadoes,
   but activity will probably be accompanied by at least some risk for
   severe hail and wind before diminishing across the lower Mississippi
   Valley Thursday evening.

   Otherwise, the secondary surface frontal wave may provide another
   focus for isolated severe storm development by Tuesday night, across
   coastal areas between southeast Louisiana into the western Florida
   Panhandle.  In the presence of strengthening deep layer wind fields
   and shear, somewhat better boundary layer moistening over the Gulf
   of Mexico may contribute to increasing instability across this area.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:      5%     - Marginal
   Hail:      5%     - Marginal

   ..Kerr.. 12/12/2018

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