Feb 3, 2018 1300 UTC Day 1 Convective Outlook
Updated: Sat Feb 3 12:49:53 UTC 2018 (20180203 1300Z Day 1 shapefile | 20180203 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180203 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Tornado Graphic
20180203 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20180203 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Large Hail Graphic
20180203 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   SPC AC 031249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0649 AM CST Sat Feb 03 2018

   Valid 031300Z - 041200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Thunderstorms are expected across the lower Mississippi Valley and
   adjoining Gulf Coast region, mainly this evening and overnight.

   ...Synopsis...
   In mid/upper levels, a longwave trough over eastern North America
   will continue broadly cyclonic flow from the Rockies to the East
   Coast.  Two primary/influential shortwave perturbations currently
   are embedded within the associated northwesterly flow field:
   1.  Leading trough now located from the Black Hills across
   eastern/southern WY, northwestern CO and eastern UT.  The northern
   part will merge with a weaker/upstream vorticity lobe now over the
   Canadian Rockies, then split eastward across the lower Missouri
   Valley region tonight.  By 12Z, the combined northern lobe will
   extend from northern IL across the Ozarks, amidst height falls
   related to the trailing/upstream trough #2 below.  Meanwhile, the
   southern lobe will dig southeastward to the southern High Plains by
   00Z, then turn eastward, become much more positively tilted, and
   weaken considerably tonight.  By 12Z, this lobe should be located
   from western MS to south-central TX. 
   2.  Upstream trough and related upper speed max, now evident in
   moisture-channel imagery over central SK, northern AB and northern
   BC.  The leading, strongest part of the related vorticity field
   should move southeastward to southern MN and SD by 12Z.

   At the surface, a large, continental/polar anticyclone covers the
   southeastern 1/3 of the nation, with ridging extending to
   northeastern MX.  The associated high will move offshore VA today
   while the ridge retreats eastward over the Gulf Coast and onshore
   flow from the western Gulf gradually becomes less anticyclonic.  A
   wavy frontal zone -- currently warm in some segments and cold in
   others, but slow-moving everywhere -- extends between weak lows over
   eastern Upper MI and western SD, arching across southern MN in
   between.  The front continues northwestward from SD through another
   weak low over central MT to the Canadian Rockies.  As the northern
   part of perturbation #1 advances, the SD low will move/consolidate
   east-southeastward to IA by 00Z, with the front accelerating
   southward across NE and northeastern WY behind it.  By the end of
   the period, the low should reach southern lower MI, with cold front
   to western IL, the KS/OK border region, and northeastern CO.  A
   prefrontal trough and confluence zone should develop tonight over
   the warm sector (such as it is, with a very immature return-flow
   regime at the surface), reaching parts of mid TN, northern AL and MS
   by 12Z.  

   ...Lower Mississippi Valley and adjoining Gulf Coast region...
   Isolated to scattered thunderstorms are possible, with episodes of
   convection shifting generally eastward over the outlook area.  The
   greatest convective coverage should be from this evening through
   overnight hours, shifting from LA/AR across parts of MS/AL.

   The prefrontal surface trough will have little direct influence on
   convective potential, given the lingering stable/low-thetae air from
   the antecedent anticyclone.  However, it will be a manifestation or
   symptom of the intensifying low-level warm advection and convergence
   underway tonight above the surface, ahead of the southern branch of
   mid/upper trough #1.  As the perturbation approaches, a 50-65-kt
   southwesterly LLJ (locally exceeding 70 kt) will support that
   regime, along with enough moisture transport to yield nearly
   saturated parcels in the 800-900 mb layer near the coast, becoming
   more elevated northward.  Forecast soundings suggest MUCAPE 300-700
   J/kg over the middle/southern parts of the outlook area, diminishing
   northward.  The stable boundary layer, weak lapse rates aloft, and
   the lack of both greater buoyancy and effective shear, should
   combine to keep severe potential too low for unconditional
   probabilities.

   ..Edwards.. 02/03/2018

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