SPC AC 060559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1159 PM CST Sun Mar 05 2017

   Valid 061200Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
   OF THE LOWER TO MIDDLE MISSISSIPPI VALLEY REGION...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF
   THE CENTRAL AND SOUTHERN PLAINS INTO THE MIDDLE TO UPPER MISSISSIPPI
   VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
   OF THE CENTRAL AND SOUTHERN PLAINS TO THE LOWER THROUGH UPPER
   MISSISSIPPI VALLEY...

   ...SUMMARY...
   Severe thunderstorms are expected mainly late this afternoon or
   evening through tonight across a part of the upper and middle
   Mississippi Valley to the Ozarks and Mid-South. A greater
   concentration of severe thunderstorms may occur across parts of
   northwestern Arkansas and southern Missouri Monday evening. Primary
   threats will be damaging wind gusts and large hail, but a few
   tornadoes will also be possible, especially from extreme northern
   Arkansas into southern Missouri.

   ...Synopsis...

   Synoptic upper trough currently from the northern Rockies to the
   Great Basin will continue northeast through the central and northern
   Plains during the day and eject negatively tilted into the upper MS
   Valley this evening. Surface low will deepen over the eastern
   Dakotas into western MN, while trailing cold front merges with the
   dry line as it advances through the central plains during the day
   and into the MS valley and southern Plains overnight. Warm front
   extending east from the low will move northward through the upper MS
   valley and Great lakes regions.

   ...Ozarks through the middle and Upper Mississippi Valley areas...

   With initial return of partially modified Gulf moisture, widespread
   low clouds are expected in warm sector today, limiting
   boundary-layer warming. The 00Z observed raob data from Sunday
   evening already show a warm layer associated with a remnant elevated
   mixed layer in place across the central Plains and middle MS Valley
   region. Northward advection of partially modified Gulf moisture
   beneath 7-7.5 C/km mid-level lapse rates will destabilize the
   atmosphere during the day with corridor mlcape from 1000-1500 J/kg
   expected to evolve from central and southern Plains into the middle
   to lower MS Valley. Instability will remain marginal over the upper
   MS valley region where moisture return will be more limited. 

   Initial storms will likely develop over the upper MS Valley region
   where deeper forcing attendant to the ejecting shortwave trough will
   likely result in erosion of capping inversion along and just ahead
   of the cold front. Initial discrete storms should rapidly evolve
   into linear segments with damaging wind and hail the primary
   threats, though a brief tornado cannot be ruled out. 

   Given the presence of capping in warm sector and tendency for the
   deeper forcing to move into the upper MS Valley, most of the warm
   sector from the central plains into the middle to lower MS valley
   will remain capped during the day. However, storms will likely
   develop along cold front by early evening as this boundary overtakes
   the dryline across eastern KS. Initially discrete storms will evolve
   into linear segments. Given very strong effective bulk shear
   exceeding 50 kt, organized storms are expected including supercells
   and bowing linear segments. Large hail and a couple tornadoes will
   be the main threats with initial storms. However, as activity
   evolves into a dominant linear mode, damaging wind will become the
   primary threat, though a couple of qlcs tornadoes will also be
   possible with any embedded mesovortices. The best chance for
   pre-frontal storm initiation appears to be within  confluent flow
   regime along conveyor belt and in association with terrain features
   from northwestern AR into southern MO where some of the
   convective-allowing models initiate discrete cells. Should this
   occur during the early evening, large 0-1 km hodographs would
   support supercells with low-level mesocyclones and an attendant
   threat for a few tornadoes.

   ..Dial/Cook.. 03/06/2017

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