SPC AC 180559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Sun Mar 18 2018

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH TX AND
   THE RED RIVER VALLEY THROUGH THE CENTRAL GULF COAST STATES TO
   SOUTHERN GA AND FAR NORTHERN FL...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK INTO OK AND KS...

   ...SUMMARY...
   Scattered severe storms are possible from North Texas and far
   southern Oklahoma through the Gulf Coast and part of the Southeast
   States.  Isolated severe storms will be possible, mainly this
   evening and tonight across central and southern Kansas into northern
   Oklahoma.

   ...Synopsis...
   A compact shortwave trough rounding the base of the western U.S.
   longwave trough by the start of Day 1 will progress east today
   reaching the southern High Plains by 00Z, with a closed cyclone
   forming within this trough as it moves through OK and southern KS
   tonight.  As this trough deepens, an accompanying 500-mb westerly
   jet will strengthen to 100+ kt across NM late this afternoon, and
   then through the Red River Valley into AR this evening through early
   Monday.  Meanwhile, in the southern stream, a lead midlevel impulse
   will track through the lower Mississippi Valley to the Southeast
   States today, while a better defined upstream trough moves into the
   southern Plains to the Ozark Plateau this afternoon and evening.

   At the surface, a cold front, attendant to a midlevel trough moving
   off the Mid-Atlantic Coast this morning, will advance south into
   southern GA and central or southern AL by this afternoon.  The
   trailing portion of this front should remain generally stationary
   from central MS to North TX, where a triple point should be located
   by this afternoon across north-central TX (near or west of the DFW
   Metroplex).  Meanwhile, strong height falls spreading into the
   central and southern High Plains, with the approach of the
   progressive Southwest States trough, will result in a deepening low
   across eastern CO this afternoon and equatorward-extending lee
   trough.  This low is expected to track into OK late tonight with a
   warm front advancing north through eastern OK into northern portions
   of the central Gulf Coast States.

   ...North and northeast TX/South and southeast OK to western MS...
   Forcing for ascent attendant to a southern-stream trough tracking to
   the east-northeast into the southern Plains by early-mid afternoon
   and height falls with the approach of the Southwest States trough
   are expected to prove sufficient for the development of a few
   thunderstorms near a triple point in north-central TX between
   19-21Z.  Surface heating from south-central OK southward along the
   dry line combined with dew points south of the stationary front in
   the 60s and cooling 500-mb temperatures will result in MUCAPE up to
   1500 J/kg in the warm sector.  This combined with strengthening bulk
   shear (exceeding 50 kt) will support supercells with very large hail
   and damaging gusts.  An increase in low-level hodograph curvature by
   late afternoon to the evening suggests a tornado threat will be
   possible as storms that form in North TX into far southern OK spread
   east into the Arklatex region this evening.  ESRL-HRRR suggests
   storm mode could become linear as storms advance into western MS
   later this evening.

   ...Lower Mississippi Valley/Central Gulf Coast and Southeast
   States...
   Thunderstorm development will be possible across the lower
   Mississippi Valley through southern parts of MS/AL into southern GA
   as the environment destabilizes.  Effective bulk shear will be
   sufficient for organized storms, with clusters of storms possibly
   focused along the track of weak midlevel impulse shifting east from
   the lower Mississippi Valley this morning.  Strong wind gusts should
   be the main severe threat, given weak midlevel lapse rates tending
   to temper the hail threat.

   ...KS/OK and eastern TX/OK Panhandles...
   Mainly elevated storms will be possible as forcing for ascent with
   the southern-stream trough moves through OK by late morning into the
   afternoon, with isolated hail being the main threat.  Thereafter,
   strong forcing for ascent and rapid cooling in the midlevels
   (between 400-600 mb) are expected to occur across parts of KS and
   across the OK/TX Panhandles into OK this evening through tonight. 
   Given that these dynamics will not arrive in this region until after
   peak heating, the potential for surface-based thunderstorm
   development is low, with greater likelihood for elevated storms.  In
   addition, meager moisture return into KS will limit stronger
   instability with north/northwest extent.  Isolated hail will be the
   main threat with the storms that form and move to the east and
   northeast this evening into tonight.

   ..Peters/Gleason.. 03/18/2018

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