SPC AC 190054

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0654 PM CST Wed Jan 18 2017

   Valid 190100Z - 191200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHEAST TX...SOUTHERN/CENTRAL LA...AND SOUTHWEST MS...

   ...SUMMARY...
   A few strong to severe storms could occur through tonight across
   parts of southeast Texas into southern/central Louisiana and
   southwest Mississippi. Isolated strong to locally damaging wind
   gusts and perhaps a brief tornado are the main threats.

   ...Southeast TX into Southern/Central LA and Southwest MS...
   Water-vapor satellite imagery depicts a closed mid/upper-level low
   over the southern and central High Plains this evening. This low
   should move only slowly eastward over the Plains through early
   Thursday morning. A belt of southwesterly mid-level winds generally
   around 40-60 kt associated with the mid/upper-level low will
   likewise spread eastward across TX into the lower MS Valley through
   12Z Thursday. At the surface, a weak low was located near the TX/LA
   border as of 00Z, with a nearly stationary front extending
   east/northeastward from this low across central LA into central MS.
   A cold front extends southward from the TX/LA low into the western
   Gulf of Mexico. The quasi-stationary front should lift northward as
   a warm front across parts of the lower MS Valley towards the
   Mid-South through Thursday morning.

   The airmass along and south of the quasi-stationary front across
   southeast TX into southern/central LA and southwest MS will probably
   remain weakly unstable through the overnight hours, as surface
   dewpoints range from the mid 60s to lower 70s. Low-level flow is not
   expected to be overly strong through the remainder of the evening,
   but some increase in surface to 850-mb flow may occur late (09-12Z)
   as a southwesterly low-level jet strengthens across this region.
   Convective coverage may also increase late in the period as
   low-level warm air advection strengthens, as indicated by multiple
   recent convection-allowing model solutions.

   The 00Z sounding from LCH along with NAM/RAP forecast soundings
   across the warm sector suggest a sufficient, albeit marginal,
   combination of instability and low- to mid-level shear will exist
   for the remainder of the Day 1 period to support an isolated strong
   to locally damaging wind gust with any thunderstorms that can be
   surface-based. In addition, effective SRH around 100-125 m2/s2
   (locally higher near the quasi-stationary/warm front), may be enough
   for a brief tornado with any sustained updraft. Poor low- to
   mid-level lapse rates and resulting weak instability are expected to
   limit a greater severe-weather risk.

   ..Gleason.. 01/19/2017

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