SPC AC 011734

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1234 PM CDT Sat Apr 01 2017

   Valid 021200Z - 031200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   TEXAS INTO WESTERN LOUISIANA...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER MOST OF
   EASTERN TEXAS INTO LOUISIANA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS
   ACROSS THE ARKLATEX AND INTO THE LOWER MISSISSIPPI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM TEXAS INTO
   MISSISSIPPI...

   ...SUMMARY...
   Dangerous severe thunderstorms capable of strong tornadoes,
   extensive wind damage and hail are possible beginning Sunday morning
   east of I-35 in Texas and developing eastward across Louisiana
   throughout the day and into the night. Severe storms are also
   possible across the Arklatex during the day and into western
   Mississippi by Monday morning.

   ...Synopsis...
   Low pressure will gradually translate northeastward through the
   period with a cold front to the west, from the lower Rio Grande
   Valley Sunday morning into Arkansas by Monday morning. Ahead of the
   low, a warm front will rapidly lift northward across east Texas
   toward the Arklatex and extend into southern Mississippi by 00Z.
   Across the warm sector, a very moist and unstable air mass will
   exist, characterized by upper 60s to near 70 dewpoints, beneath
   cooling profiles aloft and steep midlevel lapse rates. This volatile
   air mass will exist over a large area, suggesting potential for
   widespread severe weather.

   Both mid and high-level southwesterly flow aloft will increase
   throughout the period as the upper trough moves northeastward across
   TX. The northward transport of moisture and instability will be
   aided by a broad, southerly low-level jet which will increase to 50
   kt by late afternoon and will shift eastward across the lower MS
   valley overnight. This will create strong, veering winds with height
   which will clearly favor significant severe thunderstorms including
   tornadic supercells, damaging bows, and quasi-linear convective
   systems. The severe threat is expected to begin by mid morning
   across central and northern Texas, and evolve/expand eastward
   through the rest of the period to near the Mississippi river by 12Z
   Monday.

   ...Central into northeast Texas and across the Arklatex -- Sunday
   morning through afternoon...
   Model consensus is that supercells may begin forming in the 12-15Z
   time frame from near Austin TX to just east of Dallas, aided by
   convergence within the low pressure trough and where rapid moisture
   advection will be underway. Any capping inversion is expected to be
   minor, and relatively low for this part of Texas. This suggests that
   early development is indeed feasible, and increases the chances of
   strong low-level accelerations in the storms as opposed to
   situations where the LFC is much higher. The cells may take some
   time to become better organized as the low level jet will be on the
   increase during the day. However, by 18-21Z, these storms should
   pose a tornado and wind threat across northeast TX approaching the
   Arklatex, with strong tornadoes possible. CAMs suggest that
   supercells may eventually merge into an MCS, in which case damaging
   straight-line winds would be likely. In addition, re-generation of
   supercells is possible along the southern fringe or along any
   outflow boundary laid out by this earlier activity, possibly
   affecting areas along the northern edge of the Moderate Risk area
   such as Shreveport LA.

   ...East Texas into Louisiana -- Midday through evening...
   The fast erosion of any capping inversion Sunday morning and
   widespread destabilization of the air mass lends uncertainty to
   exact placement and timing of tornadic supercell development, with a
   potential extending from east TX to New Orleans, and timing anywhere
   from midday through evening across the warm sector. Some models such
   as the ECMWF produce storms over southeastern LA during day, and the
   environment would already be favorable for tornadoes. However, the
   most likely scenario is for supercells to begin developing by
   midday, near the warm front and intensifying low-level jet core
   which will be across east TX into western LA, then eventually
   spreading eastward as the cold front approaches from the west. At
   least a few strong tornadoes are expected given large looping
   hodographs with effective SRH in excess of 300 m2/s2 along with
   impressive instability profiles. Overnight, cells may merge into a
   QLCS, with both tornado and damaging wind threat persisting into
   Monday morning.

   ..Jewell.. 04/01/2017

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