SPC AC 130546

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1246 AM CDT Thu Apr 13 2017

   Valid 131200Z - 141200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHEASTERN NM AND WEST TX...

   ...SUMMARY...
   A couple of strong to severe thunderstorms posing an isolated threat
   for large hail and gusty winds will be possible this afternoon and
   early evening across parts of southeastern New Mexico and west
   Texas.

   ...Synopsis...
   As a large-scale upper trough moves northeastward across the parts
   of the western CONUS, a separate low-amplitude shortwave trough will
   translate from the southern High Plains to the central Plains by
   tonight. At the surface, low pressure will deepen across the
   northern High Plains of eastern MT, while lee troughing extends
   southward from this low across a majority of the central/southern
   High Plains. 

   ...Southeastern NM/West TX...
   In the wake of the northeastward-moving shortwave trough across the
   Plains, large-scale ascent will be minimal across southeastern NM
   and west TX through the afternoon. But, modest southeasterly
   low-level upslope flow should foster convective initiation across
   the higher terrain of this region by late afternoon. Low-level
   moisture characterized by surface dewpoints in the upper 50s to low
   60s will be present along and east of the surface lee trough. Steep
   mid-level lapse rates of 7-8 C/km in combination with this low-level
   moisture and diurnal heating will contribute to moderate/strong
   instability, with MLCAPE generally ranging from 1500-2500 J/kg. Both
   low- and mid-level flow are expected to remain weak, generally 25 kt
   or less. However, a veering wind profile should support effective
   bulk shear values of 25-35 kt, which may be sufficient for
   semi-organized multicell/marginal supercell structures. Given the
   steep mid-level lapse rates, isolated large hail will be possible
   with these thunderstorms in addition to some threat for gusty winds.
   The lack of stronger large-scale forcing will likely limit the both
   the coverage and movement of any convection that develops in the
   afternoon over higher terrain, and 5% hail/wind probabilities remain
   confined to a narrow spatial corridor across southeastern NM/west
   TX.

   ...Northwest TX/Southwestern OK...
   Thunderstorms will probably be ongoing across parts of the southern
   High Plains at the start of the period in association with the
   northeastward-moving shortwave trough. Cloudiness and precipitation
   will likely hamper substantial destabilization across much of
   western OK and northwest TX through this afternoon, and mid-level
   lapse rates are forecast to remain poor (around 6-6.5 C/km from
   700-500 mb). Still, some prospect for modest instability to develop
   appears possible on the southern fringe of the shortwave trough and
   associated morning precipitation. If this were to occur, then 25-30
   kt of effective bulk shear could allow for some multicell clusters
   posing a very isolated gusty wind threat. At this time, too much
   uncertainty remains regarding sufficient destabilization across this
   region by the afternoon to include unconditional severe wind
   probabilities.

   ..Gleason/Cook.. 04/13/2017

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