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    Day 2 Outlook >
Apr 13, 2021 2000 UTC Day 1 Convective Outlook
Updated: Tue Apr 13 21:42:59 UTC 2021 (Print Version | 20210413 2000Z Day 1 shapefile | 20210413 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
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 Forecast Discussion
   SPC AC 132142

   Day 1 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0442 PM CDT Tue Apr 13 2021

   Valid 132140Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHEAST TX INTO
   WESTERN LA...

   AMENDED FOR ADDITION OF MARGINAL RISK TO NORTHWEST TX AND REMOVAL OF
   SLIGHT RISK IN SOUTHERN LA

   ...SUMMARY...
   Isolated to scattered severe thunderstorms, with large hail as the
   primary hazard, remain possible through tonight centered on
   southeast Texas into western Louisiana.

   ...2140Z Outlook Amendment...
   An elevated supercell has formed in west TX to the northwest of
   Midland. Additional elevated severe hail cores may develop farther
   northeast across a portion of the Low Rolling Plains of northwest
   TX. Please see MCD 0380 for further information.

   Have also removed SLGT risk from the southern Louisiana region as
   the MCS has progressed offshore.

   ...20Z Outlook Update...
   Adjustments to categorical and probabilistic lines have been made to
   account for the progression of the synoptic and sub-synoptic
   features, and associated trends concerning destabilization.  Most
   notably, this includes the evolving cluster of thunderstorm over
   southeastern Louisiana, which could still produce strong surface
   gusts near coastal areas before advancing offshore by or shortly
   after 14/00Z.

   Otherwise, moderately strong instability is developing within a
   narrow corridor across the Texas coastal plain into the Piney Woods,
   ahead of a slow moving cold front.  This could become a focus for at
   least isolated severe thunderstorm development late this afternoon. 
   Based on mid-level inhibition inferred from mid-level temperature
   (particularly around 700 mb) forecasts, capping across and southwest
   of the Greater Houston Metropolitan area still appears likely to
   preclude sustained thunderstorm development.  This becomes
   progressively weaker to the northeast, and deepening convection now
   evident west-northwest through northeast of Lufkin TX could become
   the focus for thunderstorm initiation within the next couple of
   hours.  Deep-layer shear across this region, beneath 30-40 kt
   westerly flow around 500 mb, is sufficient to support supercells
   capable or producing severe hail.

   Any late afternoon/early evening storms may diminish by late
   evening,  as boundary-layer cooling progresses, but increasing new
   thunderstorm development appears possible late tonight in
   association with the approach of a weak mid-level perturbation. 
   This probably will be focused within lower/mid tropospheric warm
   advection, above/to the cool side of the outflow flow boundary
   associated with the ongoing cluster of storms, perhaps along the
   trailing west/northwestern flank just ahead of the surface cold
   front.

   ..Grams/Kerr.. 04/13/2021

   .PREV DISCUSSION... /ISSUED 1125 AM CDT Tue Apr 13 2021/

   ...LA/TX areas today into tonight...
   A cluster of slightly elevated thunderstorms is ongoing across south
   central and southeast LA as of late morning, with a few embedded
   stronger cells capable of producing isolated large hail.  The hail
   threat is supported by the influx of low-mid 70s boundary-layer
   dewpoints across the northwest Gulf coast, beneath the eastern
   extent of midlevel lapse rates near 8 C/km.  The convection this
   morning has been driven largely by weak low-level warm advection in
   a moist profile with little convective inhibition, which suggests
   that storms will likely persist through the afternoon.  Gradual
   upscale growth into a larger cluster/MCS appears possible, with a
   tendency for cold pool formation to result in slow southeastward
   propagation into this afternoon/evening.  The primary severe threats
   with these storms will be occasional large hail and isolated
   damaging gusts.

   Farther west and later this afternoon, isolated surface-based storm
   development will be possible along the stalled synoptic front across
   east TX.  Forcing for ascent will be weak and this area will be
   along the northeast edge of the stronger cap, so diurnal storm
   coverage is in question.  If storms do form this afternoon, the
   environment conditionally favors supercells capable of producing
   large hail/damaging winds.  Otherwise, another round of
   strong-severe storms appears probable from east TX into LA in
   conjunction with some increase in low-level warm advection late
   tonight.  A continued feed of rich low-level moisture from the south
   and steep midlevel lapse rates will maintain MUCAPE at or above 2000
   J/kg, with an attendant threat for at least isolated large
   hail/damaging winds.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z

        
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