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Dec 12, 2018 1730 UTC Day 2 Convective Outlook
Updated: Wed Dec 12 17:20:37 UTC 2018 (Print Version | 20181212 1730Z Day 2 shapefile | 20181212 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 121720

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1120 AM CST Wed Dec 12 2018

   Valid 131200Z - 141200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE ARK-LA-TEX REGION INTO THE LOWER MISSISSIPPI VALLEY AND CENTRAL
   GULF COAST...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Ark-La-Tex region into
   the lower Mississippi Valley and north central Gulf coast vicinity
   Thursday into Thursday night, accompanied by at least some risk for
   severe weather.

   ...Synopsis...
   Pair of shortwave troughs currently observable in water vapor
   imagery over the western CONUS will influence the sensible weather
   from the southern Plains through the Southeast on Thursday. The
   southernmost shortwave will continue to move across northern Mexico
   and will likely be centered over the far western Gulf of Mexico at
   the beginning of the Day 2 period (i.e. 12Z Thursday). Northernmost
   shortwave, currently extending across ID and into northern NV, is
   expected to take a sharp dive southward across the central Rockies,
   leading to a split for the northern stream and the development of a
   closed low over the southern High Plains by early in the Day 2
   period.

   Strong height falls attendant to the second, significantly more
   amplified shortwave will spread across the southern Plains,
   contributing to both increased forcing for ascent across the region
   as well as the development and deepening of a surface low expected
   to move across north TX. A modestly moist and unstable air mass will
   likely be in place ahead of the system, from east TX eastward
   through the lower MS Valley, with some threat for a few strong to
   severe thunderstorms.

   ...East TX/Lower MS Valley/Central Gulf Coast...
   Current surface observations reveal mid-50s dewpoints are currently
   south of a line arcing from IAH (in southeast TX) westward to LRD
   (along the TX/Mexico border in south TX). Dewpoints greater than 60
   are currently confided to the immediate southern TX coast. This
   low-level moisture is expected to advect northward/northeastward
   within the persistent low/mid-level southerly/southeasterly flow
   anticipated throughout the day today. Consensus amongst the guidance
   is that mid 50s dewpoints will reach as far north as the Arklatex
   region by 12Z Thursday, with some further increase to the upper
   50s/low 60s possible by early Thursday afternoon. 

   Interaction between the maturing cyclone and this low-level moisture
   (and resulting marginal instability) will result in the most
   coherent severe threat during the period. In this area (i.e.
   east/southeast TX and western LA), some modest air mass
   destabilization is possible between the mid-level dry slot and
   approaching surface low/occluded front. Strong vertical shear will
   likely compensate for the marginal thermodynamics and a few strong
   to severe storms are possible. Primary threat is hail but a brief
   tornado is also possible, particularly if any boundaries are left
   over from the early morning showers and thunderstorms and/or if
   southeasterly surface winds persist.

   A more spatially limited severe threat is possible farther southeast
   across southeast LA and the immediate coastal areas of south MS, AL,
   and the far western FL Panhandle. A secondary surface low will
   likely develop during the late afternoon over southeast LA near the
   triple point as the primary low occludes over northeast TX. This
   second low is then expected to track eastward along the immediate
   central Gulf Coast into the western FL Panhandle. This track will
   limit the inland penetration of the warm sector, tempering the areal
   extent of any potential severe threat. Given the strong vertical
   shear and proximity to the secondary surface low, a few storms may
   be capable of producing damaging wind gusts and perhaps even a brief
   tornado within about 75 miles of the coast.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:      5%     - Marginal
   Hail:      5%     - Marginal

   ..Mosier.. 12/12/2018

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0700Z

        
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Page last modified: December 12, 2018
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