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Feb 19, 2018 0600 UTC Day 1 Convective Outlook
Click to see valid 1Z - 12Z Day 1 Convective Outlook
Updated: Mon Feb 19 05:45:12 UTC 2018 (Print Version | 20180219 1200Z Day 1 shapefile | 20180219 1200Z Day 1 KML)
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 Forecast Discussion
   SPC AC 190545

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1145 PM CST Sun Feb 18 2018

   Valid 191200Z - 201200Z


   A few strong to severe storms are possible over a portion of the
   Southern Plains, mainly later this afternoon into tonight.


   Synoptic upper trough will continue to amplify over the western U.S.
   with a building upper ridge over the Southeast States. Between these
   two features, several weak vorticity maxima embedded within a
   southwesterly flow regime will move through the Southern Plains
   during the period. At the surface a cold front from the upper MS
   Valley into northwest KS will advance slowly south, possibly
   becoming stalled near the KS/OK border. South of this boundary, a
   dryline will mix ewd through western OK and western TX during the
   afternoon before retreating overnight as a lee cyclone becomes
   established over the central High Plains.

   ...Southern Plains region...

   Within a broad southerly flow regime, partially modified Gulf air
   with low to mid 60s F dewpoints will advect through the TX and OK
   warm sector today. Meanwhile, a modest elevated-mixed layer will
   spread eastward and overlap the western fringe of the moist warm
   sector contributing to a corridor of 500-1000 J/kg MLCAPE primarily
   from western and central OK through southwest TX. However, warmer
   temperatures aloft will contribute to a capping inversion over the
   more unstable portion of the warm sector during the day. Model
   consensus is that showers and a few thunderstorms may be ongoing
   early in of the period along warm conveyor belt, primarily from
   north central TX through eastern OK into the middle MS valley.  

   Primary uncertainty this forecast is extent of surface-based
   thunderstorm development given presence of widespread clouds,
   likelihood of at least a modest capping inversion, and tendency for
   the low-level jet to veer and shift eastward during the day.
   Potential for heating and mixing in vicinity of dryline may
   contribute to at least isolated storms by late afternoon or evening.
   Other storms may initiate over the higher terrain of northern Mexico
   and spread northeast into southwest TX. Another area of potential
   surface-based development will be near the dryline/cold front
   intersection over northern OK or southern KS, though any storms
   initiating in this area may have a tendency to become elevated as
   they move northeast and cross the frontal zone. 

   Very strong (55+ kt) 0-6 km shear will support potential for
   supercells with any storms developing along the dryline or higher
   terrain from southwest TX into western OK. Conditional upon storm
   initiation, a small window will exist for a tornado during the early
   evening, mainly from western OK into northwest TX as low-level
   hodographs become more favorable due to the strengthening low-level
   jet, and before the boundary layer stabilizes. Otherwise, primary
   severe threat  is expected to be large hail. Additional storms may
   develop later Monday night along evolving warm conveyor belt but
   within a strongly sheared environment. Extent of severe threat
   overnight is somewhat uncertain given a stable to marginally
   unstable near-surface layer. Nevertheless, some of the updrafts
   could become near the surface. 

   Have introduced a marginal risk this update, given the conditional
   nature and uncertainties regarding extent of thunderstorm initiation
   during the more favorable time of day and evening. An upgrade to
   higher probabilities could be needed in later updates over a portion
   of this area if these uncertainties can be mitigated.

   ..Dial/Jirak.. 02/19/2018



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