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Oct 18, 2017 1300 UTC Day 1 Convective Outlook
Updated: Wed Oct 18 12:50:55 UTC 2017 (Print Version | 20171018 1300Z Day 1 shapefile | 20171018 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 181250

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0750 AM CDT Wed Oct 18 2017

   Valid 181300Z - 191200Z


   Isolated thunderstorms are possible today over portions of the
   Florida Peninsula, western New Mexico and far west Texas. 
   Isolated/brief thunder also is possible overnight near the Olympic
   Peninsula of Washington.

   A progressive northern-stream pattern this period will feature
   dominant synoptic-scale cyclones moving eastward from the SK/AB
   border across Hudson Bay, and another over the Gulf of Alaska
   approaching the southern AK Panhandle and Haida Gwaii archipelago
   around 12Z.  Associated height falls will spread across the Pacific
   Northwest overnight, with enough cooling aloft and low-level
   moisture to support isolated thunder potential near the coastal
   Olympic Peninsula.

   Farther south, a southern-stream perturbation -- now evident in
   moisture-channel imagery near the central/southern CA coast -- will
   proceed eastward to near the western border of AZ by 12Z.  A
   separate, weaker perturbation now over northwestern Mexico should
   move eastward toward far west TX.  Low-level warm/moisture advection
   through the period, and diurnal heating of higher terrain today,
   should contribute marginal instability/buoyancy to support
   thunderstorm potential over parts of extreme southeastern AZ,
   southwestern NM and far west Texas. 

   At the surface, a long-lasting, quasistationary frontal zone was
   analyzed at 11Z across central FL and west-southwestward over the
   central/western Gulf.  This boundary should linger over the region
   near its present position through the remainder of the period,
   though its slope above surface may become shallower.  A modest cold
   front -- associated with the leading northern-stream shortwave
   trough -- will proceed eastward from the Dakotas across MN and Lake

   Isolated thunderstorms will be possible within and south of the
   low-level frontal zone today, as diurnal heating combined with
   surface dew points upper 60s to 70s F offsets modest mid/upper-level
   lapse rates to yield 1000-1500 J/kg MLCAPE.  Sporadic/isolated
   thunder also will be possible throughout the period near the coast
   and over adjacent waters, aided nocturnally by instability
   associated with sea-land thermal fluxes and related maintenance of
   favorable boundary-layer theta-e.  Weak vertical shear and lack of
   larger lapse rates/buoyancy will temper storm-scale

   ..Edwards.. 10/18/2017



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