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    Day 2 Outlook >
Jul 18, 2018 1630 UTC Day 1 Convective Outlook
Click to see valid 1Z - 12Z Day 1 Convective Outlook
Updated: Wed Jul 18 16:49:20 UTC 2018 (Print Version | 20180718 1630Z Day 1 shapefile | 20180718 1630Z Day 1 KML)
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 Forecast Discussion
   SPC AC 181649

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1149 AM CDT Wed Jul 18 2018

   Valid 181630Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF SOUTH DAKOTA AND NEBRASKA...

   ...SUMMARY...
   Severe thunderstorms are likely this afternoon into tonight across
   parts of the northern and central Plains including Nebraska and
   southern South Dakota.

   ...North-central Plains/Middle MO Valley...
   Severe thunderstorms are likely this afternoon into evening and
   possibly the overnight across the region, although some uncertainty
   exists related to the most likely sub-regional corridor of severe
   storms. This is attributable to some lingering influences of prior
   outflow and multi-layer cloud cover at midday. Convection-allowing
   guidance spatial variability also exists between this morning's HRRR
   runs and other 12Z-based CAMs such as the NSSL-ARW.

   Regardless, the most probable area for surface-based convective
   initiation appears to be across west-central/south-central SD into
   far northern NEB this afternoon. With strong high-level winds
   already in place, an eastward-developing belt of increasingly strong
   mid-level westerlies in conjunction with south-southeasterly
   boundary layer winds will contribute to 35-45 kt of effective shear.
   This will be favorable for supercells capable of large hail, with
   moderate buoyancy and lengthy hodographs supportive of some larger
   hail magnitudes in spite of sub-optimal lapse rates. Some tornado
   risk may exist as well with enhanced low-level SRH in proximity to
   the surface boundary. 

   Otherwise, relatively quick upscale growth should occur by evening
   with one or more southeastward-moving clusters likely to evolve.
   This would pose an increased damaging wind risk this evening across
   parts of NEB, which could continue into the overnight potentially as
   far south as portions of KS.

   ...Lower MO Valley to Mid-South/Lower MS River Valley...
   Weak outflow/zones of differential heating will spatially influence
   sub-regional corridors of diurnally intensifying storms today within
   a very moist air mass. Some of the stronger updrafts/downdrafts will
   be capable of localized wind damage.

   ...Northern AZ/Lower CO River Valley...
   Widely scattered thunderstorms are expected later today, growing in
   coverage and becoming more clustered as they shift westward through
   afternoon into early evening. Isolated severe-caliber wind gusts are
   expected. A moist air mass, with PW of 1-1.5 inches, and steep
   low-level lapse rates in an increasingly well-mixed boundary layer
   this afternoon, will contribute to MLCAPE commonly reaching
   1000-1500 J/kg, and locally exceeding 2000 J/kg. This will
   contribute to potential for wet microbursts in cores and hybrid
   wet/dry processes in deeper/lower-ground-elevation boundary layers.
   Forecast soundings reasonably suggest (given the pattern) that a
   deep layer of easterlies in the midlevels will be the dominant
   contributor to the weak steering for early-stage convection, until
   enough upscale growth occurs with westward extent that aggregated
   cold pools force forward propagation.

   ...Coastal Carolinas vicinity...
   A warm and very moist air mass to the south of a southward-sagging
   front in conjunction with sea breeze influences could yield a couple
   of strong to locally severe thunderstorms capable of isolated
   damaging wind gusts this afternoon.

   ..Guyer/Wendt.. 07/18/2018

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z

        
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Page last modified: July 18, 2018
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