NWS Storm Prediction Center - Day 1 Convective Outlook

Aug 20, 2018 2000 UTC Day 1 Convective Outlook
Updated: Mon Aug 20 19:45:07 UTC 2018
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Overview Overview

 Forecast Discussion - Day 1 Convective Outlook


   SPC AC 201945

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0245 PM CDT Mon Aug 20 2018

   Valid 202000Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHERN ILLINOIS...SOUTHEAST MISSOURI...NORTHEAST
   ARKANSAS...WESTERN KENTUCKY...WESTERN TENNESSEE...AND NORTHWEST
   MISSISSIPPI...

   ...SUMMARY...
   Scattered severe storms are likely across the Mid-South into early
   evening. Damaging winds should be the primary hazard, but a couple
   tornadoes and large hail are possible.

   ...Mid MS Valley...
   Probabilities have been trimmed across portions of AR/MO to account
   for the eastward progression of the primary band of thunderstorms.
   As this band spreads eastward through the afternoon, corridors of
   damaging wind remain possible, along with more isolated instances of
   large hail and perhaps a tornado or two. See the previous discussion
   below for more information.  

   ...Eastern IN/Western OH...
   The 5% wind and 2% tornado probabilities have been expanded to the
   north and east to cover the rest of eastern IN and more of western
   OH, to account for the cluster of thunderstorms spreading northeast
   along a surface warm front. Transient supercell structures and small
   bowing segments will remain possible with this activity through the
   afternoon. See MCD 1326 for more discussion regarding this region. 

   ...Elsewhere...
   No other changes have been made to the outlook. See the previous
   discussion below for more information.

   ..Dean/Dial.. 08/20/2018

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Aug 20 2018/

   ...Mid MS Valley...
   Only minor changes have been made to the ongoing forecast.  An
   unseasonably strong upper low is present today over MO, with a band
   of moderately strong mid-level winds rotating cyclonically around
   the base of the low into parts of MO/AR/IL/KY/TN.  It appears that
   initial convection will develop soon over south-central MO and
   north-central AR, and track eastward across the ENH risk area
   through the afternoon.  Forecast soundings show favorable winds
   aloft and sufficient CAPE for a risk of bowing line segment capable
   of damaging wind gusts.  Initial activity could also pose a threat
   of hail and perhaps a tornado or two.  Have expanded the risk areas
   a little farther north into central/southern IL where
   clearing/destabilization appears likely.  Further details will be
   available in an MCD that will be issued soon.

   ...Northern IL and vicinity...
   Easterly surface winds over northern IL, will result in marginally
   favorable hodographs for a few rotating storms later this afternoon
   along and north of the warm front lifting across the region. 
   Widespread clouds will limit heating/destabilization, but morning
   model guidance suggests the potential for a few isolated storms
   capable of brief spin ups or damaging wind gusts.

   ...NC...
   Scattered thunderstorms are expected once again today over parts of
   NC, where ample low level moisture remains.  Winds in the lower
   troposphere are weak, but the strongest cells will be capable of
   locally gusty/damaging winds.

   ...Northern Great Basin...
   A strong shortwave trough is moving across eastern OR and will
   affect parts of ID/MT/UT/WY later today.  Low level moisture is
   limited, but forecast soundings suggest steep low-level lapse rates
   and increasing risk of a few damaging wind gusts as the mid-level
   wind max overspreads the region.  Small hail will also be possible
   in the higher elevations.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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



Data courtesy the Storm Prediction Center
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