May 20, 2017 1630 UTC Day 1 Convective Outlook
Updated: Sat May 20 16:31:04 UTC 2017 (20170520 1630Z Day 1 shapefile | 20170520 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170520 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 165,237 16,947,715 San Antonio, TX...Nashville, TN...Cincinnati, OH...Lexington-Fayette, KY...Louisville, KY...
MARGINAL 416,263 66,802,343 Chicago, IL...Houston, TX...Indianapolis, IN...Columbus, OH...Austin, TX...
Probabilistic Tornado Graphic
20170520 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 188,423 21,987,191 San Antonio, TX...Indianapolis, IN...Nashville, TN...Cincinnati, OH...Lexington-Fayette, KY...
Probabilistic Damaging Wind Graphic
20170520 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 165,216 16,909,485 San Antonio, TX...Nashville, TN...Cincinnati, OH...Lexington-Fayette, KY...Louisville, KY...
5 % 415,625 66,760,715 Chicago, IL...Houston, TX...Indianapolis, IN...Columbus, OH...Austin, TX...
Probabilistic Large Hail Graphic
20170520 1630 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 82,025 11,889,184 San Antonio, TX...Columbus, OH...Cincinnati, OH...Lexington-Fayette, KY...Louisville, KY...
5 % 416,324 60,234,111 Chicago, IL...Houston, TX...Indianapolis, IN...Austin, TX...Memphis, TN...
   SPC AC 201631

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1131 AM CDT Sat May 20 2017

   Valid 201630Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE OHIO
   VALLEY SOUTHWARD INTO THE LOWER MISSISSIPPI VALLEY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTH
   TEXAS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM TEXAS TO
   THE MIDWEST AND INTO THE SOUTHERN MID-ATLANTIC STATES...

   ...SUMMARY...
   Strong to severe thunderstorms will be possible ahead of a cold
   front from south-central Texas into the lower-to-middle Mississippi
   and Ohio Valleys this afternoon and evening. Isolated damaging wind
   gusts and hail will be the most common threats.

   ...Ohio Valley into parts of the Tennessee Valley...
   The leading edge of pre-cold frontal convection extends from Indiana
   into western parts of Kentucky and Tennessee, with stronger heating
   occurring mainly south of the Ohio River.  The environment is
   characterized by moderate instability in the warm sector where
   temperatures are in the low-mid 80s and dewpoints near 70, resulting
   in MUCAPE of around 2000 J/kg.  The air mass appears to be weakly
   capped with visible imagery showing developing Cu/Tcu clouds.  

   Although dynamic forcing for large scale ascent is stronger to the
   west in association with an upper low over the central Plains,
   sufficient low level convergence and diabatic heating will promote
   development of a few strong/severe storms this afternoon.  Southwest
   mid-level flow of 30-40 kt will support organized mainly multi-cell
   convective clusters and linear segments, although backed low-level
   winds near the warm front will enhance vertical shear and may
   promote a few supercell structures.  Stronger storms will be capable
   of mainly strong/severe wind gusts and occasional hail through the
   evening hours.  See Mesocale Discussion 799 for more details.

   ...Lower Mississippi Valley Area...
   Convection is developing within several north-south oriented
   convergence zones across eastern Mississippi within a moist and
   weakly capped environment.  This is in advance additional
   pre-frontal convection moving into the Mississippi Delta and
   extending southeast into central Louisiana.  Strong heating is
   contributing to the development of a moderate instability with
   MLCAPE of 2000-3000 J/kg.  The area is on the eastern edge of modest
   south-southwesterly mid-level winds that will support primarily
   multi-cell convective storms.  Stronger activity will be capable of
   locally damaging winds this afternoon and evening.

   ...South Texas...
   A small cluster of severe storms has persisted over south Texas this
   morning and this activity is likely to spread east-southeastward
   this afternoon.  The downstream thermodynamic environment continues
   to destabilize with MLCAPE of 2000-2500 J/kg.  Strongly veering wind
   profiles in the low-mid levels are providing strong vertical shear
   which will support a severe threat through the afternoon.

   ..Weiss/Gleason.. 05/20/2017

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