May 11, 2017 1630 UTC Day 1 Convective Outlook
Updated: Thu May 11 16:37:52 UTC 2017 (20170511 1630Z Day 1 shapefile | 20170511 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170511 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 22,066 2,284,431 Tulsa, OK...Broken Arrow, OK...Fort Smith, AR...Fayetteville, AR...Springdale, AR...
SLIGHT 259,947 21,598,075 Dallas, TX...Memphis, TN...Oklahoma City, OK...Nashville, TN...Lexington-Fayette, KY...
MARGINAL 217,791 27,998,830 Houston, TX...San Antonio, TX...Austin, TX...Fort Worth, TX...Arlington, TX...
Probabilistic Tornado Graphic
20170511 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
5 % 18,565 2,076,115 Tulsa, OK...Broken Arrow, OK...Fort Smith, AR...Fayetteville, AR...Springdale, AR...
2 % 111,396 10,392,036 Dallas, TX...Oklahoma City, OK...Plano, TX...Garland, TX...Shreveport, LA...
Probabilistic Damaging Wind Graphic
20170511 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 % 264,838 22,257,749 Dallas, TX...Memphis, TN...Nashville, TN...Tulsa, OK...Lexington-Fayette, KY...
5 % 208,279 28,678,687 Houston, TX...San Antonio, TX...Austin, TX...Fort Worth, TX...Oklahoma City, OK...
Probabilistic Large Hail Graphic
20170511 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
SIG SEVERE 23,836 2,688,635 Oklahoma City, OK...Tulsa, OK...Norman, OK...Broken Arrow, OK...Edmond, OK...
30 % 22,066 2,284,431 Tulsa, OK...Broken Arrow, OK...Fort Smith, AR...Fayetteville, AR...Springdale, AR...
15 % 230,489 18,824,692 Dallas, TX...Memphis, TN...Oklahoma City, OK...Lexington-Fayette, KY...Louisville, KY...
5 % 203,453 23,996,048 San Antonio, TX...Austin, TX...Fort Worth, TX...Nashville, TN...Arlington, TX...
   SPC AC 111637

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1137 AM CDT Thu May 11 2017

   Valid 111630Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   OK/NORTHWEST AR/FAR SOUTHEAST KS/SOUTHWEST MO...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN PLAINS TO THE MID-ATLANTIC REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN PLAINS TO THE MID-ATLANTIC REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHERN ROCKIES...

   ...SUMMARY...
   Severe thunderstorms with large hail, damaging winds, and possibly a
   couple of tornadoes are expected especially across the southern
   Plains, Ozarks, and Ark-La-Tex region. Other strong to severe
   thunderstorms will be possible as far east as the mid-Atlantic
   States, with other strong storms across parts of the northern
   Rockies.

   ...Parts of OK/AR/KS/MO this afternoon and evening...
   A closed trough centered over the south-central High Plains this
   morning will continue generally east-southeastward as it gradually
   opens. While a somewhat diffuse pattern will exist at the surface
   given the evolution of the parent cyclone, a semi-focused corridor
   of severe thunderstorm occurrence is likely this afternoon
   especially in areas north/east of a weak surface wave and
   outflow-modulated effective frontal corridor. Coincident with
   relatively cool mid-level temperatures (around -15C at 500 mb into
   central OK per 12Z upper-air data) atop mid 60s F surface dewpoints,
   very steep mid-level lapse rates, moderate buoyancy, and 40+ kt
   effective shear will support initial semi-discrete supercells
   capable of large hail. Although low-level shear/SRH will not be
   strong, at least a brief tornado or two could occur owing to ambient
   vorticity related to the upper low and outflow. Multiple clusters
   may eventually merge by late afternoon/early evening with some
   concern for damaging winds as well.  

   Farther south, a somewhat separate corridor of storms is anticipated
   today across east/northeast TX as a diffuse warm front and
   boundary-layer dewpoints in the 70s shift northeastward. Supercells
   will be possible within a broader corridor of cells/clusters, with
   some tendency for upscale growth into larger clusters/line segments
   expected by this evening. Large hail and damaging winds will be the
   main risks through tonight as convection spreads eastward toward the
   MS River. Like areas farther north, relatively weak low-level shear
   will tend to limit the tornado risk to favorable storm interactions
   (if any), while hail may not be as large as areas farther north into
   OK as a result of warmer temperature profiles aloft and somewhat
   lesser mid-level lapse rates.

   ...KY/WV/VA/NC this afternoon into early tonight...
   An MCV over southern IL late this morning will continue eastward
   along the slow-moving front and lingering outflow boundaries across
   KY this afternoon, providing a focus for additional storm
   development this afternoon. Potentially moderate buoyancy (MLCAPE 
   near 1500 J/kg) and largely unidirectional wind profiles/straight
   hodographs will favor organized clusters capable of producing
   damaging winds and large hail. There is some potential for a
   cluster to persist while crossing the Appalachians this evening and
   turning more to the southeast across VA/NC, where other more
   isolated storms may also form along a stalled front this afternoon.

   ...Northern Rockies this afternoon/evening...
   A pronounced midlevel trough and low/mid-level baroclinic zone will
   move slowly eastward over the Pacific Northwest. Along and
   immediately east of the front, moisture and lapse rates will be
   sufficient for scattered thunderstorms. Given the steep lapse rates
   and strong deep-layer shear, isolated damaging outflow gusts and
   marginally severe hail will be possible with the strongest storms.

   ..Guyer/Cohen.. 05/11/2017

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