Mar 17, 2018 2000 UTC Day 1 Convective Outlook
Updated: Sat Mar 17 19:56:32 UTC 2018 (20180317 2000Z Day 1 shapefile | 20180317 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180317 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 66,277 11,919,123 Dallas, TX...Fort Worth, TX...Arlington, TX...Raleigh, NC...Greensboro, NC...
MARGINAL 87,717 8,915,682 Plano, TX...Shreveport, LA...Knoxville, TN...Chattanooga, TN...Abilene, TX...
Probabilistic Tornado Graphic
20180317 2000 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 % 21,134 3,548,954 Fort Worth, TX...Arlington, TX...Grand Prairie, TX...Waco, TX...Killeen, TX...
2 % 18,358 3,775,879 Dallas, TX...Plano, TX...Garland, TX...Irving, TX...Mesquite, TX...
Probabilistic Damaging Wind Graphic
20180317 2000 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 % 42,376 9,213,368 Dallas, TX...Fort Worth, TX...Arlington, TX...Raleigh, NC...Greensboro, NC...
5 % 96,171 10,090,971 Plano, TX...Garland, TX...Shreveport, LA...Knoxville, TN...Carrollton, TX...
Probabilistic Large Hail Graphic
20180317 2000 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 20,880 3,157,983 Fort Worth, TX...Arlington, TX...Waco, TX...Killeen, TX...Temple, TX...
15 % 63,166 11,802,392 Dallas, TX...Fort Worth, TX...Arlington, TX...Raleigh, NC...Greensboro, NC...
5 % 90,559 9,025,948 Plano, TX...Shreveport, LA...Knoxville, TN...Chattanooga, TN...Abilene, TX...
   SPC AC 171956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Sat Mar 17 2018

   Valid 172000Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   TEXAS...NORTHWEST LOUISIANA AND FAR SOUTHWEST ARKANSAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN APPALACHIANS INTO NORTHERN AND EASTERN NORTH
   CAROLINA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS AND ARKLATEX...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE OHIO AND TENNESSEE VALLEYS EASTWARD INTO VIRGINA AND NORTH
   CAROLINA...

   ...SUMMARY...
   Severe thunderstorms with wind damage and hail are expected this
   afternoon into tonight from the southern Appalachians eastward into
   parts of northern and eastern North Carolina. Severe thunderstorms
   with large hail and wind damage will also be possible across parts
   of central and northeast Texas into the Arklatex.

   ...DISCUSSION...
   Only two changes have been made to the outlook for this issuance. 
   The first change is to expand the slight risk area in central Texas
   westward to the western edge of the ongoing convection.  This change
   includes a westward expansion of the wind damage, hail and tornado
   probabilities.  The second change to the outlook is to expand the
   marginal risk in the southern Appalachians southward into far
   northeast Alabama and far northern Georgia. The HRRR is suggesting
   that convection will initiate in eastern Kentucky and middle
   Tennessee. If this occurs, a marginal severe threat may affect areas
   a bit further south.

   ..Broyles.. 03/17/2018

   .PREV DISCUSSION... /ISSUED 1132 AM CDT Sat Mar 17 2018/

   ...Central/Northeast Texas to the Ark-La-Tex...
   Coincident with the leading edge of stronger cyclonic flow aloft,
   12Z upper-air analysis sampled a mid-level cold pocket over the
   southern High Plains with a strong southern stream/sub-tropical jet
   extending from northern Mexico eastward into central/north Texas. At
   midday, low-level stratus continues to stream northward across
   south-central/east Texas coincident with increasingly prevalent
   middle/upper 60s F surface dewpoints.

   By mid/late afternoon, as clouds thin, concern exists for the
   possibility of initial surface-based storm development across the
   north-central Texas Big Country near a triple point characterized by
   a gradually deepening surface wave near a stationary front/dryline
   intersection. Some supercells can be expected in the presence of
   long hodographs influenced by strengthening mid/high-level
   westerlies. Moderate buoyancy, relatively steep lapse rates and the
   long/relatively straight hodographs should support some splitting
   supercells with large hail as the primary hazard. While low-level
   winds and related vertical shear/SRH will not be strong initially,
   some low-level strengthening will occur by early evening and there
   will be a risk for a couple of tornadoes.

   ...South-Central Appalachians/North Carolina...
   A mid-level shortwave trough moving toward northern/central Illinois
   at midday will gradually accelerate southeastward today and interact
   with an increasingly moist environment across the region along/south
   of an advancing warm front. Initial strong to severe thunderstorm
   development is likely to occur across east/southeast Kentucky this
   afternoon. Aided by steep mid-level lapse rates and strong
   deep-layer shear, this includes the possibility of supercells
   capable of large hail, with damaging winds also a concern. Storms
   should continue to increase and progress east/southeastward this
   evening into far southern Virginia and North Carolina potentially as
   a semi-organized MCS.

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