Mar 21, 2017 1630 UTC Day 1 Convective Outlook
Updated: Tue Mar 21 16:27:51 UTC 2017 (20170321 1630Z Day 1 shapefile | 20170321 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170321 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 23,755 4,439,677 Huntsville, AL...Chattanooga, TN...Murfreesboro, TN...Roswell, GA...Franklin, TN...
SLIGHT 38,086 6,323,093 Nashville, TN...Atlanta, GA...Sandy Springs, GA...Jackson, TN...Marietta, GA...
MARGINAL 129,949 20,074,634 Memphis, TN...Charlotte, NC...Sacramento, CA...Fresno, CA...Stockton, CA...
Probabilistic Tornado Graphic
20170321 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 % 25,989 5,977,526 Sacramento, CA...Fresno, CA...Stockton, CA...Modesto, CA...Roseville, CA...
Probabilistic Damaging Wind Graphic
20170321 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
30 % 23,706 4,435,035 Huntsville, AL...Chattanooga, TN...Murfreesboro, TN...Roswell, GA...Franklin, TN...
15 % 25,943 5,659,587 Nashville, TN...Atlanta, GA...Sandy Springs, GA...Jackson, TN...Marietta, GA...
5 % 102,080 16,870,500 Memphis, TN...Charlotte, NC...Sacramento, CA...Fresno, CA...Stockton, CA...
Probabilistic Large Hail Graphic
20170321 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
30 % 16,637 3,273,518 Huntsville, AL...Chattanooga, TN...Roswell, GA...Madison, AL...Rome, GA...
15 % 45,098 7,468,126 Nashville, TN...Atlanta, GA...Sandy Springs, GA...Murfreesboro, TN...Jackson, TN...
5 % 131,121 20,218,284 Memphis, TN...Charlotte, NC...Sacramento, CA...Fresno, CA...Stockton, CA...
   SPC AC 211627

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1127 AM CDT Tue Mar 21 2017

   Valid 211630Z - 221200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   AND EVENING OVER PARTS OF TENNESSEE...NORTHERN ALABAMA...AND NORTH
   GEORGIA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
   MISSOURI INTO WESTERN SOUTH CAROLINA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHERN AR
   INTO THE CAROLINAS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE PARTS
   OF THE SACRAMENTO VALLEY OF NORTHERN CALIFORNIA...

   ...SUMMARY...
   Hail and damaging thunderstorm gusts are possible today from the
   Ozarks across the Tennessee Valley to the southern Appalachians.  An
   enhanced corridor of severe threat is expected this afternoon and
   evening from middle Tennessee to northeastern Alabama and northern
   Georgia.  An isolated severe storm or two, capable of hail, damaging
   gusts and/or a tornado, may develop also across portions of the
   California Central Valley.

   ...Mid MS Valley to the Southeast States...
   The morning surface analysis shows a weak frontal boundary extending
   from a low over OK into northern AR and TN.  A cluster of
   thunderstorms has developed this morning near the front over
   southwest MO, where isolated severe hail has occurred.  These storms
   have weakened somewhat in the short-term, but are expected to
   intensify again this afternoon as strong daytime heating
   destabilizes the air mass over northeast AR and west TN.  12z model
   guidance is very consistent in depicting these storms organizing
   into an MCS that tracks east-southeastward across much of TN,
   northern AL and eventually into northern GA.  Forecast soundings
   along this corridor show favorable parameters for large hail, and
   increasing mesoscale organization will likely enhance the risk of
   damaging winds later today.  Therefore will maintain the ENH risk
   area.  The storms are expected to weaken after sunset over SC.

   ...Northern CA...
   Scattered thunderstorms are expected this afternoon and evening over
   the Sacramento Valley of northern CA.  It is unclear how much
   destabilization will occur in this region, as clouds and showers are
   prevalent at this time.  However, forecast soundings suggest
   favorable vertical shear profiles and mid level lapse rates will be
   present.  This will result in a risk of a few strong cells capable
   of hail, damaging winds, and/or a tornado or two.  Some low risk of
   severe storms extends northeastward into parts of northern NV,
   eastern OR, and southern ID as well.  However, will not extend MRGL
   risk into these areas due to cloud cover and limited instability.

   ..Hart/Coniglio.. 03/21/2017

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