Mar 17, 2021 0600 UTC Day 1 Convective Outlook
Updated: Wed Mar 17 05:52:51 UTC 2021 (20210317 1200Z Day 1 shapefile | 20210317 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210317 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
HIGH 27,773 1,462,581 Jackson, MS...Greenville, MS...Tupelo, MS...Vicksburg, MS...Clinton, MS...
MODERATE 94,609 7,437,511 Memphis, TN...Birmingham, AL...Montgomery, AL...Little Rock, AR...Tuscaloosa, AL...
ENHANCED 107,472 9,196,333 New Orleans, LA...Baton Rouge, LA...Shreveport, LA...Mobile, AL...Columbus, GA...
SLIGHT 90,562 11,243,302 Atlanta, GA...Chattanooga, TN...Beaumont, TX...Sandy Springs, GA...Macon, GA...
MARGINAL 161,464 20,060,334 Houston, TX...Nashville, TN...Kansas City, MO...Tulsa, OK...Wichita, KS...
Probabilistic Tornado Graphic
20210317 1200 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
SIG SEVERE 156,431 11,384,408 Memphis, TN...Birmingham, AL...Baton Rouge, LA...Montgomery, AL...Little Rock, AR...
30 % 27,517 1,422,897 Jackson, MS...Greenville, MS...Tupelo, MS...Vicksburg, MS...Clinton, MS...
15 % 95,004 7,516,310 Memphis, TN...Birmingham, AL...Montgomery, AL...Little Rock, AR...Tuscaloosa, AL...
10 % 106,006 9,084,978 New Orleans, LA...Baton Rouge, LA...Shreveport, LA...Mobile, AL...Columbus, GA...
5 % 87,079 10,785,658 Atlanta, GA...Chattanooga, TN...Sandy Springs, GA...Macon, GA...Murfreesboro, TN...
2 % 56,981 5,256,626 Nashville, TN...Tulsa, OK...Clarksville, TN...Beaumont, TX...Tyler, TX...
Probabilistic Damaging Wind Graphic
20210317 1200 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
SIG SEVERE 179,316 11,722,089 Memphis, TN...Birmingham, AL...Montgomery, AL...Shreveport, LA...Little Rock, AR...
30 % 215,336 15,625,293 Memphis, TN...Birmingham, AL...Baton Rouge, LA...Montgomery, AL...Shreveport, LA...
15 % 95,446 12,837,011 New Orleans, LA...Atlanta, GA...Chattanooga, TN...Metairie, LA...Lafayette, LA...
5 % 139,833 15,846,342 Houston, TX...Nashville, TN...Kansas City, MO...Tulsa, OK...Wichita, KS...
Probabilistic Large Hail Graphic
20210317 1200 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 80,271 3,622,295 Jackson, MS...Tuscaloosa, AL...Monroe, LA...Hattiesburg, MS...Alexandria, LA...
30 % 228,417 17,909,399 Memphis, TN...New Orleans, LA...Birmingham, AL...Baton Rouge, LA...Montgomery, AL...
15 % 90,956 11,333,266 Atlanta, GA...Chattanooga, TN...Clarksville, TN...Beaumont, TX...Sandy Springs, GA...
5 % 162,304 20,110,190 Houston, TX...Nashville, TN...Kansas City, MO...Tulsa, OK...Wichita, KS...
   SPC AC 170552

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1252 AM CDT Wed Mar 17 2021

   Valid 171200Z - 181200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
   LOUISIANA ACROSS NORTHERN MISSISSIPPI INTO NORTHWEST ALABAMA...

   ...SUMMARY...
   A regional outbreak of severe storms is expected today and tonight
   across portions of the lower Mississippi Valley into Alabama.
   Widespread severe storms capable of producing tornadoes (several of
   which may be intense), very large hail and intense damaging wind
   gusts are expected. More than one round of severe storms are
   possible across parts of Mississippi into Alabama during the
   afternoon into the overnight hours.

   ...Lower Mississippi Valley to Alabama...

   Early-morning water-vapor imagery depicts a well-defined upper low
   over central NM moving east toward the TX Panhandle. This feature
   will eject across OK into the Ozark Plateau by the end of the
   period. Intense large-scale forcing for ascent is currently
   spreading across the southern High Plains region where deep
   convection is currently expanding in areal coverage along the dry
   line/Pacific front as it encounters western edge of moisture plume.
   This boundary will remain active leading into the start of the day1
   period.

   Strongly diffluent flow aloft will overspread the lower MS
   Valley/central Gulf States during the day as 80kt+ 500mb flow
   overspreads increasingly moist/buoyant warm sector. Latest model
   guidance suggests several LLJ segments will increase ahead of the
   trough, each likely modulating bouts of organized severe
   thunderstorm clusters/supercells. The primary synoptic low is
   forecast to track across northeastern OK into southern MO.
   Significant elevated convection will be noted north of the warm
   front but ample surface-based buoyancy/shear south of the front
   should prove favorable for supercells as one LLJ segment focuses
   across AR into southeast MO ahead of this feature. At the same time,
   a secondary LLJ will strengthen across MS during the day and become
   the primary LLJ into the overnight hours over northwestern AL/middle
   TN. This secondary LLJ appears to be responding to a mid-level speed
   max that will translate across south-central TX into southern LA
   during the late evening hours.

   Of particular interest is the boundary-layer moisture that is now
   present along the Gulf Coast where lower 70s surface dew points are
   observed. This air mass will advance north during the day and
   diurnal heating will allow moderate instability to develop along a
   corridor from southern LA through central MS into western AL where
   SBCAPE should be on the order of 2500 J/kg. While the primary 500mb
   speed max will likely maintain convection along the surging Pacific
   front over southeast TX, an uncapped, buoyant air mass downstream
   over MS/AL should prove favorable for discrete supercell development
   ahead of the primary short wave. Forecast soundings across the HIGH
   Risk exhibit profiles favorable for strong, long-track tornadoes,
   and this is especially true from northeast LA through northern MS
   into northwest AL.

   ..Darrow/Lyons.. 03/17/2021

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