Mar 19, 2018 2000 UTC Day 1 Convective Outlook
Updated: Mon Mar 19 20:00:39 UTC 2018 (20180319 2000Z Day 1 shapefile | 20180319 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...Severe thunderstorms expected over parts of the Tennessee Valley this afternoon and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

Categorical Graphic
20180319 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 20,898 2,741,919 Huntsville, AL...Decatur, AL...Madison, AL...Gadsden, AL...Florence, AL...
ENHANCED 31,664 7,816,174 Atlanta, GA...Birmingham, AL...Chattanooga, TN...Sandy Springs, GA...Murfreesboro, TN...
SLIGHT 113,021 10,545,348 Jacksonville, FL...Nashville, TN...Montgomery, AL...Columbus, GA...Tallahassee, FL...
MARGINAL 63,383 7,129,613 Knoxville, TN...Gainesville, FL...Charleston, SC...Wilmington, NC...North Charleston, SC...
Probabilistic Tornado Graphic
20180319 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
SIG SEVERE 44,038 9,737,092 Atlanta, GA...Birmingham, AL...Huntsville, AL...Chattanooga, TN...Sandy Springs, GA...
15 % 20,898 2,741,919 Huntsville, AL...Decatur, AL...Madison, AL...Gadsden, AL...Florence, AL...
10 % 30,949 7,782,925 Atlanta, GA...Birmingham, AL...Chattanooga, TN...Sandy Springs, GA...Murfreesboro, TN...
5 % 76,065 6,665,769 Nashville, TN...Montgomery, AL...Columbus, GA...Savannah, GA...Macon, GA...
2 % 53,617 5,739,573 Tallahassee, FL...Columbia, SC...Clarksville, TN...Charleston, SC...Wilmington, NC...
Probabilistic Damaging Wind Graphic
20180319 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 % 165,750 21,089,543 Jacksonville, FL...Nashville, TN...Atlanta, GA...Birmingham, AL...Montgomery, AL...
5 % 60,269 6,554,041 Knoxville, TN...Gainesville, FL...Charleston, SC...Wilmington, NC...North Charleston, SC...
Probabilistic Large Hail Graphic
20180319 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 43,573 6,999,662 Atlanta, GA...Birmingham, AL...Montgomery, AL...Huntsville, AL...Sandy Springs, GA...
30 % 37,181 5,035,538 Birmingham, AL...Huntsville, AL...Chattanooga, TN...Murfreesboro, TN...Hoover, AL...
15 % 117,311 14,456,525 Jacksonville, FL...Nashville, TN...Atlanta, GA...Montgomery, AL...Columbus, GA...
5 % 65,216 7,687,316 Knoxville, TN...Gainesville, FL...Columbia, SC...Charleston, SC...North Charleston, SC...
   SPC AC 192000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Mon Mar 19 2018

   Valid 192000Z - 201200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF FAR NORTHEAST MISSISSIPPI...MIDDLE TENNESSEE...NORTHERN
   ALABAMA...AND NORTHWEST GEORGIA...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   MODERATE RISK AREA...AND EXTENDING EAST INTO PARTS OF CENTRAL
   GEORGIA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   MODERATE AND ENHANCED RISK AREAS...AND INCLUDING A LARGER PORTION OF
   THE SOUTHEAST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   OTHER/ASSOCIATED RISK AREAS...

   ...SUMMARY...
   Strong tornadoes, very large hail, and damaging winds are expected
   across parts of the Tennessee Valley and Southeast during the late
   afternoon and evening.

   ...Discussion...
   The existing outlook areas, and associated forecast reasoning,
   remain valid and in line with current thinking.  The main
   adjustments to the outlook at this time will be confined to minor
   tweaks, mainly to remove areas near the mid-Mississippi Valley where
   the front has progressed eastward, and some tweaks to the tornado
   risk over middle Tennessee where it has been slow to destabilize.  

   Otherwise, convection continues to increase as breaks in the clouds
   from Tennessee south to northeast Mississippi and northwest Alabama
   are allowing gradual northward destabilization to occur.  With the
   strongest ascent now spreading into the Tennessee Valley per the
   latest WV imagery, and as the deep-layer wind field across the area
   correspondingly strengthens with time over the next few hours,
   expect several severe/supercell storms to evolve along with
   attendant severe/tornado potential.

   ..Goss.. 03/19/2018

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Mar 19 2018/

   ...TN Valley and Southeast...
   Have upgraded to Moderate risk for the increasing likelihood of
   several tornadic supercells between 21-03Z, centered on northern AL
   and portions of adjacent states. Expansions to Enhanced and Slight
   risks have also occurred across parts of GA and SC for this evening
   and tonight. Lowest confidence remains on northern extent of the
   strong tornado risk where the degree of surface-based
   destabilization is quite uncertain.

   An elevated storm cluster is ongoing across far northern MS to the
   Mid-MS Valley, still removed from appreciable surface-based
   instability that is present near/south of the warm front in
   north-central MS/AL. See MCD 144 for additional short-term
   information. Guidance is highly varied in the degree of warm front
   movement today, which may be in part explained by differences in the
   handling of the ongoing convection. The NAM robustly destabilizes
   into middle TN but has a distinct absence of convective precip where
   convection is ongoing. While the RAP has substantially less buoyancy
   in TN with SBCAPE >500 J/kg remaining largely south of the state
   border. While low/deep-layer shear and hodograph size will become
   increasingly favorable for rotating storms, confidence in the degree
   of northward destabilization in the late afternoon across TN is low.
   However, farther south in parts of MS/AL/GA, confidence is greater
   in moderately large buoyancy developing with MLCAPE of 1500-2500
   J/kg becoming common south of the warm front. The northern extent of
   this instability plume with enlarged low-level hodographs should
   render the potential of several tornadic supercells during the late
   afternoon and early evening, a couple of which may be long track.
   Morning CAMs suggest the southern extent of probable supercell
   development will be across north-central AL, with convection
   becoming increasingly sparse to the south/southwest. 

   During the evening, convection should become increasingly
   clustered/semi-discrete, but a risk for a few strong tornadoes
   should continue across parts of northern/central GA near the warm
   front. Damaging wind/tornado risk should persist but become
   increasingly localized across parts of SC tonight.

   A separate area of scattered storm clusters should emanate northeast
   from ongoing convection along the FL Gulf Coast. This activity
   should be aided by a minor mid-level impulse evident over LA and
   modest warm advection atop a modifying outflow boundary in the wake
   of an early morning MCS that traversed north FL. A few embedded
   supercells capable of all hazards are possible with this activity.

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