Aug 30, 2021 0600 UTC Day 1 Convective Outlook
Updated: Mon Aug 30 05:39:02 UTC 2021 (20210830 1200Z Day 1 shapefile | 20210830 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210830 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 160,864 6,089,998 New Orleans, LA...Omaha, NE...Lincoln, NE...Mobile, AL...Metairie, LA...
MARGINAL 243,293 27,457,989 Boston, MA...Kansas City, MO...Atlanta, GA...Birmingham, AL...Baton Rouge, LA...
Probabilistic Tornado Graphic
20210830 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
5 % 46,277 3,922,707 New Orleans, LA...Mobile, AL...Metairie, LA...Gulfport, MS...Kenner, LA...
2 % 238,941 15,477,193 Atlanta, GA...Omaha, NE...Lincoln, NE...Birmingham, AL...Baton Rouge, LA...
Probabilistic Damaging Wind Graphic
20210830 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
15 % 113,414 2,168,997 Omaha, NE...Lincoln, NE...Rapid City, SD...Council Bluffs, IA...Bellevue, NE...
5 % 291,435 31,328,371 Boston, MA...Kansas City, MO...New Orleans, LA...Atlanta, GA...Birmingham, AL...
Probabilistic Large Hail Graphic
20210830 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 72,455 424,603 Rapid City, SD...Kearney, NE...North Platte, NE...Lexington, NE...Spearfish, SD...
15 % 113,508 2,173,980 Omaha, NE...Lincoln, NE...Rapid City, SD...Council Bluffs, IA...Bellevue, NE...
5 % 95,066 2,885,906 Kansas City, MO...Overland Park, KS...Kansas City, KS...Topeka, KS...Independence, MO...
   SPC AC 300539

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1239 AM CDT Mon Aug 30 2021

   Valid 301200Z - 311200Z


   Some tornado threat continues across the central Gulf States with
   remnants of Ida. Severe storms are also possible across parts of the
   northern and central Plains.


   Ida continues its slow northward advance across southeast LA this
   morning. Remnants will gradually curve northeast across northern MS
   by the end of the day1. Latest model guidance suggests strong
   low-level shear will remain confined to the eastern semicircle and
   there is reason to believe some boundary-layer heating will
   contribute to buoyancy from southern LA to the FL Panhandle. Have
   expanded higher tornado probabilities across the FL Panhandle where
   surface temperatures may warm to near 80F. Forecast thermodynamic
   profiles would yield at least 2500 J/kg MLCAPE with these
   temperatures and more robust updrafts can be expected.

   ...Northern/Central Plains...

   Broad upper ridging is forecast to continue across the southwestern
   US today as more significant troughing settles into the Pacific
   Northwest. Modest westerly flow will extend into the northern Great
   Basin-WY before turning more northwesterly across the Plains.
   Early-morning water-vapor imagery suggests a few weak disturbances
   are translating within this flow regime toward the northern/central
   High Plains. While appreciable height changes are not forecast
   across the Plains, one of these features is expected to aid
   thunderstorm development by late afternoon across the western
   Dakotas. Strong boundary-layer heating will aid destabilization such
   that parcels should be free to convect by 22-23z. Forecast sounding
   at BPP in southwest ND yields 2600 J/kg MLCAPE by this time with a
   surface temp/dew point of 83/59F. Surface-6km bulk shear is adequate
   for supercells, especially given the veering winds with height.
   Latest HREF guidance is not particularly helpful with most members
   struggling with a consistent signal. For this reason, will give more
   credence to boundary-layer heating which should prove instrumental
   in initiation. Isolated storms may also develop south across western
   NE where strong heating is expected. LLJ is forecast to increase
   during the evening and this should encourage longevity/expansion of
   thunderstorms after sunset.

   Downstream, there is some concern that convection may develop along
   the boundary draped across southeast NE where weak warm advection
   will be noted. Weak inhibition and the presence of the boundary
   suggest some potential for afternoon convection. However, stronger
   low-level convergence and more focused LLJ to the west suggest an
   upward-evolving complex will likely move into this region late. Have
   expanded the SLGT Risk to account for some uncertainty across this

   Large hail and damaging winds should be the primary threats with
   this activity.

   ...New England...

   Models continue to suggest a few robust storms are possible later
   today in association with approaching short-wave trough. Surface
   heating is not expected to be particularly strong and weak buoyancy
   should limit intensity with most storms. Even so, a few gusty winds
   could accompany the stronger cells.

   ..Darrow/Wendt.. 08/30/2021