Aug 30, 2021 1300 UTC Day 1 Convective Outlook
Updated: Mon Aug 30 12:45:01 UTC 2021 (20210830 1300Z Day 1 shapefile | 20210830 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210830 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 152,923 4,275,868 Omaha, NE...Lincoln, NE...Mobile, AL...Rapid City, SD...Council Bluffs, IA...
MARGINAL 232,093 26,969,334 Boston, MA...Kansas City, MO...Atlanta, GA...Birmingham, AL...Montgomery, AL...
Probabilistic Tornado Graphic
20210830 1300 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 % 29,095 2,046,259 Mobile, AL...Pensacola, FL...Biloxi, MS...Ferry Pass, FL...Prichard, AL...
2 % 180,411 12,937,484 Atlanta, GA...Omaha, NE...Lincoln, NE...Birmingham, AL...Montgomery, AL...
Probabilistic Damaging Wind Graphic
20210830 1300 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 % 123,119 2,223,586 Omaha, NE...Lincoln, NE...Rapid City, SD...Council Bluffs, IA...Bellevue, NE...
5 % 261,798 29,085,379 Boston, MA...Kansas City, MO...Atlanta, GA...Birmingham, AL...Montgomery, AL...
Probabilistic Large Hail Graphic
20210830 1300 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 92,790 593,154 Rapid City, SD...Grand Island, NE...Kearney, NE...North Platte, NE...Dickinson, ND...
15 % 123,986 2,228,897 Omaha, NE...Lincoln, NE...Rapid City, SD...Council Bluffs, IA...Bellevue, NE...
5 % 88,677 2,919,262 Kansas City, MO...Overland Park, KS...Kansas City, KS...Topeka, KS...Independence, MO...
   SPC AC 301245

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0745 AM CDT Mon Aug 30 2021

   Valid 301300Z - 311200Z


   Some tornado threat continues across the central Gulf States with
   remnants of Ida. Severe storms with very large hail and damaging
   winds are possible across parts of the northern and central Plains.

   ...Tropical Storm Ida today into tonight...
   Weakening Tropical Storm Ida will continue moving slowly northward
   over southwest and central MS, and then gradually turn northeastward
   tonight.  A large shield of rain has limited buoyancy inland from
   the coast, and a gradient in buoyancy will likely be maintained
   today along the east edge of the more persistent rain.  Broken
   convective bands will continue in this buoyancy gradient from the MS
   coast into southwest AL today, with the stronger flow and low-level
   shear from the west overlapping the west edge of the somewhat larger
   buoyancy toward the AL coast.  Though tornado production has been
   muted thus far, likely as a result of the weak inland buoyancy,
   there will be some potential for a bit more destabilization inland
   today across southwest AL as surface heating occurs in clouds breaks
   and Ida moves slowly northward.  Thus, a couple of tornadoes still
   remain possible with supercells along and just ahead of the main
   north-south convective band.  The tornado threat becomes more
   conditional with northeastward extent and into tonight across AL,
   though low-level shear will be strong enough to maintain a non-zero
   tornado threat overnight.

   ...Central Plains today into tonight...
   Subtle midlevel speed maxima will move southeastward over parts of
   the central Plains as a shortwave ridge begins to amplify upstream
   over the High Plains (east of a deepening trough over the Pacific
   Northwest).  A slow-moving baroclinic zone, oriented
   northwest-southeast, will be maintained from southwest SD to eastern
   NE.  This front will likely be the focus for thunderstorm
   development, potentially today in the zone of ascent along the
   boundary, and into tonight as a warm advection increases on the nose
   of a 30 kt low-level jet.  Forecast profiles are characterized by
   steep midlevel lapse rates (greater than 8 C/km) and MLCAPE of
   2000-3000 J/kg, with sufficient hodograph length and curvature for
   right-moving supercells.  Isolated very large hail (2.5 inch
   diameter or larger) will be possible with supercells along the
   boundary, and an isolated tornado or two may also occur where
   low-level shear is stronger and temperature-dewpoint spreads are
   lower along the boundary.  There is also the potential for storms to
   evolve into a cluster or two this evening into tonight, with an
   attendant threat for damaging winds and large hail.

   ...Northeast this afternoon...
   The southern extent of a midlevel low over QC will move over
   northern New England today, helping drive a cold front eastward
   during the afternoon.  Though midlevel lapse rates will be rather
   poor, there may be enough buoyancy and midlevel flow to support
   broken bands of storms along the front, with some potential for
   downward momentum transfer and isolated tree damage.  The southwest
   extent of any semi-organized wind threat is fairly uncertain, given
   the modest thermodynamic profiles and gradual decrease in midlevel
   flow/shear with southwest extent across New England.

   ..Thompson/Broyles.. 08/30/2021