Aug 30, 2021 1630 UTC Day 1 Convective Outlook
Updated: Mon Aug 30 16:25:31 UTC 2021 (20210830 1630Z Day 1 shapefile | 20210830 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210830 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 168,149 4,658,355 Omaha, NE...Lincoln, NE...Mobile, AL...Sioux City, IA...Rapid City, SD...
MARGINAL 268,593 65,517,651 New York, NY...Philadelphia, PA...Baltimore, MD...Boston, MA...Washington, DC...
Probabilistic Tornado Graphic
20210830 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
5 % 35,461 2,057,585 Mobile, AL...Pensacola, FL...Biloxi, MS...Ferry Pass, FL...Prichard, AL...
2 % 182,058 12,923,845 Atlanta, GA...Omaha, NE...Lincoln, NE...Birmingham, AL...Montgomery, AL...
Probabilistic Damaging Wind Graphic
20210830 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
SIG SEVERE 60,108 1,522,601 Omaha, NE...Lincoln, NE...Bellevue, NE...Grand Island, NE...Fremont, NE...
15 % 124,034 2,395,638 Omaha, NE...Lincoln, NE...Sioux City, IA...Rapid City, SD...Council Bluffs, IA...
5 % 192,945 54,930,812 New York, NY...Philadelphia, PA...Baltimore, MD...Boston, MA...Washington, DC...
Probabilistic Large Hail Graphic
20210830 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
SIG SEVERE 78,873 402,204 Rapid City, SD...North Platte, NE...Pierre, SD...Rapid Valley, SD...Sturgis, SD...
15 % 130,854 2,491,198 Omaha, NE...Lincoln, NE...Sioux City, IA...Rapid City, SD...Council Bluffs, IA...
5 % 83,749 1,175,330 St. Joseph, MO...Leavenworth, KS...Liberty, MO...Scottsbluff, NE...Excelsior Springs, MO...
   SPC AC 301625

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1125 AM CDT Mon Aug 30 2021

   Valid 301630Z - 311200Z


   A few tornadoes remain possible through tonight across southeast
   Mississippi, southern Alabama, and the western Florida Panhandle in
   association with Tropical Cyclone Ida. Scattered severe storms with
   very large hail and significant damaging winds are possible across
   portions of the northern and central Great Plains through tonight.

   ...Central Gulf Coast States...
   Weakening Tropical Storm Ida will continue moving slowly north over
   west-central MS, and then gradually turn northeast into northeast MS
   tonight. A large shield of rain has limited buoyancy inland from the
   coast, and a gradient in buoyancy will likely be maintained along
   the east edge of the more persistent rain.  Regenerative convective
   bands should continue in this buoyancy gradient from the MS coast
   into southwest AL, 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
   southeast MS as surface heating occurs beneath thinner cloud
   coverage. Thus, a couple of tornadoes still remain possible with
   low-topped supercells along and just ahead of north-south convective
   bands. The tornado threat becomes more conditional with northeast
   extent and into tonight across AL, though low-level shear will be
   strong enough to maintain low probabilities.

   ...Northern/central Great Plains...
   Initially elevated thunderstorm development is underway across parts
   of south-central ND in the BIS vicinity. Some of this activity may
   produce isolated severe hail through mid-afternoon, see MCD 1647 for
   additional details. With time, robust boundary-layer heating amid a
   plume of low to mid 60s surface dew points across much of SD/NE will
   yield a broad swath of 2000-2500 J/kg MLCAPE. Rather steep mid-level
   lapse rates greater than 8 C/km with a sufficiently elongated
   hodograph owing to low-level southeasterlies beneath moderate
   mid-level westerlies will support potential for a few splitting
   supercells near the ND/SD border, along with a supercell or two off
   the Black Hills. Greater uncertainty exists with sustaining storms
   along the dryline in western NE and thus the cat 2/SLGT risk is more
   conditional with southern extent in NE. Very large hail and isolated
   severe wind gusts should be the primary hazards but a couple
   tornadoes will also be possible, especially near the ND/SD border.

   A separate cluster of low-level warm theta-e advection thunderstorms
   will likely initiate around sunset across the southeast SD/northeast
   NE vicinity. Convective mode will probably be a limiting factor to a
   greater spatiotemporal threat for very large hail in this corridor.
   But upscale growth into a forward-propagating MCS is possible later
   this evening into overnight, as simulated by the bulk of ARW-based
   CAMs, especially if any remnant supercells from western to central
   SD/NE can consolidate before MLCIN becomes too prohibitive. This
   could yield an increased severe wind threat and have added a
   significant wind area to account for this possibility.

   ...New England to the Mid-Atlantic States...
   A shortwave trough will move east over QC helping to drive a cold
   front east into New England by evening. Though mid-level lapse rates
   will be poor and boundary-layer heating limited by broken cloud
   coverage, there may be enough buoyancy and mid-level flow to support
   isolated to scattered storms along the front, with some potential
   for downward momentum transfer and isolated tree damage.

   Greater boundary-layer heating and moisture will support a more
   unstable air mass across portions of the Mid-Atlantic States.
   Isolated to scattered thunderstorms initiating off the lee trough
   should yield a localized damaging wind threat. Weak deep-layer shear
   will likely limit organizational potential.

   ..Grams/Lyons.. 08/30/2021