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Monday, August 30, 2021

SPC Aug 30, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1125 AM CDT Mon Aug 30 2021 Valid 301630Z - 311200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL GULF COAST AND THE NORTHERN/CENTRAL GREAT PLAINS... ...SUMMARY... 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 Read more LIVE: spc.noaa.gov