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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Sunday, August 13, 2023

SPC Aug 13, 2023 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Sun Aug 13 2023 Valid 131300Z - 141200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER THE OZARK PLATEAU REGION... ...SUMMARY... Severe thunderstorm gusts, large hail and a tornado threat are expected today in and near the Ozarks. ...Synopsis... Though strong mid/upper-level ridging will persist over the Gulf Coast States into central/west TX, northern-stream amplification will intensify gradient flow aloft to its north. Much of that process will be related to a strong northern-stream shortwave trough -- apparent in moisture-channel imagery from a vorticity max over northwestern ND southwestward to northwestern WY, and northeastward across southeasternmost portions of SK. This feature will strengthen further and dig southeastward across the northern Plains/Upper Midwest regions through the period, reaching an axis near TVF-PIR-CYS by 00Z, and DLH-OMA-GLD by 12Z tomorrow. Well eastward in the downstream westerlies, a weaker shortwave trough now over southeasternmost ON and central NY should reach from northwestern ME to NH by 00Z, exiting the CONUS to Atlantic Canada within about 6 hours thereafter. The 11Z surface analysis showed a low over southern QC related to the lead shortwave trough, with the CONUS part of its trailing cold front extending across central NY, western PA, and extreme southern OH, becoming quasistationary over southern parts of IN/IL, and a slow-moving warm front over northeastern MO to northwestern IA. The front should move eastward across all of New England before 06Z. Meanwhile the Plains low should move/redevelop to near FSD by 00Z, With a secondary low possible over northwestern MO or northeastern KS (specific position strongly influenced by intervening convective processes). From there, the front should extend across south- central KS, northwestern OK, the TX Panhandle, and northeastern NM. By 12Z, either an eastward-shifted version of the secondary 00Z low, or a new frontal-wave low, should lie along the boundary over the western/southern IL region. A warm to stationary front should extend from there toward WV. The cold front should extend from there across northern AR, southeastern OK, north-central/northwest TX, and south-central NM. The warm to stationary front still should extend from the low roughly eastward into WV. ...Ozarks to south-central Plains, lower Missouri and Tennessee Valleys... A complex convective regime still is apparent across this region, with multiple fronts and warm-sector convective boundaries rendering considerable uncertainty -- especially around the outlook's fringes. The highest-confidence area still appears to be over and near the Ozark Plateau, where the "enhanced" area is maintained based on the most-favorable expected total-severe parameter space (hail, wind and tornado potential) late this afternoon into evening. In that corridor, and perhaps somewhat westward through KS and eastward into IL, the greatest potential exists for both warm advection and diabatic heating to favorably destabilize a richly moist air mass behind the morning activity now over parts of northern AR and southern MO. This should occur as winds aloft strengthen in the mass response to the approaching shortwave trough, ahead of the surface cold front and southwest of the warm front. Forecast soundings suggest considerable veering of winds with height, leading to enlarged, supercell-favoring hodographs and low- level wind profiles (e.g., effective SRH potentially into the 250- 400 J/kg range). Effective-shear magnitudes will be more marginal (30-40 kt), owing to the late approach of the shortwave trough. This suggests that convective mode could get clustered and messy rather quickly after initiation, but with embedded supercells and LEWP/bowing mesocirculations contributing to all-hazards severe threats. The warm-sector parameter space away from that core corridor will be characterized by 1. More-veered prefrontal surface winds westward toward the front; 2. Weaker instability northward, getting into greater influence from a mass of precip and convection initially over much of the lower Missouri Valley; 3. Cloud cover and weaker deep-layer lapse rates eastward toward the synoptic warm/stationary front and the lower Ohio Valley region. Still, discrete to clustered convection with wind and hail potential may develop over some of those areas, especially along fronts and outflow/differential/heating boundaries. ...Central/Eastern New England... Isolated to widely scattered thunderstorms are expected to form during the midday hours over western/central New England, along/ ahead of the surface cold front. The front, and slightly precursory field of large-scale ascent preceding the shortwave trough, should impinge on a destabilizing boundary layer with minimal MLCINH, and enough moisture to contribute to peak/preconvective MLCAPE in the 1500-2000 J/kg range. Deep-layer flow will be nearly unidirectional in/above the warm sector, with weak near-surface winds yielding small hodographs. Still, mid/upper-level flow will be strong enough ahead of the trough to yield effective-shear magnitudes in the 30- 35-kt range, supporting some organized multicells, and sporadic isolated pulse-severe potential in the form of marginal hail and/or gusts. ..Edwards/Dean.. 08/13/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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