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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.


Monday, July 31, 2023

SPC Jul 31, 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 0748 AM CDT Mon Jul 31 2023 Valid 311300Z - 011200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE NORTHERN/CENTRAL PLAINS...COASTAL SOUTHEAST...LOWER MISSOURI VALLEY TO WEST-CENTRAL GULF COAST...AND ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible over portions of the northern/central Plains, coastal Southeast, lower Missouri Valley to west-central Gulf Coast, and Arizona. ...Synopsis... In mid/upper levels, the center of a persistent anticyclone has shifted eastward slightly, from the Four Corners and southern Rockies regions to the south-central High Plains. This has occurred as a series of small shortwaves and accompanying convectively induced/enhanced vorticity maxima pivot northwestward out of MC, then northward around the western rim of the circulation. The northern few of that series will pivot northeastward across the northern/central Rockies and adjoining High Plains through this period. A synoptic-scale ridge will continue to extend east-southeastward from the high across the Arklatex/Mid-South region, temporarily penetrated by a prominent MCV and accompanying shortwave trough now over AR. This perturbation is progged to deamplify today as it moves southward into a regime of weakening, difluent ambient flow, but still may contribute to convection to its south and southeast (see below). Meanwhile, a small shortwave trough -- apparent in moisture-channel imagery over KY -- is expected to move quickly southeastward to the southern part of a large-scale trough over the Carolinas and GA, during the 00-06Z time frame. The 11Z surface analysis showed a low near GSO with quasistationary frontal zone southeastward across southern SC and southwestward over northern portions of GA/AL/MS. The frontal zone was interrupted by MCS cold pools across AR, MO and NE, but the associated baroclinicity should become better defined again later today, in a southeast/northwest fashion across those areas, as the outflow becomes shallower/weaker. ...Northern/central Plains... Isolated to locally scattered thunderstorms are expected to develop this afternoon from the eastern ranges/foothills of the Rockies to the frontal zone, and along residual surface boundaries in between. Isolated severe hail/gusts are possible. The environment for this activity will be characterized by adequate low-level moisture (surface dewpoints generally in the 50s and lower 60s F), steep low-level lapse rates with well-mixed sub cloud layers, and in he central High Plains, relatively weak shear but strong heating/mixing. A conditional risk for significant (2+ inch diameter) hail exists over the northern Plains part of the outlook area, where favorable vertical shear for supercells again is expected in and near the frontal zone. Southeast flow near the surface, veering sharply with height to the northwesterly and westerly winds aloft, will result in wind profiles characterized by small 0-1-km SRH but long hodographs, and effective-shear magnitudes in the 40-50-kt range. However, with generally rising heights aloft and subtle low-level forcing, placement and coverage is uncertain, with at least an isolated supercell or two possible almost anywhere in the corridor. ...Lower Missouri Valley to west-central Gulf Coast... An outflow boundary preceding the southern MCV is moving southward through LA, with the bulk of convection elevated over the still- progressive cold pool behind it. However, as the boundary encounters diurnally destabilizing, very moist Gulf air through the afternoon, additional, surface-based convection may form along it and produce strong to isolated severe gusts. Activity should remain multicellular in character, given the weak ambient shear. That outflow boundary moved well into eastern central OK and northeast TX; however, the air mass across the western and later the remainder of the outlook area may recover with warm/moist advection from a narrow corridor of relatively maximized moisture across central OK into central/eastern KS, near the morning boundary. Though not as high-theta-e as the relatively undisturbed air mass farther southeast near the Gulf Coast, moisture and diurnal destabilization ahead of the NE MCV/precip may support additional strong to locally severe thunderstorms this afternoon into tonight over the lower Missouri Valley to Ozarks. A 30-35 kt southwesterly LLJ overnight, beneath steep lapse rates and northwest flow in midlevels, also may foster sufficient moisture and effective shear to support hail potential over northern parts of the outlook area, as parcels rise isentropically to an LFC, along an elevated segment of the baroclinic zone. ...Coastal Southeast... Widely scattered to scattered thunderstorms should form along/ahead of the surface front today over portions of the Carolinas and GA, becoming scattered to numerous amid an active sea-breeze/outflow- boundary regime over the central/eastern FL Peninsula. Frontal lift is expected to be modest, given the presence of light winds with northerly component ahead of it. Still, even weak frontal lift, along with diurnal heating, should suffice to initiate convection over northern parts of the outlook area, with subtle large-scale support for the environment aloft preceding the approaching shortwave trough. The entire corridor will be characterized by pockets of strong diurnal heating amidst rich low-level moisture, with dewpoints commonly in the upper 60s to mid 70s F, along with high PW. Weak deep-layer wind profiles and related lack of shear should limit overall organization, with damaging to isolated severe gusts the main concern in the most intense multicells. ...AZ... Isolated severe gusts will be possible this afternoon into evening as convection moves over the well-heated/mixed desert boundary layer. One prominent midlevel perturbation in the aforementioned chain of them should move away from the area today. Though large-scale lift will not be as strong as the previous day, sustained heating should occur behind morning clouds/precip over the southeastern CA/southwestern AZ region. This will support scattered thunderstorms development this afternoon, initially over the higher ranges in southeastern AZ and parts of the Mogollon Rim. A more southerly mean-flow component today behind the trough will encourage northwestward cell motion, with perhaps some westward curvature where outflow pools accrete. MLCAPE values of 500-1000 J/kg (locally higher) and even larger DCAPE will support gust potential. ..Edwards/Broyles.. 07/31/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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