Temps | Gusts | WU KORD KPWK

CLICK for this month's BIG night sky ...




Cardinal SAT


MOBILE DEVICE? Turn sideways. Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

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.


Tuesday, July 25, 2023

SPC Jul 25, 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 0751 AM CDT Tue Jul 25 2023 Valid 251300Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN PARTS OF THE NORTHERN PLAINS/UPPER MIDWEST AND MID-ATLANTIC REGIONS... ...SUMMARY... Scattered severe wind/hail-producing thunderstorms are possible across parts of the Northern Plains and the Northeast this afternoon and evening. Isolated severe gusts are also possible over portions of the Interior West. ...Synopsis... In mid/upper levels, a large, synoptic-scale anticyclone will remain anchored over the southwestern CONUS, with a 598-600-decameter central 500-mb high over northern/western NM. Ridging will extend eastward across the southern Plains and Ozarks, and northward over the northern High Plains. A shortwave trough -- apparent in moisture-channel imagery over portions of MT/WY, will penetrate the larger-scale ridge through about 18Z, then pivot southeastward, reaching the Red River Valley of the North by 00Z, and the upper Mississippi Valley by 12Z tomorrow. Convective enhancement is quite probable overnight, with potential for MCS activity immediately preceding the pre-existing vorticity lobe. Upstream, an elongated cyclone now over coastal BC will move inland, reaching central AB by the end of the period, with a low-amplitude/ positively tilted trough across the ID Panhandle to near AST. Further east, a mean trough will linger over the eastern CONUS, roughly from a persistent Hudson Bay vortex southward to the southern Appalachians. However, this trough should deamplify somewhat, as a strong, basal shortwave perturbation -- initially from Lake Erie over OH, WV and northeastern TN -- ejects northeastward to inland parts of the Mid-Atlantic States and western New England by 00Z. At the surface, 11Z analysis showed a warm to quasistationary front from northwestern ND southeastward over central SD, southwestern IA, northeastern MO, and southern IL. This boundary should move diffusely northeastward through this evening over more of the eastern Dakotas, southwestern MN, IA and southern/central IL. A weak front/surface trough was drawn over central NY, east-central PA, and central VA, with some eastward shift expected today mainly north of VA. ...Northern Plains/Upper Midwest... Large-scale ascent preceding the shortwave trough will be well-timed to impinge on a favorably moist and destabilizing warm sector this afternoon. Scattered thunderstorms are expected to develop from the central Dakotas southward into NE near the surface fronts/trough, with severe hail and gusts each possible. Greater coverage and duration of convection may be with the Dakotas regime, where low-level convergence will be strongest, and where activity may evolve upscale and move southeastward as an MCS near the warm front. Diurnal heating and surface dewpoints generally in the 60s, beneath moderately steep midlevel lapse rates, will support a northward- narrowing corridor of warm-sector MLCAPE in the 2500-3500 J/kg range (locally/briefly higher). Low-level flow will be modest diurnally, limiting hodograph size. However, veering with height in the warm sector (and especially near the warm front) will boost effective- shear magnitudes into the 30-40 kt range, suggesting a mix of multicell and supercell modes is possible, and supporting an early hail threat before too much upscale development occurs. While still a conditional scenario (strongly dependent on early storm-scale evolution and how that regulates cold-pool growth/ strength), a corridor of relatively maximized severe-wind potential may evolve across the eastern Dakotas and portions of southern MN/ northern IA for several hours this evening, near and just to the left of the nose of a strengthening southwesterly LLJ. If confidence in this scenario increases based on 12Z and later numerical guidance, and/or mesoscale trends, greater wind probabilities may be added later today. In the meantime, the 15%/ "slight" unconditional line is extended downshear to give more room for this potential threat to evolve and run its course tonight. Another conditional scenario is for additional development near the warm front over the Siouxland area and western IA this afternoon, shifting eastward across the mid/upper Mississippi Valley ahead of an MCV left by ongoing convection over northwestern NE and southeastern SD. Progs are inconsistent with this in terms of timing, coverage, and even yes/no for sustained storms. This is not surprising, given the subtle nature of low-level forcing often found around summertime warm fronts. Still, the marginal line has been expanded somewhat as well to account for the possibility. ...Mid-Atlantic/New England... Scattered to widely scattered thunderstorms are expected to develop throughout this afternoon -- mainly over and east of the eastern rim of the higher elevations, from the northern VA Blue Ridge/Shenandoah regions northeastward to central ME. This will occur as low-level lift increases due to both diurnal heating and convergence near the surface trough, and as weak DCVA/large-scale lift spreads over central/southern parts of the outlook area ahead of the ejecting shortwave trough. Potential thunderstorm coverage and severe gust/hail probabilities remain relatively maximized around the Chesapeake Bay/Delmarva regions, where the greatest low-level theta-e and strong inland diurnal heating will yield the largest buoyancy available to the convective regime. Peak/preconvective MLCAPE in the 1500-2000 J/kg range will be possible. Although modest low/midlevel flow will limit bulk shear in roughly the lower half of the convective profile, strong mid/upper winds (up to about 100 kt near equilibrium/anvil level) may aid in storm organization, particularly in and near the area of greatest buoyancy. ...Northern Great Basin/Intermountain Region... Behind the departing shortwave trough, convective coverage will be rather uncertain near the mean ridge. However, sufficient mid/ upper-level flow will remain in place to aid in local/brief organization of isolated to widely scattered afternoon thunderstorms developing atop a deep, well-mixed boundary layer with very nearly dry-adiabatic subcloud lapse rates. This will support isolated severe-wind potential with the most vigorous cells. ..Edwards/Mosier.. 07/25/2023 Read more CHECK UPDATE ZOOM GRAPHIC
SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)