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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.


Saturday, September 23, 2023

SPC Sep 23, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1257 AM CDT Sat Sep 23 2023 Valid 231200Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MISSOURI VALLEY INTO NORTHEAST OKLAHOMA... ...SUMMARY... Thunderstorms, associated with large to very large hail, wind damage, and tornadoes, will be possible today across eastern parts of the Great Plains, and Mississippi Valley. A couple of tornadoes are also possible in parts of the Mid-Atlantic. ...Eastern Great Plains/Mississippi Valley... Early-morning water-vapor imagery depicts a well-defined upper low over northern WY, advancing east toward the Black Hills, in line with latest model guidance. 60kt 500mb speed max is forecast to translate across NE to near FSD by 18z, then into northern MN during the overnight hours. This evolution will encourage a surface low to lift into northeast NE by 18z, with some deepening expected during the latter half of the period as the low occludes over southeastern ND by 24/12z. A north-south cluster of strong convection has evolved ahead of the upper trough over the High Plains from western NE into southwestern SD. This activity may continue through sunrise as it propagates east, aided by large-scale ascent ahead of the trough. Additionally, latest model guidance suggests LLJ will strengthen ahead of this activity into western IA by mid day such that renewed development is likely. NAM aggressively strengthens the LLJ in excess of 60kt over south-central MN by late afternoon. Wind profiles and low-level shear will strengthen ahead of the deepening surface low. This supports the potential for supercells across the upper MS Valley, especially near/south of the northward-advancing warm front. Forecast soundings exhibit strong shear with substantial sfc-3km SRH, though lapse rates will remain weak. Aside from the threat for damaging winds with this pre-frontal activity, it appears environmental conditions also support a tornado risk. In addition to supercell threat, large-scale forcing may encourage some clustering and potential line segments. Severe risk will spread into central MN by late evening as the low occludes over the upper Red River (of the North) Valley. Farther south, high-level difluent flow will be noted across the lower MO Valley into eastern OK. 500mb flow is expected to strengthen south of I-70 to near the TX/OK Red River as weak height falls will be noted at these lower latitudes. Surface front will advance into eastern KS, arcing across central OK into northwest TX by late afternoon. Strong boundary-layer heating will be noted ahead of this wind shift, with surface temperatures forecast to rise into the mid 90s to near 100F from portions of western OK into northwest TX. As a result, convective temperatures will be breached as CINH is reduced. Scattered thunderstorms should readily develop along the wind shift, initially over eastern KS, then southwest along the boundary at least into central OK. Forecast soundings exhibit seasonally steep lapse rates with high PW values (approaching 2 inches). Wind profiles strongly favor organized convection and initial activity should be supercellular in nature. With time, one or more MCSs may ultimately evolve over the ENH Risk area, with southward propagation expected across eastern OK/western AR late in the period. Hail should be common with the initial activity, some of it likely exceeding 2 inches in diameter. While a few tornadoes may be noted with the supercells, storm mode may ultimately lead to a complex that could produce damaging winds as convection spreads southeast during the overnight hours. ...TS Ophelia... Ophelia will soon move onshore along the NC Coast, then advance inland before arcing northeast toward the Delmarva late in the period. Strong low-level shear will develop across the southern Middle Atlantic east of the low track. Convection that develops across this region will be sufficiently sheared for supercells and possibly a few tornadoes, in addition to gusty winds. ..Darrow/Moore.. 09/23/2023 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)