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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.


Tuesday, July 18, 2023

SPC Jul 18, 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 0101 AM CDT Tue Jul 18 2023 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MID-MISSOURI VALLEY INTO THE LOWER OHIO VALLEY AND THE DAKOTAS.... ...SUMMARY... Thunderstorms associated with large hail and damaging wind gusts will be possible this morning/afternoon through Missouri and again overnight across parts of the mid Mississippi/Lower-Missouri Valley. Other strong to severe storms will also be possible in various parts of the US from the Great Basin and Southwest and from the Plains to the Midwest and East Coast. ...Synopsis... A mid-level ridge across the western CONUS will flatten this morning as a trough crosses Montana. Another somewhat convectively enhanced mid-level shortwave trough across the central Plains this morning will move southeast into the Tennessee Valley tonight. A broad mid-level trough across the Great Lakes into the Northeast will shift slowly east through the day. The surface pattern is more nebulous with a diffuse surface front extending from the Northeast across the southern Great Lakes and into the Plains. Across the Plains, a warm front will become better defined as a surface low develops across Kansas. An additional cold front, currently across eastern Montana, will move east across the northern Plains and become more defined through the day. ...Lower Missouri Valley to the Lower Ohio Valley... Current convective trends and surface analysis suggests a line of elevated storms across central Nebraska currently will likely intensify as it moves into greater instability across southeast Nebraska/northeast Kansas. Several members of the 00Z HREF support this evolution with several showing the potential for a well-developed bow echo moving across Missouri this morning and potentially through the afternoon into the Mid-Mississippi/Tennessee Valley region. Even if a mature bow echo can develop, the longevity may remain questionable due to downstream destabilization as a large cloud mass could inhibit heating downstream and perhaps limit the threat for a more significant severe wind threat. Late tonight and into Wednesday morning, elevated thunderstorms are expected to develop along a northwest-southeast oriented frontal zone in the vicinity of southeast Missouri. The location of this convection remains uncertain as the location of the frontal zone will augmented by the intensity/location of convection from the thunderstorms this morning. Nonetheless, wherever this boundary aligns, supercells will pose a threat for large hail given strong elevated instability and strong deep layer shear. Eventually, some upscale growth will be possible and a severe wind threat may develop across the Mid-Mississippi Valley closer to 12Z Wednesday. ...Northern Plains... A combination of low-level moisture advection and surface heating will lead to moderate to strong instability across central North Dakota and South Dakota by this afternoon. This instability, combined with convergence from a sharpening cold front and an approaching mid-level shortwave trough should be sufficient for storm development along the cold front this afternoon. 45 to 55 knots of mid-level flow will result in supercell wind profiles and a threat for large hail, some potentially 2+ inches. ...Mid-Atlantic to the Northeast... Weak, broad ascent across an uncapped and moderately unstable warm sector across the Mid-Atlantic and Northeast may result in isolated to widely scattered thunderstorms. Some stronger flow, particularly from New York northeastward will promote more storm organization and the potential for rotating updrafts. These longer-lived updrafts may pose some threat for isolated large hail and damaging wind gusts. ...Central High Plains... A few thunderstorms are possible late this afternoon as low-level flow veers from northeasterly to easterly and becomes more upslope with low-level moisture advection on the northern periphery of the surface cyclone. The favorable period may be relatively short-lived since moisture arrives late, but a favorable environment may develop with 2000+ J/kg MLCAPE and a supercell wind profile. ...Great Basin... A deeply mixed airmass is expected today across the Great Basin with ample instability for scattered thunderstorms across much of the region. A belt of stronger mid-level flow around 30 knots will exist from east-central Nevada and across north-central Utah. This may support some storm organization with the potential for isolated severe wind gusts given the deeply mixed sub-cloud layer. ...Southern Arizona... Weak to moderate instability is expected to develop across southeast Arizona today with a LCL around 3000m. Shear will be weak in the region with less than 10 knots of flow through the troposphere, which will limit storm organization. However, this instability, coupled with sub-cloud evaporative cooling in the well mixed airmass may support some strong to severe wind gusts this afternoon/evening. ..Bentley/Wendt.. 07/18/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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