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Weather conditions on bar directly above are near Lakefront. Tabs under Moon Phases refer to O'Hare (official).

Archives for SPC Convective outlook are updated daily with a live map a the beginning of the article. Touch or click map to get possible update, and follow link at end of article for referral to NOAA/NWS Storm Prediction Center. Archives for Chicago's hourly weather data were updated 24-48 hours after end of each day prior to Dec. 2020.

Thursday, April 21, 2022

SPC Apr 21, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1250 AM CDT Thu Apr 21 2022 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS... ...SUMMARY... A severe threat is expected to develop across parts of the southern and central Plains this evening. Large hail, along with an isolated tornado threat will be possible. A marginal severe threat may also develop across parts of the lower to mid Missouri Valley. ...Southern and Central Plains... A shortwave ridge will move east-northeastward across the central Plains today, with southwest mid-level flow becoming established in the wake of the ridge. At the surface, a warm front will advance northward into southern Kansas with a dryline in place from the eastern Texas Panhandle into northwest Oklahoma. To the east of the dryline and to the south of the warm front, a moist and unstable airmass will be in place. Surface dewpoints are expected to increase into the into the lower to mid 60s F by late afternoon. This will yield MLCAPE in the 1200 to 2000 J/kg range by late afternoon. However, a capping inversion will likely prevent convective initiation during the day. Isolated thunderstorm development will become possible in the early to mid evening, as low-level convergence becomes enhanced along the warm front, and as the low-level jet strengthens. Isolated thunderstorm development could take place across northern Oklahoma, central and eastern Kansas and far southeast Nebraska. Concerning the severe potential, moderate deep-layer shear will exist across much of the southern and central Plains, where 0-6 km shear is forecast to be in the 30 to 40 knot range. A plume of steep mid-level lapse rates will also be in place from the Texas Panhandle northeastward into southern Kansas. Storms that initiate in the stronger instability and near the plume of steep mid-level lapse will likely become supercellular and produce large hail. The low-level jet will markedly increase low-level shear during the evening, which could result in an isolated tornado threat with any supercell that can overcome the cap. There is conditionality with this forecast, due to a lack of large-scale ascent. As a result, only two or three surface-based thunderstorms are expected to develop in the central Plains, but the severe potential will be considerable with any updraft that can become rooted in the boundary layer. ...Lower to Mid Missouri Valley... Westerly mid-level flow will be in place today from the lower Missouri Valley eastward into the mid Mississippi Valley. A shortwave ridge will approach from the west, as moisture advection takes place across the central Plains and lower Missouri Valley. The nose of the low-level jet is expected to become focused across northeast Kansas and southeast Nebraska by early this evening. As a result, warm advection-related thunderstorm development is expected along the eastern edge of the low-level jet, from eastern Nebraska into western Iowa. Although instability will be weak this evening in most of the lower to mid Missouri Valley, strong deep-layer shear will be in place. RAP forecast soundings south of Omaha have effective shear in the 50 to 55 knot range, with 700-500 mb lapse rates approaching 7.5 C/km. This environment will support a hail threat with elevated storms that can develop in the weakly forced environment. The hail threat could affect areas further to the northeast across south-central Iowa and northeast Missouri as a cluster of storms moves northeastward during the mid to late evening. ..Broyles/Weinman.. 04/21/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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