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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.


Friday, May 21, 2021

SPC May 21, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1253 AM CDT Fri May 21 2021 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF NORTHEAST COLORADO INTO THE NEBRASKA PANHANDLE... ...SUMMARY... A few severe thunderstorms capable of producing hail and isolated damaging wind gusts will be possible this afternoon and evening across parts of the central High Plains. ...Synopsis... A blocking pattern will persist across the CONUS today, as a longwave trough remains in place over the West, and an upper ridge persists over the East. Multiple MCVs will continue to move poleward around the western side of the ridge, with one such feature forecast to move into the upper Great Lakes today, while another moves into east TX from the Gulf of Mexico. A surface low is forecast to move northeastward along a frontal boundary across the northern Plains, while renewed cyclogenesis occurs in the vicinity of northeast CO and the NE Panhandle this afternoon. ...Central/northern High Plains... Thunderstorm development is expected by late afternoon across portions of the NE Panhandle into northeast CO, in the vicinity of the surface low, and potentially southward along a lee trough/dryline. While midlevel temperatures will likely be somewhat warmer compared to Thursday, low-level moisture may also increase slightly, resulting in MLCAPE of 1000-1500 J/kg east of the effective dryline and south of a cold front that will be moving slowly southward from southwest SD into northern NE. Effective shear of 35-45 kt will support organized convection. At least a couple of supercells are possible by late afternoon/early evening across northeast CO and the NE Panhandle. The primary threat will be large hail, though isolated severe wind gusts will also be possible, and a tornado or two cannot be ruled out with any discrete supercell that can move eastward into an environment characterized by somewhat more favorable low-level moisture/shear. Further north, scattered thunderstorms are expected to develop across western portions of the Dakotas, near and north of the cold front. The strongest of these storms will be capable of some hail, with strong wind gusts also possible with convection rooted closer to the surface near the front. ...Southern High Plains... High-based convection is expected to develop into the southern High Plains by late this afternoon. Isolated severe wind gusts will be the primary hazard, given the warm, deeply mixed boundary layer and moderate southerly low/midlevel flow expected to be in place. This threat will be diurnally driven and should eventually diminish with time this evening. ...Midwest into the Upper Great Lakes... A regime characterized by deep moisture and moderately enhanced low/midlevel flow will persist from parts of the Midwest into the upper Great Lakes today. As an MCV moves across the region this afternoon, there will be some potential for modest destabilization from eastern IA into southeast MN and much of WI. A couple loosely organized clusters and/or transient supercells cannot be ruled out, with an attendant risk of isolated strong wind gusts and a brief tornado. ..Dean/Wendt.. 05/21/2021 Read more LIVE:
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