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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.

Monday, September 26, 2022

SPC Sep 26, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1228 AM CDT Mon Sep 26 2022 Valid 261200Z - 271200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE FLORIDA KEYS... ...SUMMARY... Risk for damaging winds and brief tornadoes will increase late Monday night across the Florida Keys. ...FL Keys... Tropical Storm Ian has progressed to near 17N/81W as of late this evening and is forecast to strengthen into a major hurricane by the end of the day1 period as it tracks across the western tip of Cuba. This evolution is expected to result in strengthening wind fields across the southeastern Gulf Basin, including the FL Keys late. Forecast soundings for EYW exhibit ample buoyancy for robust updrafts within a sheared environment that will support organized rotating updrafts, as tropical air mass already resides across this region. Supercell structures are expected to materialize within the outer bands which should encroach on the Keys primarily after midnight. ...Northeastern US... Strong 500mb speed max is forecast to track into southern OH by the start of the day1 period, then progress to the southern New England Coast by 27/00z. Cooling mid-level temperatures (500mb temperatures CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SZ0L6v

Sunday, September 25, 2022

SPC Sep 25, 2022 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1234 AM CDT Sun Sep 25 2022 Valid 261200Z - 271200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The severe-thunderstorm threat is expected to be low on Monday. ...Synopsis... A deep mid/upper-level trough over the eastern CONUS is forecast to move only slowly eastward on Monday, while a weak upper ridge will persist over the Southwest. A cold front is forecast to reach the Gulf and Carolina Coasts by late afternoon/early evening, as a surface ridge settles into the Plains and mid-MS Valley. Isolated thunderstorm development will be possible during the afternoon along the front before it moves offshore. Widely scattered thunderstorms will also be possible across parts of northern New England, though instability appears too weak to support a severe threat. ...South FL Peninsula/FL Keys... Tropical Storm Ian is forecast to intensify into a hurricane and approach western Cuba by late Monday night/Tuesday morning (refer to NHC forecasts and advisories for more information on Ian). It is possible that outer rain bands associated with Ian will begin to affect the FL Keys and far southern FL Peninsula before the end of the period, but uncertainty regarding the strength of low-level flow/shear prior to 12Z Tuesday precludes the introduction of tornado probabilities at this time. ..Dean.. 09/25/2022 Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SYxzYh

SPC Sep 25, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1205 AM CDT Sun Sep 25 2022 Valid 251200Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN APPALACHIANS INTO PARTS OF THE MID ATLANTIC AND SOUTHERN NEW ENGLAND... ...SUMMARY... Scattered severe storms producing large hail and damaging winds are expected from mid to late afternoon across the northern Appalachians and parts of the Mid Atlantic and southern New England through evening. ...Portions of the Appalachians, Mid Atlantic and southern New England... Within a larger-scale upper trough, a lead wave will move from the OH Valley to the Mid Atlantic during the day, providing cooling aloft and midlevel winds of 60-70 kt, enhancing shear. At the surface, low pressure will slowly deepen from Lake Huron into NY, with a front trailing southwestward across PA, WV, eastern KY and Middle TN by late afternoon. Meanwhile, a warm front will develop over southern New England, resulting in destabilization toward evening. Dewpoints will rise into the lower 60s F there, with upper 50s to lower 60s F southwestward along the front where heating and mixing will be stronger. The warm sector will become uncapped by around 18Z from PA southward across WV, VA, KY and TN, with further destabilization 21-00Z from NJ into southern New England. MLCAPE of 1000 J/kg will be common, with locally higher values. Deep-layer shear will be strong beneath the upper jet, with values around 60 kt common from eastern TN to the DelMarVa. Precipitation may be ongoing from OH into PA and western NY early in the day, north of the midlevel jet where temperatures aloft will be cold, and as warm advection around 850 mb translates east. Given cold temperatures aloft, some of this activity could produce small hail. As the air mass destabilizes beneath the cold air aloft, some of these storms may expand and become severe across PA and NJ during the afternoon, producing hail and wind. Later in the evening, additional storms may interact with the warm front where low-level shear will be stronger, and a brief/weak tornado could occur, depending on whether surface temperatures are warm enough for surface-based parcels. Farther south, southwest winds will maintain a moist air mass along the Appalachian Front, and heating will aid development after 18Z. Long, straight hodographs should favor fast-moving storms producing hail and wind. Additional isolated activity may occur into northern GA and AL along the front, primarily late afternoon and evening. ..Jewell/Wendt.. 09/25/2022 Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SYxzJZ

Thursday, September 22, 2022

SPC Sep 22, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1221 AM CDT Thu Sep 22 2022 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MID-ATLANTIC AND NEW ENGLAND COASTS AND OVER PORTIONS OF THE NORTHERN HIGH PLAINS... ...SUMMARY... Thunderstorms with damaging winds will be possible this morning into the early afternoon hours from the Mid-Atlantic to the New England coasts. Strong to severe winds are also possible across portions of the northern High Plains this afternoon. ...Synopsis... Early-morning water-vapor imagery reveals an upper-level wave continuing to slowly amplify over the Great Lakes region as it migrates east. At the surface, an associated surface low over eastern Canada will undergo some deepening over the next 12-24 hours as it lifts northeast. A trailing surface cold front is noted in surface observations stretching from the Lower Great Lakes into the central Plains. Thunderstorm coverage has increased along this front across portions of PA and NY during the 04-05 UTC period with additional development likely through the late morning hours. To the west, an upper low over the northern Great Basin/northern Rockies will meander to the east/northeast, supporting ascent and thunderstorm chances across portions of the northern High Plains this afternoon. ...New England and Mid-Atlantic Coasts.... Elevated thunderstorms will likely be ongoing at the start of the period across the New England region due to a combination of focused ascent along the front and 500-1000 J/kg MUCAPE. Mean flow along the boundary will maintain a linear mode with winds in the 925-850 mb layer strengthening to 35-45 knots between 12-16 UTC. Limited diurnal heating will modulate low-level lapse rates and the potential for convection to become rooted in the boundary layer. However, more robust downdrafts may mix the stronger low-level winds to the surface and support isolated damaging winds. The wind threat may increase for locations that can see temperatures climb into the low 70s via daytime heating by late morning, but this scenario appears limited and will likely be confined closer to the coast. To the south across the Mid-Atlantic/Carolinas, thunderstorm development is expected along the front by early to mid afternoon. While mid-level lapse rates will be modest, steepening 0-3 km lapse rates and gradually increasing deep-layer shear will support a few strong cells capable of isolated damaging winds. Isolated to scattered thunderstorms are likely along the front into the Southern states, but weak deep-layer flow will limit the potential for organized severe convection. ...Southeast Montana and Northeast Wyoming... Increasing mid-level flow and upper-level difluence ahead of the Great Basin upper low will support lee troughing along the northern High Plains through the day. 7-8 C/km mid-level lapse rates, sampled in upstream 00 UTC soundings, are expected to advect into the region by mid afternoon amid the west/southwest flow regime. Modest moisture in the 850-700 mb layer should support adequate buoyancy for convection within the left-exit region of the upper-level speed max. Storms maturing in a deep, well-mixed boundary layer to the west of the sharpening surface trough will be capable of a few strong to severe wind gusts. ..Moore/Jewell/Weinman.. 09/22/2022 Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SYn0Jt