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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.

Wednesday, June 16, 2021

SPC Jun 16, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Wed Jun 16 2021 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN ILLINOIS INTO WESTERN PENNSYLVANIA...AND SOUTHWARD TOWARD THE OHIO RIVER... ...SUMMARY... Scattered severe storms will be possible Saturday across Illinois, Indiana and Ohio, and toward the Ohio River. A few strong to severe storms may also occur into western New York and Pennsylvania, and across northern Missouri and Kansas. ...Synopsis... A strong shortwave trough will move from the upper MS Valley across the upper Great Lakes through 00Z, and into the northeastern states by Saturday morning. Cooling aloft will occur through the period across these areas, with increasing midlevel westerlies enhancing shear. The primary surface low will move from eastern Ontario into western Quebec, with lowering pressures extending south to the OH Valley. Southwest surface winds will result in an expanse of 65-70 F dewpoints from the lower MO Valley eastward toward western PA by 12Z Saturday. Several areas of severe storm potential are expected to develop over this broad zone from IL to PA, beginning over IL and IN early Friday. Elsewhere, a tropical low is forecast to move north across the western Gulf of Mexico, with increasing moisture and shear affecting southern LA and surrounding states. ...Midwest/OH Valley... Storms, possibly with wind threat, may be ongoing Friday morning across IN, but are expected to wane with time. By afternoon, new development is expected in this region, as large-scale ascent increases. Initiation points may depend on outflow boundaries from early convection, but storms could develop with heating anywhere from IL to OH where 2000-3000 J/kg MUCAPE is possible. Increasing deep-layer mean wind speeds will favor forward propagating bows capable of damaging wind. Additional storms will be possible later in the day and overnight in the warm advection regime into NY and PA, where a cold front will eventually overtake the unstable air by morning. Portions of the Slight Risk may be upgraded categorically in later outlooks as predictability increases. Farther west across MO and into northeast KS, a front will stall, with moderate instability developing during the day. Lift will be weak, but deepening of the moist boundary layer may result in storms between 00-06Z, and localized strong gusts cannot be ruled out. ...Coastal LA and upper TX Coast... A low is forecast to move north across the western Gulf of Mexico, approaching the TX/LA coast by Saturday morning. Coincident with the low, wind fields and shear will also increase, along with tropical moisture aiding instability. A substantial amount of convection is possible from southeast TX into LA, and a couple tornadoes will also be possible should shear be as strong as currently forecast. ..Jewell.. 06/16/2021 Read more LIVE: spc.noaa.gov