THE THURSDAY WEATHER HEADLINES

–Record temps fell today. Chicagoans enjoyed a day of mid-70-deg warmth, readings more typical of mid-September than early November. In other words—the 76 at O’Hare and the 77 at Midway were readings more typical of what’s normal here nearly 7 weeks earlier.

–A SEA CHANGE IN THE WEATHER PATTERN IN CONTROL HERE IN CHICAGO IS TO BRING THE SEASON’S COLDEST AIR YET—AIR COLD ENOUGH TO GENERATE SNOW FLURRIES SATURDAY

–By nightfall tomorrow (Friday), temps will have dropped to levels more than 30-degrees colder than now. From late Thursday’s mid 70s, temps by 5pm Friday night will have fallen to the upper 30s and low 40s.

–Snow over the West and the Plains and across Canada has led to a snowpack which now covers 20% of the Lower 48—far more than the 0.1% of the country with a cover of snow a month ago. That’s important. Snow cover reflects sunlight. That means cold air from the arctic regions is able to surge farther south shielded to a great degree from warming by the reflective snowpack to our northwest.

–The expansion of cold air across the country will be eye-catching. While 33% of the Lower 48 saw temps at or above 70-deg today, by Sunday, only a little over 1% of the Lower 48 will see daytime 70s.

–By Friday morning, sub-freezing low temps are to occur over 51% of the Lower 48. The area below freezing will expand to cover 73% of the continental U.S. by Sunday morning.

–Modeling suggests EACH OF THE NEXT 15 DAYS from tomorrow forward will see BELOW NORMAL TEMPS

–Maintaining the chill much of the coming two weeks will be the development of an unseasonably mild pool of air aloft over the northwestern sections of North America. This will lead to a northward buckle in the jet stream into Alaska and northwest Canada. When then happens, upper steering winds sweep southeastward from there into the Lower 48 guiding reinforcing cold surges into the area.

–While this week is likely to average 47.7-deg, the new pattern is to produce an average temp of 29.8-deg next week. THAT’S A DROP OF 11-DEG, which is a truly significant drop for a weeklong period.

–While snow flurries may occur in an unstable atmosphere Saturday, a weather system could bring some snow or a wintry mix to the area Monday night and Tuesday.  And modeling suggests additional chances for at least flurries in the week that follows.

HERE’S THE LATEST THURSDAY CHICAGO METRO FORECAST

TONIGHT: More clouds arrive late. Chance of a sprinkle or brief shower in spots toward morning. Breezy and turning cooler. Lows by morning near 43—but mid to upper 30s inland.

FRIDAY: Morning cloudiness, possibly a sprinkle. Turning partly sunny, windy and noticeably cooler. High 47—but steady or slowly falling readings with temps in the upper 30s or low 40s by dark.

FRIDAY NIGHT: Cloudy periods develop late, blustery and colder. Snow flurries are possible in Saturday’s pre-dawn. Low 31—even mid 20s coldest inland locations.

SATURDAY: THE COLDEST AIR IN MORE THAN 7 MONTHS TAKES HOLD THIS WEEKEND. Clouds dominate—only passing peeks of sun possible but they’ll be fleeting. Cold and blustery with some snow flurries at times. Lake-effect rain and snow showers in sections of northwest Indiana and across the lake in western Michigan. High 38—a reading more than 30-deg colder than last Saturday and 12-deg below normal.

SUNDAY: Sun mixes with some clouds, cold. High 40.

MONDAY: Cloudier than not. Chilly. High 40.

TUESDAY: Cloudy with some snow and, at times, rain or a wintry mix. High 39.

WEDNESDAY and THURSDAY: Variably cloudy, cold. Chance of several snow showers or flurries—possibly a bit of mixed rain with them. High Wednesday 37. Thursday’s high 34.