Weather over the Lower 48 is pulling a radical switcheroo

They say, “If you don’t like the weather, wait 15 minutes.” For the next few days, the adage may not be that far from the truth. A dramatic seasonal reversal is set to scramble the air masses over the Lower 48, replacing summerlike warmth with chilly conditions in the West. The opposite will occur in the East as rather toasty temperatures overtake an acute autumn chill.

The national weather map has been a tale of a nation divided, with a highly amplified, or wavy, jet stream slicing across the heartland. The weather will remain split over the next week, but the warm and the cold will trade places. This will mean some remarkable temperature swings – in some places up to 70 degrees.

Amid this bifurcated weather pattern, dozens of records for heat, cold and even snow have already fallen. Marquette, Michigan, saw its heaviest two-day snowfall observed in October. A whopping 18.1 inches fell between Monday and Tuesday, pasting the city with a sludge-like snow. Just days later, even the nighttime lows are above freezing, with daytime highs heading toward the mid-60s.

Omaha – which dipped to 16 on Tuesday morning, its coldest on record so early in the season – is forecast to soar into the upper 80s by Sunday.

Earlier this week, a dip in the jet stream was present over the eastern U.S., helping cold air spill south. That air had origins as far away as Siberia. It passed over the Chukchi Sea north of the Bering Strait and then slipped over Canada before descending over the north-central United States.

As the frosty air passed over the comparatively lukewarm Great Lakes, it allowed for the development of lake-effect snow streamers. In addition to the snow that came down in Marquette, Gaylord in northern Michigan saw 3 inches, and lake-effect snows brought a couple of inches to parts of Pennsylvania and New York state.

Cold-temperature records were also set from the Northern Plains to the Southeast. Among them:

• Several record lows were set in Tennessee on Friday morning. Chattanooga tied a record low of 31 degrees, and Knoxville tied a record of 32. Jackson established a record of 28.

• Florence and Myrtle Beach, South Carolina, tied or broke record lows Friday, dipping into the 30s.

-Numerous locations established their lowest temperature on record for so early in the season Wednesday or Thursday: Tallahassee (31, Thursday); Macon, Ga. (29, Thursday); Tulsa (26, Wednesday); Augusta, Ga. (30, Wednesday); Springfield, Mo. (21, Wednesday).

• Cedar Rapids, Iowa, hit 16 degrees on Wednesday morning, beating the record of 19 degrees set in 1972.

• Montgomery, Alabama, recorded its earliest first freeze on Wednesday (previous record was Oct. 20, 1989).

-Kansas City set a record morning low at 25 degrees on Tuesday.

Across the West, a dome of high pressure brought sunny, albeit smoky, skies and unseasonable warmth. Seattle’s average mid-October high is in the upper 50s to near 6o degrees; on Sunday, the city hit 88, smashing the daily record. It also marked the latest in the year a reading that warm has ever been observed. Portland, Ore., has reached at least 80 degrees on a record 12 days this month. Consider that the previous record year – 1982 – only saw half as many such days.

Numerous record highs were also set in California during the week, with afternoon temperatures reaching near 90 in Northern California and the mid-90s to near 100 in the Central Valley and south. On Wednesday, Los Angeles and Long Beach tied record highs of 93 and 95 degrees, respectively; highs near 90 set records in the Bay Area; and Redding hit 99, its hottest Oct. 19 ever observed.

The current theme of the atmosphere is “out with the old, in with the new.” The upper-air pattern is essentially flip-flopping, with an extended period of cool weather set to become entrenched in the Pacific Northwest and along the West Coast while a resurgence of warmth builds into the East.

Record highs in the 80s and even some 90s are possible in Texas and parts of the Plains over the weekend.

Columbus, Ohio, will approach 80 degrees on Sunday and Monday, a far cry from the average high of 64. Forecast highs in Chicago are near or above 70 through Tuesday. Its average high is closer to 60.

Washington, D.C., where highs have been stuck in the 50s for several days this week, will spike into the 70s beginning Monday and lasting through much of the week.

The West will see temperatures fall below average. Readings in the Intermountain West will dip into the teens and 20s by Monday morning, with a few record-challenging lows possible. Highs, only forecast to reach the wintry 30s and 40s, will be 20 to 30 degrees below normal. In Salt Lake City, snow may mix with rain on Sunday and Sunday night. Denver could also have a few snowflakes Sunday night into Monday.

Seattle, where air quality alerts have been in effect due to smoke emanating from wildfires, will have highs in the 50s and intermittent rain over the coming days. While it’s not the balmy weather the city has enjoyed recently, it will at least purify the air.

Los Angeles, where the average high is near 80, is forecast to have highs mostly in the 60s and 70s over the next week.

Across the central U.S., a pair of developing storm systems will feed off the contrasting air masses. Low pressure will form along the Montana-Wyoming border on Sunday, shifting east. That will tug a cold front through the Rockies and central Plains, which could touch off some isolated severe storms. South-central Minnesota to northeast Kansas has been included in a level 1 out of 5 marginal risk on the Storm Prediction Center’s outlook, which means cities like Lincoln and Omaha, Kansas City, Sioux Falls, S.D., and Minneapolis ought to keep abreast of the forecast.

There could also be some strong to severe storms across the south-central Plains with a secondary low-pressure system Monday into Tuesday.