From freezing to 70s; Dueling winter forecasts?

Welcome to Minnesota's temperature roller coaster.

Fall is a season of rapid weather changes in the Upper Midwest. The jet stream snakes overhead this time of year, driving waves of passing low pressure and more frequent fronts our way. Minnesota lies in the battle zone between the last whiffs of summer, fall and the first salvos of winter. Get ready for another series of noticeable temperature corrections in the next few days.

Canadian air mass

Air masses are classified by the properties of that air they carry. Minnesota's location in the middle of a continent with no major mountain ranges or oceans nearby means air masses of all flavor sweep freely overhead.

Our current air mass is of the continental polar (cP) variety -- little moisture and cool clean air from source regions in central Canada. Our Canadian neighbors are increasingly generous with cP air masses as we move through fall. Watch the big blue "H" slide south. That's the high pressure center of our inbound air mass.

Freeze warnings expand

The perfect recipe for the first freeze of the season in the Twin Cities and much of southern Minnesota? Clear skies, calm air and longer nights. Freeze warnings and frost advisories blanket all or parts of at least 13 states Friday morning across the Midwest.

The freeze zone shifts east by Saturday morning, and will include the first freeze of the season for the inner Twin Cities metro core. Time to clip those last roses of summer and cover the Supertunias.

Here's a close look at forecast lowest temperatures Saturday morning around the Twin Cities. Deep blue on the maps these days.

Warming trend kicks in

Our weekend features frosty mornings and sunny cool afternoons. Thermometers start to nudge higher by Sunday afternoon. By Monday, full on southwest breezes push temps back to September levels. Yes mild weather fans, we're not done with the 70s just yet.

NOAA: Mild winter likely for Minnesota

This is not a big surprise if you've been listening to my weather chats, Climate Cast or reading this space. Penn State climate expert Dr. Michael Mann and I touched on the blooming El Niño and the winter forecast on today's Climate Cast.

Here's more on why NOAA's winter outlook banks on the Uber-Godzilla El Niño favoring a mild winter across the northern tier.

Forecasters at NOAA’s Climate Prediction Center issued the U.S. Winter Outlook today favoring cooler and wetter weather in Southern Tier states with above-average temperatures most likely in the West and across the Northern Tier. This year’s El Niño, among the strongest on record, is expected to influence weather and climate patterns this winter by impacting the position of the Pacific jet stream.

“A strong El Niño is in place and should exert a strong influence over our weather this winter,” said Mike Halpert, deputy director, NOAA’s Climate Prediction Center. “While temperature and precipitation impacts associated with El Niño are favored, El Niño is not the only player. Cold-air outbreaks and snow storms will likely occur at times this winter. However, the frequency, number and intensity of these events cannot be predicted on a seasonal timescale.”

The real El Niño-driven weather drama to watch this winter may be in southern California. Strong El Niño winters favor firehoses of moisture known as 'atmospheric rivers' that can dump feet of rain across California.

Prediction: The Pineapple Express makes national news once again in the coming months.

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Cohen: Not so fast on mild winter?

Siberian snow cover in fall is one of the sexier new winter forecast tools. Extensive Siberian snow cover has been linked to a negative phase of the Arctic Oscillation. A negative AO favors cold Polar Vortex style arctic outbreaks in the eastern United States.

Capital Weather Gang's Jason Samenow has more on why Siberian snow cover has some thinking a cold winter could still be in store for the eastern United States.

Every October, seasonal forecasters pay close attention to the trends in snow cover in Siberia, as they have shown to have some relationship with winter weather conditions in the eastern United States. When Siberian autumn snow is expansive and increases quickly, it tends to favor a cold winter in the East; whereas, when it’s scarce, a mild winter is more likely.

The meteorologist who discovered this relationship, Judah Cohen ofAtmospheric and Environmental Research, says this October’s Siberian snow cover is off to a fast start, which may portend another cold winter for the East.

“I think that [the Siberian snow cover] will be above normal,” Cohen said in an e-mail. “[But] it is lagging the two blockbuster Octobers of the past two years.”

In technical terms, above normal Siberian snow cover in the fall is strongly linked to the negative phase of the Arctic Oscillation (AO) during winter. A negative AO is associated with a weaker polar jet stream that tends to stray more into the mid-latitudes, unleashing blasts of Arctic air.

“The predictors that I look at all seem to be indicating to me a negative bias for the upcoming winter AO,” Cohen said. “Of course, a negative AO increases the chance of a cold winter in the eastern U.S.”

At this point my money is still on El Niño for a milder than average winter overall for Minnesota. I'll be making my full winter forecast in the first week of November.