Forecast: Last arctic blast of the season?

I love watching the weather maps this time of year.

March is here in just 6 days, and this is the time of year when we look for changes in the upper air pattern that can signal spring is on the way. Usually we get our last real shot of finger tip chilling arctic air in the next week, and then things can change for the better.

It looks like this may be the week we see our last sub-zero temperature in the Twin Cities this season.

Air mass modification:

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It's -31 this morning just north of Lake Winnipeg in Manitoba. That bone chilling air mass is oozing south today into Minnesota behind a brisk arctic cold front. Temperatures may plunge to -20 or colder in some of the chilliest nooks and crannies of northern Minnesota by Wednesday morning. In the metro temps should bottom out around -2 at Twin Cities Airport with -5 to -8 in the outer suburbs. (Read Lakeville)

After flirting with zero Wednesday and Thursday morning, temps will slowly climb as we head toward the weekend.

There's a reason we don't get to -31 in the Twin Cities even though the air mass is that cold to our north. It's called "air mass modification." Basically the higher sun angle and longer daylight as you move south injects enough solar energy into the air as it slides south to warm it up.

(Image courtesy UW Stevens Point)

Air masses modify for different reasons around different parts of earth. Coastal air masses are modified by cold or warm ocean currents. Other air masses are modified as they travel over mountains or the Great Lakes etc.

Great Lakes modify arctic air masses coming south from Canada by adding moisture and heat from warmer water. Result is heavy lake effect snow bands. (Image credit NASA)

There are signs that our upper air pattern may allow some ridging and a more southerly flow to develop next week. If this happens, we could see a significant thaw during the first week of March. That might boost temperatures well above freezing, and could signify our first big snowmelt of meteorological spring.

After that we'll have to keep an eye out for the big state tournament snow storm. There are signs a big wet sloppy storm could graze us as it passes south along about March 9th.

Stay tuned, and stay warm this week. Spring is closer than you think.

PH