Major Pattern Change: Last sub-zero night? 40s ahead?

There may be an outbreak of spring fever in Minnesota next week.

A major change in the upper air pattern over North America will bring a prolonged period of milder weather in the next two weeks. While more sub zero nights are likely in northern Minnesota, tonight could potentially be the last sub-zero night this winter in the metro.

(There's always a shot we get one more sub-zero night in early March, but the chances for another sub-zero night in February are fading with each model run.)

A look at the numbers:

5: of 9 days in February at or below zero so far in the metro.

17: season total # of days at or below zero in the metro.

30: average # of days at or below zero in winter for the metro.

So even with a colder than average December (-2.3 degrees) and January (-1.1 degrees) it looks like the metro will end up with a much lower than average number of sub-zero starts this winter season.

Increased daylight plays a role:

We're gaining 3 minutes of additional daylight per day this time of year. That's 21 minutes per week. That means less time for "radiational cooling" at night, and the sun is up earlier each day to begin the diurnal warming process.

The sun angle is also considerably higher in the sky compared to December. We're now getting twice as much incoming solar radiation as we did on December 21st. That extra energy helps "modify" air masses that do come south in the coming weeks, meaning they tend to be milder.

It gets tougher by the week to generate sub-zero cold, especially south of 45 degrees north latitude, which is where the Twin Cities sits on the map.

My hunch is we'll probably get one more sub-zero morning in early March as we typically do, but it's also possible that Thursday morning may be the last sub-zero reading of the winter at MSP airport.

The "world sunlight map" is a cool way to see daylight and darkness on the globe at any given time.

Prolonged thaw ahead!

As the upper winds begin to blow form the north Pacific instead of the Arctic by Friday, temperatures will respond. The reason is that the source region of Pacific air masses is, as you would infer, the Pacific Ocean. The water temperatures under the air are in the 30s and 40s, and that interaction determines the low level temperatures in the incoming air mass.

Take a look at the expected temperatures in the next week or so.

First 40 of 2011 next week?

We could see 4 or more days above the thawing mark in the next week or so. We may also feel the first 40 degree temperature of 2011. The last time we had a string of 4 consecutive days at or above freezing was November 17th! Our last 40 degree reading was December 30th (42 degrees).

When you add it all up you can see that we are on the verge of a major seasonal change in Minnesota. I'm not sayin' spring is right around the corner and that winery weather is over...I'm just sayin' I think we're done with the prolonged deep freeze stuff (and just maybe sub-zero temps in the metro) for this winter.

PH