Mild weekend, early signs of a warm summer of 2016?

I'm watching wilting snow piles at the Weather Lab this weekend. Emerging grassy patches expand.

Friday's odd and blustery spring-like weather across Minnesota included some pretty unusual radar returns for February. Rain, embedded hail and thunder in February? Friday's Twin Cities National Weather Service tweet below is more typical for April.

The bigger picture? The frequency of winter rainfall in Minnesota and most of the U.S. is increasing as our climate warms.

The Twin Cities is No. 5 in the list of U.S. cities recording an increase in winter rainfall. That means less precipitation is falling as snow, exactly what has been modeled by researchers like Dr. Peter Snyder at the University of Minnesota.

Gusty mild Pacific winds eat away at what's left of the snow in Minnesota this weekend. Temperatures run 10 to 15 degrees above average. That spring in your step Saturday? A weekend, plus a little twang of pre-spring fever.

In typical stoic Minnesota fashion don't get too far over your skis this weekend, a cooler air mass blows in next week with temps closer to average for the last week of February.

Winter is not done with us in Minnesota just yet. But the writing is on the proverbial weather wall.

• 45 degrees high at MSP Airport Friday

• 30 degrees average high for February 19th

• +15 degrees vs. average

• 52 degrees high at Canby in western Minnesota Friday

Shallow frost depth

Frost depth across Minnesota is remarkably shallow for this time of year. Take a look at real-time temperature data from the sod soil plot from the University of Minnesota's St. Paul Campus.

I can't remember a time when the frost depth was 5 inches in Duluth in mid-February.

Fast moving weather systems

A series of weather systems zips eats across Minnesota in a fast moving upper flow the next few days. We're in between systems on a spring-like Saturday.

Sunday brings a wintry mix of rain, sleet and snow as the next low pressure system zips by.

Temperatures return closer to average next week in the Upper Midwest. Here's the quick look at how the European Centre for Medium-Range Weather Forecasts model data break down for the next week in the Twin Cities.

Mild spring?

The latest National Oceanic and Atmospheric Administration seasonal outlooks out this week favor a milder than average spring in Minnesota.

Mark Seeley expands on thoughts on a milder than average spring this year across the Upper Midwest in this week's Weather Talk.

The NOAA Climate Prediction Center released new seasonal outlooks on Thursday of this week (Feb 18). The ensemble forecast of monthly anomalies favors a warmer than normal spring for Minnesota, March through May. The confidence or probability for this forecast is close to 70 percent.

An early spring seems relatively assured. The outlook for precipitation anomalies over March through May is less certain for Minnesota with equal chances of above or below normal values for much of the state, and slightly favoring drier than normal conditions this spring in northern counties.

Warm Summer of 2016?

Looking further ahead into the Summer of 2016, there may be some early signals for a warm bias this summer in the Upper Midwest. The record El Nino event that brought us a mild winter is forecast to fade quickly this summer.

Some of the climate models are projecting we may rapidly see tropical Pacific Ocean temperatures plunge this year, and possibly transition quickly into a cool La Nina phase by next winter.

NOAA’s Climate Prediction Center is projecting a very common pattern of a quick transition from a strong El Nino to ENSO neutral or even La Nina by next winter.

Predicting summer temperature and precipitation trends is more challenging than predicting winter trends with ENSO cycles. There is statistically less skill in summer.

That said, I ran some numbers this week on historical years when we've gone form a moderate (+1.0 C) El Nino events into a cool La Nina phase the next winter. It's a very small sample size, so I would take these with a grain (or shaker) of salt.

Still with low confidence, there may be some trends that favor a warmer than average summer across Minnesota this year.

There are 7 cases since 1964 when at least moderate La Nina events (+1.0C ) were followed the next year by La Nina events. This is hardly rock solid, but it may offer some clues to next summer.

• 5 of 7 (71%) of (El Nino-La Nina) summers (Jun-Aug) were warmer than average in the Twin Cities.

• The average of those 7 summers was +1.5F at MSP.

• The average number of 90-degree days in those 7 summers was 20 days. That’s almost twice the 30-year average for 90-degree days in the metro which is now 11 days. (1981-2010 data)

• 5 of the 7 years (71%) were also drier than average, with summer rainfall -2.42” vs. average overall. But there was high variability here with two wet summers also.

• 1988 is one of the summers in the data set. 1988 was one of the hottest and driest summers on record. 1988 set the record of 44 days at or above 90 degrees at MSP.

• 2010 is also in the data set. We set a record of 113 tornadoes in Minnesota that year.

• The 7 cases produced an average of 40 tornadoes per year in Minnesota.

So the bottom line is there may be a bias toward warmer than average temperatures and a higher than average number of 90+ degree days after El Nino in summers that transition to La Nina. There was also a slight dry bias to those 7 summers. Keep in mind it’s a very small sample size and probably not statistically valid.

My hunch? I do think there a bias toward a warmer than average summer, with a higher than average number of 90-degree days this summer.

NOAA’s official seasonal outlook for June-July-August also favors a warmer than average summer over Minnesota.

My hunch is the summer of 2016 will deliver far more than the four days of 90+ degree heat we saw last year. We may also see a more active severe weather season this year.

Stay tuned.