Sunday, March 14, 2010

Record warmth - flood risk escalates

Paul's Conservation MN Outlook for the Twin Cities and all of Minnesota

Today: Fading sun as clouds increase. Winds: NW 10-15. High: 58.

Tonight: Mostly cloudy, a shower or sprinkle. Low: 39

Tuesday: Lot's of clouds, unsettled, a passing shower or two - cooler. High: 46

Wednesday: More sun, milder. High: 54

Thursday: Partly sunny, more like April again. high: 56

Friday: Cloudy with light rain (mixing with snow central and northern MN). High: 49 (falling)

Saturday: Chance of a little wet snow early, then clearing, cooler. High: 42

Sunday: Plenty of sun, closer to "average". High: near 40

Flood Risk Escalates. The latest NWS information is here.

Time Warp. Welcome to May folks! Here is a run-down of Sunday's highs across the state. Where the sun came out, and snow was sparse, temperatures shot up 20-25 degrees above average for mid March. Cue the chirping birds (and harps). Sunday was pure meteorological magic, at least across the eastern 2/3rds of Minnesota.

Good grief, what on earth happened yesterday? Talk about a "busted forecast!" Locals are much more tolerant when the weather turns out NICER than predicted. God help you if the weather is worse than anticipated, especially on a weekend (when outdoor plans hang in the balance).

64 in the shade, on March 14....? In the Twin Cities? It was warmer here yesterday than it was in Los Angeles and Atlanta. Freaky/disturbingly mild for mid March. What happened? The computer models were all hinting at low 50s, but a glaring lack of snow on the ground meant that the sun's energy (which is considerable - as high in the sky now as it was the first week of October) was able to heat up the ground instead of melt snow. Throw in a stiff northwest breeze capable of "mixing" the atmosphere. A layer of unusually mild air aloft warmed even more as it descended toward the ground, compressing/warming along the way, warming the air in the 60s - more like May. We set a record yesterday, 64 is the warmest temperature ever recorded in the Twin Cities on March 14, at least during modern-day records, which date back to 1891. You just lived through a truly historic spell of weather, proof positive that March can truly bring anything: blizzards, floods, tornadoes, and yes - record warmth.

Minnesota Meltdown. Although there is precious little snow left from the Twin Cities to St. Cloud, as much as 10-15" of snow remains across much of southwestern Minnesota (closer to the storm track much of the winter). There is still 4-8" of water locked up in that snow pack. With highs predicted to reach 50s today across most of Minnesota a significant amount of that water will be flushed into area watersheds, increasing the threat of flooding days and weeks from now.

We can go back and reconstruct what happened, but here's the truth: the computer models (and yes, meteorologists) are not very good at predicting "record events". There is always a built-in bias to favor "average weather" for a given date. The models assess the current state of the atmosphere, temperatures at all levels of the atmosphere and how the fluid of air we call the atmosphere SHOULD behave over time, but there is always a built-in bias to temper the extremes, limit the highs and lows - everything should be close to "average" for a given date.

What month is this? Check out Sunday's highs across the state. The Twin Cities high of 64 broke the old record of 62, set most recently in 1990. Eau Claire, WI registered an awe-inspiring 66 F! For the record the average high for March 14 is 39. What happened to "average"?

The rate of snow melt during the first half of March has been nothing short of staggering - most towns have lost 10-15" of snow in 13 or 14 days, which is pretty amazing, all things considered. This has profound implications trying to predict the "high" for the day, but the computer models were essentially useless yesterday. That sounds like I'm trying to pass the buck and "blame the computers", and that may be partially true, but here's a dirty little secret: meteorologists, as a rule, as a profession, do a pretty lousy job predicting RECORD EVENTS. We are taught to be conservative, not to deviate too much from what the raw model output is telling us. If you go out on a limb, 98 out of 100 days, you will be wrong. But that 2% of the time you'll be making excuses, like my colleagues and I are making today.

Do you have spring fever yet? Were you awake/sober/conscious yesterday? What a glorious Sunday, sunnier than the models were hinting, and as an extension, 10-15 degrees warmer than even the most optimistic model was predicting. Live and learn. Yes, this is a humbling profession.

Sunday PM visible satellite. The models underestimated the amount of dry air filtering into Minnesota from the north and east yesterday. More sun + lack of snow + unusually mild air aloft = record highs for much of Minnesota, temperatures more typical of late April or early May.

The risk of significant flooding is increasing (rather dramatically) as a result of the unusual warmth, coupled with last week's significant rain event, anywhere from .5 to 1" of rain across much of the region, which accelerated the snow melt statewide. The problem: the ground underfoot is still frozen (and saturated, the result of ample rains last fall). That means melting snow and falling rain can't soak into the ground, but almost immediately runs off into streets, storm sewers and rivers, and that has implications for Minnesota's flood threat.

* Click here to read the latest NWS warnings with a complete run-down on area rivers, and which towns are most threatened. The threat won't subside for a couple of weeks, probably not until the first or second week of April. More warnings from the NWS are here.

A wrinkle of cold air aloft may spark a few (rain) showers from tonight through Tuesday, skies clearing by midweek, resulting in more unusual warmth for mid March. A cold rain arrives Friday, ending as wet snow Friday night and first thing Saturday, a coating of slush can't be ruled out across central and northern Minnesota. Skies clear over the weekend before the next chance of a rain/snow mix, around Tuesday of next week, a little more than a week away. We WILL chill down early next week (don't retire the heavy jackets just yet) but long-range (GFS) guidance is suggesting more 60s by the end of March, the last few days of the month. An early spring? Yep, but expect a few (brief/fleeting) wintry relapses in the weeks ahead. It's as likely, as imminent as taxes and more political gridlock in D.C.

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