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Winter Returns

Winter Returns:


This week the Minnesota State Climatology Office posted the headline "Winter Returns" referring to the snow and cold front that dominated the state over December 4-5.

Prior to the passage of the cold front during the afternoon and evening of Monday, December 4th many climate stations reported new record high temperatures for the date, including: Rochester and Austin with 64°F; Albert Lea and Theilman with 63°F; Grand Meadow with 62°F; Minnesota City, Fairmont, Hastings, Caledonia, Winnebago, Waseca and Winona with 61°F, Amboy, Red Wing, and Preston with 60°F; Rosemount with 59°F; La Crescent with 58°F, MSP with 57°F, and a number of other places as well. In addition MSP reported a new record high dew point on December 4th of 55°F, and the 2nd highest dew point ever reported in the month of December (only a dew point of 57°F on December 5, 2001 was higher). With the high temperatures and high dew points during the afternoon a few thunderstorms developed across areas of southern Minnesota (Red Wing among others), and rainfall amounts of 0.20 to 0.40 inches were reported from some areas.

As the cold front advanced, precipitation turned over to snowfall and many areas reported from 2 to 4 inches of snowfall with this weather system, but the most outstanding features that got people's attention were the strong winds and the dramatic temperature drop. Most areas reported wind gusts over 40 mph and some areas reported winds as high as 50-55 mph. The temperature drops caught a number of citizens unprepared and rushing for their winter parkas. While the temperature dropped 30 degrees F in the Twin Cities with the passage of the cold front late in the day, many other areas saw greater temperature drop. For example at Winnebago the temperature dropped from 60°F to 15°F (45 degree drop), while at Grand Meadow, Owatonna, and Waseca the temperature dropped 47 degrees, and at Albert Lea and Austin it dropped 48 and 49 degrees, respectively.

With the fresh snow cover, high pressure, and clear skies temperatures remained well below normal most of the week. On the morning of December 7th (Thursday) Fosston reported -6°F and Cotton reported -4°F. At least a dozen other northern Minnesota communities reported subzero temperatures as well. Many southern and western Minnesota climate stations reported their coldest temperatures since last winter, including 5°F at Browns Valley, 4°F at Montevideo, Wheaton, Lakefield, and Kimball, 3°F at Otter Tail and Worthington, and just 2°F at Pipestone.

With the colder temperatures soils are starting to freeze up again as they did for a brief time last month. At the two-inch depth soil temperatures dipped into the upper 20s and low 30s F by Thursday of this week.

Weekly Weather Potpourri:


On Thursday of this week winter storm Caroline brought strong winds and large waves to portions of western and northern Scotland. Wind gusts from 70 to 90 mph and large sea waves closed coastal highways, as well as schools in areas of Scotland. There were a number of power outages and rail and ferry services were disrupted during the storm, one of the strongest to hit portions of the UK in recent months. Some snow and ice was expected for some areas on the back side of the storm as it moved east on Friday.

Wildfires burning in the hills surrounding Los Angeles, and scattered elsewhere along the California coast down towards San Diego made the headlines this week as there were widespread evacuations, and the loss of a number of homes and commercial properties. Downtown Los Angeles has only received 0.11 inches of rain since October 1st, the 11th driest start to the Water Year (Oct 1 to Sep 30) in history there. The National Weather Service was continuing to release Red Flag Warnings Wednesday and Thursday of this week as relative humidity values ranged from only 5 to 15 percent and Santa Ana winds were gusting to 30-40 mph in places. The Weather Underground was continuing to issue updates on these fires as well.


A winter storm was bringing snow to portions of Georgia, especially higher elevations on Friday (Dec 8), with forecasts of amounts up to 3 inches in some places. The Winter Storm Warning, somewhat rare for this time of year, was in effect for areas from Rome to Blairsville where travel was difficult on untreated roads. A rare snow was also reported in southern Texas this week.
A recent study by the USDA Forest Service shows that California has the lowest urban tree canopy cover per capita of any state. With the ecosystem services provided by tree canopies this is an area where urban settings could be improved a great deal. This study provides motivation for urban planners to consider ways to improve and diversify tree canopies in some of California's urban communities.

MPR listener question:


Earlier this week at Waseca we saw a 47 degree temperature drop in less than 24 hours. What is the record 24-hour temperature drop in Minnesota history?

Answer:


According to my book, Minnesota Weather Almanac, the largest drop in temperature over a 24-hour period occurred at Lamberton, MN on April 3, 1982 when following a daytime high of 78 degrees F, the temperature dropped to just 7 degrees F overnight, a decline of 71 degrees.

MPR listener question:


After hearing the piece about the impact road salt runoff has on ponds, lakes, and rivers, I began to wonder if the increased salinity of lakes and rivers causes a [later] freeze up time [date]. I have noticed that the pond behind our house takes longer to freeze than it did when we first moved here in 1998. I think some of the later freeze time is related to climate change...but does the increased salinity also add to the later freeze time?

Answer:


I am no expert on water chemistry, but according to the NOAA National Snow and Ice Data Center the freezing point of water drops by half a degree F for each increase in salinity of 5 ppt (parts per thousand). In the Arctic Ocean where the salinity content is about 35 ppt the water begins to freeze at 28.8 degrees F. It seems to me that for smaller bodies of water like your pond, increased salinity from runoff into the pond may be a factor in the later date of freeze up. But for lakes and rivers in our state I think climate change is the primary driver of later freeze up dates. Consider this, over the 20 years since 1998 (the year you moved into your home) 18 of those years have brought a warmer than normal autumn season (Sep-Nov), and 8 of those autumn seasons rank among the 10 warmest in state history back to 1895. On that evidence alone it is no wonder you have been observing later freeze up dates.

Twin Cities Almanac for December 8th:

The average MSP high temperature for this date is 29 degrees F (plus or minus 13 degrees F standard deviation), while the average low is 15 degrees F (plus or minus 13 degrees F standard deviation).

MSP Local Records for December 8th:

MSP records for this date include: highest daily maximum temperature of 50 degrees F in 1939 and 1990; lowest daily maximum temperature of -6 degree F in 1927; lowest daily minimum temperature of -22 degrees F in 1876; highest daily minimum temperature of 40 degrees F in 1907; record precipitation of 0.44 inches in 1963, 1987, and 1995. Record snowfall on this date is 7.1 inches in 1995.

Average dew point for December 8th is 13°F; the maximum dew point on this date is 46°F in 1946; and the minimum dew point on this date is -20°F in 1978.

All-time state records for December 8th:

The all-time state high temperature for today's date is 67 degrees F at Grand Marais (Cook County) in 1913; the all-time state low for today's date is -38 degrees F at Big Falls (Koochiching County) in 1932 and again at Brimson (St Louis County) in 2013. The all-time state record precipitation for this date is 2.02 inches at Babbitt (St Louis County) in 1924. Record snowfall is 14.0 inches at Isabella (Lake County) in 1969.

Past Weather Features:


A major winter storm brought widespread heavy snow to the state over December 7-9, 1969. Many climate stations reported 10-20 inches of snowfall and in some areas schools were closed or started late. Duluth reported 21 inches of snow on their way to 38.8 inches for the month. On a statewide basis it was one of the snowiest Decembers in history.

December 8, 1990 was arguably the warmest in history on a statewide basis as over 40 Minnesota communities reported a daytime high of 50 degrees F or greater. A few places in western Minnesota topped 60 degrees F, under bright sunny skies and a south wind.

The coldest December 8th in state history was just 4 years ago in 2013. Arctic high pressure gripped the state and except for a few isolated areas of southeastern Minnesota, all observers were reporting subzero temperature readings. Over 70 climate stations reported morning lows of -20 degrees F or colder. Even the daytime temperature rose no higher than -11°F at Detroit Lakes and Hallock.

Outlook:


Partly cloudy over the weekend with warming temperatures. Highs on Sunday will be warmer than normal. A chance for snow late on Sunday and into early Monday. Then cooler temperatures again for Monday through Thursday of next week, though temperatures will be near normal. Little chance for precipitation over that time period.

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