About a month ago, I wrote about how the Northern Hemisphere experienced a Sudden Stratospheric Warming (SSW) event and how this might have lead to bitterly cold weather around mid-February for our area. The SSW was the strongest observed in 30 years with temperatures in the stratosphere rising by nearly 80 degrees in the course of a few days.
It had a sudden effect on weather patterns as it split the arctic air into two pieces; one moving into Siberia and the other into Western Europe where the cold contributed to a major London snowstorm. The cold air did not shift into Canada and the United States as often happens with such events. However, a piece of that cold air that has been in Siberia will make an appearance over the next few days, but temperatures will not be as cold as what we experienced in January.
February tends to be the least active of the three principal months of winter. The North American continent this time of year is just beginning to release it’s grip on winter. Most Februaries, North Dakota and Minnesota will experience weaker upper-level wind blowing from the northwest which form storms with little moisture.
The arctic remains cold generating areas of high pressure which frequently move in to our area increasing the amount of sunshine observed in comparison to December or early January. Fargo Moorhead has not seen an individual storm produce more than 7 inches of snow in February in the past two decades. Heavy snow is so unusual this time of year that since snow records have been kept only on February 28, 1951, has more than 10 inches of snow fallen in a single day, although there have been a few multiple day storms exceeding 10 inches.
March on the other hand has a much different reputation.
When last week’s storm moved through the area, several people contacted the WDAY Stormtracker weather center reporting lightning and hearing thunder. Almost every winter some part of this area will hear a few rumbles of thunder, but this time of year it is usually associated with snowfall.
The first recorded observation of thundersnow in this region was in February, 1820 at the cantonment of New Hope, the precursor to Fort Snelling in the Twin Cities. Besides hearing thunder, the weather observer noted that rain, sleet and snow were all observed during that storm. No matter what the season, thunder is a sign of strong updrafts occurring in the atmosphere. These updrafts when associated with snow can produce intense areas of snowfall with up to 4 inches per hour falling. Although thundersnow is uncommon everywhere, it is most commonly observed during lake effect snow events near the Great Lakes and around the Great Salt Lake in Utah.
Last week’s mild temperatures and corresponding snowmelt prompted the question as to how long does it take for our snow to melt each spring. As we learned last week, when the conditions are favorable, the snow pack can decrease quickly. Of course, each winter brings not only different snow amounts, but also differing snow types and conditions which influence the speed to which the snow will go away.
In March of 1997 the snow pack went from 24 inches to just a trace in 14 days once the temperatures warmed toward the end of that month. Of course most years, we do not have that much snow to melt, so historically generally only around one week of mild weather is required to reduce the official snow cover to a trace. But no matter how long this year’s melt takes, it will likely not occur until the last half of March.
We are now 54 days passed the Winter Solstice and the days are getting noticeably longer and the Sun is getting higher in the sky each day. The Sun angle now is the equivalent to what we experienced on Halloween. Yet with the same amount of solar energy striking our area as late October, our average high and low temperature today is 23 and 5 degrees, but on Halloween the averages are 46 and 27 degrees.
Plus, our record high on October 31 is 76 degrees in comparison to the record for today being 53 degrees. One of the many reasons for this 20 to 25 degree difference between the two dates is snow cover. The snow cover we see most winters reflects as much as 90% of the incoming solar radiation, reducing the potential air temperature. Plus, when temperatures do warm above freezing, much of the Sun’s energy goes into melting the snow, not warming the air.
The middle of January brought bitterly cold weather to not only our area, but to much of the northern half of the United States. During that cold snap Fargo Moorhead dropped down to -30 degrees and Grand Forks had a low of -38 degrees.
When this cold air moved into New England even colder temperatures were observed. On January 16, a U.S. Geological Survey stream gauge on the Big Black River near Depot Mountain in northwestern Maine recorded a low temperature of -50 degrees. The all-time coldest temperature recorded in that state was -48 degrees set 84 years ago on January 19, 1925, in Van Buren, Maine. Before this record was accepted the temperature sensor was thoroughly tested for accuracy.
After it passed all tests, it was recommended to the National Climatic Data Center that they should accept it as the new state record, which they did on February 4.
The mild temperatures from earlier in the week reduced our official snow cover to 7 inches. As of today, we have had continuous snow cover for 70 straight days and before Tuesday, we had 10 inches or more snow on the ground for 51 of those days.
Our maximum snow depth during that period was 16 inches measured on January 4. Having 16 inches of snow on the ground, may seem to be a lot of snow, but historically, our maximum snow depth in the winter averages 14 inches, so at least to this point in the winter, snow cover has not been out of the ordinary. Our maximum snow depth in the record books occurred on March 4, 1997 when the average snow depth around Fargo Moorhead was an astounding 32 inches.
Although our snow depth has lowered to 7 inches, the moisture content of the snow has increased as the recent rain was absorbed into the snow.
Fargo Moorhead averages 48 days per winter with a low temperature below zero. So far we have recorded 46 such days this season with nearly two more months of below zero potential ahead of us. Last year, a relatively cold winter, we recorded 51 days with a low below zero, so we are far ahead of the pace set last year.
The most below zero days in the record books occurred during the winter of 1883-1884 when 91 such days occurred. Although we will not be able to break that record, we certainly have the potential to come close to the 67 below zero days we recorded back in the winter of 1996-1997. Another sign of how cold this winter has been is that on 14 of the 48 days with lows below zero, our high also remained in negative territory. We average just 10 days per winter with a below zero high.
The persistently cold weather that has so far dominated our winter has also been influencing other parts of the United States. From North Dakota to Maine and from Michigan to Tennessee, January temperatures were well below average. Chicago for example recorded their 10th coldest January on record with temperatures finishing the month 6.2 degrees below normal. Records go back 137 years in the Windy City, plus considering the massive urban heat island that has developed since records began, help make getting into the top 10 even more impressive.
Usually when the eastern part of the United States is cold, the western half tends to be warm and that was definitely the case in January. Most of the Rocky Mountain States finished January well above average for temperatures. Denver residents experienced temperatures nearly 6 degrees above average last month. Whereas we are wondering when winter will end residents in Wyoming and Colorado are wondering when it will begin.
January brought an additional 7.3 inches of snow to Fargo Moorhead bringing our seasonal total to 43.3 inches. Excluding the 1.4 inches that fell and melted quickly in October, our seasonally snowfall so far contains 2.42 inches of moisture. As a comparison, last year we had 23 inches of snow to this point with a water equivalency of 1.77 inches, so locally, we are only running 0.65 inches ahead of last years pace because of the very dry nature of most of our snowfalls this winter.
As of early February 1997, we had already recorded 79 inches of snow that contained 5.35 inches of moisture. Plus, February, March and April of 1997 brought an additional 37 inches of snow that contained 5 more inches of moisture including the horrible rain, ice storm and blizzard of early April of that year. This has been an interesting winter, especially December, but it has been no where near a repeat of 1996-1997.