Warm December Pattern

There are a number of large-scale weather features which can impact our long term weather and one of them is called the Pacific-North America Oscillation (PNA).  When the PNA is positive, there is strong low pressure in the Gulf of Alaska which causes the Polar Jet Stream to drop well south of Alaska across the Pacific, where it enters western North America and bring wet weather to the West Coast.  The Jet then curves northeast into Canada, allowing mild air from the south and southwest into the Northern Plains. This is almost opposite of the pattern in November, when the PNA was strongly negative.  There are other large-scale weather features which sometimes have a greater influence than the PNA.  But the PNA is looking very strongly positive for the time being, causing me to think our weather will be mild through Christmas.  Expect lots of afternoons in the 20s and 30s with a few in the 40s.   Meteorologist John Wheeler

November Was Cold and Dry

The month of November was cold and dry.  The average high temperature was 30.9 degrees and the average low was 14.9 degrees, for an overall average of 14.8 degrees which is 6.0 degrees below the long term average.  The warmest day was 57 degrees November 2.  The coldest morning was 13 below on November 27.  There were four days in the 50s, all early in the month.  There were five days in the 40s, scattered throughout.  There were just three days in the 30s. Fourteen days were in the 20s. There were three days in the teens and just one with a high in the single digits.  Precipitation was 0.71 inches with much of that falling in a 0.44 inch rain shower November 4.  Snowfall was 3.6 inches. Average precipitation is 1.00 inches and average snowfall is 7.9 inches.  With scant snow on the ground and the Jet Stream shifting to a weaker, more westerly flow, it is likely that December will be warmer and drier than average.    Meteorologist John Wheeler

 

The Core of the Winter

It is normal for our weather to fluctuate from colder than average to warmer than average. In winter, a change in the pattern can drive out Arctic air and replace it with much warmer weather for a while.  In the fall, this happened as well, but the general trend in fall is always toward colder weather.  A rogue warm day may happen anytime, but the last half of November is never warmer, overall, than the first half.  The change in incoming solar energy just will not allow it.  In December, even though the general trend is usually toward colder weather at month’s end, it is possible for the coldest weather to happen early in the month.  Likewise, mid-January is, on average, the coldest part of the winter; however it is quite possible for the coldest week of winter to happen at any time during the winter.   Meteorologist John Wheeler

Winter Highs and Lows

The past few days, our weather has not followed the normal night and day cycle.  Instead of it being coldest in the early morning and warmest in the late afternoon, the temperature rose steadily from arctic conditions Thanksgiving morning to balmy (for November) by early Saturday.  It has been falling steadily since then. This actually happens a lot in our region in winter.  Snow on the ground reflects much of the sunlight so there is less warming during the day.  Plus, our proximity to Arctic air to the north and Chinook-warmed air to the west means a switch in the wind can cause big temperature swings.  This does create confusion with the seven-day forecast in the newspaper.  The format makes it difficult to convey such irregular temperature patterns.    Meteorologist John Wheeler

Transition to Winter is Complete

 

Looking out the window, it appears winter has settled in. The transition from summer to winter has been marked with significant moments.  The last time lightning was observed at the airport weather station was during severe early morning thunderstorms back on September 4. The last 80 degree day was September 27.  The last 70 degree day was October 24.  The first frost was October 9. The last measurable rain was November 7.  The last day without measurable snow on the ground and also the last day in the 40s was last Sunday.  Going forward, it is likely the temperature will get back into the 40s during the winter for a few days.  It is also likely we will get a light rain shower or two.  It is possible we will lose our snow cover at some point.  And it is even possible to get lightning during a winter snow shower. But there is no doubt we will consider any of these things as winter occurrences.    Meteorologist John Wheeler

1985: One Cold Start to Winter

Three record low temperatures for Fargo Moorhead set in late November of 1985 still stand.  It was 15 below on November 23 and it was 24 below on November 27 and 28.  This was part of a remarkable severe spell of winter weather the second half of November that year.  Winter started suddenly and seemed to settle in for good.  From November 18 through November 30, a total of 24.2 inches of snow fell, mostly from three heavy snowstorms.  Starting November 20, the last eleven days of the month had subzero morning temperatures.  Seven of those mornings were lower than ten below and four were at least 20 below.  Starting November 27, the temperature remained below zero even in the daytime.  Below average temperatures continued through most of December until it turned mild around Christmas.  The remainder of that winter was much less severe.   Meteorologist John Wheeler

 

Quiet Atlantic Hurricane Season

The Atlantic hurricane season officially comes to an end this weekend.  It was a good year for people and a bad year for hurricanes.  There were just eight named tropical systems (sustained winds of at least 39 mph) in the Atlantic Basin.  Six of them became hurricanes (sustained winds of at least 74 mph).  Only two became major hurricanes (Category 3,4,5 with winds of at least 111 mph).  The relative absence of hurricanes is due to the absence of good hurricane conditions.  Upper level winds over the tropical Atlantic were strong and kept clusters of thunderstorms from becoming organized.  Also, a lot of dry air was in place over the Atlantic. On the other side of the Americas, the eastern Pacific was the most active since 1992.  It is not uncommon for the two oceans to be out of sync like this.  The record year for Atlantic hurricanes, 2006, was a very quiet year across the Pacific.  Meteorologist John Wheeler

Thundersnow!

During last week’s lake effect snowstorms in western New York, there were several instances of thunder and lightning during the heavy snowfall.  Although not something witnessed routinely, thundersnow is not some freak of nature.  I have personally seen lightning during snowfall four or five times in my life.  Lightning is a product of a convective shower. Electrical charge is built up as raindrops and snowflakes bounce around and interact in the rapidly rising air within an updraft.  Most snowfalls come from larger-scale, general rising motions.  Showers are more common in warm weather when the air tends to be more unstable.  Lake effect snows are ideal for thundersnow because the cold air flowing over warmer water can produce the necessary instability.  But sometimes, even out here on the Great Plains, showers form in air cold enough to produce snow, and thundersnow can be the result.      Meteorologist John Wheeler

It Flows North

Running along the Red River recently, I was observing its frozen surface and was struck by its stillness.  Once frozen, the visual motion of the river stops for the winter.  Its hard surface gives the appearance of a thing at rest.  But underneath the frozen river surface, the Red River continues to flow all winter long.  It flows to the north, as we all know.  But this northward motion is not as singular as many of us have led ourselves to believe.  The Red is not the only other river in the United States to flow north.  There are the Kennebec and the Penobscot Rivers in Maine as well as the Willamette River in Oregon.  The only reason most rivers flow south is because the slope of the entire Mississippi watershed is to the south.  This is merely a feature of American geography and not a strange adjustment to any law of physics.  Water flows downhill, whatever direction that happens to be.  Even north.   Meteorologist John Wheeler

The North Wind Doth Blow

It has been a windy fall.  Very windy compared to last year.  Through September, October, and the first 21 days of November, there have been wind gusts of at least 20 mph on 56 of the 82 days and gusts of at least 30 mph on 19 of those 82 days.  In the fall of 2013, the same period produced just 49 days with gusts of at least 20 mph and just eight days with wind gusts of at least 30 mph.  The reason for the wind is a high frequency of storm systems which have produced a lot of changes in air pressure.  Interestingly, those same storm systems have not generated much precipitation.  Fargo Moorhead has only received 3.27 inches since September 1, and most of that came on two days.  We received 1.99 inches in a thunderstorm September 4 and 0.40 inches in a rain shower November 5.  The remaining 0.88 inches has come from occasional rain or snow showers.  To be fair, there was a significant snow storm which passed just south of the Fargo Moorhead area November 10.

I am reminded of a very old English nursery rhyme.    Meteorologist John Wheeler

The north wind doth blow,
And we shall have snow,
And what will poor robin do then?
Poor thing.

He’ll sit in a barn,
And keep himself warm,
And hide his head under his wing,
Poor thing.