Winters Can Change

In early December two winters ago, the Fargo Moorhead area had a measly inch of snow on the ground and we would still have just three inches six weeks later on January 27.  Then it started snowing.  We got five inches in January 28.  Then another ten inches fell February 10.  Four more inches fell in a series of little storms in February followed by 15 inches in March and another 17 inches in April.  Snow cover reached a maximum average depth in mid-March and we would not see the ground again until April 27.  It is impossible to predict if the remainder of this winter will be snowy or not.  But the winter of 2012-13 taught us that because winters are long in this region, they can change.  November was cold and dry.  So far, December is looking mild and dry.  But things can change.  There is a long way to go before spring.  Meteorologist John Wheeler

Cold November

November here in the Fargo Moorhead area was cold.  The month, as a whole, was six degrees below average. The first wave of cold air moved in November 9, starting an early winter run of 22 out of 24 days below freezing.  While impressive, the cold has set no records here.  We live in a region where early cold snaps must be expected from time to time.  However, as the cold air built into the Mid-South and Southern U.S., it did began setting records.  The most impressive was about a week after the initial front passed through Fargo Moorhead.  According to Dr. Ryan Maue of WeatherBELL, November 19, 2014, was the coldest November day across the Lower 40 since November 30, 1976.  A full 85 per cent of the Lower 48 was below freezing, with many locations setting both record lows and record highs for the day.  The pattern has since relaxed and now most of the U.S. is enjoying above average temperatures.  Meteorologist  John Wheeler

 

Winter Break

The milder weather coming our way is going to be a pleasant surprise for many who were shocked and depressed by the very cold and early start to winter last month.  But now the pattern is softening quite a lot, and temperatures into the 40s appear likely by late next week.  Most of us associate winter with very cold weather.  It is what we remember.  But weather in the 40s and even 50s in December is not that rare.  Last winter it was 40 degrees on December 27.  Early in December of 2012 there were three days above 40 including two at 50.  December of 2011 featured five days in the 40s including 45 Christmas Day.  Decembers in 2009 and 2010 had no days warmer than the 30s, so it doesn’t happen every year.  But any winter month has at least one day above 39 degrees more often than not.  Meteorologist  John Wheeler

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

 

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

Cold Weather Marathon or Sprint?

 

Is our present cold snap temporary or the start of another cold winter?  Many times, an early weather pattern which sends the Jet Stream so far north of Alaska and then so far south into the southern states is one which has trouble holding its place.  True, last winter brought a similar Jet Stream pattern and it lasted from early December right through into early May.  So not only was the winter cold, but the spring was mostly a continuation of the winter.  And while a continuation of the cold is certainly possible, it is probably slightly more likely that the pattern will break down in a week or so.  The break might be temporary, but it also might not.  Obviously, this is not intended to be a forecast.  Rather, this is just to point out that a cold spell in November is not a guarantee that the rest of the winter will be cold.    Meteorologist John Wheeler

Snow Means Cold

 

Most of the time, snow means colder weather. Snow cover does two things to temperature.  It reflects sunlight and it radiates Earth heat very well.  By reflecting sunlight efficiently, a lot of the potential energy coming into the air from the sun is reflected back into space.  Radiating Earth heat simply means the white color of snow allows the snow, itself, and also the air near the snow, to lose heat into space, particularly at night.  So when the ground is covered with snow, it is colder in the daytime and also in the nighttime but for different reasons.  Snow also creates a lagging effect on cold weather.  It takes energy to melt snow into liquid water.  So the process of melting snow robs the air of warmth.  Snow helps the weather get cold and also helps it stay cold. When snow covers the ground, it is possible for the weather to get warmer, but it is a lot harder than without snow.     Meteorologist John Wheeler

 

 

What the Polar Vortex Is… and Isn’t

 

The Polar Vortex is an actual thing, although the term has been badly misused in recent months.  Most cold air outbreaks are caused by high-pressure areas dropping south from the Arctic regions, displacing cold air into the mid-latitudes.  Usually, some part of the Arctic such as Alaska or The Yukon has an accompanying mild spell of weather.  The Polar Vortex, on the other hand, is a circumpolar wind at the Jet Stream level of the atmosphere.  It is not a high-pressure area nor is it a cold front.  The Polar Vortex circulation grows stronger during winter and tends to keep the coldest weather in the hemisphere bottled up over the Polar Regions where it is perpetually dark and bitterly cold in winter.  Sometimes, however, the Polar Vortex weakens or is bent out of shape.  These episodes cause the weather over the Poles to become relatively mild while displacing Polar southward into the mid-latitudes.   Meteorologist John Wheeler

 

It’s Just a Forecast

 

Even as technology improves, weather forecasting is still forecasting.  We are almost never exactly right.  Our goal on a daily basis is to be close enough to be useful, and most of the time, we are.  Sometimes, however, we do miss by a lot, like Monday’s snow storm. Most Twin Cities forecasts on the previous Friday had the heavy snow going south of the Twin Cities.  Over the weekend, most forecasts changed to having it go right through the Twin cities.  But Monday came and snowfall was an inch or two at Bloomington and Inver Grove Heights to six inches in Coon Rapids and Lino Lakes on the north side.  The heavy snow (12-17 inches) fell from St. Cloud to Cambridge.  As a forecaster, myself, I can say that the Twin Cities forecasters did pretty well with the storm.  They got the amounts right and were off by a only hundred miles. That is not bad for a highly energetic fluid dynamics problem covering an area the size of several states.   Meteorologist John Wheeler