Why Has it Been So Warm? A Brief Explanation

Since the 10th of March we have seen an unprecedented warm spell develop across the Red River Valley and Lakes Country; in fact the northern plains have been very, very warm for March. Nearly every day we've seen new record high temperatures at many locations, with record high minimum temperatures as well. But why has it been so warm? What follows is a thumbnail picture as to what has conspired to make it so warm, for so long.

The following is a thumbnail attribution for the record high temperatures**:

1. Presence of Bermuda High in the much northerly latitudes than usual. This has caused a persistent southerly warm flow.

2. Lack and early snow melt/lack of snow-cover. This causes positive feedback. The incoming solar energy is absorbed by the relatively dry, dark soils, versus reflected into space as happens when the ground is snow covered.

3. Confinement of the arctic circulation to the north of arctic circle (positive Arctic Oscillation).

** Dr. Adnan Akyuz, North Dakota State Climatologist at NDSU supplied this portion of the attribution.

Other large scale changes make this even more impressive, including the fact that our spring seasons have been generally becoming cooler as the region becomes wetter. Since 2000 the region has seen a net decrease of several degrees Farenheit to the mean temperature. Therefore the recent very warm weather is 'bucking' the trend that has been associated with the generally wetter than average spring seasons. Therefore, the dry weather the past 6 months has, in part helped explain why we have been breaking these records by such large values, not only by fractions of a degree. On March 18th the Grand Forks Airport broke the record by 17°F. That is very impressive!

For the "Solar Winter" which ended on March 19th, the period has been on an equally record calibre status. Below are the preliminary statistics for Fargo, the Grand Forks Airport and the University of North Dakota / NWS Climate Station for December 22nd through March 19th. What is interesting is that, while this certainly is a very warm period, it is not unprecedented; in fact as the data shows it's been nearly as warm in relatively recent history.

Fargo Area  (ThreadEx Station)
Extremes Highest Average Average Temperature degrees F
Days: 12/22 - 3/19
Length of period: 88 days
Years: 1881-2012

Rank  Value  Ending Date
  1    25.0    2012
  2    24.7    1987
  3    23.3    1992
  4    23.2    1931
  5    21.2    1990
  6    21.0    1983
  7    20.2    2000
  8    19.9    2006
  9    19.7    1942
 10    19.3    1998

Extremes Highest Average Average Temperature degrees F
Days: 12/22 - 3/19
Length of period: 88 days
Years: 1941-2012

Rank  Value  Ending Date
  1    21.8    2012
  2    21.7    1992
  3    20.6    1983,  1987
  5    19.4    1981
  6    19.1    2000
  7    18.6    1990
  8    17.2    1973
  9    16.4    2006
 10    16.1    2002

Extremes Highest Average Average Temperature degrees F
Days: 12/22 - 3/19
Length of period: 88 days
Years: 1890-2012

Rank  Value  Ending Date
  1    23.5    2006
  2    22.4    2012
  3    22.1    1987
  4    21.5    1992
  5    21.3    1983
  6    20.8    1931
  7    20.1    1990
  8    19.9    1981, 2000
 10    18.0    1973

Above: Preliminary Data courtesy of the Acis Program, Regional Climate Centers

Below  is an image of the net change in temperature over the past 11 years for the February - May time period. The cooling is generally associated with the overall increases in precipitation the past decade. Below that is an image with the SLP, surface wind vector and RH anomalies from March 8 - 15th (the last data ESRL data are available.) The lower than average SLP over much of Canada, the westward extension of the Bermuda Ridge (upper left), have resulted in a persistent easterly flow off the Atlantic into the southeast US, then a south flow in the plains (upper right), persistent negative RH anomaly (lower left) and drying soils (lower right) have combined to produce the recent "heat wave."

Research will continue to help better define the causes of the recent very warm weather. This is by no means an in-depth study, simply a look at some of the outstanding causes for the recent record warmth.

Image courtesy of ESRL, Boulder CO.

Image above based on the Local Climate Analysis Tool, Courtesy NOAA Climate Services

For more information please contact the NWS in Grand Forks at 701.795.5198 or contact Mark Ewens, Climate Services Focal Point at Mark.Ewens@noaa.gov

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