The early morning hours of Thursday, September 15, 2011 saw many locations across eastern North Dakota and northwest and west central Minnesota drop to the freezing mark or below. Most locations in the Red River Valley and points westward had temperatures go down into the upper 20s to lower 30s. Further east, much of northwestern and west central Minnesota dropped down into the middle and even lower 20s, bringing a hard freeze.
Below is an updated table of average first frost and freeze dates for selected cities within the Grand Forks National Weather Service Forecast Office area of responsibility. The stations listed on this table varies from the one presented in previous years for several reasons. Some stations have been closed or moved, and so the data is no longer available for climate summaries. Others have significant amounts of missing data, or data discontinuities that cannot be justified in the process of making normals. Also, please note these are based on raw data, and the final Freeze / Frost data from the National Climate Data Center, when available, may change the dates by a day or two.
On balance, the first frost and freeze dates shown below are several days later into the year than the dates based on the 1971 - 2000 normals. Many reasons, including climate change, instrument exposure and location, as well as urbanization come into play. On good example is the University of North Dakota/NWS Grand Forks temperature data. The weather equipment moved from the campus of UND in April 1997. During the time the equipment has been here, a growth in population has allowed for an increase in housing immediately to the west of the NWS Office. Where prior to 1997 there was open agricultural land west of the NWS Office, an entire housing development now exists. To the south, construction of several buildings has resulted in an increase in concrete and asphalt where once there was a grassy field. When combined with climate change, urbanization has yielded warmer temperatures. This [temperature] trend also shows up in more rural locations such as Cavalier 7NW North Dakota, and Wadena 3S Minnesota.
Remember these dates below are the climatological average first frost and freeze dates. Many variables dictate the actual first frost or freeze, including cloud cover, wind speed, soil moisture and location of the temperature sensor. Some temperature reporting sites are located in town while some are more rural. Sites in town tend to experience frosts and freezes a little later in the year, while rural sites tend to see frosts and have freezing temperatures a bit earlier.
NOAAs National Weather Service defines the first frost as occurring when air temperatures drop to between 36 and 33 degrees, a freeze occurs from 32 degrees to 29 degrees, and a hard freeze as 28 degrees or colder at 6 feet above ground level. This is the standard level of official temperature measurement sensors.
CITY FIRST FROST FIRST FREEZE / HARD FREEZE
ADA SEPTEMBER 17 SEPTEMBER 27 OCTOBER 6
ARGYLE SEPTEMBER 11 SEPTEMBER 21 OCTOBER 5
BAUDETTE SEPTEMBER 12 SEPTEMBER 23 OCTOBER 2
CROOKSTON SEPTEMBER 12 SEPTEMBER 25 OCTOBER 3
DETROIT LAKES SEPTEMBER 8 SEPTEMBER 20 OCTOBER 4
FOSSTON SEPTEMBER 4 SEPTEMBER 19 SEPTEMBER 29
ITASCA STATE PARK SEPTEMBER 14 SEPTEMBER 22 OCTOBER 4
RED LAKE FALLS SEPTEMBER 13 SEPTEMBER 24 OCTOBER 3
RED LAKE SEPTEMBER 16 SEPTEMBER 25 OCTOBER 4
ROTHSAY SEPTEMBER 19 OCTOBER 2 OCTOBER 9
THORHULT SEPTEMBER 2 SEPTEMBER 14 SEPTEMBER 24
WADENA 3S SEPTEMBER 17 SEPTEMBER 27 OCTOBER 8
WARROAD SEPTEMBER 14 SEPTEMBER 26 OCTOBER 6
CITY FIRST FROST FIRST FREEZE / HARD FREEZE
CASSELTON SEED FARM SEPTEMBER 16 SEPTEMBER 28 OCTOBER 6
CAVALIER 7NW SEPTEMBER 14 SEPTEMBER 24 OCTOBER 5
COLGATE SEPTEMBER 12 SEPTEMBER 23 OCTOBER 3
COOPERSTOWN 5E SEPTEMBER 8 SEPTEMBER 20 SEPTEMBER 30
DEVILS LAKE SEPTEMBER 20 SEPTEMBER 28 OCTOBER 6
EDMORE 1NW SEPTEMBER 7 SEPTEMBER 17 SEPTEMBER 26
FARGO AIRPORT SEPTEMBER 18 SEPTEMBER 30 OCTOBER 9
FORMAN 5SSE SEPTEMBER 18 SEPTEMBER 28 OCTOBER 6
GRAND FORKS ARPT SEPTEMBER 13 SEPTEMBER 21 OCTOBER 6
HANSBORO 3W SEPTEMBER 6 SEPTEMBER 15 SEPTEMBER 28
LANGDON EXP FARM SEPTEMBER 10 SEPTEMBER 19 SEPTEMBER 29
PETERSBURG 2N SEPTEMBER 12 SEPTEMBER 22 SEPTEMBER 30
UND/NWS GRAND FORKS SEPTEMBER 16 SEPTEMBER 30 OCTOBER 8
The data above are provided by the NOAA Regional Climate Center in Lincoln Nebraska. For more information, please contact the NOAA's National Weather Service Office in Grand Forks at 701.795.5198. Or contact Mark Ewens, Climate Services Focal Point at Mark.Ewens@noaa.gov