Facts & Data - Climate
Avg. Temperature in July 83 F
Avg. Temperature in January 11 F
Avg. Snowfall 63 inches
Avg. Rainfall 15 inches
Number of days with precipitation 103 days
Number of sunny days 187 days
Number of days less than 32 F - 155 days
Number of days greater than 90 F -- 18 days
The following information is taken from the National Weather Service Great Falls Office Historical Data Information:
Characteristics of Great Falls climate
The climate in Great Falls is generally characterized by pleasant summers with warm, mostly sunny days and cool nights. Summer rainfall usually falls in the form of showers or thundershowers, but prolonged stratiform rain events do occur during late spring and early summer.
Although Great Falls’ average annual precipitation would normally classify the area as semiarid, it should be noted that about 70 percent of the annual total normally falls during the April - September growing season. Favorable temperatures during the peak of the growing season combined with long hours of summer sunshine and nearly 10 inches of precipitation during the critical months make the climate very favorable for dry land farming.
During summer months of historical record, freezing temperatures have not occurred in July and are very rare during June and August. The transition months of May and September will normally have two or three days of freezing temperatures, while frost occurs frequently during April and October.
Winters are warmer than would be expected, as a result of the frequent chinook winds. Sub-zero weather normally occurs several times during a winter. However, the duration of a typical cold spell ranges from only several days to a week after which it can be abruptly terminated by southwesterly chinook winds. The sudden warming associated with these chinooks can produce temperature rises of nearly 40 degrees in less than a day. Conversely, strong intrusions of bitterly cold arctic air sweep down from northern Canada several times each winter bringing sharp temperature drops of 30 to 40 degrees within 24 hours.
Precipitation generally falls as snow during the winter, late fall and early spring. Rain intermittently occurs during these periods as well, although freezing rain is very rare. Summer, late spring and early fall precipitation is usually in liquid form, although snow has been known to fall as early as mid August. Hail is occasionally observed in late spring and early summer thunderstorms and is generally smaller than one quarter inch in diameter.
The average annual temperature based upon the full historical data set is 45.3 degrees Fahrenheit (°F). This is 0.5°F above the 30-year average annual temperature (1961-1990) of 44.8°F. The maximum annual temperature of 49.6°F was recorded in 1934 and the minimum of 40.4°F was recorded in 1951.
Using historical data, the average daily high temperature is 57.1°F and the average daily low is 33.5°F. These averages are 0.7°F and 0.4°F warmer than the 30-year average maximum and minimum temperatures of 56.4°F and 33.1°F, respectively. The highest temperature recorded in Great Falls was 107°F on July 25, 1933. The extreme minimum of -49°F was recorded on February 15, 1936.
A 10-year (decadal) running average of annual temperatures reveals a general decline in temperatures beginning in the early years of this century and continuing until the late 1920's. This trend is followed by increasing decadal temperatures which top out in the early 1940's then decline until the late 1950's. A brief climb in decadal temperatures occurs during the 1960's before another drop in the early 1970's. Decadal temperatures remained somewhat constant through most of the 1970's and 1980's before a sharp increase occurs just prior to 1990.
The average annual precipitation at Great Falls, as based upon the entire historical database, is 14.98 inches. The thirty-year (1971-2000) annual average is 14.89 inches, a difference of 0.09 inches. Yearly extremes in precipitation range from a maximum of 25.24 inches in 1975 to a minimum of 6.68 inches in 1904.
Thirty-year averaged monthly precipitation amounts vary from a maximum of 2.63 inches for the month of May to a minimum of 0.51 inches which occurs in February. May, 1953 is the wettest month on record with 8.13 inches. At the other extreme, November, 1917 is distinguished as the only month during the last 103 years that did not receive at least a trace of precipitation.
Decadal averages show a steady increase in precipitation totals during the early years of this century. This trend is followed by a steady decline which begins in the early teens and continues until reaching a minimum about 1940. Another steady rise in decadal precipitation continues until the mid 1950's followed by a sharp decrease which bottoms at around 1960. Decadal precipitation averages have been slowly rising over the last 30 to 35 years with the exception of a short lived increase in the late 1970's followed by a sharp but short decrease in the early 1980's.
The thirty-year average annual snowfall at Great Falls is 63.5 inches. This is considerably more than the average annual snowfall of historical record, 52.3 inches. The maximum seasonal snowfall of 117.5 inches occurred in the winter of 1988-1989. The minimum seasonal snowfall, 17.9 inches, was recorded during the winter of 1904-1905.
Decadal averages of snowfall are nearly steady for the period beginning about 1910 and continuing until the mid 1930's. A slight drop during the mid to late 1930's is followed by a substantial increase in snowfall totals from the early 1940's until the mid 1950's. Another sharp drop in decadal averages occurs during the late 1950's with averages again increasing in the late 1960's. Much greater variability is observed over the last 30 years than at any other time in the historical record. However, the overall trend in decadal snowfall averages appear more or less constant during this time frame.
It is possible that the dramatic increase in decadal snowfall averages during the 1940's may be related to the relocation of the official observation site to the airport in 1937. However, unofficial present day comparisons of snowfall amounts between downtown Great Falls and the airport do not indicate quite so large a discrepancy as has been noted in this study.
Recorded wind data started in 1942 at Great Falls. The wind direction has a profound impact on temperatures and precipitation in the area, especially during the winter months. While the prevailing winds at Great Falls are from the southwest to west-southwest, occasional north to northeasterly winds during the late winter and early spring contribute to significant upslope precipitation events. The greatest variability in wind direction in the Great Falls area results from thunderstorm outflow winds, primarily during spring and summer afternoons.
The average wind speed recorded at Great Falls between 1942 and 2002 is 12.5 miles per hour (mph). Winds averaged on a monthly basis are at a maximum (15.4 mph) during December and are lowest (9.9 mph) in July. The highest daily average wind speed recorded at Great Falls was 44.0 mph on January 29, 1974.
Daily peak wind gusts recorded between 1942-2002 average out to 28.8 mph. Monthly averaged peak wind gusts top out at 31.6 mph in December and are at a minimum of 27.6 mph in August. The peak wind gust recorded at the Great Falls International Airport was 92 mph on June 27, 1970.
Referenced Yuill, Ellan R., A Centennial Celebration, Clifford D. Yuill and Ellan R. Yuill. 1984.
For more information visit the National Weather Service Great Falls site http://www.wrh.noaa.gov/tfx/