Climate Narrative for Flathead County, Montana

Climate Narrative for Flathead County, Montana.

Prepared by the Natural Resources Conservation Service National Water and ClimateCenter, Portland, Oregon.

Climate Tables are created from climate station CRESTON and WEST GLACIER,Montana.

Thunderstorm days, relative humidity, percent sunshine, and wind information are estimated from First Order station Kalispell, Montana.

Table 1 gives data on temperature and precipitation for the survey area as recorded at CRESTON and WEST GLACIER in the period 1971 to 2000. Table 2 shows probable dates of the first freeze in fall and the last freeze in spring. Table 3 provides data on the length of the growing season.

In winter, the average temperature is 24.9 degrees F and the average daily minimum temperature is 17.2 degrees. The lowest temperature on record, which occurred at CRESTON on December 30, 1968, is -41 degrees. In summer, the average temperature is 61.6 degrees and the average daily maximum temperature is 76.2 degrees. The highest temperature, which occurred at CRESTON on August 4, 1961, is 100 degrees.

Growing degree days are shown in Table 1. They are equivalent to "heat units". During the month, growing degree days accumulate by the amount that the average temperature each day exceeds a base temperature (40 degrees F). The normal monthly accumulation is used to schedule single or successive plantings of a crop between the last freeze in spring and the first freeze in fall.

The average annual total precipitation is about 20.17 inches. Of this, about 10.27 inches, or 51 percent, usually falls in May through September. The growing season for most crops falls within this period. The heaviest 1-day rainfall during the period of record was 2.29 inches at CRESTON on June 16, 1956. At WEST GLACIER, the average annual total precipitation is about 28.76 inches. Of this, about 8.66 inches, or 30 percent, usually falls in June through September. The growing season for most crops falls within this period. The heaviest 1-day rainfall during the period of record was 3.47 inches at WEST GLACIER on June 8, 1964. Thunderstorms occur on about 24 days each year, and most occur in June.

The average seasonal snowfall is 48.1 inches. The greatest snow depth at any one time during the period of record was 35 inches recorded on January 31, 1969. On an average, 76 days per year have at least 1 inch of snow on the ground. The heaviest 1-day snowfall on record was 14.0 inches recorded on November 19, 1996. At WEST GLACIER, the average seasonal snowfall is 126.3 inches. The greatest snow depth at any one time during the period of record was 60 inches recorded on March 6, 1997. On an average, 146 days per year have at least 1 inch of snow on the ground. The heaviest 1-day snowfall on record was 20.0 inches recorded on December 20, 1992 and January 7, 1994.

The average relative humidity in mid-afternoon is about 54 percent. Humidity is higher at night, and the average at dawn is about 83 percent. The sun shines 61 percent of the time in summer and 31 percent in winter. The prevailing wind is from the south-southeast. Average wind speed is highest, 7.6 miles per hour, in April.

TABLE 1.--TEMPERATURE AND PRECIPITATION

(Recorded in the period 1971-2000 atCRESTON, MT2104)

------

| Temperature | Precipitation

|------|------

| | | |2 yrs in 10| | |2 yrs in 10|

| | | | will have | avg | | will have |avg no |

|-----|-----| |------|no of| |------|of days|avg

Month | avg | avg | avg |max | min |grow | avg | less| more|w/ 0.10|snow-

| max | min | |>than|<than|days*|(in.)|(in.)|(in.)|more

------

January | 30.4| 15.1| 22.8| 50 | -20 | 29| 1.32| 0.79| 1.80| 5 | 12.8

February | 36.1| 18.6| 27.4| 53 | -16 | 29| 1.19| 0.70| 1.63| 5 | 8.8

March | 44.5| 25.3| 34.9| 64 | 1 | 42| 1.31| 0.63| 1.89| 5 | 4.9

April | 55.0| 31.9| 43.5| 77 | 18 | 136| 1.71| 0.94| 2.39| 5 | 1.3

May | 63.8| 39.6| 51.7| 86 | 26 | 364| 2.54| 1.51| 3.46| 7 | 0.1

June | 70.8| 46.0| 58.4| 90 | 32 | 552| 2.86| 1.67| 3.93| 8 | 0.0

July | 78.5| 49.3| 63.9| 94 | 36 | 741| 1.80| 0.46| 2.86| 5 | 0.0

August | 79.4| 47.6| 63.5| 94 | 34 | 729| 1.48| 0.59| 2.23| 4 | 0.0

September | 68.2| 38.6| 53.4| 88 | 23 | 403| 1.59| 0.77| 2.32| 5 | 0.0

October | 55.4| 30.3| 42.9| 75 | 13 | 121| 1.25| 0.49| 1.89| 4 | 0.9

November | 39.8| 24.5| 32.2| 60 | -3 | 42| 1.54| 0.84| 2.15| 5 | 6.0

December | 31.5| 17.6| 24.6| 50 | -16 | 21| 1.59| 0.88| 2.22| 6 | 15.9

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Yearly : |-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Average | 54.5| 32.0| 43.3| --- | --- | --- | --- | --- | --- | --- | ---

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Extreme | 97| -33| --- | 96 | -25 | --- | --- | --- | --- | --- | ---

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Total |-----|-----|-----|-----|-----| 3209|20.18|17.04|23.17| 62 | 50.0

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

------

*A growing degree day is a unit of heat available for plant growth.

It can be calculated by adding the maximum and minimum daily temperatures,

dividing the sum by 2, and subtracting the temperature below which growth

is minimal for the principal crops in the area (Threshold: 40.0 deg. F).

Average # of days per year with at least 1 inch of snow on the ground: 50

TABLE 1.--TEMPERATURE AND PRECIPITATION

(Recorded in the period 1971-2000 atWEST GLACIER, MT8809)

------

| Temperature | Precipitation

|------|------

|-----|-----| |------|no of| |------|of days|avg

Month | avg | avg | avg |max | min |grow | avg | less| more|w/ 0.10|snow-

| max | min | |>than|<than|days*|(in.)|(in.)|(in.)|more

------

January | 29.3| 15.5| 22.4| 46 | -22 | 19| 3.16| 1.64| 4.49| 9 | 35.6

February | 34.8| 18.7| 26.8| 50 | -19 | 17| 2.19| 1.06| 3.16| 7 | 20.2

March | 43.1| 24.2| 33.7| 59 | -1 | 25| 1.83| 1.03| 2.54| 7 | 12.9

April | 54.2| 30.3| 42.3| 74 | 15 | 123| 1.78| 1.14| 2.36| 5 | 2.4

May | 64.5| 37.7| 51.1| 84 | 25 | 348| 2.66| 1.66| 3.57| 7 | 0.1

June | 71.8| 44.1| 58.0| 89 | 31 | 539| 3.22| 1.89| 4.41| 8 | 0.1

July | 78.9| 48.2| 63.6| 93 | 35 | 731| 1.97| 0.71| 3.01| 5 | 0.0

August | 78.8| 47.4| 63.1| 92 | 34 | 715| 1.67| 0.67| 2.50| 5 | 0.0

September | 67.1| 39.1| 53.1| 86 | 24 | 394| 1.87| 0.69| 2.84| 6 | 0.1

October | 53.4| 31.7| 42.6| 72 | 13 | 121| 2.07| 0.71| 3.19| 6 | 1.8

November | 37.0| 25.0| 31.0| 55 | -3 | 33| 3.10| 1.55| 4.45| 9 | 18.5

December | 29.6| 18.0| 23.8| 45 | -16 | 14| 3.22| 1.87| 4.42| 9 | 37.7

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Yearly : |-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Average | 53.5| 31.7| 42.6| --- | --- | --- | --- | --- | --- | --- | ---

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Extreme | 99| -32| --- | 95 | -27 | --- | --- | --- | --- | --- | ---

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

Total |-----|-----|-----|-----|-----| 3079|28.74|24.47|32.82| 81 |132.0

------|-----|-----|-----|-----|-----|-----|-----|-----|-----|------|-----

------

*A growing degree day is a unit of heat available for plant growth.

It can be calculated by adding the maximum and minimum daily temperatures,

dividing the sum by 2, and subtracting the temperature below which growth

is minimal for the principal crops in the area (Threshold: 40.0 deg. F).

Average # of days per year with at least 1 inch of snow on the ground: 132

TABLE 2.—FREEZE DATES IN SPRING AND FALL

(Recorded in the period 1971-2000 atCRESTON, MT2104)

------

| Temperature

------|------

Probability | 24F or lower | 28F or lower | 32F or lower

------|------

| | |

Last freezing temperature | | |

in spring: | | |

| | |

1 year in 10 later than-- | April 30 | May 18 | June 10

| | |

2 year in 10 later than-- | April 24 | May 13 | June 4

| | |

5 year in 10 later than-- | April 14 | May 5 | May 23

| | |

First freezing temperature | | |

in fall: | | |

| | |

1 yr in 10 earlier than-- |September 18 |September 14 |September 3

| | |

2 yr in 10 earlier than-- |September 26 |September 19 |September 7

| | |

5 yr in 10 earlier than-- | October 9 |September 28 |September 16

| | |

------

TABLE 2.—FREEZE DATES IN SPRING AND FALL

(Recorded in the period 1971-2000 atWEST GLACIER, MT8809)

------

| Temperature

------|------

Probability | 24F or lower | 28F or lower | 32F or lower

------|------

| | |

Last freezing temperature | | |

in spring: | | |

| | |

1 year in 10 later than-- | May 2 | May 23 | June 24

| | |

2 year in 10 later than-- | April 27 | May 19 | June 16

| | |

5 year in 10 later than-- | April 19 | May 11 | June 1

| | |

First freezing temperature | | |

in fall: | | |

| | |

1 yr in 10 earlier than-- |September 21 |September 11 |September 2

| | |

2 yr in 10 earlier than-- |September 29 |September 17 |September 6

| | |

5 yr in 10 earlier than-- | October 13 |September 28 |September 14

| | |

------

TABLE 3.—GROWING SEASON

(Recorded in the period 1971-2000 atCRESTON, MT2104)

------

| Daily Minimum Temperature

------|------

Probability | # days > 24F | # days > 28F | # days > 32F

| | |

9 years in 10 | 148 | 123 | 92

| | |

8 years in 10 | 158 | 131 | 100

| | |

5 years in 10 | 177 | 145 | 115

| | |

2 years in 10 | 196 | 159 | 130

| | |

1 year in 10 | 206 | 166 | 137

| | |

------|------|------|------

TABLE 3.—GROWING SEASON

(Recorded in the period 1971-2000 atWEST GLACIER, MT8809)

------

| Daily Minimum Temperature

------|------

Probability | # days > 24F | # days > 28F | # days > 32F

| | |

9 years in 10 | 153 | 114 | 79

| | |

8 years in 10 | 160 | 123 | 88

| | |

5 years in 10 | 175 | 139 | 104

| | |

2 years in 10 | 190 | 154 | 121

| | |

1 year in 10 | 198 | 163 | 129

| | |

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