Fall Average Frost and Freeze Dates

Fall Average Frost and Freeze Dates for Eastern Utah and Western Colorado

Dew and Frost occur due to radiational cooling. Radiational cooling happens at night when outside objects release heat into the atmosphere cooling the object. At the same time, the atmosphere radiates heat back into the object. On a clear, calm night, however, the amount of heat lost from the object tends to exceed the heat gained from the atmosphere and the object becomes cooler than the surrounding air.

With sufficient cooling, the air adjacent to the object can cool to its dew point temperature (a measure of the water vapor content present in the air) and become saturated. If the air temperature is above freezing, dew will form. If the temperature is near or below freezing, frost will develop.

Cold air is more dense than warm air and tends to sink. On a calm night, air will sink into lower elevations, creating a temperature "inversion" that keeps the colder air near the surface. Under such conditions, valleys can be much colder than the surrounding higher terrain.

On Calm, clear nights, the temperature near the ground can be three or four degrees cooler than just a few feet above. Most temperature measurments are made about 6 feet above the ground, so even if the thermometer reads about 35 or 36 degrees, the temperature near the surface can be very close to the freezing point.

Average First Freeze/Frost Dates (Colorado):

Station	Temperature <28.6° F	Temperature <32.6° F	Station	Temperature <28.6° F	Temperature <32.6° F
Aspen	9/21	9/04	Meeker	9/19	9/10
Cedaredge	10/14	10/03	Mesa Verde	10/21	10/15
Collbran	10/04	9/22	Montrose	10/17	10/05
Cortez	10/15	9/30	Norwood	10/02	9/20
Craig	9/23	9/10	Orch. Mesa	10/29	10/17
Crested Butte	9/04	8/16	Ouray	10/08	9/26
Delta	10/14	9/27	Pagosa Sp	9/21	9/07
Durango	10/04	9/21	Palisade	11/09	10/25
Fruita	10/14	10/03	Paonia	10/19	10/08
Glenwood	10/07	9/26	Rangely	10/05	9/24
Grand Junction	11/01	10/22	Rifle	10/05	9/22
Gunnison	9/11	8/29	Silverton	9/01	8/14
Hayden	9/20	9/13	Steamboat	9/07	8/20
Ignacio	10/01	9/18	Telluride	9/14	8/27
Lake City	9/15	9/10	Yampa	9/18	9/12
Maybell	9/20	9/09	Yellow Jacket	10/16	10/07

Average First Freeze/Frost Dates (Utah):

Station	Temperature <28.6° F	Temperature <32.6° F	Station	Temperature <28.6° F	Temperature <32.6° F
Blanding	10/21	10/12	La Sal	10/08	10/03
Bluff	10/22	10/09	Manila	9/30	9/19
Canyonlands	10/29	10/19	Mexican Hat	10/31	10/22
Castle Valley	10/31	10/18	Moab	10/31	10/19
Cedar Point	10/18	10/09	Monticello	10/08	9/26
Dewey	10/18	10/06	Ouray	10/09	9/25
Dutch John	9/21	9/15	Roosevelt	10/09	9/25
Ft Duchesne	10/02	9/21	Thompson	10/31	10/21
Jensen	9/29	9/19	Vernal	9/29	9/21