Back-to-back powerful Pacific storm systems to impact the Pacific Northwest and northern California through the end of this week with heavy rain, flooding, strong winds, and higher elevation mountain snow. A strong, long-duration atmospheric river will accompany the Pacific storms, bringing excessive rainfall and flash flooding to southwest Oregon and northwest California through the week. Read More >
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 |
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