An Alberta clipper will bring lake effect snow downwind of the Great Lakes, with the highest snow totals downwind of Lakes Erie and Ontario. Snow squalls may impact New Year's Eve travel during the evening and overnight hours across parts of the Great Lakes, Ohio Valley, and Northeast. Heavy rain will bring a flash flooding threat for southern California on New Year's Eve into New Year's Day. 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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