Average First Freeze & Frost Dates

Dew and Frost are the results of what is known as radiational cooling. At night, outside objects will release heat into the atmosphere, thus cooling the object. At the same time, the atmosphere will radiate heat back into the object. But on a clear, calm night the amount of heat loss tends to be higher and the object can become 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 air’s water vapor content) and become saturated. If the air temperature is above freezing, the result will be the formation of dew. However, 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 measurements 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

09/21

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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