Middletown climate

Middletown Frost Dates and Growing Season

NOAA 1991-2020 normals for Calistoga, 17.4 km from Middletown, elevation 400 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Calistoga. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around March 2 and the first fall freeze around November 23, a growing season of about 263 days.

Median at 36°F
last April 13, first November 4
Median at 32°F
last March 2, first November 23
Median at 28°F
last January 23, first December 6

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 18May 1Apr 25Apr 19Apr 13Apr 7Apr 1Mar 24Mar 10
32°FApr 18Apr 4Mar 25Mar 13Mar 2Feb 23Feb 14Feb 1Jan 19
28°FMar 6Feb 20Feb 4Jan 30Jan 23Jan 12Jan 1Dec 26Dec 12
24°FFeb 14Jan 28Jan 14Jan 5Dec 31Dec 25Dec 19Dec 11Dec 3
20°F–––––––––
16°F–––––––––

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 13Oct 22Oct 27Nov 1Nov 4Nov 7Nov 12Nov 18Nov 27
32°FNov 1Nov 7Nov 13Nov 19Nov 23Nov 30Dec 2Dec 7Dec 20
28°FNov 16Nov 25Dec 1Dec 3Dec 6Dec 12Dec 18Dec 31Jan 15
24°FNov 30Dec 3Dec 7Dec 12Dec 19Dec 25Jan 1Jan 8Jan 28
20°F–––––––––
16°F–––––––––

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F244230218210203195187178165
32°F313296282272263252242227208
28°F365352341334327318306294272
24°F365365365365365358348338326
20°F365365365365365365365365365
16°F365365365365365365365365365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
87% of years
24°F or colder
42% of years
20°F or colder
7% of years
16°F or colder
0% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
2,593
Cooling degree days, base 65°F
836
Growing degree days, base 40°F
7,373
Growing degree days, base 45°F
5,602
Growing degree days, base 50°F
3,994
Growing degree days, base 55°F
2,666
Growing degree days, base 60°F
1,620

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January493048
February381082
March3363156
April2409227
May12345388
June29137558
July2222685
August1209673
September14158594
October11452404
November3382143
December524037

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 17.4 km from Middletown. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00041312 (Calistoga). Public domain.