Jonestown climate

Jonestown Frost Dates and Growing Season

NOAA 1991-2020 normals for Austin Great Hills, 17.5 km from Jonestown, elevation 880 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Austin Great Hills. 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 11 and the first fall freeze around November 20, a growing season of about 254 days.

Median at 36°F
last March 25, first November 10
Median at 32°F
last March 11, first November 20
Median at 28°F
last March 1, first December 3

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°FApr 11Apr 4Apr 1Mar 28Mar 25Mar 21Mar 17Mar 12Mar 6
32°FMar 29Mar 23Mar 19Mar 15Mar 11Mar 7Mar 4Feb 28Feb 22
28°FMar 19Mar 13Mar 9Mar 5Mar 1Feb 26Feb 19Feb 12Jan 31
24°FMar 11Mar 4Feb 27Feb 19Feb 13Feb 6Jan 29Jan 20Jan 5
20°FMar 2Feb 20Feb 10Feb 1Jan 26Jan 17Jan 9Dec 31Dec 20
16°FFeb 10Jan 31Jan 21Jan 14Jan 9Jan 6Jan 2Dec 27Dec 18

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 27Nov 1Nov 3Nov 6Nov 10Nov 12Nov 16Nov 20Nov 27
32°FNov 3Nov 9Nov 13Nov 16Nov 20Nov 24Nov 28Dec 2Dec 9
28°FNov 12Nov 19Nov 24Nov 29Dec 3Dec 7Dec 12Dec 19Dec 29
24°FNov 26Dec 2Dec 8Dec 13Dec 20Dec 28Jan 3Jan 10Jan 27
20°FDec 5Dec 14Dec 21Dec 30Jan 3Jan 8Jan 16Jan 28Feb 14
16°FDec 15Dec 20Dec 29Jan 1Jan 4Jan 7Jan 13Jan 21Feb 4

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°F256246240235231227221215207
32°F278271265259254249243237230
28°F309299290284278272267260252
24°F349337328319310303296287274
20°F365365365360351343334325306
16°F365365365365365365365361345

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
100% of years
24°F or colder
94% of years
20°F or colder
63% of years
16°F or colder
22% 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
1,904
Cooling degree days, base 65°F
2,746
Growing degree days, base 40°F
10,035
Growing degree days, base 45°F
8,316
Growing degree days, base 50°F
6,698
Growing degree days, base 55°F
5,223
Growing degree days, base 60°F
3,901

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January510392
February34412164
March20243330
April62116505
May10290746
June0492942
July05941,059
August06001,064
September2390838
October56169580
November24933269
December4704110

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 17.5 km from Jonestown. 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 USC00410433 (Austin Great Hills). Public domain.