Damascus climate

Damascus Frost Dates and Growing Season

NOAA 1991-2020 normals for Portland WFO, 17 km from Damascus, elevation 21 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Portland WFO. 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 13 and the first fall freeze around November 22, a growing season of about 251 days.

Median at 36°F
last April 10, first November 5
Median at 32°F
last March 13, first November 22
Median at 28°F
last February 12, first December 10

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 1Apr 26Apr 19Apr 14Apr 10Apr 5Apr 2Mar 29Mar 22
32°FApr 5Mar 29Mar 24Mar 18Mar 13Mar 9Mar 4Feb 27Feb 20
28°FMar 7Feb 28Feb 24Feb 19Feb 12Feb 4Jan 28Jan 11Dec 27
24°FFeb 20Feb 11Feb 1Jan 22Jan 10Jan 2Dec 27Dec 17Dec 6
20°FFeb 16Feb 3Jan 20Jan 4Dec 31Dec 24Dec 15Dec 9Nov 30
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 20Oct 24Oct 28Nov 1Nov 5Nov 8Nov 11Nov 15Nov 22
32°FNov 3Nov 9Nov 13Nov 17Nov 22Nov 26Nov 30Dec 4Dec 14
28°FNov 15Nov 24Nov 30Dec 5Dec 10Dec 18Dec 26Jan 2Jan 22
24°FNov 27Dec 5Dec 10Dec 18Dec 26Jan 1Jan 8Jan 20Feb 7
20°FNov 27Dec 6Dec 10Dec 17Dec 24Dec 31Jan 10Jan 27Feb 11
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°F232223217211206200195188179
32°F286272264256251244238232224
28°F350334324313307300290280265
24°F365365365362351341334325312
20°F365365365365365365365350334
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
94% of years
24°F or colder
63% of years
20°F or colder
24% of years
16°F or colder
4% 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
4,258
Cooling degree days, base 65°F
439
Growing degree days, base 40°F
5,449
Growing degree days, base 45°F
3,917
Growing degree days, base 50°F
2,677
Growing degree days, base 55°F
1,707
Growing degree days, base 60°F
960

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January73503
February59206
March530037
April3733111
May21121278
June9749402
July17151600
August13155608
September7458434
October3143171
November555026
December74703

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 km from Damascus. 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 USC00356750 (Portland WFO). Public domain.