Lewiston climate

Lewiston Frost Dates and Growing Season

NOAA 1991-2020 normals for Trinity Rvr Hatchery, 2.4 km from Lewiston, elevation 1861 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Trinity Rvr Hatchery. 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 April 23 and the first fall freeze around October 22, a growing season of about 178 days.

Median at 36°F
last May 11, first October 4
Median at 32°F
last April 23, first October 22
Median at 28°F
last March 28, first November 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°FJun 1May 26May 20May 16May 11May 7May 4Apr 30Apr 25
32°FMay 11May 4Apr 30Apr 26Apr 23Apr 19Apr 15Apr 10Apr 3
28°FApr 19Apr 12Apr 6Apr 1Mar 28Mar 21Mar 14Mar 7Feb 22
24°FMar 23Mar 11Mar 1Feb 22Feb 14Feb 6Jan 24Jan 8Dec 25
20°FFeb 20Feb 8Jan 25Jan 14Jan 6Jan 1Dec 26Dec 13Nov 30
16°FJan 19Jan 10Jan 3Dec 31Dec 28Dec 21Dec 16Dec 8Dec 1

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°FSep 21Sep 27Sep 29Oct 2Oct 4Oct 8Oct 12Oct 15Oct 22
32°FOct 4Oct 9Oct 14Oct 18Oct 22Oct 25Oct 29Nov 2Nov 13
28°FOct 17Oct 23Oct 29Nov 1Nov 6Nov 14Nov 22Nov 30Dec 9
24°FNov 1Nov 10Nov 20Nov 29Dec 5Dec 12Dec 21Jan 1Jan 28
20°FNov 17Nov 30Dec 5Dec 13Dec 23Dec 30Jan 7Jan 20Feb 9
16°FNov 27Dec 5Dec 12Dec 17Dec 22Dec 28Jan 1Jan 4Jan 14

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°F168160154149145139134128119
32°F208197190184178173168163153
28°F272255244235227219211204193
24°F349331318308300287278263248
20°F365365365364353341333321309
16°F365365365365365365365365354

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
58% of years
16°F or colder
16% 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
4,034
Cooling degree days, base 65°F
856
Growing degree days, base 40°F
6,062
Growing degree days, base 45°F
4,570
Growing degree days, base 50°F
3,336
Growing degree days, base 55°F
2,322
Growing degree days, base 60°F
1,504

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January73301
February575011
March513056
April3712132
May17540337
June51128527
July3307769
August4256718
September45111516
October25712233
November540035
December76701

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 2.4 km from Lewiston. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00049026 (Trinity Rvr Hatchery). Public domain.