Bellevue climate

Bellevue Frost Dates and Growing Season

NOAA 1991-2020 normals for Bellevue L&d 12, 0.2 km from Bellevue, elevation 603 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bellevue L&d 12. 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 25 and the first fall freeze around October 16, a growing season of about 172 days.

Median at 36°F
last May 5, first October 5
Median at 32°F
last April 25, first October 16
Median at 28°F
last April 13, first October 27

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 20May 16May 12May 9May 5May 3Apr 30Apr 27Apr 21
32°FMay 11May 5May 2Apr 29Apr 25Apr 22Apr 18Apr 15Apr 10
28°FMay 2Apr 25Apr 21Apr 17Apr 13Apr 10Apr 7Apr 4Apr 1
24°FApr 19Apr 11Apr 8Apr 5Apr 3Apr 1Mar 28Mar 23Mar 15
20°FApr 7Apr 1Mar 29Mar 25Mar 22Mar 19Mar 16Mar 12Mar 7
16°FMar 29Mar 24Mar 20Mar 17Mar 14Mar 10Mar 8Mar 4Feb 27

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 23Sep 27Sep 30Oct 2Oct 5Oct 8Oct 10Oct 14Oct 19
32°FOct 1Oct 7Oct 10Oct 14Oct 16Oct 19Oct 21Oct 24Oct 29
28°FOct 13Oct 18Oct 21Oct 24Oct 27Oct 29Oct 31Nov 2Nov 8
24°FOct 24Oct 30Nov 1Nov 2Nov 5Nov 8Nov 12Nov 15Nov 20
20°FNov 2Nov 6Nov 10Nov 12Nov 16Nov 19Nov 22Nov 26Dec 1
16°FNov 8Nov 13Nov 18Nov 22Nov 25Nov 28Dec 1Dec 5Dec 11

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°F170164160156152149145140134
32°F194186180176172169164159152
28°F215207203199195190185180173
24°F236229224220216212207202194
20°F259251246242237232228223214
16°F277269263259254250246241233

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
100% of years
20°F or colder
100% of years
16°F or colder
100% 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
6,710
Cooling degree days, base 65°F
821
Growing degree days, base 40°F
5,111
Growing degree days, base 45°F
4,005
Growing degree days, base 50°F
3,021
Growing degree days, base 55°F
2,162
Growing degree days, base 60°F
1,426

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,37900
February1,14001
March900118
April504488
May21148317
June30179599
July4272733
August10221676
September11687426
October42310143
November803020
December1,19201

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 0.2 km from Bellevue. 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 USC00130608 (Bellevue L&d 12). Public domain.