How many chill hours has Boulder had this winter?

70 hours at or below 45°F from 1 November to Nov 8, 2026, estimated from the daily highs and lows at the Boulder Muni Airport station.

How many chill hours did Boulder get last winter?

1,523 hours from 1 November to 28 February (2025-26).

Which chill model is this?

The simple 45°F model: every hour at or below 45°F counts. The 32 to 45°F count, which leaves out hours below freezing, is shown as well.

Boulder, Colorado · winter 2026-27

Chill hours in Boulder this winter

Chill hours so far (45°F model)7070 hours at or below 45°F since 1 November, to Nov 8. Same date last winter: 74. Station: Boulder Muni Airport, 5 km away.

Last winter (2025-26)

1,523

1 Nov to 28 Feb

By this date last winter

1 Nov to Nov 8

Hours 32–45°F so far

the 0–45°F model leaves out freezing hours

Coldest month last winter

January

496 chill hours

Chill hours accumulated since 1 November

Hours at or below 45°F, running total. Grey: last winter; clay: this winter so far.

Winter 2026-27
Winter 2025-26

View as table

Month	Chill hours (≤ 45°F)
November 2025	319
December 2025	387
January 2026	496
February 2026	321
Total	1,523

Source: NOAA NCEI GHCN-Daily, station USW00000160; hours estimated from each day's high and low.

Fruit trees need a set number of cold hours in winter before they bloom well. Nurseries rate varieties by it: low-chill varieties need roughly 100 to 400 hours, many peaches and plums 500 to 900, and most apples and sweet cherries 800 to 1,200 or more. Your variety's rating is the number to compare with the 1,523 hours Boulder had last winter.

Chill hours here are hours at or below 45°F, estimated hour by hour from the station's daily high and low. Checked against measured hourly air temperature at 39 NOAA reference stations last winter, the estimate was within 1.9% of the measured count at the median station. How it is checked.

Chill hours nearby

Each from a different station.

City	Distance	Chill hours so far	Last winter
Brighton, CO	38 km	57	1,769
Denver, CO	39 km	49	1,597
Fort Collins, CO	65 km	68	1,681
Greeley, CO	66 km	48	1,674
Castle Rock, CO	80 km	82	1,718
Cañon City, CO	175 km	54	1,476

Questions

How many chill hours has Boulder had this winter?: 70 hours at or below 45°F from 1 November to Nov 8, 2026, estimated from the daily highs and lows at the Boulder Muni Airport station.
How many chill hours did Boulder get last winter?: 1,523 hours from 1 November to 28 February (2025-26).
Which chill model is this?: The simple 45°F model: every hour at or below 45°F counts. The 32 to 45°F count, which leaves out hours below freezing, is shown as well.

Data: Global Historical Climatology Network - Daily (GHCN-Daily), daily maximum and minimum temperature (NOAA National Centers for Environmental Information (NCEI)); GeoNames gazetteer (cities15000) (GeoNames).