Hartley reaches 100° on about 28 days a year, more than 97% of U.S. towns
The depth of winter brings overnight lows near 39°. Only 55° separates winter nights from summer afternoons. By precipitation alone, it ranks drier than 88% of U.S. towns. Garden planting can start around February 18; autumn frost returns near November 28.
A year in Hartley at a glance
Each month’s typical high and low, and what it brings.
What stands out about Hartley’s climate
Compared with towns across the U.S., with Hartley’s place in California beside it.
What a year in Hartley feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 283 frost-free days a year
In half of years the last 32° night comes by February 18 and the first by November 28. Day counts come from NOAA’s station at Vacaville, CA, 1.8 miles from the town’s center, at about the same height; frost dates and degree days from Vacaville Nut Tree Airport, 3.0 miles away.
The 2023 USDA map puts Hartley’s center in zone 9b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 26°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 23 inches of rain a year
January is the wettest month and July the driest. Rain falls on about 63 days a year. Snow is rare: about 0.0" in a normal year at Davis 2 Wsw Exp Farm, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Hartley
64% of the work is heating. Months averaging under 55° run from November through February.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Vacaville Nut Tree Airport.
Living with Hartley’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
283 frost-free days in zone 9b. The last frost comes by Feb 18 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Nov 28.
Months with highs of 62–84° and lows of 40° or more: March, April, May, October and November. 1.2 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Hartley from natural hazards, earthquakes are the largest share (56%). Normals are averages; the hazards page covers the extremes.
Natural hazards →Hartley and its neighbors
Every town next door is within a degree of Hartley in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Hartley’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Hartley, CA | 39° | 93° | 23" | 0.0" |
| Brady, TX | 35° | 95° | 27" | 0.3" |
| Corona de Tucson, AZ | 36° | 96° | 14" | 0.1" |
| Central Point, OR | 32° | 93° | 22" | 3.4" |
| Hobbs, NM | 28° | 94° | 14" | 1.8" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Hartley averaged 1.5° warmer than the 1900s. The biggest change is in January (+2.0°).
A bigger shift than in 57% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Hartley compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Hartley’s place among California’s.
Hartley weather by month
Highs, lows and precipitation from NOAA’s grid at Hartley’s center; snow, wet days and snow on the ground from Davis 2 Wsw Exp Farm, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 57° | 39° | 4.9" | 0.0" | 12 | 0 | 44° – 53° |
| February | 62° | 42° | 4.7" | 0.0" | 10 | 0 | 47° – 56° |
| March | 67° | 44° | 3.2" | 0.0" | 9 | 0 | 49° – 62° |
| April | 73° | 47° | 1.3" | 0.0" | 5 | 0 | 55° – 64° |
| May | 80° | 52° | 0.8" | 0.0" | 3 | 0 | 58° – 74° |
| June | 88° | 57° | 0.1" | 0.0" | 1 | 0 | 68° – 75° |
| July | 93° | 58° | 0.0" | 0.0" | 0 | 0 | 72° – 80° |
| August | 93° | 58° | 0.0" | 0.0" | 0 | 0 | 72° – 79° |
| September | 89° | 56° | 0.1" | 0.0" | 1 | 0 | 69° – 75° |
| October | 79° | 50° | 0.9" | 0.0" | 3 | 0 | 61° – 69° |
| November | 66° | 43° | 2.2" | 0.0" | 7 | 0 | 48° – 59° |
| December | 57° | 39° | 4.8" | 0.0" | 11 | 0 | 44° – 53° |
| Year | 75° | 49° | 22.9" | 0.0" | 63 | 0 |
How much a month can swing
A normal is an average. May swings the most: from 1991 to 2020 its average ranged from 58° to 74°. September is the most reliable, staying within 6°.
Where Hartley’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Hartley’s center.
- Snow: Davis 2 Wsw Exp Farm, CA.
- Frost dates, heating and cooling: Vacaville Nut Tree Airport, 3.0 miles away.
- Freezing nights, 90° and 100° days: Vacaville, CA, 1.8 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Hartley’s climate
What is the weather like in Hartley?
A typical July afternoon reaches 93°, a January night drops to 39°, and snow is almost unheard of. Milder January nights than 87% of U.S. towns; hotter July afternoons than 91% of U.S. towns.
How cold does it get in Hartley in winter?
December nights average 39°. About 14 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 44°.
How much snow does Hartley get?
About 0.0 inches in a normal winter at Davis 2 Wsw Exp Farm, CA, so most winters see none.
How hot does it get in Hartley?
July, with a typical high of 93° and a low of 58°. About 102 days a year reach 90° and 28 reach 100° (Vacaville Nut Tree Airport).
When is the first and last frost in Hartley?
In half of years the last spring frost (32°) comes by February 18 and the first fall frost by November 28, about 283 frost-free days, at Vacaville Nut Tree Airport.
What growing zone is Hartley in?
Zone 9b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 26°.
What is the best time of year to visit Hartley?
By one simple rule (highs of 62–84° and lows of 40° or more), March, April, May, October and November. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Hartley getting warmer?
Yes: 1991–2020 averaged 1.5° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 57% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Hartley.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.