Photo: M.O. Stevens at en.wikipedia · Public domainJuly in Hillsboro stays fresher than in 88% of U.S. towns
In January the night’s low is typically 35°. Winters are mild: January nights here are milder than in 81% of U.S. towns. Since 1901–2000, the year has warmed by 1.2°, most of all in January. Garden planting can start around April 16; autumn frost returns near October 23.
A year in Hillsboro at a glance
Each month’s typical high and low, and what it brings.
What stands out about Hillsboro’s climate
Compared with towns across the U.S., with Hillsboro’s place in Oregon beside it.
What a year in Hillsboro feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 191 frost-free days a year
In half of years the last 32° night comes by April 16 and the first by October 23. Frost and day counts come from Portland-hillsboro Airport, Hillsboro’s official weather station (the one in National Weather Service reports), 1.3 miles from the city’s center point, at about the same height.
The 2023 USDA map puts Hillsboro’s center in zone 8b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 19°. 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 5 inches of snow a winter
Snow, measured at Dilley 2 S, OR, falls mostly in January, February and December. Precipitation (rain plus melted snow) adds up to 38 inches a year; December is the wettest month and July the driest. Rain or snow falls on about 152 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Hillsboro
95% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Portland-hillsboro Airport.
Living with Hillsboro’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
191 frost-free days in zone 8b. The last frost comes by Apr 16 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 23.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October. 32 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Hillsboro from natural hazards, earthquakes are the largest share (68%); heat waves, cold waves, winter storms and ice storms together are 7%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Hillsboro and its neighbors
Every town next door is within a degree of Hillsboro in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Hillsboro’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 |
|---|---|---|---|---|
| Hillsboro, OR | 35° | 81° | 38" | 5.2" |
| Scotts Valley, CA | 39° | 79° | 37" | 0.0" |
| Kirkland, WA | 36° | 76° | 37" | 3.8" |
| Brigantine, NJ | 28° | 83° | 45" | 10" |
| Ocean City, MD | 30° | 86° | 46" | 10" |
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 Hillsboro averaged 1.2° warmer than the 1900s. The biggest change is in January (+3.0°).
A smaller shift than in 61% 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. In a city of 111,000 people, part of the change is the city itself: pavement and buildings hold heat (the urban heat island).
How Hillsboro compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Hillsboro’s place among Oregon’s.
Hillsboro weather by month
Highs, lows and precipitation from NOAA’s grid at Hillsboro’s center; snow, wet days and snow on the ground from Dilley 2 S, OR. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 47° | 35° | 5.8" | 1.6" | 20 | 2 | 35° – 46° |
| February | 51° | 36° | 4.2" | 1.6" | 15 | 1 | 37° – 49° |
| March | 56° | 38° | 4.1" | 0.0" | 18 | 0 | 44° – 52° |
| April | 61° | 41° | 2.9" | 0.0" | 16 | 0 | 46° – 56° |
| May | 68° | 46° | 2.1" | 0.0" | 12 | 0 | 52° – 61° |
| June | 73° | 50° | 1.4" | 0.0" | 8 | 0 | 58° – 68° |
| July | 81° | 54° | 0.4" | 0.0" | 3 | 0 | 62° – 71° |
| August | 82° | 54° | 0.5" | 0.0" | 3 | 0 | 65° – 71° |
| September | 76° | 50° | 1.3" | 0.0" | 6 | 0 | 59° – 66° |
| October | 64° | 44° | 3.3" | 0.0" | 12 | 0 | 49° – 58° |
| November | 53° | 39° | 5.8" | 0.3" | 19 | 0 | 40° – 51° |
| December | 46° | 35° | 6.8" | 1.7" | 21 | 1 | 36° – 44° |
| Year | 63° | 43° | 38.4" | 5.2" | 152 | 4 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 37° to 49°. September is the most reliable, staying within 7°.
Where Hillsboro’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 Hillsboro’s center.
- Snow: Dilley 2 S, OR.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Portland-hillsboro Airport, 1.3 miles from the city’s center point, at about the same height; the city’s official station.
- 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 Hillsboro’s climate
What is the weather like in Hillsboro?
A typical July afternoon reaches 81°, a January night drops to 35°, and about 5 inches of snow falls in a normal winter. Milder January nights than 81% of U.S. towns; cooler July afternoons than 88% of U.S. towns.
How cold does it get in Hillsboro in winter?
December nights average 35°. About 64 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 36°.
How much snow does Hillsboro get?
About 5.2 inches in a normal winter at Dilley 2 S, OR, most of it in January, February and December, with snow on the ground about 4 days a year.
How hot does it get in Hillsboro?
July, with a typical high of 81° and a low of 54°. About 17 days a year reach 90° and 1 reach 100° (Portland-hillsboro Airport).
When is the first and last frost in Hillsboro?
In half of years the last spring frost (32°) comes by April 16 and the first fall frost by October 23, about 191 frost-free days, at Portland-hillsboro Airport.
What growing zone is Hillsboro in?
Zone 8b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 19°.
What is the best time of year to visit Hillsboro?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Hillsboro getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 61% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Hillsboro.
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.