Hillsboro, Oregon climate: Normal weather by month, frost dates and records
Hillsboro's normal year runs from 33°F December nights to 82°F July afternoons, with 35.9 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 11.4°C, December lows of 1°C, July highs of 28°C, 913 mm of precipitation a year.
- NOAA stationPortland-Hillsboro Airport
- Station IDUSW00094261
- Location45.54°N 122.95°W
- Elevation204 ft (62 m)
- Population110,337
On October 14, the normal high in Hillsboro is 64°F and the normal low 41°F, and the chance of measurable rain or snow is 46%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Hillsboro.
- Jan 47° 34°
- Feb 51° 34°
- Mar 56° 37°
- Apr 61° 39°
- May 69° 45°
- Jun 74° 49°
- Jul 82° 52°
- Aug 82° 52°
- Sep 76° 48°
- Oct 64° 41°
- Nov 53° 37°
- Dec 46° 33°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Hillsboro each month?
July is the warmest month, with normal highs of 82°F; December the coldest, with normal lows of 33°F. The most precipitation falls in December (6.05 in), the least in July (0.37 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 47°F | 34°F | 40.4°F | 5.27 | 19 | <1 | 13 | 9 h |
| February | 51°F | 34°F | 42.3°F | 3.97 | 16 | <1 | 13 | 10 h 20 min |
| March | 56°F | 37°F | 46.2°F | 3.70 | 18 | <1 | 9 | 11 h 50 min |
| April | 61°F | 39°F | 50.1°F | 2.57 | 16 | <1 | 3 | 13 h 30 min |
| May | 69°F | 45°F | 56.7°F | 2.02 | 12 | <1 | 1 | 14 h 50 min |
| June | 74°F | 49°F | 61.0°F | 1.31 | 9 | 2 | <1 | 15 h 40 min |
| July | 82°F | 52°F | 67.2°F | 0.37 | 3 | 6 | <1 | 15 h 20 min |
| August | 82°F | 52°F | 67.1°F | 0.48 | 4 | 6 | <1 | 14 h 10 min |
| September | 76°F | 48°F | 62.0°F | 1.38 | 8 | 2 | <1 | 12 h 40 min |
| October | 64°F | 41°F | 52.3°F | 3.37 | 15 | <1 | 3 | 11 h |
| November | 53°F | 37°F | 44.6°F | 5.44 | 19 | <1 | 9 | 9 h 30 min |
| December | 46°F | 33°F | 39.8°F | 6.05 | 20 | <1 | 14 | 8 h 40 min |
| Year (annual) | 63°F | 42°F | 52.5°F | 35.93 | 159 | 17 | 64 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 8°C | 1°C | 4.7°C | 134 mm |
| February | 11°C | 1°C | 5.7°C | 101 mm |
| March | 13°C | 3°C | 7.9°C | 94 mm |
| April | 16°C | 4°C | 10.1°C | 65 mm |
| May | 20°C | 7°C | 13.7°C | 51 mm |
| June | 23°C | 9°C | 16.1°C | 33 mm |
| July | 28°C | 11°C | 19.6°C | 9 mm |
| August | 28°C | 11°C | 19.5°C | 12 mm |
| September | 25°C | 9°C | 16.7°C | 35 mm |
| October | 18°C | 5°C | 11.3°C | 86 mm |
| November | 11°C | 3°C | 7.0°C | 138 mm |
| December | 8°C | 1°C | 4.3°C | 154 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Forest Grove (8 miles away), gets 3 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094261; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Hillsboro?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, July has the fewest days with rain (3).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094261.
When is the last frost in Hillsboro?
In Hillsboro, the last spring frost (32°F) comes after April 16 in half of years and after May 3 in one year in ten; the first autumn frost comes before October 23 in half of years and before October 3 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 161 year in 10 after May 3; 9 in 10 after March 25
- First autumn frost, half of years before
- October 231 year in 10 before October 3; 9 in 10 before November 18
NOAA puts the median frost-free season at 191 days, and the season without a hard freeze (28°F) at 243 days.
A hard freeze (28°F) comes after March 13 in half of springs and before November 12 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Hillsboro in zone 8b across its 3 ZIP code areas (8b in 97124, the largest). By the map's own method, the average of each year's coldest night over 1991-2020, Hillsboro's NOAA station is in zone 8b: the coldest night of a typical year reaches 17°F (21 complete years).
Frost dates for every NOAA station in Oregon · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00094261; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
What hardiness zone is each Hillsboro ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Hillsboro's 3 ZIP code areas are all in zone 8b. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Hillsboro?
In a normal year in Hillsboro, 17 days a year reach 90°F (1 of them 100°F or more), 64 nights fall to 32°F or colder and 159 days bring measurable precipitation.
- Days at 90°F or more
- 17a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 64a normal year
- Days that stay below freezing
- 2high of 32°F or less
- Days with 0.01 inch of precipitation
- 159a normal year
The highest temperature in Hillsboro's official record (kept by the National Weather Service since 1929) is 114°F, on June 28, 2021; the lowest is −14°F, on January 21, 1930.
The wettest calendar year on that record is 1996, with 62.59 in; the snowiest season is 1949–50, with 44.1 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00094261; records: ACIS (NOAA Regional Climate Centers), NWS threaded record HIOthr. Records use complete months only; a month missing more than three days is left out.
How humid and windy is Hillsboro, and how clear are its skies?
The summer (June-August) dew point averages 52°F. The muggiest month is July, with an average dew point of 53°F; the driest air comes in December (35°F). March is the windiest month (5.4 mph on average), and July has the most clear or nearly clear hours (78%).
| Month | Dew point | Humidity | Afternoon humidity | Wind | Clear or few clouds | Overcast |
|---|---|---|---|---|---|---|
| January | 37°F | 83% | 69% | 4.7 mph | 38% | 44% |
| February | 37°F | 78% | 60% | 5.3 mph | 39% | 39% |
| March | 40°F | 76% | 55% | 5.4 mph | 38% | 36% |
| April | 43°F | 70% | 49% | 5.3 mph | 46% | 33% |
| May | 48°F | 68% | 49% | 5.0 mph | 49% | 31% |
| June | 52°F | 65% | 44% | 5.0 mph | 62% | 22% |
| July | 53°F | 61% | 38% | 5.0 mph | 78% | 12% |
| August | 51°F | 64% | 39% | 4.5 mph | 72% | 13% |
| September | 48°F | 72% | 46% | 3.9 mph | 64% | 21% |
| October | 42°F | 82% | 63% | 4.0 mph | 51% | 34% |
| November | 37°F | 85% | 73% | 4.9 mph | 38% | 45% |
| December | 35°F | 86% | 77% | 4.8 mph | 34% | 53% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00094261. Monthly averages of all hours; afternoon humidity at 3 p.m. local standard time; sky as the share of hours NOAA's observations rate clear or few clouds (a dash where NOAA publishes no sky value).
How sunny is Hillsboro?
Over a year 70% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Hillsboro, 3.7 kWh per square metre a day. July is the sunniest month (83%) and December the cloudiest (52%). Among the 459 U.S. places of 50,000 or more, that ranks tied 428th (with 16 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 54% | 1.2 |
| February | 60% | 2.1 |
| March | 59% | 3.0 |
| April | 63% | 4.3 |
| May | 68% | 5.4 |
| June | 70% | 6.0 |
| July | 83% | 6.8 |
| August | 83% | 5.8 |
| September | 78% | 4.3 |
| October | 67% | 2.6 |
| November | 56% | 1.4 |
| December | 52% | 1.0 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Hillsboro need?
A normal year in Hillsboro brings 4,830 heating degree days, 10% fewer than the median U.S. place (5,373), and 275 cooling degree days, 70% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,195 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 761 | 0 |
| February | 637 | 0 |
| March | 583 | 0 |
| April | 449 | 1 |
| May | 266 | 9 |
| June | 147 | 28 |
| July | 36 | 103 |
| August | 36 | 101 |
| September | 124 | 33 |
| October | 395 | 1 |
| November | 614 | 0 |
| December | 783 | 0 |
| Year (annual) | 4,830 | 275 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094261. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Hillsboro been warmer than normal lately?
2025 averaged 54.2°F, 1.7°F above the 1991-2020 normal of 52.5°F. 5 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 53.3°F | +0.8°F | 36.05 |
| 2022 | 52.6°F | +0.1°F | 35.84 |
| 2023 | 53.5°F | +1.0°F | – |
| 2024 | 53.6°F | +1.1°F | 40.99 |
| 2025 | 54.2°F | +1.7°F | 28.50 |
Source: observed years: ACIS, station USW00094261. A year counts only with all twelve months complete.
How does Hillsboro's climate compare?
Hillsboro is warmer than 58 of the other 104 places with their own NOAA record in Oregon, and wetter than 48. Across the 7,247 U.S. stations with normals, its annual mean of 52.5°F is warmer than 52%.
In the Köppen classification computed from these normals, Hillsboro is Csb: temperate, dry-summer, warm summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Hillsboro share this climate record?
North Plains has no NOAA station with 1991-2020 normals of its own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- North Plains, OR3,424 people · 5 mi NW
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Hillsboro's climate
What is the coldest month in Hillsboro?
December, with a normal high of 46°F and a normal low of 33°F. The warmest is July (82°F by day, 52°F at night).
Does it snow in Hillsboro?
Yes. NOAA publishes no 1991-2020 snowfall normal for Hillsboro's NOAA station; the nearest record that keeps one, Forest Grove (8 miles away), records 3 inches of snow in a normal year.
What is the rainiest month in Hillsboro?
December, with 6.05 in of precipitation in a normal year; the driest is July with 0.37 in.
What plant hardiness zone is Hillsboro in?
The USDA's 2023 map puts Hillsboro in zone 8b across its 3 ZIP code areas (8b in 97124, the largest). By the same method at Hillsboro's NOAA station, the coldest night of a typical year reaches 17°F (21 years, 1991-2020): zone 8b.
How late can frost come in Hillsboro?
In half of years the last 32°F night comes after April 16; in one year in ten it comes after May 3. Waiting until May 3 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Hillsboro in OctoberThis month day by day, its records and recent years
- Oregon climateThe statewide normals and every place in the state
- Nature Park-Beaverton, OR6 miles from this station, 55.8°F a year
- Forest Grove, OR7 miles from this station, 52.1°F a year
- Beaverton, OR9 miles from this station, 53.7°F a year
- Vancouver, WA15 miles from this station, 54.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made