Climate and average weather in Napa
In Napa, the summers are hot, dry, and clear and the winters are cool and partly cloudy.
Over the course of the year, the temperature in Napa typically varies from 42°F to 84°F, and is rarely below 33°F or above 95°F. August is the hottest month of the year, while December is the coldest.
Based on the travel score, the best time of year to visit Napa for warm-weather activities is from early April to mid November.
- Hottest
- Aug
- 84°
- Coldest
- Dec
- 42°
- Wettest
- Feb
- 4.6 in
- Driest
- Jul
- 0.0 in
- Rain / yr
- 22.7 in
- 54 wet days
- Daylight
- 9.3–14.7 h
- shortest–longest
- Elevation
- 20 ft
- 38.3°N
- Clearest
- Jul
- 10% cloud
Napa is city in Napa County, California, United States.
- Density
- 1,721/km²
- people per km²
- Founded
- 1872
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Napa weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around early April to mid November.
Temperature through the year
Daily average highs and lows in Napa, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 4.6 months, from May 28 to October 13, with daily high temperatures above 77°F. The hottest month of the year in Napa is August, with an average high of 84°F and low of 57°F.
The cool season lasts 3.1 months, from November 24 to February 26, with daily high temperatures below 62°F. The coldest month of the year in Napa is December, with an average low of 42°F and high of 57°F.
Days typically run about 22°F warmer than nights, with the widest day–night swing (around 27°F) in August.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°F) | 58 | 61 | 65 | 69 | 76 | 82 | 84 | 84 | 83 | 76 | 65 | 57 |
| Avg low (°F) | 42 | 44 | 46 | 48 | 52 | 56 | 57 | 57 | 56 | 52 | 46 | 42 |
| Avg high (°F) | Avg low (°F) | |
|---|---|---|
| Jan | 58 | 42 |
| Feb | 61 | 44 |
| Mar | 65 | 46 |
| Apr | 69 | 48 |
| May | 76 | 52 |
| Jun | 82 | 56 |
| Jul | 84 | 57 |
| Aug | 84 | 57 |
| Sep | 83 | 56 |
| Oct | 76 | 52 |
| Nov | 65 | 46 |
| Dec | 57 | 42 |
Average hourly temperature in Napa
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on August afternoons, near 84°F, and coldest before dawn in December, near 42°F.
Napa weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°F) | Rainfall (inches) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 58° / 42° | 4.6 | 9.4 | 9.6 | 4.3 |
| Feb | 61° / 44° | 4.6 | 8.6 | 10.5 | 5.1 |
| Mar | 65° / 46° | 3.4 | 8.4 | 11.7 | 6.2 |
| Apr | 69° / 48° | 1.5 | 4.9 | 13 | 7.4 |
| May | 76° / 52° | 0.8 | 3.2 | 14 | 8.4 |
| Jun | 82° / 56° | 0.2 | 0.9 | 14.6 | 8.1 |
| Jul | 84° / 57° | 0.0 | 0.1 | 14.4 | 7.6 |
| Aug | 84° / 57° | 0.0 | 0.2 | 13.5 | 7.5 |
| Sep | 83° / 56° | 0.1 | 0.4 | 12.3 | 8.0 |
| Oct | 76° / 52° | 1.0 | 2.9 | 11 | 8.5 |
| Nov | 65° / 46° | 2.2 | 5.9 | 9.9 | 6.5 |
| Dec | 57° / 42° | 4.3 | 9.3 | 9.4 | 4.3 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Napa gets about 22.7 in of precipitation a year. On a typical day the chance of rain is mostly dry, but that rises and falls sharply with the seasons.
The wetter season lasts 5.7 months, from around Oct 31 to Apr 21, peaking in February at about 34% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Jul 28.
February is the wettest month by volume, with 4.6 in over about 9 wet days; July is the driest, with 0.0 in.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 30 | 31 | 26 | 17 | 10 | 3 | 1 | 1 | 2 | 9 | 20 | 30 |
| Rain days | 9 | 9 | 8 | 5 | 3 | 1 | 0 | 0 | 0 | 3 | 6 | 9 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 30 | 9 |
| Feb | 31 | 9 |
| Mar | 26 | 8 |
| Apr | 17 | 5 |
| May | 10 | 3 |
| Jun | 3 | 1 |
| Jul | 1 | 0 |
| Aug | 1 | 0 |
| Sep | 2 | 0 |
| Oct | 9 | 3 |
| Nov | 20 | 6 |
| Dec | 30 | 9 |
Monthly rainfall
Over a full year, Napa collects about 22.7 in of rain across 54 wet days — roughly 1.9 in in an average month.
It doesn’t fall evenly. February is the wettest month with 4.6 in, while July is the driest at just 0.0 in. The three wettest months alone bring about 59% of the year’s total.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (in) | 4.6 | 4.6 | 3.4 | 1.5 | 0.8 | 0.2 | 0.0 | 0.0 | 0.1 | 1.0 | 2.2 | 4.3 |
| Rain days | 9 | 9 | 8 | 5 | 3 | 1 | 0 | 0 | 0 | 3 | 6 | 9 |
| Rainfall (in) | Rain days | |
|---|---|---|
| Jan | 4.6 | 9 |
| Feb | 4.6 | 9 |
| Mar | 3.4 | 8 |
| Apr | 1.5 | 5 |
| May | 0.8 | 3 |
| Jun | 0.2 | 1 |
| Jul | 0.0 | 0 |
| Aug | 0.0 | 0 |
| Sep | 0.1 | 0 |
| Oct | 1.0 | 3 |
| Nov | 2.2 | 6 |
| Dec | 4.3 | 9 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Napa, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around May 9 and lasts for 5.9 months, ending around November 3. The clearest month is August, when the sky is clear, mostly clear, or partly cloudy 95% of the time on average.
The cloudier part of the year begins around November 4 and lasts for 6.1 months, ending around May 8. The cloudiest month is January, when it is overcast or mostly cloudy 56% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 44 | 46 | 49 | 60 | 72 | 86 | 94 | 95 | 92 | 79 | 59 | 47 |
| Cloudier (%) | 56 | 54 | 51 | 40 | 28 | 14 | 6 | 5 | 8 | 21 | 41 | 53 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 44 | 56 |
| Feb | 46 | 54 |
| Mar | 49 | 51 |
| Apr | 60 | 40 |
| May | 72 | 28 |
| Jun | 86 | 14 |
| Jul | 94 | 6 |
| Aug | 95 | 5 |
| Sep | 92 | 8 |
| Oct | 79 | 21 |
| Nov | 59 | 41 |
| Dec | 47 | 53 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 16, brings about 14 h 42 min of light; the shortest, around December 16, only 9 h 18 min — a swing of roughly 5 h 24 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 9.6 | 10.5 | 11.7 | 13.0 | 14.0 | 14.6 | 14.4 | 13.5 | 12.3 | 11.0 | 9.9 | 9.4 |
| Sunrise (AM) | 7:30 | 7:08 | 6:28 | 5:40 | 5:03 | 4:50 | 5:02 | 5:28 | 5:56 | 6:25 | 6:58 | 7:25 |
| Sunset (PM) | 5:07 | 5:39 | 6:10 | 6:39 | 7:07 | 7:29 | 7:27 | 6:58 | 6:11 | 5:24 | 4:51 | 4:46 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 9.6 | 7:30 | 5:07 |
| Feb | 10.5 | 7:08 | 5:39 |
| Mar | 11.7 | 6:28 | 6:10 |
| Apr | 13.0 | 5:40 | 6:39 |
| May | 14.0 | 5:03 | 7:07 |
| Jun | 14.6 | 4:50 | 7:29 |
| Jul | 14.4 | 5:02 | 7:27 |
| Aug | 13.5 | 5:28 | 6:58 |
| Sep | 12.3 | 5:56 | 6:11 |
| Oct | 11.0 | 6:25 | 5:24 |
| Nov | 9.9 | 6:58 | 4:51 |
| Dec | 9.4 | 7:25 | 4:46 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Napa averages about 18 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 9 and 28 days.
The sunnier stretch runs 5.3 months, from around May 22 to Oct 30. The sunniest month is July, with roughly 28 sunny days (brilliant).
The greyest month is January, down near 10 sunny days — about 65% fewer than the July peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 10 | 9 | 11 | 14 | 18 | 24 | 28 | 28 | 26 | 21 | 14 | 11 |
| Sky | Mixed | Mixed | Mixed | Mixed | Bright | Brilliant | Brilliant | Brilliant | Brilliant | Bright | Mixed | Mixed |
| Sunny days | Sky | |
|---|---|---|
| Jan | 10 | Mixed |
| Feb | 9 | Mixed |
| Mar | 11 | Mixed |
| Apr | 14 | Mixed |
| May | 18 | Bright |
| Jun | 24 | Brilliant |
| Jul | 28 | Brilliant |
| Aug | 28 | Brilliant |
| Sep | 26 | Brilliant |
| Oct | 21 | Bright |
| Nov | 14 | Mixed |
| Dec | 11 | Mixed |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In Napa, the air stays dry or comfortable essentially all year. Even in September, the muggiest month, it feels humid or worse only about 1% of the time — humidity is not something you need to plan around here.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 99 | 99 | 99 | 98 | 96 | 89 | 76 | 71 | 83 | 92 | 96 | 97 |
| Comfortable (%) | 1 | 1 | 1 | 2 | 4 | 11 | 24 | 29 | 16 | 8 | 4 | 3 |
| Humid (%) | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | |
|---|---|---|---|
| Jan | 99 | 1 | 0 |
| Feb | 99 | 1 | 0 |
| Mar | 99 | 1 | 0 |
| Apr | 98 | 2 | 0 |
| May | 96 | 4 | 0 |
| Jun | 89 | 11 | 0 |
| Jul | 76 | 24 | 1 |
| Aug | 71 | 29 | 1 |
| Sep | 83 | 16 | 1 |
| Oct | 92 | 8 | 0 |
| Nov | 96 | 4 | 0 |
| Dec | 97 | 3 | 0 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Across the year, average wind speed in Napa is typically calm, near 5 mph, and varies little with the seasons.
The windier part of the year lasts 5.5 months, from around Mar 24 to Sep 5. The windiest month is June, averaging about 6 mph (calm).
The calmer part of the year runs from around Sep 6 to Mar 23, with November the calmest month at about 4 mph.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (mph) | 4 | 5 | 5 | 6 | 6 | 6 | 6 | 6 | 5 | 4 | 4 | 5 |
| Feels | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (mph) | Feels | |
|---|---|---|
| Jan | 4 | calm |
| Feb | 5 | calm |
| Mar | 5 | calm |
| Apr | 6 | calm |
| May | 6 | calm |
| Jun | 6 | calm |
| Jul | 6 | calm |
| Aug | 6 | calm |
| Sep | 5 | calm |
| Oct | 4 | calm |
| Nov | 4 | calm |
| Dec | 5 | calm |
Hazard calendar for Napa
When the seasonal hazards worth planning around — the rainy season, tropical-cyclone risk and dust haze — are active through the year.
Napa's rainy season runs November–March, when most of the year's rain falls.
Best time to visit Napa
To characterize how pleasant the weather is in Napa throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around mid April, Napa is still near the start of its best-weather window — great conditions with the peak-season crowds not yet at full swing.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 64°F and 82°F. Based on this score, the best time of year to visit Napa for general outdoor tourist activities is from early April to mid November, with a peak score in the second week of October.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 4.3 | 5.1 | 6.2 | 7.4 | 8.4 | 8.1 | 7.6 | 7.5 | 8.0 | 8.5 | 6.5 | 4.3 |
| Rating | fair | fair | good | good | ideal | ideal | ideal | ideal | ideal | ideal | good | fair |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 4.3 | fair |
| Feb | 5.1 | fair |
| Mar | 6.2 | good |
| Apr | 7.4 | good |
| May | 8.4 | ideal |
| Jun | 8.1 | ideal |
| Jul | 7.6 | ideal |
| Aug | 7.5 | ideal |
| Sep | 8.0 | ideal |
| Oct | 8.5 | ideal |
| Nov | 6.5 | good |
| Dec | 4.3 | fair |
The beach/pool score favors clear, rainless days with daytime highs between 75°F and 93°F. Based on this score, the best time of year to visit Napa for hot-weather activities is from late May to mid October, with a peak score in the first week of August.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for Napa, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
For a warm-season trip around August (highs near 84°F), the essentials are light clothes and sun protection. In the cold season around December (highs near 57°F), pack a warm layer and rain gear.
In August, Napa sees daytime highs around 84°F and nights near 57°F. Pack light clothes and sun protection.
Sea temperature near Napa
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea at the nearest coast (about 35 mi away) is warmest in September at about 58°F and coldest in April near 53°F.
The water stays below 68°F all year — cool enough that most swimmers want a wetsuit.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°F) | 53 | 53 | 54 | 53 | 53 | 54 | 56 | 58 | 58 | 57 | 55 | 54 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing |
| Sea temperature (°F) | Comfort | |
|---|---|---|
| Jan | 53 | Bracing |
| Feb | 53 | Bracing |
| Mar | 54 | Bracing |
| Apr | 53 | Bracing |
| May | 53 | Bracing |
| Jun | 54 | Bracing |
| Jul | 56 | Bracing |
| Aug | 58 | Bracing |
| Sep | 58 | Bracing |
| Oct | 57 | Bracing |
| Nov | 55 | Bracing |
| Dec | 54 | Bracing |
UV index (midday) in Napa by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in Napa peaks around June 23 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 13 at about 2 (moderate).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 2 | 4 | 5 | 6 | 9 | 10 | 10 | 9 | 6 | 5 | 2 | 2 |
| Level | Moderate | Moderate | Moderate | High | Very high | Extreme | Extreme | Very high | High | High | Moderate | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 2 | Moderate |
| Feb | 4 | Moderate |
| Mar | 5 | Moderate |
| Apr | 6 | High |
| May | 9 | Very high |
| Jun | 10 | Extreme |
| Jul | 10 | Extreme |
| Aug | 9 | Very high |
| Sep | 6 | High |
| Oct | 5 | High |
| Nov | 2 | Moderate |
| Dec | 2 | Low |
Average hourly UV index in Napa
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in June the burn window is concentrated in the middle of the day: about 8.5 hours a day reach index 3 (protection recommended), and 6 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 0 | 2.5 | 4.5 | 6.5 | 8 | 8.5 | 8.5 | 8 | 6 | 4.5 | 0 | 0 |
| UV ≥ 6 (h/day) | 0 | 0 | 0 | 2 | 5 | 6 | 6 | 5 | 1.5 | 0 | 0 | 0 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 0 | 0 |
| Feb | 2.5 | 0 |
| Mar | 4.5 | 0 |
| Apr | 6.5 | 2 |
| May | 8 | 5 |
| Jun | 8.5 | 6 |
| Jul | 8.5 | 6 |
| Aug | 8 | 5 |
| Sep | 6 | 1.5 |
| Oct | 4.5 | 0 |
| Nov | 0 | 0 |
| Dec | 0 | 0 |
Air quality in Napa by month
Average fine-particle pollution (PM2.5) through the year — so you can see which months the air is worst, not just the yearly average.
Air quality in Napa is worst in September — around 29 µg/m³ PM2.5 (moderate), about 4.2× the cleanest month (June, 7 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 13 | 13 | 13 | 10 | 8 | 7 | 10 | 25 | 29 | 27 | 16 | 12 |
| Level | Moderate | Moderate | Moderate | Good | Good | Good | Good | Moderate | Moderate | Moderate | Moderate | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 13 | Moderate |
| Feb | 13 | Moderate |
| Mar | 13 | Moderate |
| Apr | 10 | Good |
| May | 8 | Good |
| Jun | 7 | Good |
| Jul | 10 | Good |
| Aug | 25 | Moderate |
| Sep | 29 | Moderate |
| Oct | 27 | Moderate |
| Nov | 16 | Moderate |
| Dec | 12 | Good |
Growing season
Napa is mild enough that a frost-free day stays more likely than not even in midwinter.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 96 | 99 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 99 | 95 |
| Frost nights | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 96 | 0 |
| Feb | 99 | 0 |
| Mar | 100 | 0 |
| Apr | 100 | 0 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 99 | 0 |
| Dec | 95 | 0 |
Growing degree days
Growing degree days tally heat above 50°F: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. Napa banks about 3,977 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around August.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°F·days) | 7 | 66 | 165 | 266 | 434 | 565 | 636 | 642 | 582 | 443 | 162 | 8 |
| Growing degree days (°F·days) | |
|---|---|
| Jan | 7 |
| Feb | 66 |
| Mar | 165 |
| Apr | 266 |
| May | 434 |
| Jun | 565 |
| Jul | 636 |
| Aug | 642 |
| Sep | 582 |
| Oct | 443 |
| Nov | 162 |
| Dec | 8 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
Napa receives about 5.1 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 2.0 and 8.2 kWh/m².
The brighter stretch of the year lasts 6.1 months, from around Mar 28 to Sep 29. The brightest month is June, averaging about 8.0 kWh/m² (intense).
The dimmest month is December, down near 2.1 kWh/m² — roughly 74% less than the June peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 2.2 | 3.2 | 4.5 | 6.2 | 7.2 | 8.0 | 8.1 | 7.2 | 5.9 | 4.2 | 2.7 | 2.1 |
| Level | Moderate | Moderate | Bright | Intense | Intense | Intense | Intense | Intense | Bright | Bright | Moderate | Moderate |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 2.2 | Moderate |
| Feb | 3.2 | Moderate |
| Mar | 4.5 | Bright |
| Apr | 6.2 | Intense |
| May | 7.2 | Intense |
| Jun | 8.0 | Intense |
| Jul | 8.1 | Intense |
| Aug | 7.2 | Intense |
| Sep | 5.9 | Bright |
| Oct | 4.2 | Bright |
| Nov | 2.7 | Moderate |
| Dec | 2.1 | Moderate |
Where is Napa?
Napa sits at 38.3°N, 122.3°W, 20 ft above sea level, in United States. The nearest listed city is American Canyon, 8.7 mi away.
Topography around Napa
How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Napa.
Within 2 miles, the terrain around Napa has only modest variations in elevation — a maximum elevation change of 492 ft around an average of 79 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,585 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,895 ft.
The land around Napa is covered by artificial surfaces (45%) and trees (33%) within 2 miles, trees (38%) and grassland (38%) within 10 miles, and trees (29%) and grassland (29%) within 50 miles.
United States travel facts
- Power plugs
- Type A / B
- 120 V · 60 Hz
- Prices
- ≈ 100% of US
- price level, 2025
- GDP per capita
- $90,027
- 2025
- Happiness
- 6.8 / 10
- World Happiness, 2025
- Safe drinking water
- 98%
- of population, 2024
- Homicide rate
- 5.8
- per 100k, 2023
- Road deaths
- 12.7
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Napa (38.2971°, -122.2855°, elevation 20 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).