Napa State Hospital, California climate: Climate normals at a NOAA weather station
Napa State Hospital's normal year runs from 40°F December nights to 84°F August afternoons, with 26.7 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 15.7°C, December lows of 4°C, August highs of 29°C, 677 mm of precipitation a year.
- NOAA stationNapa State Hospital
- Station IDUSC00046074
- Location38.28°N 122.26°W
- Elevation35 ft (11 m)
On October 23, the normal high in Napa State Hospital is 76°F and the normal low 48°F, and the chance of measurable rain or snow is 15%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Napa State Hospital.
- Jan 59° 40°
- Feb 63° 42°
- Mar 68° 44°
- Apr 72° 46°
- May 77° 50°
- Jun 82° 54°
- Jul 83° 56°
- Aug 84° 56°
- Sep 84° 53°
- Oct 78° 49°
- Nov 66° 44°
- Dec 59° 40°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Napa State Hospital each month?
August is the warmest month, with normal highs of 84°F; December the coldest, with normal lows of 40°F. The most precipitation falls in December (5.53 in), the least in July (0.00 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 59°F | 40°F | 49.4°F | 4.98 | 12 | <1 | 5 | 9 h 50 min |
| February | 63°F | 42°F | 52.5°F | 5.13 | 11 | <1 | 2 | 10 h 50 min |
| March | 68°F | 44°F | 55.5°F | 3.67 | 10 | <1 | <1 | 11 h 50 min |
| April | 72°F | 46°F | 58.8°F | 1.72 | 7 | 1 | <1 | 13 h 10 min |
| May | 77°F | 50°F | 63.2°F | 1.08 | 4 | 3 | <1 | 14 h 10 min |
| June | 82°F | 54°F | 68.0°F | 0.29 | 1 | 6 | <1 | 14 h 50 min |
| July | 83°F | 56°F | 69.4°F | 0.00 | <1 | 6 | <1 | 14 h 40 min |
| August | 84°F | 56°F | 69.6°F | 0.06 | <1 | 6 | <1 | 13 h 40 min |
| September | 84°F | 53°F | 68.9°F | 0.09 | 1 | 8 | <1 | 12 h 30 min |
| October | 78°F | 49°F | 63.7°F | 1.34 | 4 | 3 | <1 | 11 h 20 min |
| November | 66°F | 44°F | 54.9°F | 2.77 | 8 | <1 | 1 | 10 h 10 min |
| December | 59°F | 40°F | 49.1°F | 5.53 | 12 | <1 | 5 | 9 h 30 min |
| Year (annual) | 73°F | 48°F | 60.3°F | 26.66 | 68 | 32 | 13 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 15°C | 5°C | 9.7°C | 126 mm |
| February | 17°C | 5°C | 11.4°C | 130 mm |
| March | 20°C | 6°C | 13.1°C | 93 mm |
| April | 22°C | 8°C | 14.9°C | 44 mm |
| May | 25°C | 10°C | 17.3°C | 27 mm |
| June | 28°C | 12°C | 20.0°C | 7 mm |
| July | 29°C | 13°C | 20.8°C | 0 mm |
| August | 29°C | 13°C | 20.9°C | 2 mm |
| September | 29°C | 12°C | 20.5°C | 2 mm |
| October | 26°C | 10°C | 17.6°C | 34 mm |
| November | 19°C | 6°C | 12.7°C | 70 mm |
| December | 15°C | 4°C | 9.5°C | 140 mm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00046074; 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.
Which months are mildest at Napa State Hospital?
Normal highs sit between 65°F and 85°F in March, April, May, June, July, August, September, October and November. Of those, July has the fewest days with rain (0).
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 USC00046074.
When is the last frost at Napa State Hospital?
In Napa State Hospital, the last spring frost (32°F) comes after February 12 in half of years and after March 13 in one year in ten; the first autumn frost comes before December 4 in half of years and before November 15 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
- February 121 year in 10 after March 13; 9 in 10 after January 3
- First autumn frost, half of years before
- December 41 year in 10 before November 15; 9 in 10 before January 4
NOAA puts the median frost-free season at 299 days, and the season without a hard freeze (28°F) at 348 days.
A hard freeze (28°F) comes after January 11 in half of springs and before December 19 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Napa State Hospital in zone 9b in ZIP code 94559, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, the station is in zone 9b: the coldest night of a typical year reaches 27°F (27 complete years).
Frost dates for every NOAA station in California · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00046074; 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.
How hot and how cold does it get at Napa State Hospital?
In a normal year in Napa State Hospital, 32 days a year reach 90°F (5 of them 100°F or more), 13 nights fall to 32°F or colder and 68 days bring measurable precipitation.
- Days at 90°F or more
- 32a normal year
- Days at 100°F or more
- 5a normal year
- Nights at 32°F or colder
- 13a normal year
- Days that stay below freezing
- fewer than 1high of 32°F or less
- Days with 0.01 inch of precipitation
- 68a normal year
The highest temperature in this station's record (since 1893) is 114°F, on September 6, 2022; the lowest is 14°F, on December 22, 1990.
The wettest calendar year on that record is 1941, with 43.09 in; the snowiest season is 1986–87, with 1.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00046074; records: ACIS (NOAA Regional Climate Centers), station USC00046074. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Napa State Hospital?
Over a year 87% of the sunlight that would reach the ground under clear skies gets through the clouds at Napa State Hospital, 5.1 kWh per square metre a day. July is the sunniest month (95%) and December the cloudiest (72%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 74% | 2.3 |
| February | 77% | 3.3 |
| March | 78% | 4.6 |
| April | 84% | 6.1 |
| May | 88% | 7.3 |
| June | 93% | 8.1 |
| July | 95% | 8.0 |
| August | 94% | 7.1 |
| September | 93% | 5.8 |
| October | 88% | 4.2 |
| November | 81% | 2.8 |
| December | 72% | 2.0 |
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 many heating and cooling degree days does Napa State Hospital record?
A normal year at Napa State Hospital brings 2,358 heating degree days, 56% fewer than the median U.S. place (5,373), and 643 cooling degree days, 29% fewer than the median (908). Four months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,959 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 485 | 0 |
| February | 349 | 0 |
| March | 295 | 2 |
| April | 197 | 12 |
| May | 99 | 45 |
| June | 23 | 113 |
| July | 5 | 141 |
| August | 4 | 147 |
| September | 14 | 131 |
| October | 89 | 49 |
| November | 305 | 2 |
| December | 493 | 0 |
| Year (annual) | 2,358 | 643 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00046074. 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.
Have recent years at Napa State Hospital been warmer than normal?
2021 averaged 60.1°F, 0.2°F below the 1991-2020 normal of 60.3°F.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 60.1°F | −0.2°F | 24.38 |
Over 108 complete years from 1878 to 2024, the station's annual mean temperature rose at a fitted 1.7°F per century (+0.09°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00046074; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Napa State Hospital's climate compare?
Napa State Hospital is warmer than 101 of the 219 places with their own NOAA record in California, and wetter than 163. Across the 7,247 U.S. stations with normals, its annual mean of 60.3°F is warmer than 76%.
In the Köppen classification computed from these normals, Napa State Hospital 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 Napa State Hospital share this climate record?
Silverado Resort 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.
- Silverado Resort, CA926 people · 5 mi N
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 Napa State Hospital's climate
What is the coldest month at Napa State Hospital?
December, with a normal high of 59°F and a normal low of 40°F. The warmest is August (84°F by day, 56°F at night).
Does it snow at Napa State Hospital?
Rarely: NOAA's normal is no measurable snow a year.
What is the rainiest month at Napa State Hospital?
December, with 5.53 in of precipitation in a normal year; the driest is July with 0.00 in.
What plant hardiness zone is Napa State Hospital in?
The USDA's 2023 map puts Napa State Hospital in zone 9b in ZIP code 94559, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 27°F (27 years, 1991-2020): zone 9b.
How late can frost come at Napa State Hospital?
In half of years the last 32°F night comes after February 12; in one year in ten it comes after March 13. Waiting until March 13 leaves about a one-in-ten chance of a later frost.
Nearby and next
- California climateThe statewide normals and every place in the state
- Napa, CA5 miles from this station, 57.7°F a year
- Fairfield, CA11 miles from this station, 61.7°F a year
- Sonoma, CA11 miles from this station, 59.0°F a year
- Vallejo, CA13 miles from this station, 61.6°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made