Port Costa, CA climate
Port Costa has warm winters and pleasant summers, with very little rain. A typical July afternoon reaches 81°, a January night drops to 40°, and snow is almost unheard of.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Port Costa feels like
Winter
Spring
Summer
Fall
Port Costa weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 57° | 40° | 4.3" | 0 | 12 | 0 | 45° – 54° |
| February | 61° | 43° | 4.0" | 0 | 11 | 0 | 47° – 57° |
| March | 65° | 44° | 3.1" | 0 | 10 | 0 | 49° – 60° |
| April | 68° | 46° | 1.4" | 0 | 7 | 0 | 53° – 61° |
| May | 73° | 50° | 0.7" | 0 | 4 | 0 | 57° – 68° |
| June | 79° | 54° | 0.1" | 0 | 1 | 0 | 63° – 69° |
| July | 81° | 55° | 0.0" | 0 | 0 | 0 | 65° – 72° |
| August | 82° | 55° | 0.0" | 0 | 0 | 0 | 65° – 73° |
| September | 81° | 54° | 0.1" | 0 | 1 | 0 | 64° – 72° |
| October | 75° | 51° | 1.0" | 0 | 4 | 0 | 60° – 69° |
| November | 65° | 45° | 2.2" | 0 | 8 | 0 | 48° – 59° |
| December | 57° | 40° | 4.1" | 0 | 12 | 0 | 45° – 53° |
| Year | 70° | 48° | 21.0" | 0.0" | 68 | 0 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Port Costa
Port Costa gets 21 inches of rain and melted snow a year. January is the wettest month and July the driest. Rain or snow falls on about 68 days a year.
A year-round growing season
Heating and cooling a home in Port Costa
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Port Costa, 71% of that work is heating and 29% is cooling.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
How Port Costa compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Port Costa averaged 1.6° warmer than the 1900s. The biggest change is in January (+2.1°). The shift is larger than in 73% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Port Costa’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. May swings the most: between 1991 and 2020 its average temperature ranged from 57° to 68°. June is the most reliable, staying within 6°.
Common questions about Port Costa’s climate
What is the coldest month in Port Costa?
January, with a typical high of 57° and a low of 40°.
What is the hottest month in Port Costa?
August, with a typical high of 82° and a low of 55°. About 36 days a year reach 90°.
How much snow does Port Costa get?
Almost none. A normal year brings 0.0 inches.
When is the first frost in Port Costa?
Frost is uncommon. Only 75% of years see a night at 32° or below.
What is the rainiest month in Port Costa?
January, with 4.3 inches of rain and melted snow. The year totals 21 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Port Costa itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Napa State Hospital, CA (17 mi, snow) and Vallejo, CA (4 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.