San Mateo weather in December

In December, San Mateo sees average daytime highs of 57°F and overnight lows near 46°F, with 3.7 in of rain across 9.3 wet days and about 9.5 hours of daylight. It is the 11th-warmest and 3rd-wettest month of the year here.

Day-to-day highs hold fairly steady near 57°F through the month. The sky is clear or mostly clear about 33% of the time in December, and the air most often feels dry.

Daylight stretches from about 9 h 36 min at the start of December to 9 h 24 min by month's end. Set against the rest of the year, December is San Mateo's 10th-clearest and 7th-windiest month. For the whole year in context, see San Mateo's year-round climate.

Daytime high
57°
11th warmest
Overnight low
46°
2nd coldest
Rainfall
3.7 in
9.3 wet days
Daylight
9 h 24 min
7:23 AM – 4:48 PM
Cloud cover
57%
10th clearest
Wind
5 mph
7th windiest
Solar energy
2.27 kWh/m²
Travel score
4.1
out of 10

San Mateo is city in San Mateo County, California, United States.

Density
2,517/km²
people per km²
Founded
1894

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in December

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 57°F through the month.

A typical December day in San Mateo reaches about 57°F in the afternoon and slips back to 46°F overnight — a 12°F spread between the day's warmth and the night's chill. On most days the high lands between 52°F and 62°F. Set against its neighbours, December runs about 6°F cooler than November and on par with January.

30°40°50°60°70°151015202531
Avg high (°F)Avg low (°F)
15947
25947
35847
45847
55847
65847
75847
85846
95846
105746
115746
125746
135746
145746
155746
165745
175745
185645
195645
205645
215645
225645
235645
245645
255645
265644
275644
285644
295644
305644
315644

San Mateo weather by month

How December compares with the rest of the year at a glance. December is the 11th-warmest and 3rd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan57° / 45°3.99.49.74.1
Feb59° / 47°4.29.310.64.5
Mar61° / 48°3.29.111.75.3
Apr63° / 49°1.65.612.96.4
May66° / 52°0.83.3147.4
Jun70° / 54°0.20.914.58.5
Jul73° / 56°0.00.214.39.1
Aug74° / 57°0.00.113.49.2
Sep74° / 57°0.10.412.39.2
Oct71° / 54°0.93118.2
Nov63° / 49°2.06106.1
Dec57° / 46°3.79.39.54.1

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 33% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 14% of December, with mostly cloudy or overcast conditions the remaining 52%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14951
24951
34852
44852
54852
64753
74654
84654
94654
104654
114654
124654
134753
144753
154852
164852
174951
185050
195050
205149
215050
225050
235149
245050
255050
264951
274852
284753
294753
304654
314654

Chance of precipitation in December

Any precipitation

San Mateo gets around 3.7 in of rain over 9.3 wet days in December. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 30% and peaks near 33% on the wettest days.

0%10%20%30%40%151015202531
Rain chance (%)
128
229
329
430
531
631
732
832
932
1033
1133
1233
1332
1432
1532
1631
1731
1830
1930
2030
2129
2229
2329
2428
2528
2628
2728
2828
2928
3029
3129

Humidity in December

DryComfortableHumidMuggyOppressiveMiserable

Most of December feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, December lands in the dry band about 96% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
1955
2955
3946
4946
5946
6946
7946
8946
9946
10955
11955
12955
13955
14964
15964
16964
17973
18973
19973
20973
21982
22982
23982
24982
25982
26982
27982
28982
29982
30982
31982

Wind in December

Winds average 5 mph in December.

Across December, daily wind ranges from about 5 mph on the calmest days to 5 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
155calm
165calm
175calm
185calm
195calm
205calm
215calm
225calm
235calm
245calm
255calm
265calm
275calm
285calm
295calm
305calm
315calm

Sunrise & sunset in December

DaylightNight

Daylight runs from about 9 h 36 min at the start of December to 9 h 24 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 12 minutes over December. Sunrise moves from 7:11 AM to 7:29 AM, and sunset from 4:47 PM to 4:56 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
19.67:114:47
29.67:124:47
39.67:134:47
49.57:144:47
59.57:154:47
69.57:164:47
79.57:164:47
89.57:174:47
99.57:184:47
109.57:194:47
119.57:194:47
129.47:204:47
139.47:214:47
149.47:224:47
159.47:224:48
169.47:234:48
179.47:244:48
189.47:244:49
199.47:254:49
209.47:254:49
219.47:264:50
229.47:264:50
239.47:274:51
249.47:274:51
259.47:274:52
269.47:284:52
279.47:284:53
289.47:294:54
299.47:294:54
309.47:294:55
319.47:294:56

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 2.27 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 2.27 kWh/m² to a high of 7.76 kWh/m² in June across the year — December's 2.27 kWh/m² sits near the bottom.

0123151015202531
Solar energy (kWh/m²)Level
12.4Moderate
22.4Moderate
32.3Moderate
42.3Moderate
52.3Moderate
62.3Moderate
72.3Moderate
82.2Moderate
92.2Moderate
102.2Moderate
112.2Moderate
122.2Moderate
132.2Moderate
142.2Moderate
152.2Moderate
162.2Moderate
172.2Moderate
182.2Moderate
192.2Moderate
202.2Moderate
212.2Moderate
222.3Moderate
232.3Moderate
242.3Moderate
252.3Moderate
262.3Moderate
272.3Moderate
282.3Moderate
292.3Moderate
302.3Moderate
312.3Moderate
Planning a trip in December

Hazard calendar for San Mateo

In seasonPeak

In December, San Mateo sits inside its rainy season season. The full year is below, with each hazard's peak months called out.

San Mateo's rainy season runs November–March, when most of the year's rain falls.

Rainy season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is December a good time to visit San Mateo?

Our two travel scores rate December for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

4.1
Sightseeing
11th-best month of the year
0.0
Beach & pool
11th-best month of the year

December is a reasonable time to visit San Mateo for sightseeing.

What to pack for San Mateo in December

From December's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In December, San Mateo sees daytime highs around 57°F and nights near 46°F. Worth packing: a warm layer and rain gear. About 9 days see rain.

a warm layerrain gear

Sea temperature near San Mateo in December

The nearest coast averages about 55°F in December — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 13 mi away) is warmest in August at about 59°F and coldest in April near 54°F.

The water stays below 68°F all year — cool enough that most swimmers want a wetsuit.

52°54°56°58°60°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°F)Comfort
Jan54Bracing
Feb54Bracing
Mar54Bracing
Apr54Bracing
May54Bracing
Jun55Bracing
Jul57Bracing
Aug59Bracing
Sep59Bracing
Oct58Bracing
Nov56Bracing
Dec55Bracing

UV index in San Mateo in December

LowModerateHighVery highExtreme

Clear-sky midday UV in December peaks around 2. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in San Mateo peaks around June 23 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 15 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJun 23UV 10Dec 15UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5Moderate
Apr6High
May8Very high
Jun10Extreme
Jul10Extreme
Aug10Very high
Sep6High
Oct5High
Nov2Moderate
Dec2Moderate

Air quality in San Mateo in December

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where December falls, not just the annual average.

Air quality in San Mateo is worst in August — around 25 µg/m³ PM2.5 (moderate), about 2.5× the cleanest month (June, 10 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateAug 1824 µg/m³Jun 1110 µg/m³
PM2.5 (µg/m³)Level
Jan15Moderate
Feb18Moderate
Mar16Moderate
Apr12Moderate
May10Good
Jun10Good
Jul11Good
Aug25Moderate
Sep17Moderate
Oct20Moderate
Nov18Moderate
Dec13Moderate
Location & terrain

Where is San Mateo?

San Mateo sits at 37.6°N, 122.3°W, 43 ft above sea level, in United States. The nearest listed city is Burlingame, 2.5 mi away.

Topography around San Mateo

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of San Mateo.

Within 2 miles, the terrain around San Mateo has only modest variations in elevation — a maximum elevation change of 643 ft around an average of 92 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,457 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,452 ft.

The land around San Mateo is covered by artificial surfaces (53%) and trees (31%) within 2 miles, water (39%) and trees (34%) within 10 miles, and water (40%), trees (23%) and grassland (21%) within 50 miles.

2 miles
643 ft
10 miles
2,457 ft
50 miles
4,452 ft
treesgrasslandcroplandartificial surfaceswaterwetland
December weather nearby: Burlingame 2.5 mi · Foster City 3.1 mi · Belmont 3.7 mi · Millbrae 4.3 mi · San Carlos 5.0 mi · San Bruno 6.8 mi · Redwood City 7.5 mi · South San Francisco 8.1 mi

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
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

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 San Mateo (37.563°, -122.3255°, elevation 43 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).