Millbrae weather in December

In December, Millbrae sees average daytime highs of 56°F and overnight lows near 49°F, with 4.0 in of rain across 9.8 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 56°F through the month. The sky is clear or mostly clear about 34% 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 Millbrae's 10th-clearest and 6th-windiest month. For the whole year in context, see Millbrae's year-round climate.

Daytime high
56°
11th warmest
Overnight low
49°
2nd coldest
Rainfall
4.0 in
9.8 wet days
Daylight
9 h 24 min
7:23 AM – 4:48 PM
Cloud cover
57%
10th clearest
Wind
8 mph
6th windiest
Solar energy
2.25 kWh/m²
Travel score
3.7
out of 10

Millbrae is city located in northern San Mateo County, California, United States.

Density
2,701/km²
people per km²
Founded
1948

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 56°F through the month.

A typical December day in Millbrae reaches about 56°F in the afternoon and slips back to 49°F overnight — a 7°F spread between the day's warmth and the night's chill. On most days the high lands between 52°F and 59°F. Set against its neighbours, December runs about 4°F cooler than November and on par with January.

40°50°60°70°151015202531
Avg high (°F)Avg low (°F)
15750
25750
35750
45650
55650
65650
75650
85650
95649
105649
115649
125649
135649
145649
155549
165549
175549
185549
195549
205548
215548
225548
235548
245548
255548
265548
275548
285548
295548
305548
315548

Millbrae 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
Jan55° / 48°4.0109.73.6
Feb56° / 49°4.29.410.63.8
Mar57° / 50°3.19.311.74.2
Apr58° / 51°1.55.312.94.8
May59° / 52°0.73.1145.5
Jun61° / 54°0.20.814.56.5
Jul63° / 55°0.00.114.37.1
Aug64° / 57°0.00.113.47.5
Sep65° / 57°0.10.512.37.7
Oct64° / 55°0.93.1117.1
Nov59° / 52°2.16.2105.1
Dec56° / 49°4.09.89.53.7

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 34% 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 53%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15149
25050
34951
44852
54852
64753
74654
84654
94654
104654
114555
124555
134555
144753
154852
164852
174852
185050
195050
205050
214951
224951
234951
244951
254852
264852
274852
284753
294555
304456
314456

Chance of precipitation in December

Any precipitation

Millbrae gets around 4.0 in of rain over 9.8 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 32% and peaks near 35% on the wettest days.

0%10%20%30%40%50%151015202531
Rain chance (%)
130
231
332
432
533
634
734
834
934
1035
1135
1234
1334
1434
1533
1633
1732
1832
1931
2031
2131
2230
2330
2430
2529
2629
2729
2829
2930
3030
3130

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 (%)
1946
2946
3946
4946
5946
6946
7946
8946
9955
10955
11955
12955
13964
14964
15964
16964
17973
18973
19973
20982
21982
22982
23982
24982
25982
26982
27982
28982
29982
30982
31982

Wind in December

Winds average 8 mph in December.

Across December, daily wind ranges from about 8 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze
318light breeze

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 7:12 AM to 7:30 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)
19.67:124:47
29.67:124:47
39.67:134:47
49.57:144:47
59.57:154:47
69.57:164:47
79.57:174:47
89.57:184:47
99.57:184:47
109.57:194:47
119.57:204:47
129.47:214:47
139.47:214:47
149.47:224:48
159.47:234:48
169.47:234:48
179.47:244:48
189.47:244:49
199.47:254:49
209.47:264:50
219.47:264:50
229.47:274:51
239.47:274:51
249.47:274:51
259.47:284:52
269.47:284:53
279.47:294:53
289.47:294:54
299.47:294:54
309.47:294:55
319.47:304:56

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 2.25 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 2.25 kWh/m² to a high of 7.64 kWh/m² in June across the year — December's 2.25 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
222.2Moderate
232.2Moderate
242.3Moderate
252.3Moderate
262.3Moderate
272.3Moderate
282.3Moderate
292.3Moderate
302.3Moderate
312.3Moderate
Planning a trip in December

Hazard calendar for Millbrae

In seasonPeak

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

Millbrae'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 Millbrae?

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

3.7
Sightseeing
11th-best month of the year
0.0
Beach & pool
8th-best month of the year

December is a weaker month for outdoor sightseeing in Millbrae.

What to pack for Millbrae in December

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

In December, Millbrae sees daytime highs around 56°F and nights near 49°F. Worth packing: a warm layer and rain gear. About 10 days see rain.

a warm layerrain gear

Sea temperature near Millbrae in December

The nearest coast averages about 54°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 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.

52°54°56°58°60°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°F)Comfort
Jan53Bracing
Feb54Bracing
Mar54Bracing
Apr53Bracing
May53Bracing
Jun54Bracing
Jul56Bracing
Aug58Bracing
Sep58Bracing
Oct57Bracing
Nov56Bracing
Dec54Bracing

UV index in Millbrae 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 Millbrae 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 Millbrae 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 Millbrae 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 Millbrae?

Millbrae sits at 37.6°N, 122.4°W, 33 ft above sea level, in United States. The nearest listed city is Burlingame, 1.2 mi away.

Topography around Millbrae

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

Within 2 miles, the terrain around Millbrae has only modest variations in elevation — a maximum elevation change of 663 ft around an average of 141 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,005 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,452 ft.

The land around Millbrae is covered by artificial surfaces (56%) and trees (22%) within 2 miles, water (44%), trees (27%) and artificial surfaces (21%) within 10 miles, and water (42%), trees (22%) and grassland (21%) within 50 miles.

2 miles
663 ft
10 miles
2,005 ft
50 miles
4,452 ft
treesgrasslandcroplandartificial surfacesbare terrainwaterwetland
December weather nearby: Burlingame 1.2 mi · San Bruno 2.5 mi · South San Francisco 3.7 mi · San Mateo 4.3 mi · Pacifica 5.6 mi · Foster City 6.8 mi · Belmont 8.1 mi · Visitacion Valley 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 Millbrae (37.5986°, -122.3872°, elevation 33 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).