San Marcos weather in December

In December, San Marcos sees average daytime highs of 64°F and overnight lows near 47°F, with 2.1 in of rain across 5.1 wet days and about 9.9 hours of daylight. It is the 11th-warmest and 4th-wettest month of the year here.

Day-to-day highs hold fairly steady near 64°F through the month. The sky is clear or mostly clear about 51% of the time in December, and the air most often feels dry.

Daylight stretches from about 10 hours at the start of December to 9 h 48 min by month's end. Set against the rest of the year, December is San Marcos's 9th-clearest and 5th-windiest month. For the whole year in context, see San Marcos's year-round climate.

Daytime high
64°
11th warmest
Overnight low
47°
2nd coldest
Rainfall
2.1 in
5.1 wet days
Daylight
9 h 48 min
6:50 AM – 4:39 PM
Cloud cover
42%
9th clearest
Wind
4 mph
5th windiest
Solar energy
3.08 kWh/m²
Travel score
6.8
out of 10

San Marcos is suburb of San Diego, California, United States.

Density
1,471/km²
people per km²
Founded
1963

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 64°F through the month.

A typical December day in San Marcos reaches about 64°F in the afternoon and slips back to 47°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 57°F and 73°F. Set against its neighbours, December runs about 6°F cooler than November and on par with January.

30°40°50°60°70°80°151015202531
Avg high (°F)Avg low (°F)
16649
26649
36649
46549
56548
66548
76548
86548
96548
106448
116448
126447
136447
146447
156447
166447
176447
186447
196446
206446
216346
226346
236346
246346
256346
266346
276346
286346
296346
306346
316346

San Marcos weather by month

How December compares with the rest of the year at a glance. December is the 11th-warmest and 4th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan64° / 47°2.95.810.16.7
Feb64° / 48°3.66.810.86.4
Mar65° / 50°2.26.211.76.8
Apr68° / 53°1.14.112.87.5
May71° / 56°0.52.113.78.1
Jun75° / 60°0.10.514.19.1
Jul80° / 65°0.10.4148.8
Aug82° / 66°0.00.213.28.5
Sep81° / 64°0.10.712.28.6
Oct76° / 59°0.72.611.28.7
Nov70° / 52°1.13.510.37.9
Dec64° / 47°2.15.19.96.8

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 51% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 12% of December, with mostly cloudy or overcast conditions the remaining 36%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
16733
26733
36634
46634
56733
66634
76634
86634
96535
106436
116535
126535
136535
146535
156436
166436
176436
186436
196436
206436
216436
226337
236337
246337
256238
266238
276238
286139
296139
306139
316040

Chance of precipitation in December

Any precipitation

San Marcos gets around 2.1 in of rain over 5.1 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 17% and peaks near 19% on the wettest days.

0%10%20%30%151015202531
Rain chance (%)
114
215
315
415
515
616
716
816
916
1016
1117
1217
1317
1417
1517
1617
1717
1817
1917
2017
2117
2217
2317
2417
2517
2618
2718
2818
2918
3018
3119

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 98% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
1973
2973
3973
4973
5973
6973
7973
8973
9973
10973
11973
12973
13982
14982
15982
16982
17982
18982
19991
20991
21991
22991
23991
24991
25991
26991
27991
28991
29991
30991
31991

Wind in December

Winds average 4 mph in December.

Across December, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm
314calm

Sunrise & sunset in December

DaylightNight

Daylight runs from about 10 hours at the start of December to 9 h 48 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 6:39 AM to 6:57 AM, and sunset from 4:37 PM to 4:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
110.06:394:37
210.06:404:37
39.96:414:37
49.96:424:37
59.96:434:37
69.96:434:37
79.96:444:38
89.96:454:38
99.96:464:38
109.96:464:38
119.96:474:38
129.86:484:38
139.86:484:39
149.86:494:39
159.86:504:39
169.86:504:39
179.86:514:40
189.86:514:40
199.86:524:41
209.86:524:41
219.86:534:41
229.86:534:42
239.86:544:42
249.86:544:43
259.86:554:43
269.86:554:44
279.86:554:44
289.86:564:45
299.86:564:46
309.86:564:46
319.86:574:47

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 3.08 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 3.08 kWh/m² to a high of 7.96 kWh/m² in June across the year — December's 3.08 kWh/m² sits near the bottom.

01234151015202531
Solar energy (kWh/m²)Level
13.2Moderate
23.2Moderate
33.2Moderate
43.1Moderate
53.1Moderate
63.1Moderate
73.1Moderate
83.1Moderate
93.0Moderate
103.0Moderate
113.0Moderate
123.0Moderate
133.0Moderate
143.0Moderate
153.0Moderate
163.0Moderate
173.0Moderate
183.0Moderate
193.0Moderate
203.0Moderate
213.0Moderate
223.0Moderate
233.0Moderate
243.1Moderate
253.1Moderate
263.1Moderate
273.1Moderate
283.1Moderate
293.1Moderate
303.1Moderate
313.1Moderate
Planning a trip in December

Is December a good time to visit San Marcos?

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

6.8
Sightseeing
9th-best month of the year
2.2
Beach & pool
10th-best month of the year

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

What to pack for San Marcos in December

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

In December, San Marcos sees daytime highs around 64°F and nights near 47°F. Little to plan around — just the basics. About 5 days see rain.

Sea temperature near San Marcos in December

The nearest coast averages about 61°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 12 mi away) is warmest in August at about 71°F and coldest in January near 59°F.

It's comfortable for a long swim from Jul 5 to Oct 7 — about 3.1 months when the water holds above 68°F.

60°65°70°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingcomfortable to swim
Sea temperature (°F)Comfort
Jan59Cool
Feb59Cool
Mar60Cool
Apr61Cool
May64Cool
Jun66Cool
Jul69Refreshing
Aug71Refreshing
Sep70Refreshing
Oct67Cool
Nov64Cool
Dec61Cool

UV index in San Marcos in December

LowModerateHighVery highExtreme

Clear-sky midday UV in December peaks around 3. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in San Marcos peaks around July 11 at about 11 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 17 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 11 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateVery highExtremeVery highHighModerateJul 11UV 11Dec 17UV 3
UV index (midday)Level
Jan4Moderate
Feb5Moderate
Mar5Moderate
Apr8Very high
May8Very high
Jun11Extreme
Jul11Extreme
Aug10Extreme
Sep8Very high
Oct6High
Nov4Moderate
Dec3Moderate

Air quality in San Marcos 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 Marcos is worst in September — around 26 µg/m³ PM2.5 (moderate), about 3.4× the cleanest month (May, 8 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateSep 1625 µg/m³May 168 µg/m³
PM2.5 (µg/m³)Level
Jan12Good
Feb12Moderate
Mar12Moderate
Apr11Good
May8Good
Jun11Good
Jul11Good
Aug15Moderate
Sep26Moderate
Oct14Moderate
Nov12Moderate
Dec16Moderate
Location & terrain

Where is San Marcos?

San Marcos sits at 33.1°N, 117.2°W, 581 ft above sea level, in United States. The nearest listed city is Escondido, 5.0 mi away.

Topography around San Marcos

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

Within 2 miles, the terrain around San Marcos has only modest variations in elevation — a maximum elevation change of 814 ft around an average of 699 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,093 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 8,537 ft.

The land around San Marcos is covered by artificial surfaces (54%) and trees (20%) within 2 miles, trees (35%) and artificial surfaces (32%) within 10 miles, and shrubs (27%) and water (24%) within 50 miles.

2 miles
814 ft
10 miles
2,093 ft
50 miles
8,537 ft
treesshrubsgrasslandcroplandartificial surfacesbare terrainwater
December weather nearby: Escondido 5.0 mi · Vista 5.6 mi · Encinitas 11 mi · Carlsbad 11 mi · Oceanside 13 mi · Rancho Penasquitos 13 mi · Poway 14 mi · Mira Mesa 16 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 Marcos (33.1434°, -117.1661°, elevation 581 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).