Climate averages 1991–2020
San Marcos weather
in December.
A mild, moderately wet month: one of the coolest and the 9th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
December is a mild month in San Marcos: daytime highs average 16.7°C and nights cool to about 6.2°C. By daytime temperature it is one of the coolest months of the year.
Expect about 54 mm of rain on roughly 5 days, which makes December a moderately wet month (the 9th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 10 h 00 min on an average December day.
The nearest other city in this atlas is Escondido (8 km away). In December its highs average 17.4°C, 0.7°C warmer than San Marcos, with 59 mm of rain.
Among the 498 cities listed in the United States, San Marcos ranks 117th of 498 for the warmest December highs and joint 162nd of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; San Marcos is 6.2°C warmer than that mean.
From December to January, average highs rise by 0.1°C to 16.8°C, and monthly rainfall rises from 54 mm to 73 mm.
The annual picture
December in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
San Marcos climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 16.8°C6.1°C | 6.1°C | 73 | 5.8 | 10.210 h |
| February | 16.7°C6.9°C | 6.9°C | 92 | 6.8 | 11.011 h |
| March | 17.6°C8.5°C | 8.5°C | 57 | 6.2 | 12.012 h |
| April | 19.1°C10.3°C | 10.3°C | 28 | 4.1 | 13.013 h |
| May | 20.7°C12.7°C | 12.7°C | 13 | 2.1 | 13.814 h |
| June | 23.2°C14.8°C | 14.8°C | 2.5 | 0.5 | 14.314 h |
| July | 25.8°C17.2°C | 17.2°C | 2.0 | 0.4 | 14.114 h |
| August | 26.9°C18.2°C | 18.2°C | 1.0 | 0.2 | 13.413 h |
| September | 26.2°C17.3°C | 17.3°C | 3.9 | 0.7 | 12.412 h |
| October | 23.3°C13.7°C | 13.7°C | 17 | 2.6 | 11.411 h |
| November | 20.0°C9.4°C | 9.4°C | 28 | 3.5 | 10.510 h |
| December, selected | 16.7°C6.2°C | 6.2°C | 54 | 5.1 | 10.010 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
December in nearby cities
- Escondido in DecemberUnited States · 8 kmHigh 17.4°C · Low 5.7°C · 59 mm rain
- Vista in DecemberUnited States · 10 kmHigh 17.6°C · Low 6.6°C · 54 mm rain
- Oceanside in DecemberUnited States · 21 kmHigh 16.9°C · Low 8.6°C · 46 mm rain
- Temecula in DecemberUnited States · 39 kmHigh 17.9°C · Low 5.3°C · 52 mm rain
- El Cajon in DecemberUnited States · 43 kmHigh 17.7°C · Low 7.9°C · 47 mm rain
- Murrieta in DecemberUnited States · 46 kmHigh 17.6°C · Low 4.8°C · 52 mm rain
- San Diego in DecemberUnited States · 48 kmHigh 17.3°C · Low 8.8°C · 40 mm rain
- Chula Vista in DecemberUnited States · 56 kmHigh 17.0°C · Low 9.4°C · 47 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for San Marcos) is explained once on the San Marcos year overview and on the Sources, method and limits page.
Vista lies in the same rainfall cell, so its rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.