December weather forecastSan Mateo, CA
December
Weather in December
December in San Mateo ushers in the winter season, concluding the calendar year with the coolest temperatures. Compared to November, December witnesses a marginal drop in average temperatures, recording a low of 47.5°F (8.6°C). December's unique characteristic is its high% of cloud cover, indicating the onset of winter. The decrease in sunlight, the prevalence of cooler temperatures, and increased cloud cover make it abundantly clear that winter has arrived in San Mateo. Despite this, the weather remains manageable and opportunities for outdoor activities endure.Temperature
December, having an average high-temperature of 55.8°F (13.2°C) and an average low-temperature of 47.5°F (8.6°C), is the coldest month in San Mateo.Humidity
The average relative humidity in December is 72%.Rainfall
In San Mateo, in December, during 5.5 rainfall days, 0.35" (9mm) of precipitation is typically accumulated. In San Mateo, during the entire year, the rain falls for 32.6 days and collects up to 2.13" (54mm) of precipitation.Daylight
The month with the shortest days is December, with an average of 9h and 36min of daylight.On the first day of December, sunrise is at 7:06 am and sunset at 4:51 pm. On the last day of the month, sunrise is at 7:23 am and sunset at 5:01 pm PST.
Sunshine
December has the least sunshine of the year, with an average of 5.9h of sunshine.UV index
February and December, with an average maximum UV index of 3, are months with the lowest UV index. A UV Index of 3 to 5 symbolizes a medium health hazard from unsafe exposure to UV radiation for average individuals.Note: A daily maximum UV index of 3 in December translates into the following instructions:
Take precautions - Protection against sun damage is advised. Minimize direct exposure to the Sun during midday when its radiation is at its peak. On days when the sun blazes, arm yourself with sunglasses that block UVA and UVB radiation.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in December
San Mateo, CA
- Average high temperature in December: 55.8°F
The warmest months (with the highest average high temperature) are August and September (71.2°F).
The month with the lowest average high temperature is December (55.8°F).
- Average low temperature in December: 47.5°F
The month with the highest average low temperature is September (56.7°F).
The coldest month (with the lowest average low temperature) is January (46.9°F).
Average pressure in December
San Mateo, CA
- Average pressure in December: 30.11"Hg
The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is September (29.92"Hg).
Average wind speed in December
San Mateo, CA
- Average wind speed in December: 6.9mph
The windiest month (with the highest average wind speed) is April (8mph).
The calmest months (with the lowest average wind speed) are August, September and October (5.9mph).
Average humidity in December
San Mateo, CA
- Average humidity in December: 72%
The months with the highest relative humidity are March and August (76%).
The months with the lowest relative humidity are October and November (70%).
Average rainfall in December
San Mateo, CA
- Average rainfall in December: 0.35"
The wettest month (with the highest rainfall) is February (0.55").
The driest months (with the least rainfall) are June, July and August (0").
Average rainfall days in December
San Mateo, CA
- Average rainfall days in December: 5.5 days
The month with the highest number of rainy days is March (6.8 days).
The month with the least rainy days is July (0.3 days).
Average daylight in December /
Average sunshine in December
San Mateo, CA
- Average daylight in December: 9h and 36min
The month with the longest days is June (Average daylight: 14h and 42min).
The month with the shortest days is December (Average daylight: 9h and 36min).
- Average sunshine in December: 5h and 54min
The month with the most sunshine is July (Average sunshine: 12h and 0min).
The month with the least sunshine is December (Average sunshine: 5h and 54min).
Average sunshine days in December
San Mateo, CA
- Average sunshine days in December: 24.4 days
The month with the most sunshine days is July (30.4 days).
The month with the least sunshine days is February (23.3 days).
Average UV index in December
San Mateo, CA
- Average UV index in December: 3
The months with the highest UV index are June, July, August and September (UV index 5).
The months with the lowest UV index are February and December (UV index 3).
Average cloud cover in December
San Mateo, CA
- Average cloud cover in December: 34
The month with the most cloud cover is March (Cloud cover 35).
The month with the least cloud cover is July (Cloud cover 11).
Average visibility in December
San Mateo, CA
- Average visibility in December: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
