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December Weather at Half Moon Bay Airport California, United States

Daily high temperatures are around 59°F, rarely falling below 52°F or exceeding 66°F. The lowest daily average high temperature is 58°F on December 26.

Daily low temperatures are around 45°F, rarely falling below 37°F or exceeding 53°F. The lowest daily average low temperature is 44°F on December 31.

For reference, on October 2, the hottest day of the year, temperatures at Half Moon Bay Airport typically range from 51°F to 66°F, while on December 30, the coldest day of the year, they range from 44°F to 58°F.

Average High and Low Temperature in December at Half Moon Bay Airport

Average High and Low Temperature in December at Half Moon Bay AirportDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313135°F35°F40°F40°F45°F45°F50°F50°F55°F55°F60°F60°F65°F65°F70°F70°FNovJanDec 2658°FDec 2658°F44°F44°FDec 160°FDec 160°F46°F46°FDec 1159°FDec 1159°F45°F45°F
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature in December at Half Moon Bay Airport

Average Hourly Temperature in December at Half Moon Bay AirportDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNovJancoldcoldcool
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Valparaíso, Chile (5,878 miles away) and Vilaflor, Spain (5,843 miles) are the far-away foreign places with temperatures most similar to Half Moon Bay Airport (view comparison).

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The month of December at Half Moon Bay Airport experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 49% to 53%.

The clearest day of the month is December 7, with clear, mostly clear, or partly cloudy conditions 51% of the time.

For reference, on January 11, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 54%, while on August 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 91%.

Cloud Cover Categories in December at Half Moon Bay Airport

Cloud Cover Categories in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJanDec 151%Dec 151%Dec 3147%Dec 3147%Dec 1151%Dec 1151%Dec 2149%Dec 2149%clearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. At Half Moon Bay Airport, the chance of a wet day over the course of December is essentially constant, remaining around 26% throughout.

For reference, the year's highest daily chance of a wet day is 29% on February 21, and its lowest chance is -0% on July 19.

Probability of Precipitation in December at Half Moon Bay Airport

Probability of Precipitation in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%0%5%5%10%10%15%15%20%20%25%25%30%30%NovJanDec 1828%Dec 1828%Dec 124%Dec 124%Dec 3126%Dec 3126%rain
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during December at Half Moon Bay Airport is gradually increasing, starting the month at 2.9 inches, when it rarely exceeds 6.0 inches or falls below 0.5 inches, and ending the month at 3.3 inches, when it rarely exceeds 7.0 inches or falls below 0.3 inches.

Average Monthly Rainfall in December at Half Moon Bay Airport

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average snowfall.

Over the course of December at Half Moon Bay Airport, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 34 minutes of daylight and the longest day is December 1, with 9 hours, 45 minutes of daylight.

Hours of Daylight and Twilight in December at Half Moon Bay Airport

Hours of Daylight and Twilight in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrNovJanDec 219 hr, 34 minDec 219 hr, 34 minnightnightdaydayDec 19 hr, 45 minDec 19 hr, 45 min
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month at Half Moon Bay Airport is 7:06 AM on December 1 and the latest sunrise is 18 minutes later at 7:24 AM on December 31.

The earliest sunset is 4:51 PM on December 6 and the latest sunset is 11 minutes later at 5:02 PM on December 31.

Daylight saving time is observed at Half Moon Bay Airport during 2024, but it neither starts nor ends during December, so the entire month is in daylight saving time.

For reference, on June 20, the longest day of the year, the Sun rises at 5:49 AM and sets 14 hours, 45 minutes later, at 8:34 PM, while on December 21, the shortest day of the year, it rises at 7:21 AM and sets 9 hours, 34 minutes later, at 4:55 PM.

Sunrise & Sunset with Twilight and Daylight Saving Time in December at Half Moon Bay Airport

Sunrise & Sunset with Twilight and Daylight Saving Time in December at Half Moon Bay AirportDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMNovJan7:06 AM7:06 AMDec 14:51 PMDec 14:51 PM7:24 AM7:24 AMDec 315:02 PMDec 315:02 PM7:15 AM7:15 AMDec 114:52 PMDec 114:52 PM7:21 AM7:21 AMDec 214:55 PMDec 214:55 PMSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of December. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

Solar Elevation and Azimuth in December at Half Moon Bay Airport

Solar Elevation and Azimuth in December at Half Moon Bay AirportDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNovJan00101020203030001010202030
northeastsouthwest
Solar elevation and azimuth over the course of December 2024. The black lines are lines of constant solar elevation (the angle of the sun above the horizon, in degrees). The background color fills indicate the azimuth (the compass bearing) of the sun. The lightly tinted areas at the boundaries of the cardinal compass points indicate the implied intermediate directions (northeast, southeast, southwest, and northwest).

The figure below presents a compact representation of key lunar data for December 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

Moon Rise, Set & Phases in December at Half Moon Bay Airport

Moon Rise, Set & Phases in December at Half Moon Bay AirportDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM4 AM4 AM8 AM8 AM12 PM12 PM4 PM4 PM8 PM8 PM12 AM12 AMNovJanNov 15:48 AMNov 15:48 AMNov 151:29 PMNov 151:29 PMNov 3010:22 PMNov 3010:22 PMDec 151:02 AMDec 151:02 AMDec 302:28 PMDec 302:28 PMJan 132:28 PMJan 132:28 PMJan 294:37 AMJan 294:37 AM7:50 AM7:50 AM6:08 PM6:08 PM4:41 PM4:41 PM8:02 AM8:02 AM6:46 AM6:46 AM4:16 PM4:16 PM4:06 PM4:06 PM7:59 AM7:59 AM7:36 AM7:36 AM4:43 PM4:43 PM5:02 PM5:02 PM8:19 AM8:19 AM7:42 AM7:42 AM5:56 PM5:56 PM
The time in which the moon is above the horizon (light blue area), with new moons (dark gray lines) and full moons (blue lines) indicated. The shaded overlays indicate night and civil twilight.
Dec 2024IlluminationMoonriseMoonsetMoonriseMeridian PassingDistance
1
0%7:49 AMSE5:00 PMSW-12:24 PMS245,100 mi
2
3%8:49 AMSE5:53 PMSW-1:21 PMS243,008 mi
3
7%9:43 AMSE6:54 PMSW-2:19 PMS240,871 mi
4
14%10:30 AMESE8:01 PMWSW-3:16 PMS238,724 mi
5
23%11:10 AMESE9:11 PMWSW-4:10 PMS236,585 mi
6
33%11:43 AMESE10:21 PMWSW-5:02 PMS234,474 mi
7
44%12:12 PMESE11:31 PMW-5:50 PMS232,430 mi
8
50%12:38 PME--6:37 PMS230,531 mi
9
67%-12:40 AMW1:04 PME7:24 PMS228,897 mi
10
78%-1:51 AMW1:30 PME8:13 PMS227,686 mi
11
87%-3:03 AMWNW1:59 PMENE9:04 PMS227,070 mi
12
94%-4:18 AMWNW2:34 PMENE10:00 PMS227,209 mi
13
98%-5:35 AMWNW3:15 PMENE10:59 PMS228,203 mi
14
100%-6:50 AMNW4:06 PMNE--
15
100%-7:59 AMNW5:06 PMNE12:01 AMS230,060 mi
16
99%-8:58 AMNW6:13 PMNE1:04 AMS232,674 mi
17
95%-9:46 AMWNW7:22 PMENE2:03 AMS235,833 mi
18
89%-10:24 AMWNW8:30 PMENE2:57 AMS239,260 mi
19
81%-10:54 AMWNW9:35 PMENE3:46 AMS242,658 mi
20
73%-11:20 AMWNW10:36 PME4:31 AMS245,746 mi
21
63%-11:43 AMW11:35 PME5:12 AMS248,292 mi
22
50%-12:04 PMW-5:51 AMS250,123 mi
23
44%12:33 AME12:25 PMW-6:30 AMS251,135 mi
24
34%1:30 AME12:46 PMWSW-7:09 AMS251,294 mi
25
25%2:29 AMESE1:11 PMWSW-7:50 AMS250,634 mi
26
17%3:30 AMESE1:38 PMWSW-8:34 AMS249,250 mi
27
10%4:33 AMESE2:12 PMWSW-9:22 AMS247,289 mi
28
5%5:36 AMSE2:53 PMSW-10:15 AMS244,931 mi
29
1%6:38 AMSE3:44 PMSW-11:11 AMS242,379 mi
30
0%7:36 AMSE4:43 PMSW-12:10 PMS239,831 mi
31
1%8:26 AMSE5:50 PMWSW-1:08 PMS237,456 mi

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy at Half Moon Bay Airport is essentially constant during December, remaining around 0% throughout.

For reference, on September 8, the muggiest day of the year, there are muggy conditions 0% of the time, while on November 28, the least muggy day of the year, there are muggy conditions 0% of the time.

Humidity Comfort Levels in December at Half Moon Bay Airport

Humidity Comfort Levels in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%NovJanDec 10%Dec 10%Dec 310%Dec 310%Dec 110%Dec 110%Dec 210%Dec 210%comfortablecomfortabledrydryhumidhumid
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed at Half Moon Bay Airport is essentially constant during December, remaining within 0.2 miles per hour of 10.3 miles per hour throughout.

For reference, on May 8, the windiest day of the year, the daily average wind speed is 11.2 miles per hour, while on October 4, the calmest day of the year, the daily average wind speed is 8.2 miles per hour.

The highest daily average wind speed during December is 10.6 miles per hour on December 13.

Average Wind Speed in December at Half Moon Bay Airport

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The hourly average wind direction at Half Moon Bay Airport throughout December is predominantly from the north, with a peak proportion of 39% on December 9.

Wind Direction in December at Half Moon Bay Airport

Wind Direction in December at Half Moon Bay AirportWNDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%20%80%40%60%60%40%80%20%100%0%NovJanwestsoutheastnorth
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Half Moon Bay Airport is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature at Half Moon Bay Airport is essentially constant during December, remaining within 1°F of 54°F throughout.

Average Water Temperature in December at Half Moon Bay Airport

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

Temperatures at Half Moon Bay Airport are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.

Time Spent in Various Temperature Bands and the Growing Season in December at Half Moon Bay Airport

Time Spent in Various Temperature Bands and the Growing Season in December at Half Moon Bay Airportgrowing seasonDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJan99%Dec 199%Dec 190%Dec 3190%Dec 3197%Dec 1197%Dec 1194%Dec 2194%Dec 21very coldcoldcoolcomfortable
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days at Half Moon Bay Airport are gradually increasing during December, increasing by 87°F, from 1,828°F to 1,915°F, over the course of the month.

Growing Degree Days in December at Half Moon Bay Airport

Growing Degree Days in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031311,600°F1,600°F1,700°F1,700°F1,800°F1,800°F1,900°F1,900°F2,000°F2,000°F2,100°F2,100°F2,200°F2,200°F2,300°F2,300°FNovJanDec 11,828°FDec 11,828°FDec 311,915°FDec 311,915°FDec 111,861°FDec 111,861°FDec 211,890°FDec 211,890°F
The average growing degree days accumulated over the course of December, with 25th to 75th and 10th to 90th percentile bands.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy at Half Moon Bay Airport is essentially constant during December, remaining within 0.1 kWh of 2.3 kWh throughout.

The lowest average daily incident shortwave solar energy during December is 2.2 kWh on December 22.

Average Daily Incident Shortwave Solar Energy in December at Half Moon Bay Airport

Average Daily Incident Shortwave Solar Energy in December at Half Moon Bay AirportDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310.0 kWh0.0 kWh0.5 kWh0.5 kWh1.0 kWh1.0 kWh1.5 kWh1.5 kWh2.0 kWh2.0 kWh2.5 kWh2.5 kWh3.0 kWh3.0 kWh3.5 kWh3.5 kWh4.0 kWh4.0 kWh4.5 kWh4.5 kWhNovJanDec 222.2 kWhDec 222.2 kWhDec 12.4 kWhDec 12.4 kWhDec 112.3 kWhDec 112.3 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

For the purposes of this report, the geographical coordinates of Half Moon Bay Airport are 37.515 deg latitude, -122.500 deg longitude, and 39 ft elevation.

The topography within 2 miles of Half Moon Bay Airport contains very significant variations in elevation, with a maximum elevation change of 961 feet and an average elevation above sea level of 132 feet. Within 10 miles contains very significant variations in elevation (2,051 feet). Within 50 miles contains large variations in elevation (4,314 feet).

The area within 2 miles of Half Moon Bay Airport is covered by water (37%), artificial surfaces (17%), herbaceous vegetation (16%), and trees (12%), within 10 miles by water (59%) and trees (14%), and within 50 miles by water (57%) and grassland (13%).

This report illustrates the typical weather at Half Moon Bay Airport, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

Half Moon Bay Airport has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.

In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.

The stations on which we may fall back include but are not limited to San Francisco International Airport, Naval Air Station Alameda (historical), Oakland International Airport, Hayward Air Terminal Airport, Moffett Federal Airfield, Norman Y. Mineta San José International Airport, Gnoss Field, and Buchanan Field Airport.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for airports and weather stations are provided by AskGeo.com .

Maps are © OpenStreetMap contributors.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.

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