December Weather in Half Moon Bay, United States

Last updated: February 24, 2025

December in Half Moon Bay offers a captivating glimpse of winter on the coast, with temperatures ranging from a brisk 6°C (44°F) at night to a comfortable 19°C (67°F) during the day. The average temperature settles around 12°C (53°F), creating a cool yet inviting atmosphere. Visitors can expect 92 mm (3.6 in) of precipitation spread over approximately 10 days, contributing to the lush landscape characteristic of the region. With an impressive humidity level of 79%, December showcases the unique coastal climate that enhances the mesmerizing beauty of Half Moon Bay in winter, making it a delightful destination for those seeking a refreshing seasonal escape.

December Temperature in Half Moon Bay

In December, Half Moon Bay experiences a subtle yet noticeable drop in temperatures as the year draws to a close. With minimums hovering around 6°C (44°F) and maximums reaching up to 19°C (67°F), the weather is characterized by a mild chill, inviting cozy gatherings. The month maintains an average temperature of 12°C (53°F), similar to late fall. This slight cool down from November suggests a gradual transition to winter, while the comfortable daytime highs still allow for outdoor activities along the beautiful coast. As the festive season approaches, the crisp air offers a refreshing backdrop for exploring the scenic beauty of this coastal gem.

December Weather in Half Moon Bay: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in Half Moon Bay, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec525253545558586062595653
Data source: Temperature data for Half Moon Bay generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

December Precipitation in Half Moon Bay

In Half Moon Bay, December brings a significant uptick in precipitation, with 92 mm (3.6 in) recorded over 10 days of rain. This month's rainfall, while lower than the heavier deluge in January and February, marks a notable shift from the dry summer months, where barely a trace of rain was recorded. November also experiences a wetter spell with 48 mm (1.9 in), but December stands out as a precursor to the winter downpours that will dominate the following months. The increase in precipitation during this month signals the transition into a more temperate climate, leading to a seasonal resurgence of vibrant greenery. Overall, December sets the stage for the winter season, highlighting the region's distinct wet and dry cycles.

December Precipitation Trends in Half Moon Bay

The chart displays monthly precipitation patterns in Half Moon Bay, with values for each month alongside December's data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December's conditions compare to those of other months.
JanFebMarAprMayJunJulAugSepOctNovDec1021017834224333274892
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Half Moon Bay

In Half Moon Bay, December brings a slight dip in humidity, averaging 79%, a trend that continues from the previous month. As the year closes, the coastal climate demonstrates a seasonal shift, with humidity levels typically peaking during the summer months of July and August at 87%. The transition into winter sees a gradual decrease, reflecting the generally cooler and drier conditions. Notably, while December's humidity aligns with the lower levels of November, it stands in contrast to the dampness felt earlier in the year, especially in the spring and summer. Overall, this pattern emphasizes Half Moon Bay's characteristic coastal moisture, while also highlighting the more comfortable, crisp air that December can bring.

December Average Humidity in Half Moon Bay

This chart illustrates the average monthly humidity levels in Half Moon Bay, with December's data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, allowing you to see how December's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec85%82%82%79%83%84%87%87%86%80%79%79%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Half Moon Bay

In December, Half Moon Bay experiences a moderate UV Index of 3, indicating that sun exposure poses a lower risk for most individuals, with a burn time of approximately 30 minutes. This trend of moderate UV levels is consistent with the winter months, following a peak summer intensity where the UV Index rises to extremes in June and July, reaching levels of up to 11. As the year progresses from cooler winter months to the summer, there's a noticeable escalation in UV radiation, peaking in the late spring and summer. By the time autumn rolls around, the UV Index begins to decline again, aligning with seasonal changes. Understanding these fluctuations is essential for sun safety. For more information on UV levels throughout the year, visit Half Moon Bay UV Index.

Maximum UV Index Levels in Half Moon Bay for December

The chart shows the monthly maximum UV Index (UVI) for Half Moon Bay in December, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111109743
Data source: Half Moon Bay December UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

December Sunshine in Half Moon Bay

In December, Half Moon Bay experiences a noteworthy transition as it welcomes 194 hours of sunshine, creating a cozy atmosphere amidst the holiday season. While this marks a decrease from the sun-drenched heights of May and June, it still provides a gentle glow that brightens the shorter days of winter. As sunlight hours taper off from their summer peak in July, they gradually decline, but December's sun persists, offering a comforting contrast to the cooler temperatures. As we observe the year unfold, it’s clear that while winter sets in, Half Moon Bay continues to enjoy a significant amount of daylight, reminding residents and visitors alike that even in the depths of winter, warmth is always within reach.

Monthly Sunshine Duration in Half Moon Bay: December Highlighted

The December sunshine duration represents the total number of hours Half Moon Bay experiences direct sunlight during the month of December, excluding cloudy or obstructed periods. This chart compares the sunshine duration of December with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec151h216h263h296h341h355h349h320h299h276h225h194h
Data source: Half Moon Bay December Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Half Moon Bay During December

As the year draws to a close, December in Half Moon Bay brings a notable dip in sunny days, with the likelihood of sunshine sitting at just 35%. This decline follows a general trend observed throughout the fall, where the percentage of sunny days consistently wanes from November's 43%. Looking at the broader seasonal landscape, one can see that winter is ushered in with a notable reduction in sun, contrasting sharply with the sunniest months of March and April, which enjoy over 60% sunlight. As residents and visitors prepare for the festive season, they may find themselves reaching for umbrellas more than sunglasses, marking December as a month where cozy indoor activities often take precedence over sun-soaked outings.

Percentage of Sunny Days in December in Half Moon Bay

The chart illustrates the percentage of sunny days in Half Moon Bay throughout the year, with December highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Half Moon Bay experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec39%56%60%44%57%45%30%43%47%50%43%35%
Data source: Half Moon Bay December chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Half Moon Bay in December

As December arrives in Half Moon Bay, daylight begins to wane, offering just 9 hours of sunlight—the shortest duration of the year. This trend marks a gradual decline from the sunny 14-hour days of summer in June, July, and August. Following a steady decrease through the fall months, with 10 hours in November, December sets the stage for winter’s shorter days. The daylight duration this month reminds us of nature's rhythm, as we anticipate the gradual return of longer days starting in January, when sunlight will once again stretch to 9 hours. Each passing month showcases a beautifully predictable cycle, encouraging us to embrace the cozy magic of the holiday season while looking forward to brighter days ahead.

Average Daylight Hours in Half Moon Bay for December

The chart illustrates the variation in daylight duration in Half Moon Bay throughout the year, with December highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 54m10h 49m11h 59m13h 11m14h 11m14h 41m14h 25m13h 31m12h 22m11h 10m10h 8m9h 36m
Data source: Half Moon Bay daylight hours, calculated by summing the hours between sunrise and sunset for each day.

December Winds in Half Moon Bay

As December settles in Half Moon Bay, the winds whisper a gentle lullaby, with an average wind speed of 4.1 m/s (9 mph). This month's breezy embrace is a slight uptick compared to the preceding months, notably November's calmer 3.0 m/s (7 mph), signaling a modest revival in coastal gusts as winter approaches. The wind pattern throughout the year shows a fascinating ebb and flow, peaking in May at 5.4 m/s (12 mph) before tapering off during the summer's quiet months of July and August. However, December's winds remind us that coastal life is never dull, as they bring a refreshing chill just before the year comes to a close. This wind consistency, cradled within the tranquil ambiance of the bay, offers both locals and visitors a delightful dance of nature’s breath right as the holiday spirit begins to swirl in the air.

Average December Wind Speed in Half Moon Bay

The chart displays monthly wind speed patterns in Half Moon Bay, with values for each month shown alongside December's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how December's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec3.54.34.24.55.44.33.43.33.13.83.04.1 m/s
Data source: Half Moon Bay December wind data, generated using information from the Copernicus Climate Change Service.

How December Weather in Half Moon Bay Compares to Other Months

The weather in Half Moon Bay changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of December's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Half Moon Bay and find detailed weather information for every month.

December and January present mild weather conditions, but there are some notable differences. In December, temperatures range from a minimum of 6°C (44°F) to a maximum of 19°C (67°F), with an average of 12°C (53°F). The month sees about 92 mm (3.6 in) of precipitation over 10 days, accompanied by a humidity level of 79%. In contrast, January features slightly cooler minimum temperatures at 5°C (41°F) and a maximum reaching 20°C (68°F), resulting in a similar average temperature of 11°C (53°F). Precipitation increases to 102 mm (4.0 in) over 9 days, with humidity rising to 85%. For more detailed information about January weather, check out Half Moon Bay weather in January.

December and February exhibit similar temperature patterns, with average temperatures hovering around 12°C (53°F) and 11°C (53°F) respectively. Both months experience mild weather, with February slightly warmer at a maximum of 20°C (69°F) compared to December's 19°C (67°F). Precipitation levels in February are slightly higher at 101 mm (4.0 in), compared to December's 92 mm (3.6 in), although both months see a similar number of rainy days, with December experiencing precipitation on 10 days and February on 9 days. Additionally, the humidity is a bit higher in February at 82%, compared to 79% in December, making February feel a touch more humid. For a deeper look into February weather specifics, check out Half Moon Bay weather in February.

When comparing the weather in December and March, we see some notable similarities and slight differences. Both months feature a range of temperatures, with minimums around 6-7°C (44°F), averages at 12°C (53°F), and maximums reaching 19°C (67°F). However, December experiences slightly more precipitation, totaling 92 mm (3.6 in) over about 10 days, compared to March's 77 mm (3.0 in) across 11 days. Humidity levels are also close, with December at 79% and March slightly higher at 82%. For more specifics about March weather patterns, check out Half Moon Bay weather in March.

In December, the weather tends to be cooler with temperatures ranging from a minimum of 6°C (44°F) to a maximum of 19°C (67°F) and an average of 12°C (53°F). The month is characterized by higher precipitation, totaling around 92 mm (3.6 in) over approximately 10 days, while the humidity remains steady at 79%. In contrast, April experiences slightly warmer temperatures, with a minimum of 7°C (45°F) and a maximum of 25°C (78°F), while the average also hovers around 12°C (55°F). Additionally, April sees significantly less rainfall, accumulating only 34 mm (1.3 in) over just 5 days, with humidity levels maintaining at 79%. For more insights on the weather during April, check out Half Moon Bay weather in April.

When comparing the weather in December and May, December is characterized by cooler temperatures and higher precipitation. The average temperature in December ranges from a minimum of 6°C (44°F) to a maximum of 19°C (67°F), with about 92 mm (3.6 in) of rain distributed over 10 days. Humidity levels sit at 79%, contributing to a damp and chilly atmosphere. In contrast, May sees slightly warmer conditions, with temperatures ranging from a minimum of 9°C (48°F) to a maximum of 21°C (69°F). Rainfall is significantly lower in May, with only 22 mm (0.9 in) expected over just 2 days. The humidity also rises slightly to 83%. For more details on the climate during this time, check out Half Moon Bay weather in May.

In December, temperatures range from a minimum of 6°C (44°F) to a maximum of 19°C (67°F), with an average of 12°C (53°F). The month sees a higher level of precipitation at 92 mm (3.6 in), occurring over about 10 days, and the humidity hovers around 79%. In contrast, June experiences warmer weather, with temperatures ranging from a minimum of 10°C (51°F) to a maximum of 27°C (81°F), with an average of 15°C (58°F). Rainfall is minimal in June, with only 4 mm (0.2 in) recorded and no rainy days, and the humidity increases slightly to 84%. For more detailed information on June weather, visit Half Moon Bay weather in June.

The weather in December contrasts significantly with that of July. In December, temperatures range from a minimum of 6°C (44°F) to a maximum of 19°C (67°F), with an average of 12°C (53°F). During this month, precipitation is relatively high, totaling 92 mm (3.6 in) over about 10 days, and humidity sits at 79%. In contrast, July enjoys milder temperatures, with a minimum of 11°C (51°F), an average of 15°C (59°F), and a maximum of 20°C (69°F). Notably, July is much drier, with only 3 mm (0.1 in) of precipitation and no rainy days, despite a slightly higher humidity level of 87%. For a closer look at July's weather, visit Half Moon Bay weather in July.

December and August in Half Moon Bay offer contrasting weather experiences. December brings cooler temperatures, with a minimum of 6°C (44°F) and an average of 12°C (53°F), while August enjoys warmer conditions, featuring a minimum of 11°C (53°F) and an average of 16°C (61°F). Additionally, December is significantly wetter, with 92 mm (3.6 in) of precipitation over 10 days, compared to almost dry August, which boasts just 3 mm (0.1 in) of rainfall over 0 days. The humidity also varies slightly, with December at 79% and August at a higher 87%. For a detailed look at the weather specifics, you can check Half Moon Bay weather in August.

In comparing the weather of December and September, notable differences emerge. December experiences cooler temperatures, with a minimum of 6°C (44°F) and an average of 12°C (53°F), peaking at 19°C (67°F). Additionally, it sees more precipitation, with 92 mm (3.6 in) falling over 10 days, and a humidity level of 79%. In contrast, September boasts warmer weather, with a minimum of 11°C (52°F) and an average temperature of 16°C (62°F), soaring to a maximum of 31°C (88°F). Remarkably, it records minimal precipitation at just 3 mm (0.1 in) over 0 days, accompanied by a higher humidity of 86%. For further details on September's climate, check out Half Moon Bay weather in September.

In comparing the weather between December and October, October tends to be milder, with temperatures ranging from a minimum of 9°C (49°F) to a maximum of 27°C (80°F), and an average temperature of 15°C (60°F). In contrast, December's temperatures are cooler, with a minimum of 6°C (44°F) and a maximum of 19°C (67°F), averaging at 12°C (53°F). Furthermore, October experiences significantly less rainfall, with only 27 mm (1.1 in) over just 2 days, while December sees much heavier precipitation totaling 92 mm (3.6 in) over 10 days. Humidity levels remain similar, with October at 80% and December slightly lower at 79%. For more detailed information, check out Half Moon Bay weather in October.

December weather shows a slight drop in temperature compared to November, with minimums averaging 6°C (44°F) and maximums reaching 19°C (67°F), while November boasted minimums of 7°C (45°F) and maximums of 21°C (70°F). Precipitation levels in December are significantly higher, totaling 92 mm (3.6 in) over 10 days, compared to November's 48 mm (1.9 in) over just 5 days. Both months share the same humidity level of 79%, but December tends to be a wetter month, making it feel cooler and more humid overall. For a more detailed look, you can visit Half Moon Bay weather in November.

Compare Half Moon Bay's Climate with Cities Worldwide

Conclusion: What to Expect From December Weather in Half Moon Bay

As December rolls in, Half Moon Bay transforms its climate into a cooler and more humid experience compared to the warmer months. The temperatures dip significantly, with crisp highs around 19°C and chilly lows reaching 6°C, contributing to a cozy atmosphere perfect for winter festivities. Unlike the drier summer months, December sees an increase in precipitation, averaging about 92 mm over approximately 10 days, which brings lushness to the surrounding landscapes. The relatively high humidity level of 79% can make the cooler temperatures feel more pronounced, adding to the season's charm. Embrace the unique weather of this coastal haven by exploring more at Half Moon Bay Climate.