May Weather in Napa, United States

Last updated: February 24, 2025

In Napa, United States, the weather in May presents a delightful mix of warmth and mild conditions. With a maximum temperature reaching a sizzling 37°C (99°F), the average temperature settles at a comfortable 18°C (64°F), while the minimum drops to a cool 5°C (41°F). Residents and visitors can expect some moisture, as the area sees 19 mm (0.8 in) of precipitation over just 2 days, contributing to a humidity level of 74%. This combination of warm days and cool nights, along with occasional showers, makes May a captivating time to experience the beauty of Napa’s vineyards and landscapes.

May Temperature in Napa

In May, Napa experiences a delightful transition into warmer weather, with temperatures showcasing a noteworthy increase. The month begins with a minimum of 5°C (41°F), climbing to an average of 18°C (64°F), and peaks at a sizzling 37°C (99°F). This pattern marks a significant shift from April, where the highs reached 33°C (92°F), reflecting the onset of summer's embrace. The steady rise in temperatures not only heralds longer, sun-drenched days but also invites residents and visitors alike to partake in the region's renowned outdoor activities and vineyard tours, making May a vibrant month in the heart of Napa.

May Weather in Napa: Daily Temperature Highs, Lows, and Averages

The chart illustrates May temperature patterns in Napa, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec505254596470707070655550
Data source: Temperature data for Napa generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

May Precipitation in Napa

In Napa, United States, May marks a significant transition in the precipitation pattern as rainfall dips to just 19 mm (0.8 in) over a mere 2 days. This decline follows a steady decrease from the 33 mm (1.3 in) seen in April, further showcasing the shift towards the arid summer months. As spring concludes, Napa experiences a stark reduction in moisture, with the looming dry season ahead, characterized by no rain in June and July. This trend of diminishing precipitation is reflective of the region's Mediterranean climate, leading to sunny days perfect for wine country activities, yet highlighting the stark contrasts to the wetter winter months.

May Precipitation Trends in Napa

The chart displays monthly precipitation patterns in Napa, with values for each month alongside May's data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how May's conditions compare to those of other months.
JanFebMarAprMayJunJulAugSepOctNovDec1201138133192001294391
Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

May Humidity in Napa

As spring gives way to summer in Napa, May witnesses a notable drop in humidity, settling at a comfortable 74%. This decline marks a significant improvement compared to the wetter months of winter and early spring, where humidity levels hover around the 84% to 83% range. The gradual decrease from 81% in April to 64% in June highlights a transition toward drier, more pleasant conditions that characterize the region's summer climate. Consequently, May serves as a delightful bridge, offering a warm embrace without the intense muginess, making it a perfect time for outdoor activities and wine tasting in the beautiful vineyards.

May Average Humidity in Napa

This chart illustrates the average monthly humidity levels in Napa, with May's data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, allowing you to see how May's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec84%84%83%81%74%64%44%37%44%65%84%83%
Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Napa

In May, Napa experiences a UV Index of 10, categorizing the exposure as very high, which means you could get sunburned in just 15 minutes without protection. This marks a continuation of the notable upward trend in UV levels since January, where the index started at a more moderate 3. As spring transitions into summer, the UV index escalates rapidly—April saw a jump to 9, setting the stage for May's peak. With the summer months ahead presenting even more extreme UV conditions, it’s essential to stay vigilant and protect your skin. For more detailed insights on UV exposure in Napa, check out Napa UV Index.

Maximum UV Index Levels in Napa for May

The chart shows the monthly maximum UV Index (UVI) for Napa in May, 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.
JanFebMarAprMayJunJulAugSepOctNovDec3579101111109643
Data source: Napa May 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.

May Sunshine in Napa

As the days lengthen and the warmth of spring gives way to summer, May shines brightly in Napa, boasting an impressive 357 hours of sunshine. This month marks a notable uptick from the 296 hours recorded in April, reflecting the gradual ascent of daylight hours that leads into the radiant summer months. Following May, June and July continue this trend, peaking with 384 and 394 hours, respectively. The increased sunshine during these months not only enhances the beauty of Napa’s picturesque vineyards but also fosters an inviting atmosphere, perfect for wine tasting and outdoor festivities. As the summer wanes, the sunlight begins to wane slightly, yet May's vibrant glow undoubtedly sets the stage for the season's splendor.

Monthly Sunshine Duration in Napa: May Highlighted

The May sunshine duration represents the total number of hours Napa experiences direct sunlight during the month of May, excluding cloudy or obstructed periods. This chart compares the sunshine duration of May with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec141h210h257h296h357h384h394h356h314h280h220h185h
Data source: Napa May Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Napa During May

As the seasons change in Napa, the likelihood of sunny weather reaches a delightful peak in May, boasting an impressive 82% chance of sunshine. This marks a significant increase from earlier months, with January starting at just 38%. The transition from April's 70% sun-filled days sets the stage for even more radiant afternoons, while June maintains the same sunny disposition. Following May, the summer months exhibit a slight dip, with July at 73% and August at 79%, yet they still promise plenty of warmth and light. Overall, May stands out in Napa's climate calendar as a time to embrace the beauty of the outdoors under a brilliant sun.

Percentage of Sunny Days in May in Napa

The chart illustrates the percentage of sunny days in Napa throughout the year, with May 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 Napa experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec38%58%63%70%82%82%73%79%76%53%45%31%
Data source: Napa May chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Napa in May

In Napa, the progression of daylight duration throughout the year showcases a remarkable transformation, particularly evident in May. As spring unfolds, residents and visitors alike enjoy an impressive 14 hours of daylight, a peak that not only enhances outdoor activities but also signifies the onset of the warmer months. The gradual increase becomes clear as daylight jumps from 9 hours in January to 10 hours in February, steadily reaching 11 hours in March and 13 hours in April. This trend continues into June, July, and August, where daylight duration plateaus at 14 hours, offering a vibrant backdrop for the region's famed vineyards and festivities. As autumn approaches, the days begin to shorten, reminding us of the cycle of seasons that beautifully influences life in Napa.

Average Daylight Hours in Napa for May

The chart illustrates the variation in daylight duration in Napa throughout the year, with May highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 50m10h 46m11h 59m13h 13m14h 15m14h 46m14h 29m13h 33m12h 22m11h 8m10h 4m9h 32m
Data source: Napa daylight hours, calculated by summing the hours between sunrise and sunset for each day.

May Winds in Napa

In May, Napa experiences a gentle increase in wind speed, reaching an average of 3.1 m/s (7 mph), which is notably higher than the preceding months. This upward trend, beginning in April, hints at the shift towards warmer summer days. The winds during this month carry the fragrant scents of blooming vineyards and add a refreshing touch to outdoor activities, making it an ideal time for wine tastings and leisurely strolls through the lush landscapes. As summer approaches, the persistent breezes not only enhance the beauty of Napa's iconic vineyards but also provide a delightful contrast to the rising temperatures, creating a perfect harmony of nature.

Average May Wind Speed in Napa

The chart displays monthly wind speed patterns in Napa, with values for each month shown alongside May's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how May's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec2.02.42.52.73.1 m/s3.33.02.72.42.31.62.0
Data source: Napa May wind data, generated using information from the Copernicus Climate Change Service.

How May Weather in Napa Compares to Other Months

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

May and January exhibit a stark contrast in weather conditions. In May, temperatures range from a chilly 5°C (41°F) at night to a warm 37°C (99°F) during the day, making it an ideal month for outdoor activities with only 19 mm (0.8 in) of precipitation over just 2 days. The humidity sits at a comfortable 74%. In comparison, January brings colder temperatures with a minimum of -2°C (29°F) and a maximum of 25°C (77°F), averaging around 10°C (50°F). Additionally, January is much wetter, featuring 119 mm (4.7 in) of precipitation over 8 days, along with a higher humidity level of 84%. For more details on January weather, check out Napa weather in January.

When comparing the weather between May and February, it's clear that May brings warmer temperatures, with an average of 18°C (64°F) and a maximum that can reach up to 37°C (99°F). In contrast, February experiences cooler conditions, with an average temperature of 11°C (53°F) and a maximum of 27°C (80°F). Additionally, February sees significantly more precipitation, totaling 113 mm (4.5 in) over about seven days, whereas May has a much drier climate with just 19 mm (0.8 in) over two days. The humidity levels are also slightly higher in February at 84%, compared to May's 74%. For more detailed insights, you can check out Napa weather in February.

When comparing the weather in March and May, notable differences emerge. March experiences cooler temperatures, with a minimum of 1°C (34°F) and an average of 12°C (55°F), while May warms up significantly, with a minimum of 5°C (41°F) and an average of 18°C (64°F). The maximum temperatures in March reach up to 30°C (87°F), whereas May can peak at a much hotter 37°C (99°F). Additionally, March sees considerably higher precipitation, totaling 81 mm (3.2 in) over 9 days, compared to May's 19 mm (0.8 in) over just 2 days. Humidity levels are also slightly higher in March at 83%, compared to 74% in May. For a detailed look at the weather patterns, you can visit Napa weather in March.

In comparing the weather of April and May, it is evident that May tends to be warmer with a minimum temperature of 5°C (41°F) and an average of 18°C (64°F), while April features slightly cooler conditions, with a minimum of 3°C (38°F) and an average of 15°C (60°F). The maximum temperatures in May reach up to 37°C (99°F), surpassing April's high of 33°C (92°F). Additionally, May experiences less precipitation, recording only 19 mm (0.8 in) over 2 days compared to April's 33 mm (1.3 in) across 5 days. Humidity levels are slightly lower in May at 74%, while April retains a higher humidity at 81%. For a more detailed look at April's weather, you can visit Napa weather in April.

May and June showcase a notable transition in weather patterns. In May, temperatures range from a minimum of 5°C (41°F) to a maximum of 37°C (99°F), with an average of 18°C (64°F). The month brings some precipitation, totaling 19 mm (0.8 in) over two days, and a higher humidity level of 74%. In contrast, June sees warmer temperatures, with a minimum of 10°C (51°F), an average of 21°C (70°F), and a peak of 41°C (106°F). Precipitation is significantly lower at just 2 mm (0.1 in), and the month experiences no rainy days, resulting in lower humidity at 64%. For more detailed information about June weather in Napa, you can check Napa weather in June.

In May, temperatures range from a minimum of 5°C (41°F) to a maximum of 37°C (99°F), with an average of 18°C (64°F). The month experiences some rain, with about 19 mm (0.8 in) of precipitation over 2 days and higher humidity at 74%. In contrast, July brings warmer conditions with a minimum of 11°C (53°F) and a maximum of 40°C (104°F), averaging 21°C (70°F). Notably, July is significantly drier, with no recorded precipitation and lower humidity at 44%. For more details on July weather, you can check Napa weather in July.

In comparing the weather of May and August, it's evident that August tends to be warmer and drier. May experiences a wider temperature range, with a minimum of 5°C (41°F) and a maximum of 37°C (99°F), coupled with moderate humidity at 74% and some precipitation at 19 mm (0.8 in) over two days. In contrast, August records a minimum of 12°C (53°F) and a maximum of 42°C (108°F), with notably low humidity at 36% and no precipitation at all. This stark difference highlights the transition to a hotter and more arid climate in August. For more details, you can check out Napa weather in August.

May and September present contrasting weather patterns. In May, temperatures range from a minimum of 5°C (41°F) to a maximum of 37°C (99°F), with an average temperature of 18°C (64°F). The month experiences moderate humidity at 74%, along with some precipitation totaling 19 mm (0.8 in) over 2 days.

In contrast, September offers warmer temperatures, with a minimum of 8°C (46°F), an average of 21°C (70°F), and an impressive maximum of 44°C (111°F). This month is characterized by much lower humidity at 44% and negligible precipitation, totaling only 1 mm (0.0 in) with no rainy days. The stable and dry conditions of September make it a distinctly different experience compared to the transitional weather of May. For more detailed insights, you can check out Napa weather in September.

May and October exhibit similar average temperatures, with May showing a slight edge in maximum temperatures (37°C vs. 36°C in October). Both months experience mild minimum temperatures, around 5°C in May and 4°C in October. However, October tends to be wetter than May, with precipitation increasing from 19 mm in May to 29 mm, despite both months having similar days of precipitation. Additionally, humidity levels are higher in May at 74%, compared to October's 65%. For a more detailed look at October conditions, you can check out Napa weather in October.

May and November present contrasting weather patterns. In May, temperatures can vary significantly, with minimums around 5°C (41°F) and maximums soaring up to 37°C (99°F), leading to an average of 18°C (64°F). This month typically sees lower precipitation, with only 19 mm (0.8 in) over about 2 days, combined with a humidity level of 74%. In contrast, November features cooler temperatures, with a minimum of 0°C (32°F) and a maximum of 30°C (86°F), resulting in a more moderate average of 13°C (56°F). Rainfall is more frequent during this month, totaling 43 mm (1.7 in) over 5 days, and higher humidity at 84%. For detailed insights, check the weather specifics for Napa weather in November.

May and December present quite contrasting weather conditions. In May, temperatures range from a chilly 5°C (41°F) at night to a hot 37°C (99°F) during the day, with an average temperature of 18°C (64°F). The month experiences relatively low precipitation, with only 19 mm (0.8 inches) over approximately two days, and humidity levels at 74%. In stark contrast, December's temperatures are cooler, with a minimum of 0°C (32°F) and a maximum of 24°C (75°F), resulting in an average of 10°C (50°F). December also sees significantly more rainfall, totaling 91 mm (3.6 inches) over nine days, and a higher humidity of 83%. For a deeper dive into the December climate, check out Napa weather in December.

Compare Napa's Climate with Cities Worldwide

Conclusion: What to Expect From May Weather in Napa

As May unfolds in Napa, it marks a notable transition in weather, showcasing a delightful blend of warmth and freshness. With average temperatures maintaining a comfortable 18°C, the month features occasional highs reaching a sizzling 37°C, while minimums dip comfortably around 5°C during the nights. The low precipitation, totaling just 19 mm over a couple of days, coupled with a humidity of 74%, brings a pleasant, mild ambiance that’s perfect for outdoor adventures. This inviting weather sets May apart as a lovely prelude to the summer months, making it an ideal time for visitors to explore the vineyards and landscapes. For a deeper understanding of the weather patterns throughout the year, check out Napa Climate.