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Average Weather in Pomona California, United States

In Pomona, the summers are hot, arid, and clear and the winters are long, cool, and partly cloudy. Over the course of the year, the temperature typically varies from 43°F to 92°F and is rarely below 36°F or above 101°F.

Climate Summary

comfortablewarmhotwarmcomfortableJanFebMarAprMayJunJulAugSepOctNovDec91%91%56%56%clearovercastprecipitation: 3.0 inprecipitation: 3.0 in0.0 in0.0 inmuggy: 6%muggy: 6%0%0%drydrytourism score: 7.9tourism score: 7.92.32.3
Click on each chart for more information.

Based on the tourism score, the best time of year to visit Pomona for warm-weather activities is from late May to mid October.

Temperature

The hot season lasts for 3.0 months, from June 25 to September 23, with an average daily high temperature above 87°F. The hottest day of the year is August 22, with an average high of 92°F and low of 65°F.

The cool season lasts for 3.9 months, from November 23 to March 19, with an average daily high temperature below 71°F. The coldest day of the year is December 25, with an average low of 43°F and high of 66°F.

Average High and Low Temperature

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 entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature

Average Hourly Temperature in PomonaJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMcoldcoldcoldcoldcoolcoolcoolcomfortablewarmhotvery cold
The average hourly temperature, color coded into bands: 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 shaded overlays indicate night and civil twilight.

Youssoufia, Morocco (5,955 miles away) is the far-away foreign place with temperatures most similar to Pomona (view comparison).

Clouds

In Pomona, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Pomona begins around April 25 and lasts for 6.3 months, ending around November 4. On September 7, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 91% of the time, and overcast or mostly cloudy 9% of the time.

The cloudier part of the year begins around November 4 and lasts for 5.7 months, ending around April 25. On February 20, the cloudiest day of the year, the sky is overcast or mostly cloudy 44% of the time, and clear, mostly clear, or partly cloudy 56% of the time.

Cloud Cover Categories

Cloud Cover Categories in PomonaclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Sep 791%Sep 791%Feb 2056%Feb 2056%Apr 2573%Apr 2573%Nov 473%Nov 473%clearovercastmostly clearmostly cloudy
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Pomona varies throughout the year.

The wetter season lasts 4.4 months, from November 22 to April 3, with a greater than 10% chance of a given day being a wet day. The chance of a wet day peaks at 20% on February 19.

The drier season lasts 7.6 months, from April 3 to November 22. The smallest chance of a wet day is 0% on June 21.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 20% on February 19.

Daily Chance of Precipitation

Daily Chance of Precipitation in PomonawetwetdryJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Feb 1920%Feb 1920%Jun 210%Jun 210%Jan 117%Jan 117%Nov 2210%Nov 2210%Apr 310%Apr 310%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 months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Pomona experiences significant seasonal variation in monthly rainfall.

The rainy period of the year lasts for 6.1 months, from October 20 to April 23, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around February 19, with an average total accumulation of 3.0 inches.

The rainless period of the year lasts for 5.9 months, from April 23 to October 20. The least rain falls around June 30, with an average total accumulation of 0.0 inches.

Average Monthly Rainfall

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 liquid-equivalent snowfall.

Sun

The length of the day in Pomona varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 53 minutes of daylight; the longest day is June 20, with 14 hours, 26 minutes of daylight.

Hours of Daylight and Twilight

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 is at 5:39 AM on June 11, and the latest sunrise is 1 hour, 35 minutes later at 7:13 AM on November 4. The earliest sunset is at 4:41 PM on December 4, and the latest sunset is 3 hours, 25 minutes later at 8:06 PM on June 29.

Daylight saving time (DST) is observed in Pomona during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.

Sunrise & Sunset with Twilight and Daylight Saving Time

Sunrise & Sunset with Twilight and Daylight Saving Time in PomonaJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 115:39 AMJun 115:39 AM8:06 PMJun 298:06 PMJun 29Dec 44:41 PMDec 44:41 PM7:13 AMNov 47:13 AMNov 4Mar 12DSTMar 12DSTDSTNov 5DSTNov 5daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2017. 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 transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

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 perceived humidity level in Pomona, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, staying within 3% of 3% throughout.

Humidity Comfort Levels

Humidity Comfort Levels in PomonaJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Feb 200%Feb 200%Aug 116%Aug 116%humidhumidcomfortablecomfortabledrydry
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

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 in Pomona experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 5.9 months, from November 10 to May 7, with average wind speeds of more than 6.5 miles per hour. The windiest day of the year is December 31, with an average hourly wind speed of 7.8 miles per hour.

The calmer time of year lasts for 6.1 months, from May 7 to November 10. The calmest day of the year is September 8, with an average hourly wind speed of 5.2 miles per hour.

Average Wind Speed

Average Wind Speed in PomonawindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph2 mph4 mph6 mph8 mph10 mph12 mph14 mphDec 317.8 mphDec 317.8 mphSep 85.2 mphSep 85.2 mphMay 76.5 mphMay 76.5 mph
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction in Pomona varies throughout the year.

The wind is most often from the west for 4.4 months, from February 19 to July 1 and for 1.8 months, from September 2 to October 26, with a peak percentage of 50% on May 22. The wind is most often from the south for 2.0 months, from July 1 to September 2, with a peak percentage of 46% on July 23. The wind is most often from the north for 3.8 months, from October 26 to February 19, with a peak percentage of 35% on January 1.

Wind Direction

Wind Direction in PomonaNWSWNJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%westsouthnortheast
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

Pomona 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 water temperature experiences some seasonal variation over the course of the year.

The time of year with warmer water lasts for 3.2 months, from July 5 to October 12, with an average temperature above 67°F. The day of the year with the warmest water is August 20, with an average temperature of 69°F.

The time of year with cooler water lasts for 4.6 months, from December 10 to April 27, with an average temperature below 61°F. The day of the year with the coolest water is February 4, with an average temperature of 59°F.

Average Water Temperature

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

Best Time of Year to Visit

To characterize how pleasant the weather is in Pomona throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Pomona for general outdoor tourist activities is from late May to mid October, with a peak score in the first week of July.

Tourism Score

Tourism Score in Pomonabest timeJanFebMarAprMayJunJulAugSepOctNovDec02468107.97.92.32.37.87.8 precipitationprecipitationcloudscloudstemperaturetemperaturetourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Pomona for hot-weather activities is from early July to mid September, with a peak score in the last week of August.

Beach/Pool Score

Beach/Pool Score in Pomonabest timeJanFebMarAprMayJunJulAugSepOctNovDec02468105.45.40.40.4precipitationprecipitationcloudscloudsbeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

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 in Pomona 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

Time Spent in Various Temperature Bands and the Growing Season in Pomonagrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%90%Jan 2090%Jan 2090%Dec 1890%Dec 18Jul 4100%Jul 4100%very coldcoldcoolcomfortablewarmhotsweltering
The percentage of time spent in various temperature bands: 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 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.

Growing Degree Days

The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 experiences extreme seasonal variation over the course of the year.

The brighter period of the year lasts for 3.8 months, from April 25 to August 19, with an average daily incident shortwave energy per square meter above 7.5 kWh. The brightest day of the year is June 18, with an average of 8.6 kWh.

The darker period of the year lasts for 3.2 months, from November 6 to February 12, with an average daily incident shortwave energy per square meter below 4.1 kWh. The darkest day of the year is December 25, with an average of 3.0 kWh.

Average Daily Incident Shortwave Solar Energy

Average Daily Incident Shortwave Solar Energy in PomonabrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh1 kWh2 kWh3 kWh4 kWh5 kWh6 kWh7 kWh8 kWh9 kWh10 kWhJun 188.6 kWhJun 188.6 kWhDec 253.0 kWhDec 253.0 kWhApr 257.5 kWhApr 257.5 kWhAug 197.5 kWhAug 197.5 kWhNov 64.1 kWhNov 64.1 kWhFeb 124.1 kWhFeb 124.1 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.

Topography

For the purposes of this report, the geographical coordinates of Pomona are 34.055 deg latitude, -117.752 deg longitude, and 886 ft elevation.

The topography within 2 miles of Pomona contains only modest variations in elevation, with a maximum elevation change of 456 feet and an average elevation above sea level of 859 feet. Within 10 miles contains only modest variations in elevation (5,000 feet). Within 50 miles also contains extreme variations in elevation (10,807 feet).

The area within 2 miles of Pomona is covered by artificial surfaces (81%) and shrubs (19%), within 10 miles by artificial surfaces (55%) and shrubs (33%), and within 50 miles by shrubs (51%) and artificial surfaces (23%).

Data Sources

This report illustrates the typical weather in Pomona, 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

There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Pomona.

For each station, the records are corrected for the elevation difference between that station and Pomona according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

The estimated value at Pomona is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Pomona and a given station.

The stations contributing to this reconstruction are: Ontario International Airport (60%, 10 kilometers, east); Chino Airport (31%, 14 kilometers, southeast); Fullerton Municipal Airport (8%, 29 kilometers, southwest); and Mount Wilson (1.0%, 35 kilometers, northwest).

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 aiports and weather stations are provided by AskGeo.com .

Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.

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.