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Climate and Average Weather Year Round in Fairfax Virginia, United States

In Fairfax, the summers are warm and humid, the winters are very cold and snowy, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 26°F to 87°F and is rarely below 13°F or above 94°F.

Based on the tourism score, the best times of year to visit Fairfax for warm-weather activities are from early June to early July and from early August to late September.

Climate in Fairfax

very coldcoldcoolwarmhotwarmcoolcoldJanFebMarAprMayJunJulAugSepOctNovDecNowNow65%65%48%48%clearovercastprecipitation: 3.6 inprecipitation: 3.6 in2.4 in2.4 inmuggy: 64%muggy: 64%0%0%drydrytourism score: 6.5tourism score: 6.50.30.3
Fairfax weather by month. Click on each chart for more information.

The hot season lasts for 3.6 months, from May 29 to September 15, with an average daily high temperature above 78°F. The hottest month of the year in Fairfax is July, with an average high of 86°F and low of 67°F.

The cold season lasts for 3.1 months, from November 30 to March 2, with an average daily high temperature below 51°F. The coldest month of the year in Fairfax is January, with an average low of 27°F and high of 42°F.

Average High and Low Temperature in Fairfax

Average High and Low Temperature in FairfaxhotcoldcoldJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F10°F10°F20°F20°F30°F30°F40°F40°F50°F50°F60°F60°F70°F70°F80°F80°F90°F90°F100°F100°FJan 3042°FJan 3042°FJul 2087°FJul 2087°F26°F26°F68°F68°FMay 2978°FMay 2978°FSep 1578°FSep 1578°FNov 3051°FNov 3051°FMar 251°FMar 251°F58°F58°F59°F59°F35°F35°F32°F32°FNowNow
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.
AverageJanFebMarAprMayJunJulAugSepOctNovDec
High 42°F46°F55°F66°F74°F82°F86°F84°F77°F67°F56°F46°F
Temp. 33°F36°F44°F55°F64°F72°F77°F75°F68°F56°F46°F37°F
Low 27°F29°F36°F45°F54°F63°F67°F66°F59°F47°F38°F31°F

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 in Fairfax

Average Hourly Temperature in FairfaxJanFebMarAprMayJunJulAugSepOctNovDec12 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 AMNowNowfreezingvery coldvery coldcoldcoldcoolcoolcomfortablewarmhotfreezingfreezing
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.

Tbilisi, Georgia (5,797 miles away) is the far-away foreign place with temperatures most similar to Fairfax (view comparison).

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© OpenStreetMap contributors

Compare Fairfax to another city:

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

The clearer part of the year in Fairfax begins around July 1 and lasts for 4.3 months, ending around November 12.

The clearest month of the year in Fairfax is September, during which on average the sky is clear, mostly clear, or partly cloudy 64% of the time.

The cloudier part of the year begins around November 12 and lasts for 7.7 months, ending around July 1.

The cloudiest month of the year in Fairfax is January, during which on average the sky is overcast or mostly cloudy 51% of the time.

Cloud Cover Categories in Fairfax

Cloud Cover Categories in FairfaxclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Sep 2265%Sep 2265%Jan 548%Jan 548%Jul 156%Jul 156%Nov 1257%Nov 1257%NowNowclearmostly 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.
FractionJanFebMarAprMayJunJulAugSepOctNovDec
Cloudier 51%50%49%48%48%45%41%37%36%37%44%50%
Clearer 49%50%51%52%52%55%59%63%64%63%56%50%

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

The wetter season lasts 4.4 months, from April 9 to August 21, with a greater than 30% chance of a given day being a wet day. The month with the most wet days in Fairfax is July, with an average of 11.7 days with at least 0.04 inches of precipitation.

The drier season lasts 7.6 months, from August 21 to April 9. The month with the fewest wet days in Fairfax is January, with an average of 6.6 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Fairfax is July, with an average of 11.7 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 40% on July 12.

Daily Chance of Precipitation in Fairfax

Daily Chance of Precipitation in FairfaxwetdrydryJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Jul 1240%Jul 1240%Oct 1920%Oct 1920%Apr 930%Apr 930%Aug 2130%Aug 2130%NowNowrainmixedsnow
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).
Days ofJanFebMarAprMayJunJulAugSepOctNovDec
Rain 4.0d4.3d7.1d8.8d10.9d11.3d11.7d10.1d7.7d6.7d6.3d5.5d
Mixed 1.5d1.5d0.7d0.0d0.0d0.0d0.0d0.0d0.0d0.0d0.4d1.0d
Snow 1.1d1.0d0.3d0.0d0.0d0.0d0.0d0.0d0.0d0.0d0.1d0.5d
Any 6.6d6.7d8.1d8.9d10.9d11.3d11.7d10.1d7.7d6.8d6.8d7.0d

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. Fairfax experiences some seasonal variation in monthly rainfall.

Rain falls throughout the year in Fairfax. The month with the most rain in Fairfax is May, with an average rainfall of 3.6 inches.

The month with the least rain in Fairfax is January, with an average rainfall of 1.8 inches.

Average Monthly Rainfall in Fairfax

Average Monthly Rainfall in FairfaxJanFebMarAprMayJunJulAugSepOctNovDec0 in0 in2 in2 in4 in4 in6 in6 in8 in8 inMay 193.6 inMay 193.6 inJan 301.8 inJan 301.8 inSep 283.4 inSep 283.4 inNowNow
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.
JanFebMarAprMayJunJulAugSepOctNovDec
Rainfall 1.8″1.9″2.9″3.3″3.6″3.3″3.1″3.0″3.3″3.2″3.0″2.5″

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Fairfax experiences significant seasonal variation in monthly snowfall.

The snowy period of the year lasts for 4.3 months, from November 17 to March 27, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Fairfax is February, with an average snowfall of 7.1 inches.

The snowless period of the year lasts for 7.7 months, from March 27 to November 17. The least snow falls around July 17, with an average total accumulation of 0.0 inches.

Average Monthly Snowfall in Fairfax

Average Monthly Snowfall in FairfaxsnowsnowJanFebMarAprMayJunJulAugSepOctNovDec0 in0 in5 in5 in10 in10 in15 in15 in20 in20 inFeb 57.5 inFeb 57.5 inJul 170.0 inJul 170.0 inNov 171.0 inNov 171.0 inMar 271.0 inMar 271.0 in
The average snowfall (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 rainfall.
JanFebMarAprMayJunJulAugSepOctNovDec
Snowfall 6.5″7.1″2.3″0.0″0.0″0.0″0.0″0.0″0.0″0.1″0.8″4.0″

The length of the day in Fairfax varies significantly over the course of the year. In 2024, the shortest day is December 21, with 9 hours, 27 minutes of daylight; the longest day is June 20, with 14 hours, 54 minutes of daylight.

Hours of Daylight and Twilight in Fairfax

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.
Hours ofJanFebMarAprMayJunJulAugSepOctNovDec
Daylight 9.8h10.8h12.0h13.3h14.3h14.8h14.6h13.6h12.4h11.1h10.1h9.5h

The earliest sunrise is at 5:43 AM on June 13, and the latest sunrise is 1 hour, 55 minutes later at 7:38 AM on November 2. The earliest sunset is at 4:47 PM on December 6, and the latest sunset is 3 hours, 51 minutes later at 8:38 PM on June 27.

Daylight saving time (DST) is observed in Fairfax during 2024, starting in the spring on March 10, lasting 7.8 months, and ending in the fall on November 3.

Sunrise & Sunset with Twilight and Daylight Saving Time in Fairfax

Sunrise & Sunset with Twilight and Daylight Saving Time in FairfaxJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 135:43 AMJun 135:43 AM8:38 PMJun 278:38 PMJun 27Dec 64:47 PMDec 64:47 PM7:38 AMNov 27:38 AMNov 2Mar 10DSTMar 10DSTDSTNov 3DSTNov 3daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunsetNowNow
The solar day over the course of the year 2024. 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.

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 Fairfax

Solar Elevation and Azimuth in FairfaxJanFebMarAprMayJunJulAugSepOctNovDec12 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 AM0001010101020202030303040404050506060700001010102020202030304040505060702875NowNow
northeastsouthwest
Solar elevation and azimuth over the course of the year 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 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.

Moon Rise, Set & Phases in Fairfax

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.

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.

Fairfax experiences extreme seasonal variation in the perceived humidity.

The muggier period of the year lasts for 4.0 months, from May 24 to September 24, during which time the comfort level is muggy, oppressive, or miserable at least 16% of the time. The month with the most muggy days in Fairfax is July, with 18.7 days that are muggy or worse.

The month with the fewest muggy days in Fairfax is February, with 0.0 days that are muggy or worse.

Humidity Comfort Levels in Fairfax

Humidity Comfort Levels in FairfaxmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Feb 190%Feb 190%Jul 2764%Jul 2764%May 2416%May 2416%Sep 2416%Sep 2416%NowNowoppressiveoppressivemuggymuggydrydrycomfortablecomfortable
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.
JanFebMarAprMayJunJulAugSepOctNovDec
Muggy days 0.0d0.0d0.0d0.1d3.3d11.7d18.7d16.3d7.3d1.3d0.1d0.0d

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 Fairfax experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 6.5 months, from October 25 to May 7, with average wind speeds of more than 7.1 miles per hour. The windiest month of the year in Fairfax is March, with an average hourly wind speed of 8.7 miles per hour.

The calmer time of year lasts for 5.5 months, from May 7 to October 25. The calmest month of the year in Fairfax is July, with an average hourly wind speed of 5.5 miles per hour.

Average Wind Speed in Fairfax

Average Wind Speed in FairfaxwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph0 mph2 mph2 mph4 mph4 mph6 mph6 mph8 mph8 mph10 mph10 mph12 mph12 mph14 mph14 mphFeb 268.9 mphFeb 268.9 mphJul 315.3 mphJul 315.3 mphOct 257.1 mphOct 257.1 mphMay 77.1 mphMay 77.1 mphNowNow
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Wind Speed (mph) 8.38.78.78.06.86.05.55.56.27.07.57.8

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

The wind is most often from the north for 2.0 weeks, from March 7 to March 21, with a peak percentage of 32% on March 9. The wind is most often from the west for 1.3 months, from March 21 to April 30; for 1.2 months, from June 19 to July 24; and for 4.9 months, from October 10 to March 7, with a peak percentage of 36% on July 5. The wind is most often from the south for 1.6 months, from April 30 to June 19 and for 2.5 months, from July 24 to October 10, with a peak percentage of 34% on August 15.

Wind Direction in Fairfax

Wind Direction in FairfaxWNWSWSWJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%NowNowwestsouthnortheast
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).

Fairfax 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 extreme seasonal variation over the course of the year.

The time of year with warmer water lasts for 3.3 months, from June 22 to October 1, with an average temperature above 69°F. The month of the year in Fairfax with the warmest water is August, with an average temperature of 76°F.

The time of year with cooler water lasts for 3.5 months, from December 20 to April 4, with an average temperature below 44°F. The month of the year in Fairfax with the coolest water is February, with an average temperature of 37°F.

Average Water Temperature in Fairfax

Average Water Temperature in FairfaxwarmcoolJanFebMarAprMayJunJulAugSepOctNovDec30°F30°F40°F40°F50°F50°F60°F60°F70°F70°F80°F80°FAug 1077°FAug 1077°F36°FFeb 636°FFeb 6Jun 2269°FJun 2269°FOct 169°FOct 169°FDec 2044°FDec 2044°FApr 444°FApr 444°FNowNow
The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.
WaterJanFebMarAprMayJunJulAugSepOctNovDec
Temperature 39°F37°F40°F47°F56°F67°F74°F76°F72°F64°F54°F45°F

To characterize how pleasant the weather is in Fairfax 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 times of year to visit Fairfax for general outdoor tourist activities are from early June to early July and from early August to late September, with a peak score in the first week of September.

Tourism Score in Fairfax

Tourism Score in Fairfaxbest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810106.56.50.30.36.06.05.75.7NowNowtemperaturetemperature cloudscloudsprecipitationprecipitationtourism 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 Fairfax for hot-weather activities is from late June to late August, with a peak score in the last week of July.

Beach/Pool Score in Fairfax

Beach/Pool Score in Fairfaxbest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810106.06.00.00.0NowNowtemperaturetemperature cloudscloudsprecipitationprecipitationbeach/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.

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).

The growing season in Fairfax typically lasts for 6.7 months (206 days), from around April 5 to around October 28, rarely starting before March 19 or after April 22, and rarely ending before October 11 or after November 14.

Time Spent in Various Temperature Bands and the Growing Season in Fairfax

Time Spent in Various Temperature Bands and the Growing Season in Fairfaxgrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%50%Apr 550%Apr 550%Oct 2850%Oct 2890%Apr 2290%Apr 2290%Oct 1190%Oct 1110%Mar 1910%Mar 1910%Nov 1410%Nov 140%Dec 140%Dec 14Jul 14100%Jul 14100%NowNowfreezingvery coldcoldcoolcomfortablewarmhotfrigid
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.

Based on growing degree days alone, the first spring blooms in Fairfax should appear around March 22, only rarely appearing before March 6 or after April 7.

Growing Degree Days in Fairfax

Growing Degree Days in FairfaxJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F500°F500°F1,000°F1,000°F1,500°F1,500°F2,000°F2,000°F2,500°F2,500°F3,000°F3,000°F3,500°F3,500°F4,000°F4,000°FMar 2287°FMar 2287°FJun 7900°FJun 7900°FJul 151,800°FJul 151,800°FDec 313,877°FDec 313,877°FNowNow
The average growing degree days accumulated over the course of the year, 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 experiences significant seasonal variation over the course of the year.

The brighter period of the year lasts for 3.8 months, from April 27 to August 22, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest month of the year in Fairfax is June, with an average of 6.8 kWh.

The darker period of the year lasts for 3.1 months, from November 5 to February 9, with an average daily incident shortwave energy per square meter below 3.0 kWh. The darkest month of the year in Fairfax is December, with an average of 2.1 kWh.

Average Daily Incident Shortwave Solar Energy in Fairfax

Average Daily Incident Shortwave Solar Energy in FairfaxbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh0 kWh1 kWh1 kWh2 kWh2 kWh3 kWh3 kWh4 kWh4 kWh5 kWh5 kWh6 kWh6 kWh7 kWh7 kWh8 kWh8 kWh9 kWh9 kWhJun 226.9 kWhJun 226.9 kWhDec 232.0 kWhDec 232.0 kWhApr 275.9 kWhApr 275.9 kWhAug 225.9 kWhAug 225.9 kWhNov 53.0 kWhNov 53.0 kWhFeb 93.0 kWhFeb 93.0 kWhNowNow
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Solar Energy (kWh) 2.33.24.45.56.46.86.76.15.13.82.72.1

For the purposes of this report, the geographical coordinates of Fairfax are 38.846 deg latitude, -77.306 deg longitude, and 433 ft elevation.

The topography within 2 miles of Fairfax contains only modest variations in elevation, with a maximum elevation change of 187 feet and an average elevation above sea level of 394 feet. Within 10 miles also contains only modest variations in elevation (466 feet). Within 50 miles contains only modest variations in elevation (3,343 feet).

The area within 2 miles of Fairfax is covered by artificial surfaces (88%) and trees (12%), within 10 miles by artificial surfaces (64%) and trees (34%), and within 50 miles by trees (46%) and cropland (27%).

This report illustrates the typical weather in Fairfax, 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 5 weather stations near enough to contribute to our estimation of the temperature and dew point in Fairfax.

For each station, the records are corrected for the elevation difference between that station and Fairfax 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 Fairfax is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Fairfax and a given station.

The stations contributing to this reconstruction are:

To get a sense of how much these sources agree with each other, you can view a comparison of Fairfax and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.

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.

Please review our full terms contained on our Terms of Service page.