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Average Weather at Iruma Ab Japan

At Iruma Ab, the summers are short, warm, oppressive, wet, and mostly cloudy and the winters are very cold and mostly clear. Over the course of the year, the temperature typically varies from 30°F to 87°F and is rarely below 24°F or above 95°F.

Climate Summary

coldcoolcomfortablewarmhotwarmcoolcoldJanFebMarAprMayJunJulAugSepOctNovDec76%76%28%28%clearovercastprecipitation: 7.3 inprecipitation: 7.3 in1.4 in1.4 inmuggy: 93%muggy: 93%0%0%drydrybeach/pool score: 6.2beach/pool score: 6.20.00.0
Click on each chart for more information.

Based on the beach/pool score, the best time of year to visit Iruma Ab for hot-weather activities is from late July to early September.

Temperature

The hot season lasts for 2.6 months, from June 27 to September 15, with an average daily high temperature above 79°F. The hottest day of the year is August 7, with an average high of 87°F and low of 74°F.

The cold season lasts for 3.5 months, from December 2 to March 18, with an average daily high temperature below 55°F. The coldest day of the year is January 21, with an average low of 30°F and high of 47°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 at Iruma AbJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMvery coldvery coldcoldcoldcoolcoolcomfortablewarmhotwarmvery coldvery coldfreezing
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.

Chincoteague, Virginia, United States (6,883 miles away) and Lankaran, Azerbaijan (4,764 miles) are the far-away foreign places with temperatures most similar to Iruma Ab (view comparison).

Clouds

At Iruma Ab, 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 at Iruma Ab begins around October 7 and lasts for 5.8 months, ending around March 31. On December 27, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 76% of the time, and overcast or mostly cloudy 24% of the time.

The cloudier part of the year begins around March 31 and lasts for 6.2 months, ending around October 7. On July 2, the cloudiest day of the year, the sky is overcast or mostly cloudy 73% of the time, and clear, mostly clear, or partly cloudy 28% of the time.

Cloud Cover Categories

Cloud Cover Categories at Iruma AbclearerclearercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Dec 2776%Dec 2776%Jul 228%Jul 228%Oct 751%Oct 751%Mar 3152%Mar 3152%clearovercastmostly clearpartly cloudymostly 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 at Iruma Ab varies significantly throughout the year.

The wetter season lasts 6.7 months, from March 23 to October 13, with a greater than 30% chance of a given day being a wet day. The chance of a wet day peaks at 50% on June 24.

The drier season lasts 5.3 months, from October 13 to March 23. The smallest chance of a wet day is 10% on December 30.

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 50% on June 24.

Daily Chance of Precipitation

Daily Chance of Precipitation at Iruma AbwetdrydryJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jun 2450%Jun 2450%Dec 3010%Dec 3010%Mar 2330%Mar 2330%Oct 1330%Oct 1330%rainmixed
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. Iruma Ab experiences extreme seasonal variation in monthly rainfall.

Rain falls throughout the year at Iruma Ab. The most rain falls during the 31 days centered around September 20, with an average total accumulation of 7.3 inches.

The least rain falls around January 1, with an average total accumulation of 1.3 inches.

Average Monthly Rainfall

Average Monthly Rainfall at Iruma AbJanFebMarAprMayJunJulAugSepOctNovDec0 in2 in4 in6 in8 in10 in12 in14 inSep 207.3 inSep 207.3 inJan 11.3 inJan 11.3 inJun 296.2 inJun 296.2 in
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.

Snowfall

The sliding 31-day liquid-equivalent quantity of snowfall at Iruma Ab does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.

Average Liquid-Equivalent Monthly Snowfall

Average Liquid-Equivalent Monthly Snowfall at Iruma AbsnowJanFebMarAprMayJunJulAugSepOctNovDec0 in1 in2 in3 in4 in5 in6 in7 in8 inJan 310.2 inJan 310.2 inJul 310.0 inJul 310.0 inDec 290.1 inDec 290.1 inMar 130.1 inMar 130.1 in
The average liquid-equivalent 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.

Sun

The length of the day at Iruma Ab varies significantly over the course of the year. In 2017, the shortest day is December 22, with 9 hours, 44 minutes of daylight; the longest day is June 21, with 14 hours, 36 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 4:25 AM on June 13, and the latest sunrise is 2 hours, 28 minutes later at 6:53 AM on January 7. The earliest sunset is at 4:28 PM on December 6, and the latest sunset is 2 hours, 34 minutes later at 7:02 PM on June 29.

Daylight saving time (DST) is not observed at Iruma Ab during 2017.

Sunrise & Sunset with Twilight

Sunrise & Sunset with Twilight at Iruma AbJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PMJun 134:25 AMJun 134:25 AM7:02 PMJun 297:02 PMJun 29Dec 64:28 PMDec 64:28 PM6:53 AMJan 76:53 AMJan 7daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
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.

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.

Iruma Ab experiences extreme seasonal variation in the perceived humidity.

The muggier period of the year lasts for 3.5 months, from June 11 to September 28, during which time the comfort level is muggy, oppressive, or miserable at least 23% of the time. The muggiest day of the year is August 8, with muggy conditions 93% of the time.

The least muggy day of the year is February 13, when muggy conditions are essentially unheard of.

Humidity Comfort Levels

Humidity Comfort Levels at Iruma AbmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Feb 130%Feb 130%93%Aug 893%Aug 8Jun 1123%Jun 1123%Sep 2823%Sep 2823%miserablemiserableoppressiveoppressivemuggymuggydrydry
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 at Iruma Ab experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 4.8 months, from December 23 to May 18, with average wind speeds of more than 7.3 miles per hour. The windiest day of the year is March 25, with an average hourly wind speed of 8.3 miles per hour.

The calmer time of year lasts for 7.2 months, from May 18 to December 23. The calmest day of the year is August 1, with an average hourly wind speed of 6.3 miles per hour.

Average Wind Speed

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 at Iruma Ab varies throughout the year.

The wind is most often from the north for 3.1 months, from January 13 to April 15 and for 2.9 months, from September 17 to December 13, with a peak percentage of 50% on February 24. The wind is most often from the south for 4.7 months, from April 15 to September 7, with a peak percentage of 45% on July 24. The wind is most often from the west for 1.0 months, from December 13 to January 13, with a peak percentage of 45% on January 1.

Wind Direction

Wind Direction at Iruma AbWNSENWJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%westsoutheastnorth
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

Iruma Ab 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 significant seasonal variation over the course of the year.

The time of year with warmer water lasts for 2.5 months, from July 14 to September 29, with an average temperature above 74°F. The day of the year with the warmest water is August 18, with an average temperature of 79°F.

The time of year with cooler water lasts for 4.0 months, from December 25 to April 25, with an average temperature below 61°F. The day of the year with the coolest water is February 24, with an average temperature of 57°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 at Iruma Ab 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 Iruma Ab for general outdoor tourist activities is from late July to early October, with a peak score in the first week of September.

Tourism Score

Tourism Score at Iruma Abbest timeJanFebMarAprMayJunJulAugSepOctNovDec02468106.16.10.00.05.55.55.25.2 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 Iruma Ab for hot-weather activities is from late July to early September, with a peak score in the second week of August.

Beach/Pool Score

Beach/Pool Score at Iruma AbJanFebMarAprMayJunJulAugSepOctNovDec02468106.26.20.00.0 precipitationprecipitationcloudscloudstemperaturetemperaturebeach/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).

The growing season at Iruma Ab typically lasts for 8.5 months (260 days), from around March 21 to around December 6, rarely starting before March 3 or after April 8, and rarely ending before November 18 or after December 23.

Time Spent in Various Temperature Bands and the Growing Season

Time Spent in Various Temperature Bands and the Growing Season at Iruma Abgrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%50%Mar 2150%Mar 2150%Dec 650%Dec 690%Apr 890%Apr 890%Nov 1890%Nov 1810%Mar 310%Mar 310%Dec 2310%Dec 230%Jan 290%Jan 29Jul 28100%Jul 28100%very coldcoldcoolcomfortablewarmhot
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.

Based on growing degree days alone, the first spring blooms at Iruma Ab should appear around April 2, only rarely appearing before March 22 or after April 14.

Growing Degree Days

Growing Degree Days at Iruma AbJanFebMarAprMayJunJulAugSepOctNovDec0°F500°F1,000°F1,500°F2,000°F2,500°F3,000°F3,500°F4,000°F4,500°FApr 284°FApr 284°FJun 10900°FJun 10900°FJul 191,800°FJul 191,800°FDec 314,198°FDec 314,198°F
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 significant seasonal variation over the course of the year.

The brighter period of the year lasts for 4.5 months, from April 12 to August 27, with an average daily incident shortwave energy per square meter above 5.3 kWh. The brightest day of the year is May 22, with an average of 5.9 kWh.

The darker period of the year lasts for 3.1 months, from November 1 to February 4, with an average daily incident shortwave energy per square meter below 3.3 kWh. The darkest day of the year is December 20, with an average of 2.6 kWh.

Average Daily Incident Shortwave Solar Energy

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 Iruma Ab are 35.842 deg latitude, 139.411 deg longitude, and 249 ft elevation.

The topography within 2 miles of Iruma Ab contains only modest variations in elevation, with a maximum elevation change of 322 feet and an average elevation above sea level of 258 feet. Within 10 miles contains only modest variations in elevation (1,532 feet). Within 50 miles contains very significant variations in elevation (10,764 feet).

The area within 2 miles of Iruma Ab is covered by artificial surfaces (60%), cropland (23%), and trees (12%), within 10 miles by artificial surfaces (40%) and cropland (29%), and within 50 miles by trees (42%) and cropland (27%).

Data Sources

This report illustrates the typical weather at Iruma Ab, 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

Iruma Ab 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 Yokota Air Base, Tokyo, Atsugi United States Naval Air Station, Tokyo International Airport, Shimofusa Ab, Yokosuka Fwf, Tateyama Ab, and Narita International 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 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.