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Average Weather in December in Altamont Oregon, United States

The lowest daily average high temperature is 38°F on December 26.

Daily low temperatures decrease by 3°F, from 25°F to 22°F, rarely falling below 8°F or exceeding 36°F. The lowest daily average low temperature is 22°F on December 23.

For reference, on August 4, the hottest day of the year, temperatures in Altamont typically range from 50°F to 85°F, while on December 23, the coldest day of the year, they range from 22°F to 38°F.

Average High and Low Temperature in December

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 hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, 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 December

Average Hourly Temperature in December in Altamont18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM4 AM8 AM12 PM4 PM8 PM12 AMNovJanfreezingfreezingvery coldcold
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.

Tornavacas, Spain (5,484 miles away); Altınyayla, Turkey (6,680 miles); and Dedeköy, Turkey (6,531 miles) are the far-away foreign places with temperatures most similar to Altamont (view comparison).

Clouds

The month of December in Altamont experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 65% throughout the month.

The clearest day of the month is December 13, with clear, mostly clear, or partly cloudy conditions 36% of the time.

For reference, on January 10, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 67%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 87%.

Cloud Cover Categories in December

Cloud Cover Categories in December in Altamont1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJanDec 134%Dec 134%Dec 3134%Dec 3134%Dec 1136%Dec 1136%Dec 2135%Dec 2135%clearpartly cloudymostly cloudyovercastmostly clear
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. In Altamont, the chance of a wet day over the course of December is decreasing, starting the month at 33% and ending it at 28%.

For reference, the year's highest daily chance of a wet day is 33% on November 30, and its lowest chance is 4% on August 4.

Over the course of December in Altamont, the chance of a day with only rain decreases from 21% to 14%, the chance of a day with mixed snow and rain remains an essentially constant 8% throughout, and the chance of a day with only snow increases from 4% to 6%.

Probability of Precipitation in December

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 month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during December in Altamont is gradually decreasing, starting the month at 2.3 inches, when it rarely exceeds 4.8 inches or falls below 0.5 inches, and ending the month at 2.1 inches, when it rarely exceeds 5.1 inches or falls below 0.2 inches.

The highest average 31-day accumulation is 2.4 inches on December 9.

Average Monthly Rainfall in December

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

We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day liquid-equivalent snowfall during December in Altamont is essentially constant, remaining about 0.5 inches throughout, and rarely exceeding 1.6 inches or falling to 0.0 inches.

The highest average 31-day liquid-equivalent accumulation is 0.6 inches on December 22.

Average Monthly Liquid-Equivalent Snowfall in December

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

Over the course of December in Altamont, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 6 minutes of daylight and the longest day is December 1, with 9 hours, 19 minutes of daylight.

Hours of Daylight and Twilight in December

Hours of Daylight and Twilight in December in Altamont1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrNovJanDec 219 hr, 6 minDec 219 hr, 6 minnightnightdaydayDec 19 hr, 19 minDec 19 hr, 19 min
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 of the month in Altamont is 7:16 AM on December 1 and the latest sunrise is 19 minutes later at 7:35 AM on December 31.

The earliest sunset is 4:34 PM on December 8 and the latest sunset is 10 minutes later at 4:44 PM on December 31.

Daylight saving time is observed in Altamont during 2017, but it neither starts nor ends during December, so the entire month is in standard time.

For reference, on June 21, the longest day of the year, the Sun rises at 5:30 AM and sets 15 hours, 16 minutes later, at 8:46 PM, while on December 21, the shortest day of the year, it rises at 7:32 AM and sets 9 hours, 6 minutes later, at 4:38 PM.

Sunrise & Sunset with Twilight and Daylight Saving Time in December

Sunrise & Sunset with Twilight and Daylight Saving Time in December in Altamont18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMNovJan7:16 AM7:16 AMDec 14:35 PMDec 14:35 PM7:35 AM7:35 AMDec 314:44 PMDec 314:44 PM7:25 AM7:25 AMDec 114:34 PMDec 114:34 PM7:32 AM7:32 AMDec 214:38 PMDec 214:38 PMSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of December. 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.

The chance that a given day will be muggy in Altamont is essentially constant during December, remaining around 0% throughout.

For reference, on July 9, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.

Humidity Comfort Levels in December

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 Altamont is essentially constant during December, remaining within 0.1 miles per hour of 6.7 miles per hour throughout.

For reference, on March 16, the windiest day of the year, the daily average wind speed is 6.9 miles per hour, while on August 3, the calmest day of the year, the daily average wind speed is 4.9 miles per hour.

The highest daily average wind speed during December is 6.8 miles per hour on December 1.

Average Wind Speed in December

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The hourly average wind direction in Altamont throughout December is predominantly from the south, with a peak proportion of 44% on December 1.

Wind Direction in December

Wind Direction in December in Altamont1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJanwestsoutheastnorth
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).

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 in Altamont typically lasts for 3.6 months (112 days), from around June 3 to around September 22, rarely starting before May 15 or after June 22, and rarely ending before September 3 or after October 11.

The month of December in Altamont is reliably fully outside of the growing season.

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

Time Spent in Various Temperature Bands and the Growing Season in December in Altamont1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJan-0%Dec 16-0%Dec 160%Nov 300%Nov 30freezingvery coldcoldfrigidcool
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.

The average accumulated growing degree days in Altamont are essentially constant during December, remaining within 1°F of 2,056°F throughout.

Growing Degree Days in December

The average growing degree days accumulated over the course of December, 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 in Altamont is essentially constant during December, remaining within 0.1 kWh of 1.7 kWh throughout.

The lowest average daily incident shortwave solar energy during December is 1.7 kWh on December 16.

Average Daily Incident Shortwave Solar Energy in December

Average Daily Incident Shortwave Solar Energy in December in Altamont1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310.0 kWh0.5 kWh1.0 kWh1.5 kWh2.0 kWh2.5 kWh3.0 kWh3.5 kWh4.0 kWhNovJanDec 161.7 kWhDec 161.7 kWhDec 11.8 kWhDec 11.8 kWhDec 311.7 kWhDec 311.7 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 Altamont are 42.207 deg latitude, -121.737 deg longitude, and 4,150 ft elevation.

The topography within 2 miles of Altamont contains significant variations in elevation, with a maximum elevation change of 627 feet and an average elevation above sea level of 4,168 feet. Within 10 miles contains significant variations in elevation (2,415 feet). Within 50 miles contains large variations in elevation (7,825 feet).

The area within 2 miles of Altamont is covered by artificial surfaces (49%), shrubs (37%), and cropland (10%), within 10 miles by shrubs (53%) and cropland (31%), and within 50 miles by shrubs (52%) and trees (33%).

Data Sources

This report illustrates the typical weather in Altamont year round, 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Altamont.

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

The stations contributing to this reconstruction are: Klamath Falls Airport (99%, 7 kilometers, south) and Rogue Valley International - Medford Airport (1.3%, 95 kilometers, west).

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.