Climate and Average Weather Year Round in Siem Reap Cambodia

In Siem Reap, the wet season is oppressive and overcast, the dry season is muggy and partly cloudy, and it is hot year round. Over the course of the year, the temperature typically varies from 70°F to 95°F and is rarely below 64°F or above 102°F.

Based on the beach/pool score, the best time of year to visit Siem Reap for hot-weather activities is from mid November to early March.

The hot season lasts for 2.1 months, from March 12 to May 16, with an average daily high temperature above 93°F. The hottest month of the year in Siem Reap is April, with an average high of 95°F and low of 81°F.

The cool season lasts for 3.7 months, from September 26 to January 15, with an average daily high temperature below 87°F. The coldest month of the year in Siem Reap is December, with an average low of 71°F and high of 85°F.

In Siem Reap, 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 Siem Reap begins around November 4 and lasts for 4.7 months, ending around March 27.

The clearest month of the year in Siem Reap is January, during which on average the sky is clear, mostly clear, or partly cloudy 53% of the time.

The cloudier part of the year begins around March 27 and lasts for 7.3 months, ending around November 4.

The cloudiest month of the year in Siem Reap is August, during which on average the sky is overcast or mostly cloudy 92% of the time.

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

The wetter season lasts 5.9 months, from April 26 to October 22, with a greater than 37% chance of a given day being a wet day. The month with the most wet days in Siem Reap is August, with an average of 21.5 days with at least 0.04 inches of precipitation.

The drier season lasts 6.1 months, from October 22 to April 26. The month with the fewest wet days in Siem Reap is December, with an average of 0.9 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 Siem Reap is August, with an average of 21.5 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 72% on September 3.

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. Siem Reap experiences extreme seasonal variation in monthly rainfall.

The rainy period of the year lasts for 9.4 months, from February 15 to November 28, with a sliding 31-day rainfall of at least 0.5 inches. The month with the most rain in Siem Reap is September, with an average rainfall of 8.4 inches.

The rainless period of the year lasts for 2.5 months, from November 28 to February 15. The month with the least rain in Siem Reap is December, with an average rainfall of 0.2 inches.

The length of the day in Siem Reap varies over the course of the year. In 2024, the shortest day is December 21, with 11 hours, 20 minutes of daylight; the longest day is June 21, with 12 hours, 55 minutes of daylight.

The earliest sunrise is at 5:36 AM on June 1, and the latest sunrise is 55 minutes later at 6:31 AM on January 25. The earliest sunset is at 5:34 PM on November 19, and the latest sunset is 1 hour, 2 minutes later at 6:35 PM on July 9.

Daylight saving time (DST) is not observed in Siem Reap during 2024.

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.

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.

Siem Reap experiences significant seasonal variation in the perceived humidity.

The muggier period of the year lasts for 10 months, from February 9 to December 19, during which time the comfort level is muggy, oppressive, or miserable at least 66% of the time.

The month with the fewest muggy days in Siem Reap is January, with 17.3 days that are muggy or worse.

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 Siem Reap experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 3.2 months, from May 30 to September 5, with average wind speeds of more than 5.6 miles per hour. The windiest month of the year in Siem Reap is August, with an average hourly wind speed of 6.5 miles per hour.

The calmer time of year lasts for 8.8 months, from September 5 to May 30. The calmest month of the year in Siem Reap is April, with an average hourly wind speed of 4.7 miles per hour.

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

The wind is most often from the south for 2.2 months, from February 24 to April 30, with a peak percentage of 44% on April 27. The wind is most often from the west for 5.3 months, from April 30 to October 8, with a peak percentage of 76% on August 9. The wind is most often from the north for 2.7 months, from October 8 to December 31, with a peak percentage of 59% on November 30.

To characterize how pleasant the weather is in Siem Reap 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 Siem Reap for general outdoor tourist activities is from early December to early February, with a peak score in the first week of January.

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 Siem Reap for hot-weather activities is from mid November to early March, with a peak score in the second week of February.

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).

Temperatures in Siem Reap 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.

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.

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 some seasonal variation over the course of the year.

The brighter period of the year lasts for 2.2 months, from January 22 to March 28, with an average daily incident shortwave energy per square meter above 5.6 kWh. The brightest month of the year in Siem Reap is February, with an average of 5.9 kWh.

The darker period of the year lasts for 4.2 months, from June 5 to October 11, with an average daily incident shortwave energy per square meter below 4.4 kWh. The darkest month of the year in Siem Reap is September, with an average of 4.1 kWh.

For the purposes of this report, the geographical coordinates of Siem Reap are 13.362 deg latitude, 103.861 deg longitude, and 59 ft elevation.

The topography within 2 miles of Siem Reap is essentially flat, with a maximum elevation change of 69 feet and an average elevation above sea level of 58 feet. Within 10 miles is essentially flat (420 feet). Within 50 miles contains only modest variations in elevation (1,683 feet).

The area within 2 miles of Siem Reap is covered by artificial surfaces (63%) and cropland (31%), within 10 miles by cropland (64%), and within 50 miles by cropland (35%) and trees (33%).