January – April: January is the driest and coolest month of the year in Siem Reap with an average temperature of 27°C, making this a good time to visit northern Cambodia to see the the temples of Angkor and explore the surrounding region. Humidity is also at its lowest in January but rises significantly throughout the period, as does the temperature, peaking at an average of 31°C in April, the hottest month of the year in Siem Reap. January to March sees little rain and although water levels remain high in Tonle Sap lake in January and February, levels do begin to fall in March. With temperatures and humidity high in April full day excursions tend to be avoided and sightseeing is more pleasant earlier or later in the day.
May - October: Although the rainy season in Siem Reap is by no means the heaviest in Asia, the weather in northern Cambodia over these months is characterised by high temperatures, averaging 30°C, and high humidity. May is the first month of the year to produce a large amount of rain with 176mm falling throughout the month. The rains are a welcome relief however and there is often still plenty of sunshine at this time of year. As the Monsoon season in northern Cambodia continues, rainfall increases and is at its highest in August and September. Although humidity remains high, temperatures drop making it far more pleasant to explore the temples and this can be a good time of year for nature lovers as wildlife flourishes around Tonle Sap. Access to some of the more rural areas may be difficult at this time. By October the heaviest of the rains are over and the temperature is at a very comfortable 27°C. Following the monsoon the country is lush and green at this time of year and this season is a a good time to visit northern Cambodia to take advantage of shoulder season promotions.
November - December: Rainfall in northern Cambodia drops dramatically in November and with the rainy season in Siem Reap finally over, expect clear skies and a slightly cooler climate with average temperatures of 28°C, dropping further into December. The combination of cooler weather, reduced humidity, low rainfall and high water levels make these the best months to visit northern Cambodia.