The weather at the Doi Inthanon site is known to have not only a large seasonal variation but also significant fluctuations of conditions from one night to the next and within the same night. In particular, humidity can vary from extremely dry in some winter nights (below 10% RH), to condensing conditions even when the sky is clear. A set of rules to open and close the dome are put in place and will be followed by the Telescope Operator in charge. Astronomers are asked to respect these procedures.
Weather statistics are still incomplete. It is recommended that requesters apply only for the time strictly needed for their observations, without allowance for weather factors. Similarly, the seeing conditions are not yet fully characterized. Experience shows that seeing can be as good as 0.8”, and is generally better than 2”. A rough average of 1.3” at the zenith may be assumed.
Due to the La Nina, Cycle 9 lost roughly half of the observation time due to weather conditions. We expect the weather outlook for Cycle 10 to be similar or wetter since the La Nina still persists. For TNO, we expect to start the observation season on November 16, 2022 and close on May 15, 2023.