Stay aware of the weather conditions while observing. Look outside occasionally. There are many weather resources available, including the EAO weather summary.

In case of adverse weather, close the shutter immediately. Remember it takes quite a long time (15 min) to close the shutter completely.

When observers are present at the telescope, any of the following conditions preclude observing. Close the shutter if any occur:

• Relative humidity outside the dome above 80%.
• Wind speed at the JCMT sustained above 35 mph (16 m/s).
• Rain, snow, sleet, ice, fog, or other precipitation.

Remote observations require better conditions. Do not observe if any of these occur:

• Relative humidity outside the dome above 60%.
• Wind speed at the JCMT sustained above 30 mph (13 m/s).
• Rain, snow, sleet, ice, fog, or other precipitation.

• The CSO hygrometer and thermometer are mounted inside the dome. So if the shutter is closed, the temperature is usually higher and the relative humidity lower than outside.
• The CSO does not have a working anemometer. As a proxy, watch the JCMT wind speed. If the JCMT anemometer is off line, watch the SMA wind speed.

• Do not become stranded by adverse weather. Anticipate the need for a quick evacuation if weather conditions deteriorate.

• Ice
  • Icy conditions can occur anytime of the year.
  • Icy conditions can occur quickly and without warning.
  • If the temperature below freezing (0 °C) and the humidity is high, ice can accumulate easily everywhere including on vehicles and on the road.
  • Beware of falling ice! If ice has formed on buildings do not park near them and use caution when entering the dome. Shutter movement may cause ice to fall!

• Wind
  • If wind speeds exceed 60 mph (27 m/s), evacuate.
  • Park vehicles pointed into the prevailing wind. Take care opening vehicle doors.

• Snow
  • If it starts snowing, evacuate.
  • If snow is expected, stow the dome 90 degrees to the prevailing wind direction before leaving.

• Always put vehicles in the lowest gear possible when descending. This is especially important if conditions are icy.
• Be prepared to mount chains on your vehicle.
• Comply with MKSS recommendations regarding observatory access and chain usage.
  • Watch the HP white board near the main entrance for current road conditions.
  • If MKSS issues an absolute evacuation order or closes the road, all facilities must comply.
• Emergency phone numbers are posted near the control room phone and on the Contact Information page as well as in the notebooks in the vehicle glove boxes. Cell phone reception is sporadic above HP.