ARC 3.5m | Weather Closure Conditions

The enclosure will be closed by the Observing Specialist under the following conditions. When conditions become threatening the APO Weather Status page displays the values of concern in yellow for warnings and darkening to red when values exceed closure limits.

≥ 35 mph
Dewpoint Difference
≤ Less than 2.0 degrees C
visible or on local radar

≤ 5 degrees F (-15 C)

≥ 4000 1 micron dust counts

Precipitation threat visible or nearby radar returns
Overcast skies
Snow and/or ice on enclosure or roof



This policy will be consulted whenever there are questions or disagreements concerning closure of the APO 3.5-meter telescope due to hazardous conditions or situations, at times when telescope operations are being overseen by an APO Observing Specialist.


Policy: Operation of the 3.5-meter shall be suspended whenever, in the opinion of the Observing Specialist, weather, atmospheric conditions, signs of imminent mechanical malfunction, or any other situation exists which poses a risk to either the facility or on-site personnel. This policy will be enforced conservatively, i.e., even though it may be probable that operations could be continued safely, the telescope will be closed unless the risk is considered negligibly small by the on-duty Observing Specialist.

Rationale: The long-term scientific return from the 3.5-m and associated facilities requires avoiding equipment damage in the pursuit of short-term scientific goals. Also, the need to provide a safe working environment is self-evident. Disagreements on telescope closure usually result from situations in which the danger is relatively small. However, our operational procedures must consider the long-term accumulated risk and be appropriately conservative.

Policy: The on-duty Observing Specialist has the full responsibility, and sole authority, to suspend operations for the reasons described in the previous policy. In some instances, measurable quantities (e.g., wind speed) and preset limits will guide such decisions (these quantitative closure limits are listed on the Observatory web pages). In many circumstances, an informed but somewhat subjective judgement will be necessary. Regardless of their position within ARC, academic rank, or other qualifications, those scheduled to use the telescope may not overrule the on-duty Observing Specialist or "assume responsibility" for such decisions themselves.

Rationale: Our policy is consistent with practice at other major observatories, which recognizes and protects against the possibility of conflicts of interest.

Policy: Users of the telescope must not attempt to influence the on-duty Observing Specialist to continue telescope operations which are or might be suspended due to safety concerns. This prohibition is to be interpreted very broadly; polite expression of differing opinion, angry argument, extended musings on the unfortunate consequences of the lost observing time, continued expression of disappointment, frequent requests to check for possibly improved conditions (the Observing Specialist will be monitoring weather conditions regularly without such prompting) and so forth are all included in this ban.

Rationale: It is hazardous to have the decisions of the Observing Specialists influenced in the direction of taking greater risks in marginal situations; the variations in people's personalities, levels of self confidence and so forth are such that this might happen in some cases. Also, such behavior creates a serious morale problem for the Observing Specialists and is inconsiderate. The staff of the Observatory in general, and the 3.5-m Observing Specialists in particular, are strongly committed to helping its users do excellent science and can be counted on to work hard toward that goal in all respects, but at the same time, they are explicitly charged with the responsibility for safe operations as a major requirement of their jobs.

Policy: Observatory management will not consider real-time appeals of decisions of the on-duty Observing Specialist. Questions, suggestions, or complaints about either these policies in general or some specific instance of their implementation should be brought to the attention of the Director and/or the Site Operations Manager at some appropriate later (i.e., not during the actual suspended operations) time.

Rationale: The Observing Specialist will have better information and more experience upon which to base decisions than anyone else who might be consulted.

Suzanne Hawley Director, and

Mark Klaene Site Operations Manager