Which observation schedule describes taking observations at an interval not to exceed 35 minutes when there has been a change of 0.01 inch Hg or more since the last ALSTG value?

• A. Automated Meteorological Observing System
• B. LOCAL altimeter setting
• C. METAR altimeter setting
• D. AMOS

Answer: (B)

Keeping the local altimeter setting accurate as pressure changes ensures pilots have a current reference for altitude corrections in the area. When the pressure change since the last ALSTG value reaches or exceeds 0.01 inch Hg, updating the local altimeter setting within 35 minutes keeps the value from becoming stale and supports safe local operations. METAR altimeter settings are typically reported on an hourly basis and aren’t tied to such short-interval triggers, while automated systems like AMOS follow their own general reporting schedules. So the local altimeter setting schedule is the one that describes updating within 35 minutes in response to a 0.01 inch Hg change.