Significant Weather (SIGWX) charts are made available by Meteorological Office. High level charts are from FL250 to FL630. Medium level charts are from FL100 to FL450. Check the validity time of the chart to make sure it coincides approximately to the mid-point of the expected flight. SIGWX charts are issued every 6 hours.

• Valid 0000Z - available at 0800Z.
• Valid 0600Z - available at 1400Z.
• Valid 1200Z - available at 2000Z.
• Valid 1800Z - available at 0200Z.