ForeFlight’s Prog Charts image set is drawn from the Weather Prediction Center’s (WPC’s) Short Range Forecasts and is updated at the same frequency. Prog Charts in ForeFlight may seem out of order or duplicated due to the staggered update schedule from the Weather Prediction Center (WPC). The charts are updated twice daily at different times based on the following schedule:
- 6 HR and 12 HR: approximately 1400 and 0200Z
- 18 HR and 24 HR: approximately 1630 and 0430Z
- 30 HR, 36 HR, and 48 HR: approximately 1930 and 0730Z
- 60 HR: approximately 2000 and 0800Z
This staggered timing creates brief periods (1–3 hours) where some images are refreshed with new data while others still show older data. For example, between 1400Z and 1630Z, the 6 HR chart might show new data, while the 18 HR chart still reflects older forecasts, causing a perceived duplication or misordering.
A close examination usually reveals differences in fronts, circulation, and pressure systems. These differences are a byproduct of how the WPC receives and publishes updated weather, which can also be seen on the WPC website.
At 1530Z, ForeFlight’s 6 and 12 HR weather appears to be repeated on the 18 and 24 HR images.
At 1530Z, this screenshot from the WPC website shows the same apparent duplication between the 6 and 18 HR images and between the 12 and 24 HR.
To mitigate confusion, ForeFlight includes labels on each Prog Chart image indicating the expected update times.
Additionally, precipitation updates from local National Weather Service offices occur every three hours, making the image issuance times more frequent than WPC’s schedule.
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