Synoptic chart (also termed "synopsis"): - A weather chart reflecting the state of the atmosphere over a large area at any given (current or recent) moment.
Prognostic chart (also termed "prognosis"): - A weather chart reflecting the
likely (or estimated) state of the atmosphere over a large area at any given time period in the future. These times can be 12, 24, 36, or 48 hr periods.
Aviation prognostic charts give possible weather changes over much shorter time frames, than general forecasts, which can run up to 4 days ahead. New prognostic charts for aviation are usually issued every 6 hrs.
Lots of info here - make sure you read right through to the bottom of the webpage...
Aviation Weather Reporting, Weather Charts, and Aviation Weather Forecasts
Previous informative thread...
http://www.pprune.org/tech-log/41931...her-chart.html