The animation shows a sequence of 31 frames representing the state of the 500mb flow at 00Z on successive days. The first 15 frames are past analyses, and are denoted by the green title bar and green portion of the clock in the upper left corner. The analyses are based on observations (weather balloons, aircraft measurements, satellite measurements) assimilated into the computer model of the atmospheric circulation. The animation pauses at day 0, representing the most recent observed state of the atmosphere, and the start of the current forecast cycle. The next 8 frames (yellow color keyed) are the first week of the AVN high-resolution forecast. The final 7 frames (red keyed) are the continuation of the AVN forecast at a lower resolution.
The red and blue shading indicate positive and negative vorticity respectively. The black contours show the 500mb geopotential height with a contour interval of 120 meters. The heavy contour is 5400m. The form of these maps are essentially the same as the 500mb forecast and analysis maps - see the key for the forecast maps for more details.