Northern Hemisphere Animation

The animation shows a sequence of 31 frames representing the state of the 500mb level 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 from the GFS high-resolution forecast. The final 7 frames (red keyed) are the continuation of the GFS forecast at a coarser resolution.

The colored shading shows the temperatures at 500mb. The black contours show the 500mb geopotential height with a contour interval of 100 meters. The heavy contour is 5400m. The areas highlited with purple are where the 500mb wind speed is greater than 35 m/s. Additional contours for wind speed are 40, 50, 60, 70, and 80 m/s.

Things to notice:
• The features tend to "spin" coutnerclockwise around the North Pole, reflecting the pervasive west-to-east circulation in the troposphere. The rate of motion is considerably slower at low latitudes, with features in the tropics appearing rather stationary, or even moving clockwise.
• The features in the graphics become "smoother" in the interval from Day 8 to Day 9. This reflects the reduction in resolution of the model at that point. Presumably, the higher the resolution, the better the forecast.