This is a computer forecast at 500 millibars, which is about 18 thousand feet above the ground, for for 1 PM EST for the date indicated at the bottom of the map. This is normally the day after tomorrow. Height contours are in yellow. Temperatures in degrees Celsius are shows as dashed green lines. Wind speeds are in knots. The shaft of the wind has a small dot at the end. The wind blows along the shaft toward the dot. The wind barbs which come out at right angles to the shaft show the wind speed. Each full barb is 10 knots, each half barb is 5 knots, each flag is 50 knots. 10 knots equals about 11.5 mph.