Maps Jet stream analysis maps attempt to highlight the location and strength of the jet streams. For the Eastern Pacific and Northern Hemisphere overviews , the jet stream analyses comes only from the initialization of the AVN model. The eta model results typically come several hours earlier than the AVN results do. These also come from NCEP's computer model initializations.
Longer arrows represent faster winds.
However, the atmosphere is a complicated place that often defies our attempts to make simple generalizations about it, and sometimes the polar jet stream splits into two branches or one or both jet streams fail to be continuous or well-defined. As air races through the sinuous jet-stream pattern, there are some parts of the pattern where air tends to converge , thereby increasing the total weight of air above the earth's surface in those areas, which implies higher pressure at the earth's surface below. Moreover, convergence of air within the jet stream tends to force air beneath the jet stream downward. As air descends in the atmosphere, the pressure on it increases and compresses it, thereby warming the sinking air, which evaporates any existing clouds or prevents clouds from forming in the first place. Such areas generally experience clear weather.