MAP KEY: G/WX Maps contain the following information (see Symbol Key, Sample Maps, and Sample Verification Maps for examples):
· The Map Period Date is located on the upper left corner of the G/WX map.
· The Map Generation Date is located the lower left corner of the G/WX map.
The circles represent Percent Probability of High Atmospheric Pressure (+); from 50% (smallest circle) to 100% (largest circle). Areas of High Pressure are typically warm to hot, and colored in shades of red/yellow.
The rectangles represent Percent Probability of Low Atmospheric Pressure (-); from 50% (smallest rectangle) to 100% (largest rectangle). Areas of Low Pressure draw in cool to cold arctic source air, and are colored in shades of blue.
The dark blue line indicates the approximate path of the Polar Jet Stream, and the green line indicates the approximate path of the Sub-tropical Jet Stream. These jet stream lines represent the likely path of storm systems and temperature variance distribution. They represent the Long-Wave Pattern in the Northern Hemisphere, which is the ‘Big Weather Picture,’ technically known as the Synoptic Scale Pattern.
Expect the G/WX Long-Wave pattern to be the primary feature during any two or three-day Map Period, and the occasional 4–day Map Period. The G/WX forecast Long-Wave Pattern often does not fully mature until the last day of the period, as in the some of the samples as the comparative ‘actual’ NWS maps indicate.
The G/WX Maps cannot show Short-Wave impulses embedded in the Long-Wave Pattern. These disturbances can generate significant short-term local weather. Therefore, it is important to pay attention to the ‘Verification Guidelines’ at the end of this section.