Wind Data

The jet stream map on this page plots current 250 mb wind speeds with a dashed axis line traced through the fastest wind at each longitude, showing exactly where the jet core sits. The polar jet typically meanders between about 30°N and 60°N, dipping south with cold-air outbreaks and lifting north during warm spells.

The jet stream is a narrow band of fast-moving air near the tropopause, roughly 30,000 to 40,000 feet up, where wind speeds commonly reach 100 to 200 mph. It forms along strong temperature gradients between air masses, steers surface storm systems from west to east, and its ridges and troughs largely determine which regions get warm, settled weather versus cold and stormy weather.

Vertical wind shear is the change in wind speed or direction with height, most often measured between 850 mb and 200 mb. Low shear under about 20 knots lets tropical cyclones stack vertically and intensify, while high shear tears their circulation apart. In mid-latitude severe weather the opposite holds: strong shear is what organizes supercells and enables rotation.

Shear tendency is the change in vertical wind shear over the past 24 hours. Falling shear over a tropical system signals an increasingly favorable environment for strengthening, while rising shear signals an increasingly hostile one — which makes it a useful leading indicator alongside the raw shear value.