National Weather Service United States Department of Commerce

Prolonged Atmospheric River Will Impact the Northwest Early this Week

A weather system in the Pacific Northwest will produce rain throughout the day, before a potent atmospheric river produces a prolonged round of heavy rainfall, widespread urban and river flooding, and high elevation snow to the region Monday through Wednesday. Showers and thunderstorms may produce isolated damaging winds, a brief tornado, and locally heavy rainfall across parts of Florida today. Read More >

Automatically generated image showing areas of 0-3 km storm relative helicity.

 

Thumbnail of an automatically generated image showing areas of 0-3 km storm relative helicity. Thumbnail of an automatically generated image showing areas of 0-3 km storm relative helicity. Thumbnail of an automatically generated image showing areas of 0-3 km storm relative helicity.
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Helicity (0-3 Km) 

This is the 0-3 km (0-10,000 Ft. AGL) storm relative helicity which is a measure of the amount of wind shear available from the ground to roughly 700 MB.   Values greater than 250 m**2/s**2 suggest an increased threat of tornadoes, but high values with this index do not necessarily suggest that the environment is supportive of supercell structures (look at 0-6 km shear).  Larger values are generally better, but there are no clear "boundaries" between non-tornadic and significant tornadic supercells.  Negative values suggest that anti-cylonic (left moving) supercells will dominate.

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