National Weather Service United States Department of Commerce

Cold Front Moving Through the Northeast U.S. Monday; Atmospheric River to Impact the Pacific Northwest Midweek

A cold front will cross the Great Lakes and Northeast U.S. through Monday with gusty winds and areas of rain showers. A strong atmospheric river is expected to move into the Pacific Northwest by midweek bringing a threat for moderate to heavy rainfall, gusty winds, and mountain snows for parts of Washington, Oregon, northern California, and the Sierra Nevada. Read More >

Automatically generated image showing areas of storm relative helicity.

 

Thumbnail of an automatically generated image showing areas of storm relative helicity. Thumbnail of an automatically generated image showing areas of storm relative helicity. Thumbnail of an automatically generated image showing areas of storm relative helicity.
Hour - 1 Hour - 2 Hour -3

4 Panel Display | Animated Loop

Helicity (0-1 Km) 

This is the 0-1 km (approximately 0-3,000 Ft. AGL) storm relative helicity which is a measure of the amount of low level wind shear available for tornadogenesis. This is not a good indicator of supercell potential which is related more strongly to 0-6 KM vertical shear. Values greater than 100 m**2/s**2, do suggest an increased threat of tornadoes provided a supercell is present.  Larger values are generally better, but there are no clear "boundaries" between non-tornadic and significant tornadic supercells.

The arrows indicate the approximate right supercell storm motion using the Bunkers technique.

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