Instability Vortices over the NW United States


On the 6th of October, a series of vortices developed over the northwestern portion of the United states over a region high horizontal wind shear aloft.  This was preceded on the 5th by a large cutoff low over the US SW and a sharp shortwave trough along the US-CAN border.  A region of deformation develops later on the 5th seen here in WV:

This deformation zone transitions into a region of strong cyclonic shear on the 6th, streamlines on WV :

The NAM also captures this region of enhanced cyclonic vorticity (250 hpa):

From there, a vortex street develops, seen here in WV:

Seems to be a case of barotropic instability, but there are other potential (or simply other mechanisms) theories on the development of these vortices including stratospheric intrusions.  Unfortunately I do not have cross section data, so this simple analysis will have to suffice for this post.

http://journals.ametsoc.org/doi/full/10.1175/1520-0493(1997)125%3C2504:SOIVAM%3E2.0.CO;2

Update:  It is very well possible the unusually sharp shortwave (PV anomaly) trough penetrated the stratosphere resulting in the very dry air behind the system, resulting in a combination of the two effects discussed above.

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About jason ahsenmacher

I am a meteorologist, and I like baroclinic instability. View all posts by jason ahsenmacher

3 responses to “Instability Vortices over the NW United States

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