Saturday, September 24, 2011

Weak 500 mb Trough Moves Into Arizona

The 500 mb short wave (see WV image above for 1400 UTC) that has been malingering off the California coast for several days is being pushed ashore by a stronger wave off the Washington/Oregon coasts. Models predict that troughiness will remain over the Southwest for next several days. The visible satellite image (below) or 1500 UTC shows two cloud bands over Arizona - one to the west with the trough and one to the east that is being pulled up from western Sonora.

These are mostly shallow altocumulus but they are icing out with the cold middle-level temperatures and producing virga (see north view from Kitt Peak below). Models predict showers, and perhaps an isolated thundershower, over south-central Arizona off and on through sunrise tomorrow. This would be an interesting situation if the lower half of troposphere wasn't so dry. So, given the low PW values that are present well south into Mexico, perhaps we'll see some sprinkles and dusty outflows this afternoon.

Note that Hilary (see WV image at top) remains a Cat. 4 hurricane this morning and models indicate a wandering course that may eventually take her remnants toward Baja.

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