The next short wave at 500 mb is digging down the west coast and will cutoff over the Great Basin during the next 24-hours. The above image is from a web cam near Lake Tahoe this morning - snow is flying in the high Sierra Nevada. The surface plot below shows that by 8 am MST this morning the precipitation shield had reached south into the LA Basin. - note the snow reported at the Lake Tahoe Airport.
Above is this morning's NAM forecast for 500 mb valid at noon tomorrow (1800 UTC Thursday October 6). The strong vorticity band with the cutoff extends across northern Arizona. The correspondng NAM forecast of precipitation, surface pressue, and 1000-500 mb thickness is shown below. A band of showers is forecast to be approaching the Tucson area by noon tomorrow. Given the sparse rainfall in south central Arizona yesterday, conditions remain favorable for blowing dust. Note that the thickness pattern indicates that the primary surface front is far to the east (i.e., yesterday's front) and that the showers are along a secondary front, but one with the thickness gradient packed very tightly. So, another interesting weather day on tap tomorrow.
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