Unsettled Weather To Return To Southwest Later This Week

First - the string of freezing or below morning lows here at house ended yesterday when the low was only 35F. The freezing string was ten days - not at all a record for here at house.

This morning very cold air covers the north-central and much of the eastern U.S. - above is 850 mb 12z analysis this morning from NCAR RAL. Coldest 850 temperature in U.S. is -27C at Green Bay, Wisconsin. Out in the West, a strong, cold high pressure area covers the Great Basin Region. The 850 mb temperature of -12C at Salt Lake is helping keep stagnant surface air trapped below an inversion, so that air pollution has reached to very unhealthy levels (see Steenburgh's blog about the Salt lake City "Ick").

Out in the Pacific this morning, the 1200 UTC water vapor image (above) shows a very large plume of upper and middle level moisture extending from south of 10N all the way north to Alaska. The next two 500 mb short waves that will affect the Southwest appear to have a much better chance of picking up more moisture than did the last two systems. So, some changes happening that may bring a return of weather to southeast Arizona.

The composite PW product from CIMSS at Univ. of Wisconsin (above) indicates substantial low-level moisture extending north to the east of the low-latitude upper-low that is centered north of 20N at about 135W. This will be the first system that will affect the Southwest toward the end of the work week.

This morning's early run of Atmo's WRF-GFS model already shows nearby radar echoes by 5 pm MST on Thursday afternoon (above), The echoes forecast at that time are weak and would be producing only virga and light sprinkles. However, activity should increase Thursday night into Friday.