Tuesday, November 12, 2013

Backdoor Front Easing Into Southeast Arizona

Edited to add - An interesting walk this morning along the Rillito. Here at house before sunrise it was calm and 43F. By the time I neared the Rillito at north end of Country Club strong east winds broke through with gusts of 20+ mph and instant warming of at least 15F. Headed west on north side of Rillito. When I neared the Campbell bridge the wind went calm again and then became light westerly with an instant change back into the cold air. This continued until the north end of Cactus and then winds went calm with a temperature about half way between the cold and warm air masses. Back at the house a bit before 8 am and east winds were blowing again with the temperature at 64F, which was 21F warmer than when I had left an hour earlier.

Some problems noted this morning - the Tucson NWS website seems to have been down since about 10 pm last night due to problems at NWS Western Region in Salt Lake. The early WRF runs at atmo were not complete, with the NAM version making it out to midnight tonight and the GFS version only good for a couple of hours.

The strong cold front, which has brought really cold temperatures to the central U.S. this morning, is easing into southeast Arizona. A 12 UTC surface plot is shown above. Temperatures in northeastern New Mexico are in the low 20s F - more than 40 F colder than temperatures here in Tucson. Note the pressure gradient from here to El Paso is almost 10 mb and surface pressures are over 1040 mb off at the east edge of the plot. The front is probably just aloft above cooler surface air at this time, and once heating and mixing occurs this morning it will appear to jump over into south-central Arizona.

The WRF-NAM forecast of 10-m winds valid at 11 pm tonight is shown below. The winds increase all day in the NAM forecast and become very strong during the night. So, significant changes underway this morning, Wind and dust but alas no precipitation. However, the GFS ensembles continue to indicate some hope for a precipitation event for the weekend.

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