Sunday, November 27, 2016

Strong Short Wave Tonight - Second Freeze Here Wednesday AM

Early sun catching parts of Kitt Peak telescopes this morning a bit after 7:00 am MST above. 

A strong, 500 mb, short wave will move across Arizona tonight, accompanied by a leading jet streak at about 250 mb with maximum wind speeds over 150 kts - quite impressive. A trailing short wave, digging southward across the Four-Corners, will bring cold temperatures to southeast Arizona early Wednesday morning.

The event tonight is, unfortunately, another one that is very starved for moisture. The GEFS plumes for QPF at TUS (above) indicate a good chance for light showers tonight across the metro area. The 06 UTC WRF-GFS forecast for total precipitation through 11:00 am next Wednesday morning (below on the 5.4 km grid) indicates an event that mostly impacts the mountains of the Southwest, with little or no precipitation at lower elevations.

The forecast for the 500 mb level from the same run is shown below (again 5.4 km grid and valid at 6:00 am next Wednesday morning) and indicates cold to very cold temperatures (-30 C and colder over Four-Corners region), as the trailing short wave slides across northeastern Arizona and northern New Mexico. The surface temperature forecast for metro Tucson from the WRF-GFS runs indicate low temperatures dropping into the low to mid 30s F early Wednesday morning. 

Here in the north part of the City of Tucson, along the Rillito wash, it is likely that we'll have our second freeze of the Fall (the first on November 18th only did slight damage to some tender, potted plants here), but if the WRF forecast verifies it is likely that we'll experience a hard freeze here with temperatures of 28 F or colder for a few hours. Will wait to see what happens - my basic approach to living in this cold zone of the City is that what survives belongs and what doesn't doesn't - so I don't go to the trouble of covering any of the landscape plants during the winter. 

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