Moisture-Starved Short Wave Passing By Today

Water vapor image above indicates the short wave in upper troposphere is located, south-to-north, over western Arizona this morning (image is from 6:30 am MST on 21 January). The blended PW analysis below (from CIRA at Colorado State, valid at 5:00 am) shows how little PW is accompanying this short wave over most of Arizona.

Shown above and below are several radar images (all from around 6:40 am MST). Above is a base scan (0.5 degree tilt) from the PHX NWS radar that indicates some light precipitation over higher elevations to its northwest; substantial ground clutter noise over metro Phoenix; and little to the south. However, there is a wedge to the radar's south where the 0.5 degree tilt is blocked by the San Tan Mountains, so no radar coverage at lowest levels over that wedge. Image below is also from the PHX radar (KIWA is its ID) and shows echoes at the 3.5 degree tilt. Echoes at that elevation tilt extend into Pinal and Pima Counties from north to west of the Tucson metro area. These echoes are from middle and high clouds ahead of the short wave. There is little precipitation currently, except far to the north over higher elevations.

The image at the bottom is from the NWS TUS radar (KEMX is its ID) and this product uses the dual polarization signals to estimate types of hydrometeors - in this case the echoes aloft are identified as dry snow and ice crystals. These various radar products are available at the CoD weather page - link to right.

Finally, a quick look at the 06Z WRF-NAM forecasts indicates that the model forecasts precipitation only to the north over the White Mountains and the Rim Country. Winds are forecast to shift to the west today as the short wave passes. The model then forecasts a period of moderately strong easterly winds to intrude over the Continental Divide into southeastern Arizona, as the weather system heads into the Southern Plains. These east winds are forecast to occur Thursday night into Friday morning, putting the Tucson metro area back onto the temperature roller-coaster.