20160812

Initially, I wasn't going to post today especially as I stayed up all night watching meteors, but the weather has conspired against me.  As I'm starting so late, I'll be making this a short post.

Day 1
Somewhat surprisingly, some of the model runs have activity in and near Tucson later this afternoon and evening as 700-600mb steering flow has become favorable for steering higher elevations storms into the lower elevations of SE Arizona as seen on the FHU profiler (thanks for the link Art Douglas!).

Moisture continues to be more than sufficient for storms as IPW is around 40mm at Tucson. Afternoon IPW hangs in there as a weak surge continues to import low-level moisture in spite of drying aloft.

By late afternoon, considerable CAPE exists with a moderately well-mixed PBL.  Steering isn't very strong but is from a favorable northeasterly direction.

WRFNAM

Most of the activity remains over far SE Arizona, but the WRFRRx does bring a few storms into the Tucson area early this evening as it has stronger NE flow.

WRFRRx

Day 2
The WRFNAM is quite a bit drier in the PBL tomorrow.  It's typical for the model to dry the atmosphere out too quickly thus I'm going with the somewhat wetter WRFRRx and WRFGFS.  850mb dewpoints are now down around 10-12C which are becoming marginal for activity in the lower deserts.

What has improved, is steering, as it's a very favorable NE direction from 700mb to nearly 500mb.  The WRFRRx has quite strong flow at around 20-25 knots.  Below is the more conservative WRFNAM with only 5-10 knots.  So, there is some uncertainty if there will be enough moisture and steering is strong enough.

In spite of the above-mentioned differences, all three runs develop very strong storms over the higher terrain of eastern and southeastern Arizona and move them to the WSW and by late afternoon, they are threatening the Tucson area.   I have a fair amount of confidence in this forecast because of the model consistancy.

With the drying, the PBL now has the chance to mix deeper thus the risk for strong outflow winds is much higher.  The WRFGFS below has fairly weak steering while the other two have 10-20 knots at 700-500mb.  CAPE is more than sufficient to support deep convection.

Strong outflows are ejected into the lower deserts between Tucson and Phoenix during the early evening.  The WRFNAM is in the middle of the road with respect to coverage and intensity.  The WRFRRx has stronger and more widespread winds.

WRFNAM

It is unlikely for any development in the Phoenix area as it's dried out too much there.  However, note the large inverted V profile and deeply mixed PBL conducive for strong/severe winds.