20190809

Previous Forecast
Another day with limited or no low elevation storms as once again, anvils spread out and killed any chances.  I've lost most of the plots from yesterday so can't really say which forecast run was best. From memory, they pretty much all had a good handle on the situation.

Initializations
Most of the Mexican upper-air stations were missing this morning.  A weak IT/MCV is somewhere around the Tucson area.  Radar shows on a small area of cyclonic rotation just south of town.  This feature seems to be embedded in a broader IT which can be seen on the 500mb plot.  WV imagery also indicates a weak upper IT moving into far eastern Sonora.  Another much larger trough is located over the southern Gulf of California.

The 12Z initial conditions have the mid to upper trough initialized OK in spite of all the missing data.  It is crucial the initialization is correct as this feature is going to have a significant impact on Arizona weather tomorrow.  Clouds and showers are present over much of southern Arizona and are generally going to put a damper on any deep convection today.  The RR has the best initialization, followed by the GFS.  They are both somewhat too cloudy in far southeastern Arizona as it's now mainly clear there.  The NAM does not have nearly enough clouds and what clouds it has, are in the wrong place. Note that Sonora has greened up quite a bit.

The NAM, again, has large PW errors in Mexico.  The WRFRR and WRFGFS initialized reasonably well considering the complexity of the situation.

Day 1
A Gulf Surge continues to import moisture into Arizona today, and by afternoon, lower elevations are mainly around 40mm while wetter air is out along the Colorado River valley.  Note the extreme moisture gradient.  Blyth's current Td is 37F.

Areas of eastern Arizona under clouds and showers have little or no CAPE. Western Arizona has a plume of very high to extreme CAPE, so if storms develop there, they could be severe.

Wow! You don't see a Skew-T like this in Arizona very often. Enormous CAPE and some vertical and directional shear.  All that area needs for severe storms is some sort of lifting to break the strong cap at 850mb.  Will heating along be enough?

The WRFRR develops isolated severe storms along I-10 in western Arizona by late afternoon.

The 15Z WRFRR is out far enough to say there is a chance for storms over far SE Arizona which seems logical as it's been clear there.

Day 2
The various WRF runs have all been forecasting a big event as the IT moves over Arizona during the morning hours and that forecast continues to be unchanged in the 12Z runs.  The IT is near Douglas by 12Z with an unusually strong mid-level jet on the east side.

An Gulf Surge is underway with very moist air over south-central Arizona.  CAPE is also very high, nearly 3000 J/kg as well as out west along the dryline.

Confidence on the details of how the severe weather event will evolve is low, but it looks likely there is going to be a major outbreak somewhere in the high CAPE area(s).   The forecast Tucson Skew-T plot has all the ingredients necessary as CAPE is around 2k J/kg, OK wind profile, plus the IT is approaching.  The mid-level easterly flow could be better, but it's likely to increase at the IT gets closer.  

The various runs have different timings on developing the strongest storms as the WRFGFS develops storms during the morning hours, and these storms aren't very intense.

The WRFRR delays the onset until the afternoon, and with some heating, these are severe.

Scattered strong storms move towards the Phoenix area during the late afternoon, but don't quite make it there.  

The potential for severe weather is also present in the Phoenix Skew-T with over 2000 J/kg of CAPE.

The WRFGFS redevelops storms in Maricopa and Pinal Counties during the evening hours.