20160716

Initializations
There was an issue with the IPW correction routine for the 0Z, 6Z, and 12Z WRFRR runs and the problem has been fix for later runs.   Unfortunately, there has been a large initialization wet bias in NW Mexico recently so those runs are likely to have too much moisture.  I manually reran the WRFRR 12Z routine and it was way too wet in NW Mexico.  My guess is the uncorrected model runs, (including the NWS) are too wet.

12z RR

The 12Z NAM was also pretty bad as there was a 8mm wet bias centered on Hermosillo.  The 12Z GFS was significantly better with mainly small errors.

The morning 500mb map indicates that the high center is just to the east of Tucson and is taking it's sweet time moving into NM.  Of interest are the continued cool air with temperatures from -7 to -9C over the SW US.  Morning satellite imagery shows a weak cyclonic circulation  (MCV probably) moving out over the Gulf of California from central Sonora.  To their credit, both the RR and NAM have a weak mid level circulation in the area.

Mainly thin clouds are present over southern Arizona with somewhat thicker clouds in NW Mexico. Initializations were fine.  Overall, if it wasn't for the IPW problem in NM Mexico, all initializations would be very good.  The GFS is the best today and the NAM is OK.  The WRFRR without correction applied will probably have too much activity.

Day 1, July 16
The outflow surge did materialize and IPW is up into the low 30mm range across southern Arizona. Southerly flow continues to advect moisture into southern Arizona during the day.  Looking at the 15Z forecasts, the WRFGFS is very close to observed while the WRFNAM is somewhat too wet over SW AZ and the WRFRR is way too wet there. (due to the poor initialization in Mexico)  It is certainly nice to have all the GPSMET IPW sites working and this goes to show you the importance of the Suominet network IPW data for both model initializations, model evaluation,   Suominet will have no funding to continue past December and the NWS will be processing their own data to calculate IPW and not making it available outside of the NWS.  Weak southerly flow continues to advect moderate amounts of  moisture into Arizona by afternoon.

The outflow surge is fairly shallow as seen by the drier air out to the west, but higher 850mb Td air is present across central into southeastern Arizona.   Note the classic surge pattern of low level southerly flow up the gulf and how it curls around and flows upslope into SE Arizona.  A good set up for propagating storms (if there is some easterly mid level flow) as outflows moving to the NW will set up low level convergence.

As Bob Maddox mentioned, there isn't any mid level steering this morning and that continues into the afternoon as seen below thus large scale propagation is unlikely today and storms are likely to stick to the higher terrain.  Also, the PBL is not mixed very deeply and CAPE is only moderate at best thus it looks unlikely for any deep convection in the Tucson area.

Not until late afternoon do the  WRFNAM and WRFGFS develop storms over the higher terrain of far southern Arizona and mainly stay there throughout the evening.

Scattered activity continues across far SE Arizona into the evening hours.

Day 2, July 17
Due to the overnight activity, it's likely that widespread debris clouds will be present during the morning hours which could throw a monkey wrench into the works.  Both model runs dissipate clouds by late morning.

The thinking yesterday was that the tropical system (now Estelle) may just get close enough to get a weak surge going along the length of the Gulf of California and that continues to be the case.

In spite of continued moisture increase, CAPE isn't all that impressive as the PBL cools and mid levels warm, but enough to support deep convection over the higher terrain of eastern 1/3 of the state.

Typically, a strong surge can cause cooling in the PBL.  In spite of this one not being very strong, temperatures are only in the upper 90's at Tucson by late afternoon (morning clouds too?).  Another negative is the warming seen in the mid layers.  Lastly, mid level winds continue to be light and variable.  Thus what was looking like a quite active day for Tucson looks much less so.

The two runs are similar over the White Mountains and Rim as they both have widespread activity there during the afternoon.  Both also develop storms over SE Arizona during the late afternoon. The WRFGFS (below) has some storm development over the higher terrain of central Pima county.

By early evening, the WRFGFS moves the dissipating storms into southern Maricopa county which sends an outflow into the Phoenix area.  Also note the activity north of Phoenix.  Strong convection continues across SE Arizona with the possibility of some activity near/in the Tucson area.

There is a chance of outflow convergence over the Phoenix area during the evening and looking at the WRFGFS Skew-t, the PBL is mixed fairly deeply and some CAPE is present.  With the right combination of events, deep convection could form in and around Phoenix during the evening.

As only a single model run is forecasting this, plus the low probability of timing and locations working out, I'd not say this is very likely.  Wait and see.