20200827

Previous Forecast

Zzzzzzzzz.

The forecasts weren't much good except for the WRFGFS.  The RR initializations, again, did not have enough activity and totally missed the strong storms in western Pima County.  

I've been keeping my eye on the HRRR to see if it has the same problem as both the HRRR and WRFRR are initialized by the RR.  Many times, the HRRR is better, including yesterday as the 12-15Z runs all predicted the Pima County deep convection.  I took a close look at PW and MCAPE at 7 hours into the forecast (20Z) and the WRFRR was essentially the same as the HRRR.  My WRF configuration is similar to the HRRR configuration so I'm stumped why the WRFRR is having this problem.  The exact same configuration is used for the WRFNAM and WRFGFS and they perform as well or better than the HRRR.  This is something I'm going to look closely at after the monsoon is over.

Discussion

The center of the anticyclone continues over the Four Corners resulting in weak easterly to southerly flow over most of the state, except for the northwestern part as it's now southwesterly due to a trough moving through the northwestern CONUS.   Heights have decreased by about 20 to 40m over the past few days, and temperatures have remained about the same.   There is an inverted trough over the Big Bend of Texas as seen in water vapor imagery and the 500mb map.  I was thinking this might drift our way to help organize storms, but it's not moved much.

PW continues to be moderate over much of south-central and southwest Arizona so it looks like another marginal day.  Dry air is still present over far southeastern Arizona so little or no activity there.

Generally, CAPE over the state is <500 J/kg, but Phoenix has a bit more than that as the morning MLCAPE was 700 J/kg.  However, this increase in CPAE and moisture has resulted in cooling and a cap.  We'll have to see later in the forecasts if this can be overcome.   The wind profile is unfavorable for moving storms off of the higher terrain as it's generally light and variable below 500mb.

Tucson has better steering flow, but worse CAPE.  (insert sound of a head banging on the wall here)

There is some hope on the horizon.  Tropical Storms Hernan will transition to a favorable location to initiate a Gulf Surge in about 24 hours.

Initializations

The 6Z NAM was way too wet, as usual.  Other than that, all other initializations were fine.

Day 1

The moist air is losing.  Very dry air is moving into western Arizona, while the dry air remains entrenched over southeastern Arizona.  Thus, this narrow area has the only hope for significant activity today.

As the Phoenix 12z sounding indicated, CAPE is a bit higher in this narrow band, and likely to support a moderate amount of activity.

Thunderstorms develop first, as usual, over the higher terrain, including around the Tucson area.

This looks like one of the better days for Tucson in some time.  The boundary layer is mixed deeply, and the vertical wind profile is good as it has 15 knots of southeasterly flow.  CAPE is marginal at about 3-500 J/kg.  (the surface based CAPE calculation is too high)  

Only the WRFNAM has storms close to Tucson as all the other runs keep them to the south and west.  The only thing I can say in the WRFNAM's favor is that generally, the more active runs have been verifying. 

Despite the CAPE that was observed in the morning sounding, the chance for any significant storms in Phoenix seems remote.   CAPE is only about 500 J/kg, and it appears that there is dry air advection into the mixed layer above 850mb. 

About the most Phoenix can expect are scattered showers and maybe a few weak storms over the higher terrain.

Day 2

Hernan to the rescue?  By midday, moist air is poised to jump the wall and enter Arizona as Hernan's location is optimal for moist air advection up the Gulf of California and the coastal plain of Sinaloa and Sonora.

What is this??? No CAPE?  I don't believe it.  

400mb and above have warmed significantly over the past 36 hours resulting in the lack of CAPE, even at one of the best locations, Nogales.  However, threre is enough in southeastern Arizona and along the Rim and White mountains to support low topped convection.