20200825

 Previous Forecast

Strong to severe storms developed over central and western Pima County yesterday afternoon, which was a couple of hours earlier compared to the WRF forecasts.  Thus, my forecast for good sunset lightning didn't work out.  The HRRR did a better job as it developed the storms a couple of hours earlier.  Showers and a few weak storms struggled over Pinal County after sunset.

Except for the timing, generally, the WRF runs were accurate. The WRFRR run had too much activity around Tucson though.

Discussion

Not much has changed the past 24 hours as the 500mb anticyclone is still centered near the Four Corners, and steering flow is still generally weak easterly to southerly.  There is a large inverted trough over far northeastern Mexico and perhaps that could edge closer to Arizona the next few days.

PW has remained mainly the same or increased slightly.  It is around 40mm out in southwestern Arizona and drops to about 30mm for Tucson and Phoenix.  Very dry air is still in SW NM and far SE Arizona.  CAPE is quite low for much of the state, thus the outlook for thunderstorms isn't very good.  What else is new.

There isn't much good to say about either 12Z sounding as they both are devoid of CAPE and have light and variable winds through most/all the profiles.  At least the temperature profile exhibits no inversions.

Initializations

There is an ongoing area of showers and a few storms over far SW Arizona and this activity was generally in the initializations.   PW initialization by the 6Z NAM was terrible.  All the rest had only minor errors.  Again, the 6Z NAM will be discarded.

Day 1

A weak surge gets underway today, resulting in some increase in moisture for central Arizona.  Dry advection continues over far eastern parts of the state.

It looks like another day of limited CAPE.  Trump's wall is really doing well at keeping it in Mexico.

Most runs have limited activity, even for the higher terrain.

The 15Z WRFRR does manage to develop a few storms around eastern Pima County by the late afternoon.  The forecast Skew-T does have about 500 J/kg of CAPE, and a well-mixed CBL.  Steering flow improves to about 10 to 15 knots from the northeast.

I've been waiting around for the 12Z WRFGFS and it's the most active of any morning runs.  It develops strong to severe storms over central Pima County by late afternoon.

Outflows from these storms manage to trigger a few storms in western Maricopa County this evening.

Day 2

There hasn't been run to run consistency about the moisture situation tomorrow.  Some forecasts push the dry air all the way to Phoenix.  The 15Z WRFRR keeps it in southeastern Arizona.

There may be enough CAPE and the cap weak enough to allow a few strong storms over parts of Pima County.  CAPE is low to none for much of the rest of the state.  How long is this going to go on!!!!

The 15Z WRFRR develops strong to maybe severe storms in central Pima County during the late afternoon and early evening.  I don't have much confidence in this forecast for two reasons.  The first is that the Day 2 forecasts for much of the summer have had too much activity.  The second is that the WRFRR is the only one forecasting significant activity.  There is sufficient CAPE for scattered showers and weak storms for afternoon storms over the high country.