20190804

Previous Forecast
It was bust for Phoenix as storms formed on multiple outflow boundaries incoming from the north and the south.  All runs missed the central/western Pima County storms and the resulting outflows.  Some runs had a little activity for Tucson, but that was a bust too as anvils put a stop to any deep convection.  The 15Z WRFRR was least bad as at least it had the storms in Yavapai and Gila Counties.

Drying was forecast for western Pima and Maricopa Counties for the afternoon hours which was initially correct. However, moisture started to increase after 0Z.   The 0Z Phoenix sounding was unimpressive with only 735 J/kg of MLCAPE, but obviously, it increased during the evening as moisture increased.  Also, the PBL was mixed to nearly 700mb and didn't have much further to go until the LFC.

The WRFRR and WRFGFS forecast Skewt-T plots looked similar to the 0Z observed.  I don't know why WRF has been struggling the past few days.  Generally, the model forecasts have been entirely accurate, especially the RR.

I was a bit down about the bust, but I got this nice email from Jerrod Harris:
"Your AZ-WRF-15Z dragged me up to the I-17 & Bloody Basin Road, from Phoenix, for the 3:30 pm storms. Saw a tiny funnel at the same spot from 3:24-3:27, if you squint hard enough you just might see it, then got bolts at sunset. I planned on traversing to Humboldt Mountain for sunset but a new storm fired up and kept on going.  Love the RR this year."

Initializations
The 12Z 500mb map has a departing IT over northern Arizona.  Perhaps this played a role with the busted forecast?  No other significant features were seen in either the upper air data or satellite imagery.  Note that there has been slight cooling as Tucson reported -7C.

Clouds dissipated this morning, and now it's mostly clear. All initializations were accurate except the NAM as it was too cloudy.  The RR had the smallest PW errors, followed by the GFS, and these are the two favored initializations today.

Day 1
Without looking at any maps or model runs, I expect a down day due to the widespread cooling from all the storms last night.  The Phoenix sounding confirmed this.  PW has decreased quite a bit over the past 6 hours over much of southern Arizona.  In spite of weak southerly flow up the Gulf of California, moisture does not increase, and by early afternoon, 850mb dew-point temperatures are marginal.   It's quite moist over in southern NM with the weak easterly low-level flow.

CAPE is adequate for some storms over the higher terrain while the lower elevations have little or none.

Most activity is restricted to the higher elevations from Flagstaff eastward.

The 15Z WRFRR does develop some storms over far SE Arizona this evening.  Will there be more activity compared to the forecast?  Perhaps.

It's possible for some activity in the Tucson area as the PBL is deeply mixed and near the LFC as well as moderate CAPE.  Negatives are steering winds are nonexistent and upper winds are again strong and will shear anvils off and over the Tucson area if convection develops south of the valley.

Day 2
Dry air continues over western Arizona, but eastern Arizona and western NM are quite moist with Td from 10 to 14C.

CAPE is high over much of southeastern Arizona and SW NM.

Steering flow is better as the mid-level high is forecast to be centered over far northern Arizona, resulting in 5-15 knots of northeasterly flow.

Mainly higher elevation storms during the afternoon hours.

Only the 15Z WRFRR has activity in the lower deserts tomorrow evening, so this isn't a very high confidence forecast.  Gotta have something to look forward to!