Arizona WRF Discussion: 20220727

Previous Forecast

It rained a lot at quite a few locations. Even parts of Tucson got some decent rain. Phoenix remained quiet as it was mostly cloudy during the morning, which didn't allow much heating. "Much," meaning Phoenix stayed below 100F.

The WRFRR runs have had significant problems with way too much deep convection firing shortly after initialization, resulting in some inaccurate runs. For now, some RR runs have been replaced with the HRRR. (0Z, 18Z). The runs had the right idea, keeping Phoenix quiet and a few storms in Tucson. They also had a handle on the heavy precipitation in Yavapai and Mojave Counties. Not bad, considering the complex situation.

Discussion

The large inverted trough continues to spin to the east of Arizona. At 300mb, it's centered over El Paso and continues to Arizona and Sonora in a favorable difluent/divergent upper-level pattern.

At 500mb, the circulation is displaced a bit to the west, near Douglas, AZ. This circulation might be a large MCV. It's hard to tell. There are at least three(!) other MCVs spinning over the state: far NE Arizona, along the Mogollon Rim, and another SW of Phoenix (for a third day). All are pretty much stuck as the height field over all the southwest is flat, with no flow. I never recall a situation like this before.

See yesterday's discussion.

PW has increased to 54mm since the 12Z sounding!

Initializations

The one slight change is that there are more clouds this morning. The HRRR and GFS were pretty good, but again, the RR goes nuts right off the bat, with deep convection from Phoenix and to the southwest. Those runs will be ignored, at least for those areas. None of the initializations were able to capture the complex MCV situation. They generally have a broad oblong weak cyclonic circulation from NE Arizona to SW Arizona. Not unreasonable, IMO. They are missing the little MCV over far SE Arizona and instead have a broad area of cyclonic circulation centered south of the border. Also, not unreasonable. The 12Z HRRR seems to have the best handle on the situation.

Day 1

Our good friend, the 850mb cyclonic circulation just west of Baja moves a bit more to the west and weakens. This results in a mainly light and variable flow over the Gulf of California and into Arizona. So, at least at 850mb, the Surge has ended.

At the surface, the Surge is weaker but still going. PW remains extremely high.

CAPE is low to moderate for much of eastern 1/2 of the state. It's another day of heavy rain with slow-moving storms for those mid to high-elevation locations. There isn't much from Phoenix and to the southwest, which looks reasonable. Thus, not much activity is expected there.

Storms fire before noon for locations that get partial sun. It takes SE Arizona a while to get going, but by mid-afternoon, storms are present east of Tucson. Once again, other strong storms with extremely heavy rain are present in Coconino and Yavapai Counties.

It's looking good for Tucson later today as CAPE becomes relatively high, above 1500 J/kg, and there is a little bit of steering flow at 5-10 knots and a little low-level shear. The PBL has a weak inversion at the top but is approaching the LFC, which was a low 750mb. Anvils could be a problem if storms form to the northeast.

There is a remarkable consistency between runs as they all develop a broken line of strong to isolated severe storms (wet microbursts) from eastern Pima county up towards the Rim later this afternoon and early evening.

It's hard to say what will happen as the storms move toward Phoenix. CAPE isn't all that impressive despite 48mm of PW. However, the PBL is mixed nearly to the LFC, so even a weak outflow could trigger deep convection. If storms do form, they aren't going anywhere as mid-level flow is light and variable.

Storms struggle to form in the Phoenix area, at least according to WRF. My guess is there will be a bit more activity, considering Phoenix is starting to clear. As of 17Z, storms are already beginning to fire north of the valley, which may result in anvils later, so maybe not. We'll have to wait and see.