Arizona WRF Discussion: 20190828

Initializations
It was very active in NW Mexico overnight and into this morning. Some showers were ongoing over far southeastern Arizona too. The clouds were initialized well, but the showers were mainly missing. This shouldn't be an issue as they've dissipated as of 16Z. Animating the imagery, there is a pronounced IT over far northeastern Sonora and another IT/MCV associated with the activity over southern Baja.

500mb data shows both of these cyclonic circulations. The 30-knot wind at Empalme is a bit suspect, though. 500mb temperatures have finally cooled to a more seasonable -6 to -7C. The atmosphere over Arizona is generally more favorable for deep convection due to steeper lapse rates and hopefully, weaker subsidence inversions. The RR has the best upper-air initialization followed by the NAM. The GFS is missing the Sonoran IT and has only a broad IT over NW Mexico. All had minimal PW errors in the western CONUS, but the GFS and NAM were a bit too wet in Mexico. Overall, the initializations were good with the best being the RR.

Day 1
Finally, we are rid of those hellishly warm mid-level temperatures. However, the moisture remains. PW has increased to 40mm at Tucson, and the forecast is for moisture to stay about the same as a weak surge continues. Unfortunately, more than 1/2 of the Suominet sites continue to be missing in Arizona, including all of the Phoenix areas, so it is not possible to assess model performance there.

Moist air is present at 850mb too, so the surge is relatively deep. So far, so good!

Tucson's morning sounding looked good as it indicated 1500 J/kg of MLCAPE and no significant inversions until just above 500mb. Steering was crappy though. Even Phoenix had around 900 J/kg MLCAPE. By early afternoon, more than enough CAPE is present to support strong to isolated storms, especially over far southern Arizona. Is today is the day????

Eastern NM looks primed for a big day too.

This is more like it! Strong storms develop over the typical high elevation locations by mid-afternoon. It's been infrequent that I've been able to say that this year. All three runs are similar with regards to timing and location.

The only real negative is the mid-level steering never becomes much more than about 10 knots. At least it's northeasterly through southeasterly as the anticyclone is forecast to be located over the White Mountains. Will it be enough to nudge the high elevation activity into the deserts?

The late afternoon Skew-T plot indicates 1300-1500 J/kg for Tucson. The wind profile isn't too bad as upper winds will blow anvils away to the east. There are some mid-level easterly steering and good low-level shear.

By late afternoon/early evening, an impressive area of intense storms moves into the Tucson area.

Finally, storms generate strong outflow winds, and these move into Pinal county during the evening. 12Z Tucson DCAPE was an impressive 1400 J/kg, so the potential is there for strong to isolated severe winds from storms.

Of course, it's not an easy forecast for Phoenix. There is a moderate amount of CAPE (the surface-based CAPE is too high), and the wind profile is good. However, there is a weak inversion at the top of the mixed layer; thus, a strong outflow or intersecting outflow boundaries will be necessary to kick off some storms.

Storms develop/move into Pinal County during the evening.

All of the 12Z runs do develop some showers and weak storms during the late evening in and around Phoenix.

The 15Z WRFRR is now available, and it's generally like the 12Z runs as it brings strong storms through the Tucson area during the late afternoon. Later, storm outflow boundaries into Pinal County. Note the outflow entering eastern Maricopa County from storms east of there as this may provide the necessary intersecting OFB.