20200712

Previous Forecast

Tucson got walloped by a severe storm yesterday evening with strong/severe winds and widespread blowing dust.  Most of the 12Z runs did not have enough activity and this seems to be a common problem so far this monsoon season.  The WRFNAM did have a fair amount of activity and lucky for me, I did lean toward it in the discussion yesterday.  Something I saw but didn't mention was the 1900 J/kg of DCAPE on the 12Z sounding.  No wonder the winds were so strong.  What is even stranger is that the previous day forecasts are typically better!  For example, the 15Z WRFRR forecast developed a strong storm over the Rincons and then moved it across Tucson.

Precipitation was mainly light except for just east of Tucson where almost an inch was estimated.

The 12Z WRFNAM was the least bad of the 12Z runs.  The various WRFRR runs have performed the worst so far this season as they typically under forecast, by a lot, storm activity for the first 24 hours.

Discussion

500mb heights have decreased slightly from yesterday so the end is near for the heatwave.  The center of the anti-cyclone is in the vicinity of Flagstaff which puts southern Arizona in decent easterly steering flow again.  However, temperatures are around -7 to -5C.  

Moisture has decreased over southeastern Arizona as PWs are in the mid to upper 20mm range.  The rest of the state has remained about the same as PWs there are in the 30 to 36mm range.

Initializations

The 6Z initialization struggled with moisture as they initialized 3-8mm too wet.  The 12Z NAM also initialized too wet, but not as bad as the 6Z runs.  The 12Z RR was good.  It's possible that some runs may be somewhat too active, but with the low bias, they've had recently, maybe that is a good thing.

Day 1

The backdoor dryline is located around Tucson with dry air advection to the east.  Weak moist advection continues over central and western Arizona.

CAPE is quite low for most of the state except for some moderate amounts along the dryline which is sufficient to support storms over the mid and high terrain.

Scattered activity is present over much of the higher terrain of northern Arizona this afternoon.

The Tucson Skew-T forecast looks much the same as it did yesterday with good steering flow and 500-1000 J/kg of CAPE.  Maybe a repeat of yesterday?  The negative is the warm layer above 500mb.  As it was yesterday, the main risk is very strong winds due to the large inverted V profile.  Morning DCAPE was quite high at 1700 J/kg.

A few storms develop in eastern Pima county by late afternoon and into the early evening.  

Some runs keep them going and moves them into Pinal county which is certainly possible as there is some CAPE present there.  Thunderstorm outflows weren't forecast to be very strong, but they are likely to stir up a lot of blowing dust.

Day 2

The overall situation is becoming more favorable for storms in eastern and southeastern Arizona.  The 500mb monster anti-cyclone moves a bit to the east as another NW CONUS trough moves in.  Mid-level flow is still southeasterly over southern Arizona and 500mb temperatures cool off a bit.

Another favorable development is a Gulf Surge gets underway and PW increases over much of the state, especially southeastern Arizona.

CAPE is sufficient to support storms mainly over eastern and southeastern Arizona.

Strong storms develop over eastern and northeastern Arizona tomorrow afternoon and additional strong storms form over southeastern Arizona during the late afternoon/early evening.