20200802

Previous Forecast

As it was clear that Tucson was not going to see any activity, in spite of >2000 J/kg, I decided to go visit the storms in Cochise County as it was likely they were going to be organized and easy to chase.  Storms developed over the higher terrain of Graham and Greenly Counties and moved/developed to the SSW, right along the boundary of the high CAPE air to the west, and drier air to the east.  I came upon Brian Snyder and his group south of Benson where we watched multiple severe warned cells to our northeast.  Lighting was frequent, but almost all obscured by heavy rain.  We got hit with some strong outflow boundaries from the storms to the north and northeast.  It was fun to see the chasers in action!

 

The model runs all had the general idea of moving storms into Cochise County during the evening, but there were issues.  The WRFRR has been struggling with not enough activity and that was the case again, both in SE Arizona and NE of Phoenix where there were some good storms.  The WRFNAM was too wet and had storms too far west, which was discounted in yesterday's discussion.  As was the case last year, the WRFGFS seems to be the best so far as it's doing a better job at QPF.

I've started up the 15Z WRF based on the developmental version of the RR, kindly made available to me by GSD.  I've only run it a few times this year and it's been working quite well.  For example, it did the best at predicting the QPF for the storms around northern Gila County. It will run daily now, just after the 15Z WRFRR.  Some day, I'll come up with some real ensemble products using all these runs as it's just too hard to sort through them all.

 

Discussion

The 500mb high continues over Arizona along with moderately cool air of -6 to -8C.  Steering flow is mostly light and variable.  

CAPE continues to be quite high, and at Tucson, the most unstable layer is elevated at around 750mb, which is unusual for here.  There is a big improvement in moisture in this layer as yesterday, there was a lot of dry air advection.  The inversion around 450mb is less pronounced today too.  Steering is mainly NNE at 10 to 15 knots, and generally, it looks like there is a better chance for storms around the Tucson area today.

Phoenix also has quite a bit of elevated CAPE, but the vertical profile is dominated by westerlies, which is very unusual for what is normally the peak of the monsoon.

There was a large MCS over Sonora last night which may result in an outflow induced surge at some point today.  Satellite imagery does show an outflow boundary moving into SE Arizona which is keeping the clouds going there.

Initializations

Some clouds and a few showers are moving through far southeastern Arizona.  The morning initialization did not do a good job with them as all are missing this activity.  They also mostly missed the clouds and activity associated with the MCS over Sonora.  As mentioned, an outflow is moving into far SE Arizona, which was not initialized,  The various runs are going to struggle there today.  We'll have to see if some of the later RR initialization are any better.  Suominet is still down so I have no idea how well the PW is initialized.  I will assume the NAM was too wet.  I compared the RR to the NAM and the NAM PW is 5mm or higher over much of NM.  I'm starting to think that the WRFNAM should be retired, especially without the PW corrections being applied.

The 15Z RR just became available and its cloud initialization in far eastern Arizona is better, but still not enough.

There is a large area of smoke that has moved into central Arizona, reducing irradiance and heating.

Day 1

It continues to be moderately moist over much of southern 1/2 of Arizona as southerly flow, perhaps strengthened by the MCS outflow,  continues the moist advection.

CAPE continues to be moderate to high over much of southern and central Arizona.  It's probably too high over SE Arizona though.  

Deep convection is surprisingly limited for areas along the Rim and White Mountains.  My guess is the higher CAPE air must be capped, ever there.  My guess is that Cochise County is too active.

The 15Z WRFRR delays convection until the evening over Cochise County, which is probably more realistic. 

Tucson is close.  The mixed layer is much deeper vs yesterday, and near the LCL/LFC by the early evening. The wind profile has only light steering so storms will need strong outflows to initiate.

 

Big storms are likely again along the border and these could generate the needed outflow.

Storms get close.  Some runs develop storms in eastern Pima County during the evening.

Just in, the 15Z WRFRRx and it does have clouds initialized accurately over southeastern Arizona.  It develops strong storms along the border tonight. 

Day 2

Well, that looks like about it for quite a while as dry air moves in.  We could still see occasional intrusions of moist air into southern Arizona that might result in some storm activity, but the synoptic pattern is generally unfavorable as a large trough is again present over the western CONUS in the medium range.