20190723

Previous Forecast
Most of the model runs performed well in spite of the widespread morning cloud cover that I thought may have been an issue, especially for Phoenix.  It was the most widespread event so far, and quite a bit of rain fell in some spots with as much as 2".   Note: I'm uploading images directly into Blogger now so you can click on them to get the full size.

In general, the WRFGFS and 15Z WRFRR were the best runs.

There were quite a few reports of severe winds over southeastern Arizona and several power outages in the Phoenix due to strong winds.  This part of the forecast also verified well. 

I'd like to talk a little about the Phoenix area as the 0Z sounding only had around 700 J/kg of CAPE and a shallow mixed layer. Just going on that, it looked like there wouldn't be much chance for any deep convection.  Another reason to think there wouldn't be any was that the temperature forecast was significantly too warm as the model runs didn't have nearly enough clouds. 

None of that mattered much as a thunderstorm outflow moved in from the south and was sufficient in strength to trigger a few storms across the Phoenix area.  My thinking was that Phoenix would need intersecting outflows, but to me, it appeared to be a single outflow boundary moving in from the southeast.  If anyone has another opinion about what happened in Phoenix, I'd like to hear it.

It was quite cloudy in the Tucson area during the morning hours too, and I was afraid the forecast was going to have too many storms.  It cleared off around noon, and the afternoon observed temperature was quite close to the forecast.

Initializations
The story for today is a worked over airmass plus extensive clouds.  The Tucson morning sounding does show a wet and cool surface layer, but it's not too bad, considering all the activity around yesterday.   Note that the low-level easterlies have made it to Tucson.  These downsloping winds are usually unfavorable for widespread lower elevation storms.

The 500mb pattern has the center of the anticyclone over southern Utah, putting Arizona mainly in southerly to easterly flow.  There appears to be an IT near Flagstaff which may be the MCV that is moving towards Vegas this morning.  Note the excellent upper air sounding coverage today with even Yuma reporting.  The NAM is missing the MCV over west-central Arizona, and no other cyclonic features are apparent in either observed or model data.

Scattered to broken clouds are present over much of the state, especially near the MCV.  By the way, I'm curious why some people think that MCV's enhance deep convection as I've seen this discussed more than once this summer.  It's typically the other way around as they have extensive clouds associated with them plus they are warm-core.   Sometimes, thunderstorms are enhanced in areas that are in the vicinity of an MCV like occurred in far SE NM yesterday.  Note the MCV in EC NM which is devoid of deep convection but over far SE NM, it was very active.  2256Z yesterday with GOES lightning GED overlayed.

The WRFNAM quickly went off the rails this morning as it developed convection over southern Arizona.  Both the RR and GFS initialized clouds well, but the 12Z WRFGFS held on to clouds a bit too long this morning.   I'm a little surprised about the WRFNAM as the NAM PW initialization was actually OK this morning as was the other two models.  I'd say the RR or GFS will be the better runs today.
Day 1
It is still quite wet over much of the state today and including far eastern Arizona where low-level flow southeasterly flow is present.  Even there it's wet as upstream in southern NM remains wet too.  Easterly flow has pushed a bit to the west as the surge has stopped and weak westerly flow is present.  There is still a low-level convergence zone, but it's much weaker compared to yesterday.  Is it enough to act as a zone for initiation for deep convection?  I don't know.

CAPE is quite a bit lower today as most areas have only 500-1000 J/kg.  This is still sufficient to support some storms.

All the runs are warmer than observed, especially around the Phoenix area where they are running 4-7F too warm. My guess is the various runs will be somewhat too active today.  The least amount of activity is in the 12Z WRFRR, and it develops deep convection only over the higher terrain.

Isolated storms continue into the evening hours.

The 15Z WRFRR is now available, and it is quite a bit more active in eastern Maricopa and Pinal Counties this evening.  I think this is less likely because it had very few clouds initialized and its 2m temperatures were also quite a bit too warm. I don't discount it totally as it's been pretty accurate so far this summer.

Day 2
Another surge gets underway and advects very wet air into southwestern Arizona as PW approaches 50mm. 

There is quite a discrepancy with tomorrow's CAPE forecast as the WRFGFS and NAM have around 1500 J/kg over much of the state.  The WRFRR has less over the deserts but is quite high over the higher terrain, so it's likely to be an active day there.  Hopefully, enough rain will fall to help with the Museum fire near Flagstaff.

Scattered storms are present over the higher terrain tomorrow afternoon.  Strong storms forms on the nose of the very high CAPE located over far southern Arizona.

The forecast for the lower elevations is quite uncertain as the WRFGFS/NAM has a lot more CAPE then the WRFRR.  The WRFRR has a substantial warm layer at 500mb reducing CAPE. 

Phoenix looks better than Tucson, for once, as CAPE is higher.  Steering is weak, so my guess is little or no activity for Phoenix in spite of higher CAPE.