20200821

 Previous Forecast

It was the most active day of the monsoon season, at least for the lower deserts around Tucson and Phoenix.  Storms formed along the Rim and White mountains and generally moved to the southwest, initiating new storms mainly due to outflow boundaries, as these were quite strong.  Scattered reports of damage were reported in both Tucson and Phoenix.

The 12Z WRFNAM was the best, by far, and was even able to accurately predict some of the heavy precipitation amounts correctly.   All the rest of the runs were not good as they did not have nearly enough activity.  As I mentioned yesterday, forecasters shouldn't rely on the explicit QPF and convection forecasts.  Even for the runs that didn't predict much precipitation, the CAPE and Skew-T plots made it obvious that it was going to be an active period.  Hell, I didn't even need the models to say it was going to be an active day-it was right there on the 12Z soundings.   

I was watching HRRR performance also, and while it wasn't as good as the WRFNAM, it was better than the other WRF runs.  The HRRRx was also fairly accurate.

Discussion

The center of the 500mb anticyclone continues to be centered somewhere over northern Arizona.  This continues to provide a weak to moderate east to southeasterly flow over the state.  The tropical system is located off the coast of central Baja in a position that continues moist air advection into the state.  The 25 knot SE flow at Tucson is mainly due to a large MCV spinning over northcentral Pima County.

Both the Tucson and Phoenix 12Z soundings exhibit the typical "onion" profile after a significant precipitation event. Mid and upper levels are saturated with dry air below.  The lowest part of the atmosphere is cool and moist resulting in an inversion below 700mb.  MLCAPE is nearly zero.  Just based on this, it's unlikely for any significant activity today.

Initializations

The MCV has resulted in a large area of thick clouds over southwestern Arizona.  The 6Z initializations didn't have quite enough cloud cover, while the 12Z initializations did quite well.  The 12Z RR had the circulation of the MCV most accurately depicted.  The others had a diffuse inverted trough over SW Arizona into far NW Sonora, which wasn't too bad, considering the complexity of the situation.

PW was initialized very poorly by the 6Z NAM for southern Arizona, which I've found typically the case during and after periods of deep convection.  The 12Z was almost as bad as there are 8-12mm errors over southern Arizona.  The RR and GFS had only minimal errors.

Day 1

Flow around Genevieve continues to advect high amounts of moisture into Arizona today.  850mb dewpoints are a moist 13 to 14C.

CAPE is mainly low in areas where there was a lot of morning clouds and previous activity.  CAPE is quite high over the Rim and into Yavapai County so it looks like that will be the area of interest for today.

It looks like the only activity of significance is around Coconino and Yavapai Counties later this afternoon and early evening.

No activity is expected this afternoon or early evening for the lower elevations of Arizona due to the strong cap and shallow mixed layer.  Too bad as the wind profile and CAPE are great.

Some runs do develop late night activity over eastern Arizona, but this is not a high confidence forecast.

Day 2

Hard to believe, but the moisture increases even more due to the ongoing surge and southerly flow around the tropical depression, which stalls off of the central Baja coast.  It looks to be the highest values of the summer, at least so far.  Thanks, Genevieve!

Wow!  And this is the WRFNAM which is the lower of the various runs.  My guess with the amount of moisture, this CAPE is going to be capped.

And at Phoenix, it is.  Too bad, as everything else about this Skew-T plot is great.

Tucson?  Fuggetaboutit.

Even the high country has only limited activity.