20200702

Discussion
Moisture advection into southern Arizona continues and is very impressive for this time of year.  Amado AZ is up to nearly 38mm, and Hermosillo is almost 50mm! 

Associated with all that moisture are clouds, and they are going to throw a giant monkey wrench into yesterday's forecast which called for scattered storms.  Clouds are very thick and widespread over southeastern Arizona and are going to restrict heating.  Radar and cloud animation does indicate that a weak MCV or inverted trough is also located over southeastern Arizona.

The 500mb pattern remains mostly the same with a significant longwave trough over the NW CONUS and a prominent ridge over the center of the country. Arizona has mainly southerly flow. 

Model Initializations
Those who have read these discussions in previous years know that one of the major weaknesses with the WRF forecasts during the monsoon season are situations like this where there is significant morning cloud cover.  WRF typically would have not enough clouds in the initialization and/or burn clouds off too quickly, which resulted in too much heating.  Too much heating led to too much deep convection.  WRF has a couple of ways it deals with subgrid clouds, and the "best" was a technique developed by the WRF cloud master, Greg Thompson.  The initial version had a lot of issues and needed significant tuning, but was still better than the other schemes.  Since WRFv4, his routine is much improved and does a good job forecasting sub gird clouds and improves the optical thickness of resolved clouds.  Below is the irradiance forecast for 15Z from the 12Z WRFRR.  As you can see, cloud coverage and thickness are quite good over Arizona.  It's not so good over eastern NM, and this appears to be an RR initialization problem as some of the 6Z runs were better.

The weak cyclonic circulation was not initialized by the runs, but the 6Z GFS and 12Z NAM do have a weak trough in the vicinity.  As was typical last year, PW initialization errors are minimal for most sites, which is a great thing to see.  There are some small errors in Mexico as the NAM, and RR initialized around 3-5mm too wet at some locations.    Accurate PW initialization is critical for good forecasts during the monsoon season.

Day 1
All model runs keep widespread clouds over southern Arizona into the early afternoon, restricting heating.  The good news is it looks like high temperatures are only going to make it to around 90-92F!    The bad news is it is unlikely it's going to get warm enough to support deep convection over the lower elevations.

Moisture is more than enough, especially over southern Arizona, as PW continues to be around 35mm.

Note the big CAPE hole over southeastern Arizona due to the lack of heating.  I think this map tells the story for this afternoon and evening, which is minimal activity.  Higher terrain along the border may see some storms as CAPE is more favorable.

Sad!  Only scattered showers and maybe a thunderstorm or two this afternoon and evening.   It looks like the first opportunity for good storms is a dud.   How appropriate for the 4th of July.

Western portions of Maricopa County may get enough heating to trigger a few weak storms this evening.

Day 2
Moisture continues to move north and is all the way into southern NV by tomorrow afternoon.  It remains to be moderately wet over southern Arizona.

The forecast calls for mostly clear morning hours; thus, CAPE becomes low to moderate over parts of the state by early afternoon.  It's enough to support more activity than today.

The forecast Skew-T diagrams for Tucson and Phoenix do not look favorable for deep convection despite around 500 to 1000 J/kg of CAPE.  Both have multiple warm layers and are dominated by southwesterly flow and dry air aloft.

What a waste of suitable moisture.  Only isolated storms over the high terrain of northern Arizona and a few in southeastern Arizona.