20190716

Ken Howard send me a correction regarding some of the things I said the other day about the possibility of a new radar for Arizona.
"For clarification, there is a new 5cm dual pol radar (NOT a NextRad) installed in Alamosa, CO which will be part of MRMS real time data flow in late September.

The operational MRMS system is being updated at NCO in September 2020.  However, the experimental MRMS v12 products are reviewable at https://mrms.nssl.noaa.gov/qvs/mrms_v12/.  Individual forecast offices can tap the real time experimental feed by contacting Paul Kirkwood at SRH.  

There is a plan to install a new 5cm dual pol radar in the Durango area (again not a NextRAD) as soon as a year from now.  Once this radar is built it will be come part of the MRMS data flow as well.  

I have no knowledge of what ADOT is doing nor ASU.  Our primary interest and effort is on operational radars.  The Alamosa and the forthcoming  Durango radar will be operated in a operational mode and will be part of MRMS product suites."

Previous Forecast

The WRFRR performed reasonably well on Sunday as quite a bit of activity was present over central and western Pima County.  The 15Z WRFRR was the best as it had both the intensity and coverage forecast accurately. 

The forecast for yesterday was also accurate as what looked like it could have been an active day for the lower elevations of SE Arizona due to moisture and CAPE, turned out not to be as drying kicked in during the afternoon. This resulted in deep convection only over the higher terrain.

Art Douglas sent me an updated Mexican precipitation anomaly map, and it’s not gotten any better as much of the country is below average with some areas way below normal.  While some MCS activity has been present over NW Mexico the past few days, it’s still been relatively inactive. One recent period of activity was able to send an outflow driven gulf surge into Arizona this past weekend.

Initializations

Clouds and a few showers were present over southern and up into east-central Arizona this morning, and as time has gone on, coverage has decreased, so it’s now mostly clear.  Neither the RR or NAM had any clouds while the GFS was better as it had scattered/broken clouds over southern Arizona. These errors shouldn’t impact the forecast too much as mentioned earlier, the clouds are dissipating.   Not much to see on the 500mb map as no inverted troughs are apparent.  

The NAM has a general wet bias across much of the SW US and into Mexico.  The GFS and RR have minimal errors and are the favored initializations today.

Day 1

A new gulf surge is forecast to begin today, which should result in increased activity in southern Arizona.  I’m not sure of the mechanism as the storms in Sonora and Sinaloa weren't that strong to generate significant outflow into the Gulf.  The outer domain indicates the surge is present all along the Gulf of California. It appears that the recent activity over the southern Gulf combined with the very hot temperatures in the SW US has triggered a traditional surge.

850mb dew-points are too low to support much activity except for SE Arizona.

Tucson’s PBL is mixed deeply, and along with a little CAPE, there is likely to be storm activity nearby.  Will it make it into the valley? My guess is probably not as the steering flow is pretty weak. The upper part of the vertical wind field is starting to look like the monsoon as the southwesterly flow has become light and variable.  

The spread for the various runs goes from almost no activity, to very active for southeastern Arizona.  The 15Z WRFRR is somewhere in the middle and has mostly higher elevation activity for southeastern Arizona later this afternoon.

Day 2

The surge continues overnight and results in much higher PW by tomorrow.  It’s the highest so far this season as PW is in the mid to upper 30mm range over southern Arizona. 

 The surge is deep as at 850mb, dew-point temperatures are the highest of the year, ranging from 10 to 15C which should support widespread activity especially for southeastern Arizona.

Along with the moisture increase, CAPE is very high over southeastern Arizona, which will support some very strong storms with heavy rain. 

The Tucson forecast Skew-T plot has an enormous (for us) amount of CAPE.  The common problem with the first day of a surge event is the cooling of the PBL and the presence of a weak cap/inversion keeping lower elevation convection to a minimum.   The wind profile is bad as there is no steering; thus, storms will have a difficult time moving much. In situations like this, it’s usually the higher elevations that get pounded with only isolated activity for the lower elevations where storms might form on outflow boundaries.

Intense deep convection gets underway over Santa Cruz and southern Cochise Counties during the mid-afternoon.  With this much CAPE, I’d expect to see some small hail with these storms. All of the 12Z runs are very similar to the intensity and location, so confidence is high.  Some of the storms could produce isolated severe winds due to hybrid microbursts.

Storms continue over the higher terrain into the late afternoon.  

At this point, it looks all Tucson will get is a big outflow from the activity from the south.  No runs develop deep convection in Tucson.