20210629

 Previous Forecast

Very heavy rain fell over the past 24 hours over SE NM and south into Texas.  MRMS Q3 says as much as 6 inches.  A few storms developed over eastern Arizona and moved south towards Tucson, and other stronger storms developed just south of Santa Cruz County.

Generally, the location and amounts of precipitation were forecast well, including the area of extreme rain in NM/TX.  However, the strong winds never materialized at either Tucson or Phoenix.  The 15Z WRFRR and the 6Z WRFGFS (below) were quite accurate.

Discussion

The upper-air pattern hasn't changed much as the Omega block is still in place over the NW CONUS and a broad trough over the central into the southwestern US.  The NM cutoff low has drifted northward over the AZ/NM border and is responsible for the heavy rain and widespread clouds in NM.

Moisture continues to increase as PW values are now in the 25-32mm range.  Both the Tucson and Phoenix soundings indicated a bit of CAPE, resulting in storm activity later.  Tucson had quite a bit of cooling in the lowest levels. Thus, there is a cap in place.  Phoenix is well mixed already with elevated CAPE thus the ongoing activity to the NW and SW.

Enrique has weakened and has lost all deep convection as it approaches southern Baja.  Mid-level moisture continues to stream to the NE into NM.  Looks like their drought is over, at least for central and eastern NM.

Initializations

It's a complicated situation this morning, so it will be tough to get a good initialization.  The 6Z GFS looks quite good as it has the morning activity over NW Arizona and the widespread clouds and rain in NM.  The 12Z  RR is also pretty good but has a bit too many clouds around the Phoenix area.  The 12Z NAM was unable to initialize the Arizona morning activity but did well in NM.  PW errors are mainly under 2mm for all initializations.  I think the 6Z GFS was the best, but there are no major issues with any of them.

Day 1

Moisture continues to increase today due to advection from both the east and up the Gulf of California.

CAPE has also increased over central and western Arizona and is sufficient to support scattered storms later today.

By mid-afternoon, scattered storms are located over much of the higher terrain of the state.  The 12Z WRFNAM is probably too active as it had more heating (and moisture) than the other more recent runs.  The 6Z WRFGFS (below) falls somewhere in the middle.

The Phoenix area PBL becomes deeply mixed by late afternoon and 3-600 J/kg of CAPE, which is likely to support scattered activity in the area.  Steering flow is light and variable, so storms probably won't move much or become organized.

The situation is similar in Tucson as some CAPE is present.  The steering flow is a bit better.

A few storms may develop by early evening in and around the Tucson and Phoenix areas.  

Not much precipitation is expected, but there could be some strong winds and blowing dust.

Day 2

PW continues to increase and is over 40mm at some locations, which is very wet for this time of year.  Thus, the risk of heavy rain increases for any storms that may form.

With the increasing moisture comes increased CAPE.  It becomes quite high over southcentral and central Arizona, which will support stronger and more widespread storm activity.

Steering flow is a bit more favorable for southeastern Arizona, with about 5-10 knots from the NE, which will help move higher elevation storms towards the lower deserts.  Some more positives are 500mb temperatures around -10C and eastern Arizona generally under cyclonic flow.  Tomorrow looks like the best chance for storms for Tucson and Phoenix so far this season.

Storms develop over the higher terrain during the afternoon hours and maybe even some activity in the Tucson area.

Storms continue into the evening, covering areas of the lower elevations of south-central Arizona.