20220730

 Previous Forecast

The model forecasts were pretty good, especially the 6Z WRFGFS.  The WRFHRRR also got the very heavy rain over in Texas.

Discussion

Finally, some real action looks to be in the cards today, so I'll get right to the good part.  The Tucson sounding has an impressive 1200 J/kg of MLCAPE, which is the best in some time.  It also had a surface dewpoint of 70F, which is unusual for Tucson.  PW is a very moist 45mm.  The steering also appears to be better, with 15 knots at 700mb.  The negative is the subsidence inversion at 500mb, but it shouldn't be a problem with enough heating.  Anvil-level winds could be better, but at least they are 45 degrees from the steering flow.

Phoenix is also much improved with nearly 900 J/kg of MLCAPE.  MU is a respectable 1300 J/kg.  PW is still a very high 52mm.  In fact, PW in SW Arizona and far NW Sonora is incredible.  Yuma is 57mm, and Puerto Penasco peaked at 62mm this morning!

The center of the 500mb anticyclone is around northern Nevada, but the flow is still primarily light and variable over Arizona.  500mb temperatures are quite high at -6 to -4C.  It looks like an old MCV or IT is between Flagstaff and Vegas.

300mb is interesting as an upper-level IT is moving westward from the Big Bend.  This feature puts NW Mexico and southern Arizona under favorable upper divergence/difluence.  Satellite imagery shows another TUTT located over the central Gulf of Mexico, moving our way. 

Initializations

Much of eastern and central Arizona is clear, for once.  Cloud initializations were fairly good.  The 6Z GFS was a bit too cloud over the Phoenix area.  The IT over Vegas was also well initialized.  The 12Z WRFRR did develop too much activity south of Flagstaff but was fine elsewhere.  There is no favored initialization, and model accuracy should be pretty good today.

Day 1

"Here we go," finally!  After days of boring gunked-over conditions for Tucson and Phoenix, the situation looks favorable for strong/severe storms in Tucson and perhaps Phoenix.  I'm amazed by the longevity of the Gulf Surge as it's been going strong for many days now and continues to do so this morning.  PW remains at extreme levels over southwestern Arizona and very high everywhere else.

The WRF has been trying to weaken the Surge over the past few days, but according to the 850mb, that still isn't the case, and it's actually deepened, up to 850mb again.  The firehose of moisture continues except for SE Arizona, where somewhat drier air has moved in.  As mentioned yesterday, this has resulted in a convergence zone over SE Arizona and could be a trigger point for storm development.

With some decent heating, CAPE becomes moderate to high for most of southern and central Arizona.

By mid-afternoon, the morning runs consistently develop strong to isolated severe storms over the higher terrain of western Cochise and eastern Pima Counties.  These storms move into the Tucson area.

The Skew-T forecast supports a big day for Tucson with 1500 J/kg of CAPE, low-level shear, and good mid-level steering.  Storms should easily push off into the valley and break the weak cap at the top of the mixed layer.  Heavy rain and wet microbursts are likely.

It's looking pretty good for Phoenix, based on the Skew-T.  The PBL is mixed deeply, CAPE is 1600 J/kg, and there isn't a cap holding things back.  Any outflows should get things going.

The morning runs are about 50/50 for strong/severe storms in the Phoenix area.  Strong to severe storms continue south of Phoenix and central and western Pima County.

The 12Z WRFHRRR is especially active, with widespread strong to severe storms this evening.  The forecast Skew-T certainly supports something like this.

Activity may continue all the way to the Colorado river.  Also, some runs develop a large MCS in northern Sonora and into southern Arizona for another round of storms.  It's very unusual for two waves of storms, so I don't have much confidence in Tucson getting hit again.

MCS formation is likely, though, as difluence/divergence over northern Sonora is pronounced.

No Day 2.