Only minimal activity occurred yesterday over most of the state. Right at sunset, a few storms moved off the higher terrain and moved into the southern 1/2 of Tucson and busted my forecast. Literally, it was the only storm in all of southern Arizona!
The model forecasts had the right idea of only limited activity. The WRFGFS and WRFRR were the best, but none had any storms moving into Tucson. No forecasts correctly predicted the activity northeast of Yuma either.
Initializations
The 500mb high center has moved only slightly to the east, but it is enough to put southern Arizona in very light southerly flow. It's still very warm as temperatures are around -5C.
300mb is interesting as there is an upper level IT over southern Baja which results in upper divergence just south of Arizona. Maybe it will help out far SE Arizona later today or tonight?
Day 1
It's another very high CAPE day for southern Arizona as Tucson reported almost 1900 J/kg MLCAPE. Even Phoenix had 1100 J/kg MLCAPE. As mentioned earlier, winds are no longer southwesterly, but not favorable for steering storms. The warm (hot?) air continues from 550mb up to 350mb. There is an inversion at the top of the old mixed layer at 700mb which is likely to keep a lid on most convection at least for a while.
Flow is light in the lower troposphere; thus, the moist air hasn't gone anywhere. By early afternoon PW is still reasonably high over much of the state. I wouldn't call it a surge but a moist, shallow, and weak southerly flow continues over the northern Gulf of California.
CAPE remains impressive over much of eastern Arizona as some areas are over 2000 J/kg. Those values are very high for Arizona.
500mb temperatures remain in the -4 to -6 range over Arizona with even warmer air over the Big Bend. I'm experimenting with a different color map as the old one made it difficult to differentiate temperatures in this range.
Deep convection is again suppressed as only a few storms are present during the afternoon.
The forecast Skew-T plot tells the sad story of relatively cool air in the PBL and warm air aloft with weak inversions present. Moderate winds continue above 300mb thus anvils will shear off to the NW.
Phoenix is worse as the inversion at the top of the boundary layer is quite sharp with subsidence above. We need the 500mb high to go elsewhere!
Like last night, activity does pick up around sunset for southeastern Arizona. The three 12Z runs are consistent with this forecast, so confidence is high.
Day 2
It's about the same story as a decent amount of moisture remains over the state. Moisture decreases just a little compared to today, which may help the PBL head up a bit more.
The 500mb pattern looks a bit more favorable as temperatures are 1 to 2C cooler. There is good easterly steering as the high center moves over the Four Corners.
CAPE continues to be impressive for much of eastern Arizona. It looks like some areas are around 2500 J/kg! With the subtle improvements, it seems to me like it will be much more active tomorrow.
That is the case as storms initiate quickly over the high terrain and by early afternoon, strong to severe storms are underway.
Tucson is deeply mixed by mid-afternoon, but warm air is still lurking around 500mb. CAPE is good at around 1200 J/kg, and the vertical wind profile is also favorable. Steering flow is 15-20 knots. Winds are quite strong around 250mb so anvils will again move out ahead of storms, perhaps inhibiting heating.
For once, storms propagate off of the high terrain towards the lower deserts. Strong outflow boundaries are forecast, and of interest for Tucson, they are predicted to intersect with boundaries from the south. Both the WRFRR and WRFNAM are quite similar.
Strong and isolated severe storms develop over parts of Pima and Cochise Counties by late afternoon.
It appears Phoenix does not have enough CAPE to support deep convection.
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