Storms northeast and southwest of Phoenix did in fact cause outflow boundaries to develop this evening. They did move into the Phoenix area but due to a lack of instability (as pointed out earlier) they did not result in much additional storm development. The 00Z KPSR sounding (below) indicates that there was just a few hundred J/kg of CAPE which is definitely not enough to generate thunderstorms let alone severe storms. The Severe Thunderstorm Watch that the Storm Prediction Center issued at 615 PM (until 12 AM, canceled early) appears to have missed the mark; a Slight Risk earlier issued in the Day 1 Outlook looked good though. One Severe Thunderstorm Warning was issued for 60+ MPH winds, though no damage as of now was reported. There was some rain – the Phoenix Rainfall Index was 0.02″ with 26% of the Valley getting rain (maximum single gage was 0.94″), officially at Sky Harbor there was a Trace (it rained, but not enough to measure at least 0.01″).
00Z 4 July 2011 KPSR (Phoenix) sounding. This was close to being an idea sounding – boundary layer was deep (high Lifting Condensation Level (LCL)), steering winds in the cloud-bearing layer (where the instability is) was from the SE at about 20 kts. Only thing really missing was more CAPE; computed CAPE was a paltry 150 J/kg. I’d like to see at least 800 J/kg for even the possibility of severe storms, and a much better value would be 1200-1500 J/kg.
Still some showers going on at this time across Southwest Arizona (see above), mainly due to outflow boundaries propagating through the very moist air. That activity should continue into the early morning hours. So you’ll probably wake up to some cloudy skies in Phoenix and maybe palm tree shards in your yard.
What will tomorrow bring? There are still some big thunderstorms going over Sonora MX. Remnant forcing from those will push NW into Southeast California and Southern Nevada, along with all the moisture in the boundary layer. Mid-level (500 mb) temperatures will also cool slightly. Combined this will push CAPE values up quite a bit in those areas so I’d expect an active day there thunderstorm-wise. For Central and Southeast Arizona, there is still quite a bit of dry and warm(er) air coming in from New Mexico which will keep CAPE values down and inhibit thunderstorm development (see below). The winds will still have a favorable easterly component. For Phoenix, I think we’ll see storms over the Rim and Southeast Arizona Sky Islands, but they’ll struggle again to make it into Phoenix. Isolated storms with gusty outflow winds in the evening and blowing dust (again).
Drier and warmer (not shown) air is moving clockwise around the mid-level anti-cyclone near the Four Corners, south through New Mexico and into Southeast Arizona. There is also another patch of dry air moving up the Rio Grande Valley. The very moist air will continue to push north along the Lower Colorado River Valley, well into Southern Nevada.
Like Sunday, the best instability will be west of a Phoenix-Tucson line
Chance of measurable rain (at least 0.01″). Note the doughnut hole where Phoenix is. This is actually very common, caused by several factors (topography being the biggest one).
