DISCUSSION
Subtropical high pressure over the SW Conus continues to weaken and shift south in response to anomalous troughing and jet energy punching into the central/southern California coast. A 594dm anti- cyclone center was analyzed over far SW Arizona early this afternoon, and excellent forecast confidence exists that this feature will deteriorate further through the weekend eventually reaching 591dm and shifting into northern Sonora. WV satellite imagery already depicts substantial midtropospheric drying entering the region which has resulted in eroding moisture towards the top of the boundary layer. Although near surface moisture will be less apt to erode, additional drying aloft and growing convective inhibition through at least early next week will result in dwindling thunderstorm chances, albeit not entirely precluding the threat for isolated activity and gusty outflow winds at times.

Morning KPSR and KTWC 12Z sounding data sampled a nearly classic convectively overturned environment along with the introduction of reduced 8-9 g/kg mixing ratios in the H8-H7 layer. Not surprisingly given this type of sounding, midday sfc temperatures have been slow to respond yielding limited MLCape under larger CinH profiles across lower elevations. While the preponderance of HRRR membership convincingly shows scattered deep convection continuing to develop across the Rim and Whites with moist upslope flow into this evening, more limited DCape may limit stronger outflow potential likely incapable of dislodging convective potential over lower elevations.
This does not completely precluding showers and storms over lower elevations, however the better opportunity may actually arrive late night in the form of midlevel accas showers in association with a shortwave descending south from the four corners interacting with residual moisture and steep lapse rates.

As the ridge retreats into Sonora through the weekend, temperatures will cool slightly, however still remain a couple degrees above normal with nearly steady readings through the first half of next week. Shower/storm chances will also continue to diminish substantially during the first half of next week as westerly midtropospheric drying becomes even more pronounced, and even the more preferred areas of Gila County only justify modest POPs. Thus, there is good forecast confidence of an extended period of more quiet weather over the entire region through at least the middle of the week.

During the latter half of the week, ensembles are in excellent agreement of the southern plains subtropical ridging retrograding back into the four corner while rapidly intensifying above 596dm (with a handful of members suggesting a 600dm high pressure center).
In conjunction with an inverted trough ejecting north into southern California, this pattern would bring the region back into the more traditional SE deep layer monsoon flow. However, there is extremely large uncertainty regarding the availability of better quality moisture return with this transition as models indicate boundary layer mixing ratios holding 8 g/kg or less into the end of the week essentially precluding more than outflow boundaries into lower elevations. Even official NBM output seems to be identifying this contingency with abnormally low POPs for the beginning of August.
Eventually with such a flow pattern, deep moisture profile will return though it may not be until next weekend before better thunderstorm chances come to fruition.

AVIATION
Updated at 1728Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concern through tonight will be the potential for gusty northerly outflow winds early to mid evening. In the meantime, expect winds turning westerly through around noon with higher terrain showers and storms developing mid to late afternoon. The convective potential today will be considerably less than yesterday with only around a 10-20% chance of showers or an isolated thunderstorm mainly in northern parts of Phoenix this evening.
Chances for outflow winds anywhere from the northeast to the northwest look fairly good early this evening with gusts between 20- 30kt possible. Winds should eventually drift back to the east after midnight with a chance of another modest outflow boundary coming from the southeast.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns will exist through the forecast period with just a few passing high clouds expected. Winds at KIPL will generally favor southeast this afternoon and then southwest starting this evening, while KBLH will predominantly see southerly winds.



FIRE WEATHER
Thunderstorm chances should remain confined primarily to the higher terrain areas of eastern districts through the beginning and middle of next week. Even over these locations, storm coverage and chances for wetting rainfall will be much less than experienced the past week. Aside from any thunderstorm outflows, winds will follow typical upslope/downvalley patterns with intermittent afternoon gusts in the 15-20 mph range. Minimum humidity values will trend somewhat lower through early next week with lower elevations falling into the teens while eastern district higher terrain near 25%. This will follow widely varying overnight recovery ranging from poor 20% in western districts to fair to good 40-60% in eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...Excessive Heat Warning until 8 PM MST this evening for AZZ530- 532.

CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ560>570.