textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Temperatures will increase significantly the remainder of the week with Extreme Heat Warnings in effect as readings approach near record levels.

- High pressure responsible for the extreme heat will also restrict thunderstorm development with chances retreating well into the mountains through the weekend.

- Above normal temperatures may begin to relax early next week as better thunderstorm coverage returns to the region.

SHORT TERM /Today through Friday/

Early afternoon satellite WV imagery showed a weak cyclonic circulation centered over southern Utah, aiding in thunderstorm development around the Four Corners region. Further to the south across south-central Arizona, drier conditions are beginning to settle in with PWATs dropping to around 1.5-1.8" according to the latest mesoanalysis. Given the drier, more stable atmosphere, thunderstorm activity will be limited in coverage today and primarily confined to the higher terrain/orographic features east of Phoenix. NBM PoPs are highest across southern Gila County (~20%) this afternoon, quickly dropping below 10% across the lower elevations, before all areas see chances fall below 10% Thursday.

The larger weather hazard over the next several days will be building heat as strong subtropical ridging retrogrades back into the SW Conus. Ensemble members are in excellent agreement depicting the central anti-cyclone becoming established over western New Mexico by Friday with H5 heights settling near 597-598dm. Surprisingly given the agreement among the entire ensemble suite, numerical spread is fairly wide likely owing to differences in boundary layer moisture content across the CWA. Given the current low level dewpoint status in south-central Arizona and lack of strong flow throughout the troposphere, it's more likely modest moisture lingers and some of the more extreme forecasts above the 75th percentile will not come to fruition. However across the western CWA where moisture is not as plentiful, upper end readings above 115F will be more likely. Regardless, widespread major HeatRisk (and local extreme HeatRisk) with afternoon highs 5F-10F above normal will become common, and an Extreme Heat Warning continues.

LONG TERM /Saturday through Tuesday/

Strong high pressure will continue to be the dominant synoptic feature through early next week with H5 heights 596-598dm sprawling across the forecast area. Unsurprisingly given this pattern, widespread major HeatRisk will continue with clear cut warning criteria persisting through the weekend as temperatures hover 5F-10F above normal. The preponderance of ensemble output suggests the center of the subtropical anti-cylcone slowly lifting through the four corners and into Colorado during the first part of next week allowing easterly flow, subtle shortwaves, and stronger, moist outflows to return to Arizona. Easterly wave energy will also help erode some of the higher midlevel heights and temperatures while also aiding the displacement of the anti-cyclone center. These combined efforts should allow local H5 heights to fall below 594dm though the timing at which this evolution occurs is somewhat uncertain. Among GEFS members, there is fairly convincing evidence of enhanced convection Sunday allowing deeper outflow intrusions while H5 heights fall below 594dm reducing or eliminating the extreme heat threat Monday. EPS members are more suggestive of better convective potential delayed until Monday evening, but regardless temperatures should return to near normal levels by the middle of next week with the diurnal thunderstorm risks also returning to the region.

AVIATION

Updated at 0500Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are expected throughout the TAF period. The overall wind pattern will continue to favor light and diurnal tendencies along with extended periods of variable conditions. FEW to occasionally SCT mid to high level cloud decks with bases as low as 10 kft will be common throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under a FEW mid to high level cloud decks are expected throughout the TAF period. The overall wind pattern will favor light and diurnal tendencies along with extended periods of variable conditions.

FIRE WEATHER

Thunderstorm chances will dwindle the remainder of the week with only slight chances remaining over high terrain areas of far eastern districts. Instead, temperatures will warm significantly with much above normal readings and Extreme Heat Warnings. Despite the warmer, drier conditions, humidity levels will not fall substantially with minimum afternoon readings 15-30% the next couple days falling closer to a 10-25% range over the weekend. Correspondingly, overnight recovery will mostly stay in a fair to good range of 30- 60%. Winds should be fairly light through the period with only local afternoon gusts 20-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Monday for AZZ530-532.

Extreme Heat Warning from 10 AM Thursday to 8 PM MST Monday for AZZ531-533>555-559.

CA...Extreme Heat Warning until 8 PM PDT Monday for CAZ562>570.

Extreme Heat Warning from 10 AM Thursday to 8 PM PDT Monday for CAZ560-561.