textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion

KEY MESSAGES

- Extreme heat will build over the region over the next couple of days and last through at least the weekend. Expect record to near record temperatures Friday through Sunday. - Extreme Heat Warnings are in effect areawide from today through Sunday. - Drier air over the region will confine any chances for showers and thunderstorms over far eastern Arizona high terrain through at least Sunday.

SHORT TERM /TODAY THROUGH FRIDAY/

The main forecast concern over the next several days will be the building extreme heat across the region as the subtropical ridge strengthens and shifts directly over Arizona starting Friday. H5 heights are forecast to rise from the current 592-594dm to 598-600dm later on Friday and last through Saturday. Guidance continues to indicate the strength of the ridge will reach climatological record levels across much of the Southwestern U.S. for Friday into Saturday.

Current objective analysis shows the ridge center over southeast New Mexico with south southwesterly flow across Arizona. IR imagery also shows extensive higher level clouds across Sonora from a decaying MCS and some of this moisture and clouds are expected to pass over southeast and south-central Arizona today. Drier air already infiltrated the region yesterday, especially in the lower levels where mixing ratios have dropped to around 9-10 g/kg in the Phoenix area to as low as 4-5 g/kg in southeast California. This drier air is helping to cool off nighttime temperatures across the western deserts where lows this morning may reach into the lower 80s, but higher boundary layer moisture in the Phoenix area will keep lows in the upper 80s to the lower 90s.

High temperatures today will easy top 110 degrees across the western deserts and potentially reaching 115 degrees in some spots. The scattered high clouds over central and eastern Arizona may help to keep temperatures right around 110 degrees in the Phoenix area, but the latest NBM forecast highs show 110-113 degrees as strong mixing is likely to quickly lower surface moisture. Just like the last couple of days, little if any convective activity is forecast for today with the only 10% or greater PoPs in the White Mtns and the Rim. Once the ridge center moves overhead on Friday, temperatures will climb another 2-3 degrees under generally sunny skies as highs should reach 115 degrees for the hottest lower desert locales. Would not surprising to even have some spots hit 117-118 degrees, but it seems more likely the hottest day will be Saturday. Extreme Heat Warnings go in effect later this morning across the entire CWA and last through the upcoming weekend.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Model ensembles have changed little from yesterday's runs showing the peak of the ridge and temperatures occurring on Saturday before the ridge weakens Sunday into Monday. NBM foreast highs have come down a degree or so from yesterday, but it is hard to find a good reason why. Forecast confidence remains high that some daily heat records are likely to be broken this weekend with southeast CA lower deserts reaching 115-120 degrees to 113-117 degrees across the Arizona lower deserts. To give some prospective, Phoenix has only reached 116 degrees or higher 18 times after July 30th, half of which occurred since 2023 and only reached 117 degrees or higher 6 times. The probability of KPHX hitting at least 116 degrees Friday-Sunday is 20%, 67%, and 35% respectively. For Saturday, the NBM also shows a 20-25% probability of tying the all-time hottest temperature in August of 118 degrees which occurred August 7, 2025. We will have some relief from the extreme heat at night, more so across the western deserts where lows should still dip into the mid to upper 80s. The bulk of the Phoenix metro should have lows only in a 90-95 degree range Friday-Sunday.

Any potential rain chances over the weekend are trending even lower with guidance mostly showing any decent moisture advection holding off until late Sunday into Monday. Some members still show some improved chances over the eastern Arizona high terrain convection as early as Sunday with potential for outflows into the Phoenix area Sunday evening, but it seems more likely that will not occur until Monday at the earliest. Guidance does agree on the ridge noticeably weakening by Monday with H5 heights dropping to 594-596dm, but the residual heat over the region may still keep extreme heat conditions through Monday. The ridge center should also begin to drift back to the northeast, closer to the Four Corners area by around next Tuesday. If and when this happens, it should open up portions of the region for better moisture advection out of the southeast. Monsoon storm chances are expected to gradually improve going into the middle of next week, while NBM forecast highs drop back to within a few degrees of normals.

AVIATION

Updated at 1052Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. Uncertainty is present again if KPHX will see an easterly shift this morning, most likely VRB winds, before returning back to westerly by 17-19Z. KIWA is expected to see an easterly shift while KDVT and KSDL will be light and VRB this morning before also shifting west yet again later in the morning through the afternoon. Wind speeds throughout the period will be mostly aob 10kts. FEW-SCT high cirrus clouds will be passing over the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period. Trends in winds should be very similar to the past 24 hours featuring a preference towards a southerly direction at KBLH and more southeasterly at KIPL after a period of VRB this morning. Speeds are expected to be mostly aob 10kts, and skies will remain mostly clear.

FIRE WEATHER

Strong high pressure will gradually build over the region through the rest of the week while increasingly dry air confines any rain chances to over far eastern Arizona. Expect humidities to continue to lower over the next couple of days with MinRHs settling at 10-15% by Friday, while falling overnight RHs offer only little to modest relief. Record to near record temperatures are also forecast for Friday and through the upcoming weekend. Winds will mostly follow diurnal patterns, but west southwesterly winds will be dominant much of the time with afternoon gusts of 15-20 mph at times.

CLIMATE

Record high temperatures:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Jul 31 116 in 2020 119 in 1957 119 in 2020 Aug 1 116 in 1972 117 in 1993 118 in 1993 Aug 2 114 in 2025 117 in 1918 117 in 1969 Aug 3 116 in 2024 116 in 1998 117 in 2021

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530-532-537- 540-542>544-546-548-550-551.

Extreme Heat Warning from 10 AM this morning to 8 PM MST Sunday for AZZ531-533>536-538-539-541-545-547-549-552>563.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ567-569-570.

Extreme Heat Warning from 10 AM this morning to 8 PM PDT Sunday for CAZ560>566-568.