textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion

KEY MESSAGES

- Extreme Heat Warnings remain in effect through Saturday with daily Major to Extreme HeatRisk.

- High temperatures will reach or exceed 110 degrees nearly every day this week, peaking right around daily records Tuesday through Thursday. - Monsoon storm chances for the upcoming workweek will be very limited with chances briefly coming to an end starting Tuesday before slowly returning by next weekend.

SHORT TERM /TODAY THROUGH THURSDAY/

Early morning lingering showers and a few thunderstorms will gradually diminish by sunrise leaving a somewhat overturned atmosphere and slightly cooler temperatures across much of southern and central Arizona. The subtropical high, which is currently centered along the New Mexico/Texas border, is set to shift westward today into Tuesday with the center reaching western New Mexico on Tuesday. Drier air is already starting to move in from the south and this will continue through at least Tuesday, dropping low level mixing ratios to between 6-8 g/kg. This drier air in combination with increasing subsidence from the ridge will basically end rain chances beginning Tuesday. For today however, there should still be enough lingering moisture and not too high of CIN for a few isolated showers or weak storms across higher terrain areas across Arizona and southeast California. Rain chances should then fall to below 10% starting Tuesday and likely stay that way through Thursday with the ridge eventually moving directly over southeast Arizona and southwest New Mexico.

The main forecast concern for the rest of the week will be the late August extreme heat. Extreme Heat Warnings remain in effect for the majority of the area through Saturday with expectations of some expansion of the warning into higher terrain locations for the latter half of the week. The slightly rain-cooled air should keep daytime highs today mostly in a 106-110 degree range, but that will quickly change beginning Tuesday. The drying conditions and increasing heights for the middle part of the week are expected to push daytime highs well above 110 degrees. The latest NBM temperatures have trended downward over the past couple of days of runs, but with the NBM's recent track record of under doing temperatures, we have bumped highs up a degree or two. Daytime highs are likely to reach 112-116 degrees Tuesday through Thursday, potentially tying or breaking a few daily records. Very warm overnight lows are also forecast, eventually leading to fairly widespread Extreme HeatRisk by Wednesday.

LONG TERM /FRIDAY THROUGH SUNDAY/

Ensemble guidance favors some weakening of the subtropical high starting Friday as it starts to shift back to the east. This shift assumes a Pacific trough moving into the Northwestern U.S. late week. Models also favor some gradual moisture advection by Friday and lasting through the upcoming weekend. Given the expected increase in moisture and weakening subsidence, rain chances should return as early as Friday but more likely over the weekend. NBM/WPC PoPs show 10-15% chances over high terrain areas Friday and Saturday before increasing and expanding into the lower deserts by Sunday. These PoPs may be underdone somewhat considering what the latest models runs show, so we anticipate higher PoPs soon from the NBM. Temperatures should also begin to improve late week and through the weekend as moisture increases and heights gradually lower. The latest forecast highs still maintain or even top 110 degrees through Saturday before dropping to below 110 degrees by Sunday or Monday of next week.

AVIATION

Updated at 1045Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No major aviation concerns are expected through this TAF period. The storms that brought gusty winds, thunderstorms and reduced visibilities last night have moved away from the terminals are is now expected to go back to mostly diurnal tendencies with periods of VRB and an early westerly shift by 18Z this morning. Winds will generally be aob 10kts, however some elevated wind speeds with gusts in the low-mid teens will be possible later this afternoon/evening. FEW- SCT high cloud decks will be common throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns under FEW-SCT mid/high cloud decks can be expected throughout the TAF period. Winds will generally be out of the southeast at KIPL and will fluctuate between the south- southeast to southwest at KBLH. Overall wind speeds will range between 8-15 kts, highest at KBLH.

FIRE WEATHER

Hot and seasonally dry conditions will prevail for much if not all of the coming week. Strong high pressure will settle over the region by midweek with gradual drying conditions. Minimum RHs today will mostly fall between 20-30%, before dropping back into the teens starting Tuesday. Temperatures will be around 5-10 degrees above normal, with lower desert highs eclipsing 110 degrees nearly every afternoon. Expect overall light winds following typical diurnal tendencies with some modest afternoon upslope gustiness.

CLIMATE

Record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 24 115 in 2020 119 in 1985 117 in 1985 Aug 25 113 in 2011 116 in 1962 117 in 1962 Aug 26 117 in 2011 115 in 2020 115 in 1981 Aug 27 114 in 2023 120 in 1981 117 in 1981 Aug 28 117 in 2023 118 in 2023 117 in 2009 Aug 29 116 in 2023 117 in 1954 117 in 2005

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Saturday for AZZ530>555-559- 560.

CA...Extreme Heat Warning until 8 PM PDT Saturday for CAZ562-565>567- 569-570.