textproduct: NWS Phoenix

KEY MESSAGES

- Extreme Heat Warnings remain in effect through Saturday across much of the area.

- Lower desert highs in excess of 110 degrees and overnight lows in the eighties to lower nineties will be common this week, resulting in Major to Extreme Heat Risk.

- Monsoon storm chances will be very limited before a pattern change occurs this weekend, which will result in an increase in moisture and promote temperatures dropping closer to late August normals by Sunday or early next week.

SHORT TERM /TODAY THROUGH THURSDAY/

The subtropical ridge can been seen positioned along the AZ/NM boarder advecting drier air into the lower deserts. The drier conditions will to last through the end of the week, with forecasted PWATs expected to fall near 1" in south central AZ and even below 1" in the eastern high terrain by Wednesday. This is accompanied by forecasted mixing ratios also falling to around 6-8 g/kg. However, some isolated, terrain-anchored thunderstorms may develop each afternoon for the next few days before a pattern change occurs heading into this weekend, drawing in better moisture from over Sonora/the Gulf of California.

The more note worthy condition for this week will be the heat. H5 heights will peak Wednesday-Thursday with heights ranging between 595- 598 dam, or above the 99th percentile of climatology. Many areas across the lower deserts will be flirting with record high temperatures, with Phoenix showing around a 50% chance of at least tying the record, and a 20% chance of surpassing the record high of 117F set in 2011 on Wednesday. Then on Thursday Phoenix has about another 50% chance of tying and a 30% chance of surpassing the record of 114F set in 2023. Needless to say this week is going to be hot with the lower deserts region ranging between 112F-118F, and very little relief with the overnight lows remaining in the upper 80s to lower 90s. Widespread Major to Extreme HeatRisk will continue through the end of the week, as a result the Extreme Heat Warning will also remain in effect through the end of the week and even into the weekend. Ensure to stay hydrated and follow heat safety tips.

LONG TERM /FRIDAY THROUGH TUESDAY/

The subtropical ridge is still expected to weaken and shift back eastwards by Friday according to ensembles. This is due to a troughing pattern pushing into the NW CONUS and along the West Coast. As the trough pushes eastward, PWATs will begin to improve, reaching near 1.5"-1.7" by Saturday and lasting through at least the weekend. Mixing ratios will also significantly improve going from mid week's 6-8 g/kg to 10-12 g/kg by this weekend, generating better support for storm formation in the lower deserts. With that being said NBM/WPC continue to show PoPs over the weekend between 20-35% across South-Central AZ, and now even up to 50% in the eastern high terrain. WIth these PoPs the NBM/WPC QPE totals over the weekend are forecasted between 0.10"-0.25" to locally higher in the higher terrain areas. Continued monitoring of this system will be needed but models continue to show support for activity developing this weekend. In other good news, temperatures are forecast to drop closer to late August normals by Sunday and into early next week as falling midlevel heights and an increase in moisture/cloud cover over the eastern CWA support a cooling trend (more pronounced across South-Central AZ).

AVIATION

Updated at 0510Z.

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

No major aviation weather concerns under FEW-SCT mid/high cloud decks can be expected throughout the TAF period. The overall wind pattern will continue to exhibit the typical diurnal tendencies with the easterly wind shift at KPHX likely around 12z. Heading into early Wednesday evening, wind directions become highly uncertain as there are indications from guidance of potentially a couple of outflows from storm activity north and east of Phoenix and across southeast AZ impacting the terminals with one outflow from the northeast and another from the southeast. Confidence is low of these outflows materializing and surviving into the Phoenix area and thus have not been included in the latest TAF package.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation weather concerns under FEW-SCT mid/high cloud decks can be expected throughout the TAF period. Winds will mostly oscillate between the southeast and west with overall speeds ranging between 7-12 kts. An extended period of light and variable winds will be common Wednesday morning.

FIRE WEATHER

Hot and seasonally dry conditions will prevail for much of the rest of the week. Strong high pressure will settle over the region starting today with dry conditions continuing throughout the workweek. Afternoon minimum humidities will mostly fall into the teens through the rest of the week before improving back above 20% this weekend, except the western CA districts. Temperatures will be around 5-10 degrees above normal, with lower desert highs eclipsing 110 degrees nearly every afternoon through at least Friday. Outside of distant thunderstorm outflows, expect overall light winds (below 15 mph) following typical diurnal tendencies with some modest afternoon upslope gustiness.

CLIMATE

Record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 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.

Extreme Heat Warning until 8 PM MST Friday for AZZ556-561-562.

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

Extreme Heat Warning until 8 PM PDT Friday for CAZ561-563-564- 568.