textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Extreme heat will persist through the start of the week with high temperatures topping out in the 110 to 118 degree range over much of the lower deserts, hovering right around record levels.

- Extreme Heat Warnings are in effect regionwide through Tuesday.

- High pressure and drier air over the region will confine showers and thunderstorms primarily to far eastern and southeastern Arizona areas through at least Monday.

- Shower and thunderstorm chances increase across south-central Arizona by the second half of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

A strong ridge of high pressure remains situated over the Desert Southwest and continues to promote well above normal temperatures across the region this afternoon. This morning's 12Z PHX and 18Z FGZ soundings sampled a 500 mb height of 598 dm; though the ridge remains quite strong, a weakening trend is underway as a trough passes through the Pacific NW/BC/Alberta. By tomorrow, 500 mb heights will lower to around 594-595 dm, which is still above the 90th climatological percentile. Afternoon temperatures Monday are forecast to see a ~2-4 degree drop from today with highs topping out between 111-116 degrees for most lower desert locations. Morning lows will also remain quite warm, offering limited relief from the heat as temperatures only fall into the mid/upper 80s to low 90s. As a result, Major to Extreme HeatRisk will be in place across many lower desert locales Monday, though seeing a notable decrease from the widespread coverage in place today. Afternoon temperatures Tuesday will see another ~2-4 degree drop, however, guidance continue to favor increasing boundary layer moisture heading into the middle part of the week, which will make for more humid conditions. This added moisture will push heat indices upwards of 112-118 degrees, particularly across southeast California and southwest Arizona. Extreme Heat Warnings remain in effect for much of the area through Tuesday evening.

Monsoonal activity is expected to remain limited across our area through the start of the new workweek with limited moisture and strong high pressure promoting subsidence. For today, storms will again favor far eastern and southeastern Arizona. Strong outflows emanating from these storms are expected to push into southern Gila County and may be enough to pop off a few isolated showers and storms. Any new storm development that were to occur would be capable of producing strong, erratic winds. Storm activity will continue to primarily favor eastern and southeastern portions of the state as northeasterly steering flow keeps much of this activity outside of our CWA. Monday looks to be a particularly active day for southeast AZ, with favorable shear and instability for some organized storm clusters. Given high DCAPE magnitudes (>1500 J/kg), the storms in southeast AZ Monday will be capable of sending outflows, potentially strong and with dust, westward and northward through Pinal County. These outflows and a gulf surge Monday night will be the driver of the increase in moisture heading into Tuesday. While this sounds promising for storm chances across the lower deserts heading into Tuesday, with much better instability, subsidence, persistent very warm temperatures aloft, and fairly high inhibition will continue to counter/hinder convective potential. Thus, NBM PoPs remain low for our area, with the best chances residing across far southern and eastern Gila County where chances climb to 20-30% by Tuesday.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

After weakening slightly to start the weak, global ensembles support the subtropical high restrengthening during the second half of the week, back up to a 600dam high, but also drifting a little further north toward/into UT. H5 heights over the local area are forecast to climb back up to a peak of around 596-597dam by Friday. Coolest temperatures over the next week are forecast for Wednesday, but temperatures will still be above normal with lower desert highs in the 106-112 degree range. Despite the restrengthening of the high, high temperatures are not forecast to see a significant increase again, roughly 1 degree each day through Saturday, likely due to the the increased moisture. However, the forecast calls for just enough warming to once again increase the coverage of Major HeatRisk. Morning low temperatures will likely remain quite warm - barring any cooling from storms - mostly in the 80s to right around 90 degrees.

With the small movements of the subtropical high midweek and shift north late week, there will be a better fetch of easterly winds across southern New Mexico, southern Arizona, and northern Mexico. Above normal moisture is also shown to stick around through the end of the week and next weekend, with 60s dew points. This pattern will at least support daily robust thunderstorms developing over the AZ high terrain, but there is still uncertainty whether storms can fire off or survive into lower desert areas like Phoenix and points further west. Still, this looks like the best chance of the summer so far for thunderstorms in portions of southwest AZ and southeast CA, who have been lacking for rain so far this summer. Latest NBM/WPC forecast continues to show 10-30% PoPs across much of south-central Arizona by Thursday and continuing through the end of the week. A period of stronger mid-level easterlies and perhaps and easterly wave/IT will certainly improve the odds of storm chances across the area Strong to severe wind gusts will be possible with most storms and an increase in mixing ratios up to 11-12 g/kg late week will support very heavy rainfall.

AVIATION

Updated at 0623Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The primary aviation weather concern and potential impact will be strong thunderstorm outflow winds moving through the Phoenix area late Monday evening from the south. There is moderate to high confidence that an outflow will move through at some point in the evening, currently favored between 03-06Z, but there is uncertainty on how strong winds will be. There is model support for gusts as high as 35-40 kts and winds of this magnitude may also bring a wall of dust into the area, enough to reduce visibility to 5SM or less. Storms are expected to stay well east and south of the area, but there is still a 5-10% something pops up or drifts into the metro.

Ahead of Monday evening's outflow, winds will continue to follow typical diurnal tendencies, with some gusty (20-25 kt) westerly winds in the afternoon. There is also a low chance for a few spotty high based showers around daybreak. Mid and high clouds will be common through the TAF period, with bases dropping down to around 10K ft AGL Monday evening.

Southeast California/Southwest Arizona including KIPL and KBLH: Gusty southerly winds, primarily at KBLH Monday afternoon, will be the main aviation weather issue throughout the TAF period under mostly clear skies. At KIPL, winds will generally be out of the southeast following a period of southwest tonight. At KBLH, winds will generally fluctuate out of the south to south-southwest. Overall wind speeds will fluctuate between 8-13 kts, with gusts near 20-25 kts in the afternoon at KBLH that increase further in the evening upwards of 25-30 kts. Localized dust streamers and widespread lofted dust may be generated by the winds Monday night, which may impact slantwise visibility.

FIRE WEATHER

Strong high pressure and very hot temperatures, with dry conditions, will persist into the start of the new workweek. Afternoon high temperatures will range between 110-115 degrees for many lower elevation locations over the next couple of days. Min RHs will gradually improve with values ranging between 15-20% Monday before climbing to around 20-25% Tuesday. Overnight Max RHs will also improve, rising from 35-50% overnight tonight to 50-70% Tuesday morning. The increasing moisture will result in an increase in shower and storm chances. Initially, storm chances this weekend through the start of the week will focus in far eastern and southeastern AZ, with potential for storm outflow winds to progress into south-central AZ. Slight chances for storms (15-30%) then spread to south-central AZ by the middle and second half of the week. Outside of storm outflows, winds will mostly follow diurnal patterns, but west southwesterly winds will be dominant much of the time with afternoon gusts of 15-25 mph at times.

CLIMATE

Record high temperatures:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 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 Tuesday for AZZ530>544-546- 548>551-553>555-559.

Extreme Heat Warning until 8 PM MST Monday for AZZ545-547-552- 556>558-560>563.

CA...Extreme Heat Warning until 8 PM PDT Tuesday for CAZ562-563- 565>567-569-570.

Extreme Heat Warning until 8 PM PDT Monday for CAZ560-561-564- 568.