textproduct: NWS Phoenix

UPDATE...Updated 00z Aviation Discussion

KEY MESSAGES

- Extreme heat will persist through the end of the workweek with increasing moisture pushing heat indices to around 110 to 115 degrees for the latter half of the week.

- Shower and thunderstorm chances will favor eastern and southeastern Arizona today with a low chance for a few isolated storms to develop this evening across south-central Arizona. Strong winds and blowing dust will be the primary concerns.

- Day to day mostly eastern Arizona high terrain storm chances are expected through the rest of the week with hot and humid conditions persisting.

SHORT TERM /TODAY THROUGH TUESDAY/

Extreme heat continues across the region as a strong ridge of high pressure remains in place. This morning, Phoenix Sky Harbor recorded a low temperature of only 97 degrees, which ties for the all-time record warm low for Phoenix provided we don't see temperatures cool below this prior to midnight tonight. The persistent strong ridge will yield afternoon highs of 112-116 degrees today, resulting in fairly widespread Major HeatRisk across the region with Extreme HeatRisk focused across the Phoenix metro area. The weakening trend of the ridge will allow for afternoon high temperatures to trend downward over the next couple of days. Temperatures Tuesday afternoon are forecast to top out around 108-113 degrees across the lower deserts and will result in localized areas of Major HeatRisk. Extreme Heat Warnings remain in effect Tuesday for our entire area, with the exception of our higher terrain areas east of Phoenix, and have now been extended through Friday evening (see Long Term discussion for details).

Monsoonal activity across south-central Arizona over the next couple of days is expected to remain limited, though the forecast remains conditional and uncertain. An active day is expected across southeast Arizona where strong to severe thunderstorms are expected to develop this afternoon in an environment favorable for producing strong outflows. East-northeasterly steering flow will keep most of this activity confined to the south of our area, while a few showers and storms may move into far eastern Gila County this afternoon. Despite the monsoonal activity across southeast Arizona remaining focused south of our area, CAMs continue to support strong outflows moving up from the south toward the Valley this evening. Given this, areas of dense blowing dust may occur this evening, particularly across Pinal County. The forecast then becomes more conditional and uncertain in regards to whether or not we see new thunderstorm development occur across south-central Arizona. The HRRR remains consistently optimistic, suggesting the potential for colliding outflows over the Valley this evening to trigger new shower and thunderstorm development. While CAPE values are expected to be around 1,000 J/kg, there will be a fair amount of inhibition that will need to be overcome, thus yielding an uncertain forecast around whether or not outflows this evening will be enough to punch through this. With DCAPE values in excess of 1,500 J/kg, any storms that were to develop would be capable of producing strong wind gusts.

Thunderstorm activity Tuesday will again be focused across eastern and southeastern Arizona with easterly steering flow keeping this activity focused south of our area. A few isolated showers and storms may push into southern Gila County Tuesday afternoon with PoPs currently around 20%. Hi-res guidance support thunderstorms across southeast Arizona sending an outflow northward into our area, which could lead to dense blowing dust concerns. However, chances for new convective development into south-central Arizona Tuesday evening is low.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Hot and humid (at least for this region) conditions are forecast for the latter half of the week as the subtropical ridge will strengthen once again with peak H5 heights likely reaching 597-599dm over northern Arizona, southern Nevada, and southern Utah. The strength looks to be just shy of what just occurred this past weekend, but guidance shows the ridge center to our north instead of directly over central Arizona.

Afternoon temperatures Wednesday are forecast to drop into the 107-111 degree range across the lower deserts, resulting in very localized coverage of Major HeatRisk. However, we will see increasing moisture into the region as dew points surge into the 60s to as high as the lower/mid 70s across far southwest Arizona and southeast California. The increased moisture will lead to heat indices upwards of 110-115 degrees with higher values possible across portions of southeast California. Beyond Wednesday, a resurgence of the ridge is expected to begin to raise temperatures again with highs drifting 2-3 degrees higher by Friday. Given the restrengthening of the ridge later this week along with higher heat indices expected through much of the latter half of the week, the Extreme Heat Warning has been extended through Friday evening for most of the area.

Monsoon storm potential for the rest of the week looks to be fairly low to at most mid grade with 20-40% chances most days over the eastern Arizona high terrain to 10-20% into the Arizona lower deserts. There are some hints at a potential increase in convective activity maybe by the weekend into early next week, but we do not put much faith in the long range models for monsoon activity. Although, as long as the high center ends up staying positioned far enough to our north, it at least seems quite plausible any minor easterly wave could march on through providing enhanced chances at some point.

AVIATION

Updated at 2325Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: A southerly outflow producing gusty winds and blowing dust this evening are the main aviation weather issues throughout the TAF period. In the meantime, westerly winds with occasional elevated gusts upwards of 20-25 kts will continue through early this evening. Thereafter, indications are that a potentially robust southerly outflow emanating from convective activity across SE AZ is likely to make its way into the terminals after 03-04z. Uncertainty is high with respect to how strong the winds will become as this outflow moves through as everything is conditional to the intensity and overall coverage of the convective activity across SE AZ, however, potential is there for gusts in excess of 30-35 kts along with areas of blowing dust reducing visibilities to MVFR conditions. In terms of any shower/thunderstorm activity developing along the outflow, probability of occurrence continues to remain low at less than 20%. Wind speeds will weaken after 06z with an easterly direction becoming more favored, however, directions could become more variable. Heading into Tuesday, westerly winds will develop by the mid to late morning hours with occasional afternoon peak gusts once again between 20-25 kts. FEW- SCT mid to high level clouds with bases as low as 10 kft will be common throughout the TAF period, with the greater cloud coverage expected this evening with the outflow passage.

Southeast California/Southwest Arizona including KIPL and KBLH: Gusty southerly winds, especially at KBLH, will be the main aviation weather issue throughout the TAF period under mostly clear skies. Winds will generally be out of the southeast at KIPL and out of the south at KBLH. At KBLH, winds will generally range between 20-25 kts through tonight, occasionally higher, before speeds subside early Tuesday morning. Another period of elevated gusts between 20-25 kts will be common once again for Tuesday afternoon. The gusty winds may generate localized areas of dust streamers and widespread lofted dust, resulting in slantwise visibility issues. Wind speeds at KIPL will be significantly weaker, generally ranging between 8-12 kts.

FIRE WEATHER

Hot temperatures will continue all week, but with increasing low level moisture and improving humidities over the next couple of days. Shower and storm potential will favor eastern and southeastern Arizona over the next couple of days, while rain chances remain lower across south-central Arizona. Storms across eastern and southeastern Arizona may send strong outflows toward the Phoenix metro area over the next couple of evenings, which could spark a few isolated showers and storms. Min RHs will continue to improve, climbing to around 20-30% by Wednesday, while overnight recoveries range between 40-70%. 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. Similar low-grade monsoon storm conditions are expected through the rest of the week with humidities staying fairly elevated and temperatures above normal.

CLIMATE

Record high temperatures:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 3 116 in 2024 116 in 1998 117 in 2021

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530>544-546- 548>551-553>555-559.

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

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ560>570.