textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Isolated to scattered thunderstorms, some strong to severe, are expected this evening across south-central Arizona.

- Increasingly less favorable conditions for thunderstorms will develop starting Monday with virtually no chances for rain from Tuesday through the rest of the week.

- High temperatures will reach or exceed 110 degrees nearly every day this week and will be near daily records, while morning lows remain unusually warm.

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

SHORT TERM /TODAY THROUGH MONDAY/

Some upper level jet support and mid-level gravity waves helped spark off a line of high-based scattered showers and storms across southwest AZ this morning. This activity has since weakened and dissipated. Surface-based moisture has also increased across southwest AZ and areas south of I-8. Dew point temperatures at midday in Yuma County to western Pima County were up to 65-75 degrees. This moisture return in southern AZ will likely help fuel later afternoon and evening thunderstorms. Overall, model guidance still suggests this afternoon through this evening becoming a somewhat busy monsoon period.

Outside of southern AZ, where the best moisture return was, boundary layer conditions remain similar to the past couple of days with sub-optimal moisture (mixing ratios around 8 g/kg) and limited instability (few hundred J/kg MLCAPE). Initially through much of, if not all of, this afternoon storms should favor higher terrain areas, including portions of La Paz County, and it may even look like it will not become active at all. However, hi-res guidance continues to show the best time period for activity across south-central AZ coming around and after sunset. Guidance shows storms being a bit slower to develop in Pima County, but when they do they do they will have the best potential to become strong to severe, tapping into the best moisture and instability. The storms to the south this evening will then be capable of pushing one or multiple strong and dusty outflows northward into south-central AZ, which may then trigger additional storms. Some hi-res model runs also suggest outflow collisions may occur, with outflows also from the north, but confidence in outflows coming down from northern AZ is low. Additionally, there are indications the storms to the south may develop into an MCV and track northward through Phoenix this evening. Strong to locally severe wind gusts will be the primary weather hazards, with very high DCAPE values up to 1800-2000 J/kg. Localized flash flooding may also become a threat with any slow-moving storms or training of storms, with the best potential southwest of Phoenix where moisture will be highest.

Convective chances for Monday are even more uncertain as guidance generally shows at most a 10% chance despite moisture and instability being better than today. However, subsidence will be much stronger on Monday as the subtropical ridge begins to move westward back into our region. We will have to wait until tonight to have a better idea on the storm potential for Monday, but it does seem to be considerably lower than this afternoon/evening.

Temperatures today will again be right near record highs with lower desert readings from 110-115 degrees. The increased boundary layer moisture expected for Monday should hold daytime highs down a bit with NBM forecast highs currently between 106-111 degrees, but heat indices will mostly match what are expected today.

LONG TERM /TUESDAY THROUGH SATURDAY/

Forecast attention turns away from monsoon storm potential and back toward the extreme heat conditions starting Tuesday. The subtropical high center will continue to shift westward into our region into the middle part of the week with the center likely settling somewhere over southern Arizona from Wednesday through at least Friday or Saturday. Forecast H5 heights are also shown to reach 594-597dm for the latter half of the week which places it just shy of climatological records for late August. NBM temperature guidance remains quite consistent showing highs rising into a 112-116 degree range for the latter half of this week as conditions dry out. Daily temperature records in Phoenix will continue to be in jeopardy through the entire week, but are likely to fall short in Yuma and El Centro. Once the high center moves overhead by Wednesday, rain chances will essentially go to 5% or less. As of now, conditions for any monsoon storm activity do not look good through next weekend.

AVIATION

Updated at 0550Z.

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

Gusty winds and SHRA/TSRA activity in the vicinity during the next couple of hours will be the main aviation weather concern throughout the TAF period. SHRA/TSRA activity, with the greatest concentration to the southwest of the terminals will continue through 07Z, with VCSH lingering a bit longer into the overnight period. Wind directions through at least the first part of the overnight will continue to remain erratic due to convective activity nearby before becoming light and variable to light easterly by sunrise through early Monday morning before shifting out of the west by the late morning hours. Much quieter conditions are expected on Monday with no threat of outflows/thunderstorms. SCT-BKN mid to high clouds will continue through the overnight period before coverage decreases to FEW-SCT during the day Monday.

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 temperatures will prevail through the entire week with shower thunderstorm chances mainly today and possibly Monday. Strong gusty winds will be possible late this afternoon and evening with any thunderstorms, while chances for wetting rains will remain below 20%. Minimum RHs will improve through Monday with readings of 15-25% today and 20-30% Monday, before dropping back into the teens into the middle part of the week. Temperatures will be around 5-10 degrees above normal, with lower desert highs eclipsing 110 degrees nearly every afternoon. Outside of thunderstorm outflow winds, winds will follow the typical diurnal tendencies with some modest afternoon upslope gustiness.

CLIMATE

Record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 23 114 in 2011 115 in 2011 116 in 1969 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.