textproduct: NWS Phoenix

KEY MESSAGES

- Isolated to scattered thunderstorms, some strong to possibly even 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/

Today could shape up to be another somewhat busy monsoon day, but unlike last Wednesday moisture and the amount of instability will be more limited. Atmospheric conditions at the moment are not very conducive for convection due to the limited moisture, but the upper levels are somewhat favorable for development. The subtropical high has shifted far enough to the east (eastern New Mexico/western Texas) to decrease the subsidence inversion. An upper level trough has also moved in along the West Coast placing much of our region within or near the more favorable right entrance region of a weak upper jet. So, despite the overall meager moisture currently in place, other atmospheric ingredients are more favorable and better moisture is expected to advect northward today potentially putting southern and central Arizona back in the game for monsoon storms.

Given the anticipated scenario for late this afternoon and evening, we are becoming more confident in our chances for isolated to scattered thunderstorms. Part of this confidence comes from the 06Z HRRR which shows storms developing north of Phoenix and over Pima County late this afternoon with both clusters sending outflows toward the Phoenix metro. With forecast MUCAPEs near 1000 J/kg and CIN falling to below 100 J/kg late this afternoon, any decent outflow collision seems likely to spark off additional storm development. The 06Z HRRR shows this exact progression with storms developing over or near the Phoenix metro early this evening. Additionally, since moisture will be more limited, DCAPEs will be very high (1700-2000 J/kg) supporting strong to locally severe wind gusts. Forecast PoPs have been raised into a 20-30% range, which better matches the latest high- res guidance.

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 0910Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concern will be the gusty outflows and potential for reduced visibilities and thunderstorms. Until then easterly winds will continue through the overnight and morning hours shifting out of the west near 19-20Z this afternoon. Another round of activity is expected to develop to the northeastern high terrain and in southern parts of AZ this afternoon and evening. Outflow boundaries will likely develop and push into the metro from the NE and S. KPHX and KIWA will likely be affected by the southern outflow between 04-07Z, while models show KSDL and KDVT affected by the northeastern outflow a little earlier, near 01-05Z tonight. This is reflected in the most recent TAF package but is subject to change in future packages depending on how models handle each outflow accordingly. Chances for direct TS impacts this evening remain at up to 30% chance but enough uncertainty remains that no PROB30 was introduced at this point in time. FEW- SCT mid/high cloud decks will be common throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected through the TAF period. KIPL will maintain west winds through the overnight period then going SE'rly by 15Z. TS activity over the Baja spine may send an southwesterly outflow into KIPL by the late afternoon hours, with a less than 20% chance for direct TS impacts. KBLH will swing between south to SW'rly winds, favoring the SW. Otherwise FEW-SCT mid to high cloud decks will be common through the period.

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.