textproduct: NWS Phoenix

KEY MESSAGES.

- As high pressure builds over the region through the upcoming week, temperatures will heat up several degrees above normal levels as lower desert highs climb above 110 degrees.

- Extreme Heat Warnings will be in effect throughout the week as widespread Major HeatRisk materializes.

- Thunderstorm activity through the majority of the upcoming week will be mostly confined to the Arizona High Terrain and southeast Arizona.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest objective analysis continues to indicate southwest flow aloft entrenched across much of the Desert Southwest as general trofiness persists to the northwest while the subtropical high is positioned near the south-central states. The southwest flow will continue to advect drier air into the region. Thus, mainly quiet weather with no convective activity can be expected across the forecast area for today. With 500 mb heights rising slightly from the previous couple of days, afternoon high temperatures across the lower deserts will top out in the mid to upper 100s.

The subtropical high will gradually build over the region during the first half of the week. As the high begins to build, 500 mb heights will rise closer to 594-596dam, which will represent the 97th percentile of climatology for this time of the year. Therefore, temperatures will climb another 3-5 degrees through Tuesday with afternoon highs breaching the 110 degree mark across the lower deserts. These afternoon high temperatures combined with early morning lows in the mid to upper 80s will result in a major spatial expansion of the Major HeatRisk Category and thus the Extreme Heat Warnings will start to go into effect across all the lower deserts starting Monday and for the San Carlos area in southern Gila County starting Tuesday. Convective activity during the first half of the week, will be mainly confined to the eastern and southeastern third of AZ with very little to no activity expected elsewhere given the below normal moisture values that will be in place, resulting in little to no instability.

LONG TERM /WEDNESDAY THROUGH SATURDAY/.

The subtropical high will continue to remain entrenched across the region through at least the end of the week, with 500 mb height fields remaining steady between 595-597dam. Therefore, temperatures will continue to run a good 4-7 degrees above normal as afternoon highs across the lower deserts will range between 108-113 degrees. There will also be little overnight relief as an increase in low- level moisture will cause overnight lows to only bottom out between the mid 80s to low 90s with the low 90s expected in the Phoenix area. Therefore, widespread Major HeatRisk will continue to remain in place with Extreme Heat Warnings in effect through Friday evening.

The latest guidance does show the high eventually moving northeastward into the Four Corners region by the end of the week into next weekend, putting the region under a more favorable moisture advection pattern as the east to southeast flow increases. Therefore, an increase in monsoonal activity is more likely during this timeframe, mostly across the higher terrain areas. Although, it will certainly be possible for convective activity to impact the south-central AZ lower deserts at some point as well, it is still too far out to know what days could be active as it will be dependent on mesoscale processes such as outflow evolutions and/or any easterly waves that are difficult to pinpoint several days out. As of right now, NBM PoPs across the south-central AZ lower deserts starting next Thursday range between 10-20%.

AVIATION

Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Sunday night under periods of thick mid/high cloud decks. Wind behavior will be nearly identical to the past 24 hours featuring a later than usual overnight easterly wind shift, and extended periods of variable directions during the typical wind shifts.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather concerns will exist through Sunday night under occasional mid/high cloud decks. Trends in winds will be similar to the past 24 hour including modest afternoon/evening gusts, and periods of nearly calm conditions in the morning.

FIRE WEATHER

Near normal temperatures will prevail today before rising above normal starting Monday. Little to no monsoon activity is expected through the first half of the week, with only a few isolated thunderstorms expected across the far eastern districts. Thunderstorm chances increase somewhat, mainly for south-central AZ, by the latter half of the week. Afternoon MinRHs during the next several days will range between 15-20% across the lower deserts and 20-25% across the far eastern districts. Outside of thunderstorm winds, the overall winds will follow the typical diurnal tendencies with some modest afternoon upslope gustiness.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Monday to 8 PM MST Friday for AZZ530>544-546-548>551-553>555-559.

Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Friday for AZZ560.

CA...Extreme Heat Warning from 10 AM Monday to 8 PM PDT Friday for CAZ562-565>567-569-570.