textproduct: NWS Phoenix

KEY MESSAGES

- Extreme heat will persist through the start of next 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 Monday.

- 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 next week.

SHORT TERM /TODAY THROUGH MONDAY/

A very hot weekend is underway as an anomalously strong ridge of high pressure sits over the region. This morning's 12Z PHX sounding sampled a 500 mb height of 601 dm with mesoanalysis showing the ridge centered over south-central Arizona. The ridge will be at peak intensity today, yielding well above normal and potentially record-breaking temperatures, before beginning to weaken as a trough passes through BC/Alberta. As the ridge weakens, 500 mb heights will drop from 598-600 dm today to around 595-597 dm tomorrow. Regardless of the ridge weakening tomorrow, temperatures will remain well above normal with forecast highs ranging from 112-118 degrees across the lower deserts Sunday afternoon. Afternoon temperatures Monday will see ~2-4 degree drop from Sunday as the weakening trend of the ridge continues into the start of the new workweek. While daytime highs remain well above normal into early next week, morning lows will also offer little relief from the heat as temperatures only cool into the upper 80s to low 90s each morning. The combination of these very hot daytime temperatures and warm morning lows will lead to widespread Major HeatRisk along with Extreme HeatRisk across the Phoenix metro through Sunday. Thus, Extreme Heat Warnings remain in effect through the start of the new workweek.

With the strong ridge promoting subsidence over the region along with forecast soundings showing limited moisture primarily focused around 500 mb, monsoonal activity will remain quite limited for our area this weekend with thunderstorms favoring the White Mountains. Given the dry sub-cloud layer and high DCAPE values, these thunderstorms could generate strong outflows that could aid in developing a few isolated shower/storms this weekend into southern Gila County. This may become more likely tomorrow as HREF guidance support increasing thunderstorm activity across far eastern AZ tomorrow afternoon. Better moisture will begin to creep back into the area Monday and will allow for increasing thunderstorm activity primarily across southeast Arizona Monday afternoon. Northeast steering flow will keep this activity away from our area, while a few storms may develop/move into southern Gila County.

LONG TERM /TUESDAY THROUGH FRIDAY/

The monsoon high is forecast to weaken Sunday into Monday with H5 heights dropping to 594-596dam, or right around the 90th percentile of climatology, by the end of the day Monday. The high will also become flatter and more stretched out across the southern tier of the CONUS and likely persist through the end of the week. Despite the high weakening, the residual heat dome will take some time to cool. High temperatures are forecast to cool 1-3 degrees into Tuesday, from Monday's readings, and another 1-3 degrees into Wednesday. Lows will remain quite warm each day, mainly in the mid 80s to around 90F across the lower deserts. The extreme heat footprint will decrease as the temperatures decline, but a continuation of the Extreme Heat Warning through Tuesday may be needed for at least the Phoenix area with lingering widespread Major HeatRisk across the metro area based on the current forecast. Most other areas will fall to the Moderate risk level by Tuesday. Temperatures are then forecast to remain fairly similar day-to-day Wednesday through the end of the week, with minimal synoptic changes, barring any storm influences.

With the weaker and flatter high, and being on the southern half of the high, there will be a longer fetch of easterly winds across southern New Mexico, southern Arizona, and northern Mexico by Tuesday. This pattern shift will allow moisture to begin to increase again across southern and eastern Arizona Monday through the middle of the week. As a result, convective potential will tick upwards early next week, and the easterly steering flow across southern Arizona will be a better trajectory across the area to help spread convection more into the lower deserts by the second half of next week. Latest NBM/WPC forecast show 10-30% PoPs across south-central Arizona by Wednesday and continuing through the end of the week. Despite lower PoPs on Tuesday, strong outflow winds may at least progress through south-central Arizona. The synoptic pattern next week will open the door for some easterly waves/inverted troughs to progress across the area and enhance convective potential, but it is still too early for models to fully resolve any of these features to help determine what day, if any, will have better odds for storms across the lower deserts.

AVIATION

Updated at 1715Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns this TAF period under FEW-SCT mid to high clouds. Typical diurnal trends expected for winds with westerly component this afternoon/evening back to easterly overnight into Sunday morning. Some occasional gusts around 20kts are likely for a short period this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns this TAF period. Clear skies outside of some passing SCT high clouds and winds generally AOB 10kts. At KIPL, winds will generally be out of the southeast with the exception of a short period of a westerly component overnight. At KBLH, winds will vary between the south-southeast to southwest.

FIRE WEATHER

Strong high pressure and very hot temperatures, with dry conditions, will persist through this weekend. Afternoon high temperatures will be up to 112-118 degrees across lower elevations and minimum RH values will be around 10-15%. Temperatures then decline a few degrees each day through the first half of the week and moisture levels will slowly rise. Minimum RHs will still be around 15-20% Monday, but will increase up to 20-30% starting Tuesday. Overnight RH recoveries will be fair to good this weekend at 30-45% and then increase up to 45-70%. 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 15-20 mph at times.

CLIMATE

Record high temperatures:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 1 116 in 1972 117 in 1993 118 in 1993 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 Monday for AZZ530>563.

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