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 now 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/

The 00Z sounding out of Flagstaff sampled an H5 height of 601dam, which ties for second highest based on the SPC Sounding Climatology page for Flagstaff. The sounding also measured an H5 temperature of -4.5C, which is above the 90th percentile, and mesoanalysis shows even warmer 500mb temperatures toward the central CA-NV border. Suffice to say, the atmosphere is very hot right now and extreme heat will continue to be the primary weather hazard through this weekend as high pressure remains centered over the area and H5 heights hold near 598-600dam. High and low temperatures will be near or tying/breaking daily records across the region through Monday. High temperatures today and Sunday will be very similar, with the lower deserts peaking near 114-119 degrees. Then, as the high starts to weaken slightly into the start of next workweek, high temperatures will come down 1-3 degrees for Monday. Morning lows in the 80s to lower 90s will offer minimal relief from the heat and the combination of these high and low temperatures will lead to widespread Major HeatRisk and many areas of Extreme HeatRisk, including across all of Phoenix. Extreme HeatRisk means the entire population is at risk for significant heat health impacts. An Extreme Heat Warning remains in effect today through the start of the workweek.

With the very warm air aloft, subsidence, and near to below normal moisture levels, it is no surprise that this strong high pressure is inhibiting monsoon thunderstorms across much of the region. The next few afternoons and evenings storms will continue to favor primarily the White Mountains and across Southeast AZ, and a northeasterly steering flow will keep these storms progressing to the southwest. Isolated storms may start clipping into far southeastern Gila County beginning as early as Sunday, with the main impact being strong gusty outflow winds. Distant outflows may also begin reaching into portions of south-central AZ starting Sunday, but the winds with them are not likely to be very strong initially, given the northeasterly steering flow, and no additional convection is expected to be generated by these outflows given the poor environment in south-central AZ. Despite this, a few high-based showers cannot be fully ruled out during the early morning hours, even this morning just to the east and southeast of Phoenix as some hi-res models have suggested.

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 0445Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns under FEW-SCT mid to high- level cloud decks can be expected throughout the TAF period. Generally westerly winds will prevail throughout the TAF period, although a period of light easterly to variable conditions can be expected early Saturday morning. Some occasional gusts in the mid to upper teens are likely Saturday afternoon/early evening. There may be a period of virga showers early Saturday morning, mainly to the east of the terminals.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under some passing high cirrus cloud decks can be expected throughout the TAF period. At KIPL, winds will generally be out of the southeast with the exception early Saturday evening, when a temporary shift out of the west is likely. At KBLH, winds will vary between the south-southeast to southwest with periods of variable conditions likely early Saturday morning. Overall wind speeds will generally remain aob 10 kts, with some occasional afternoon gusts into the mid to upper teens at KBLH.

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.