textproduct: NWS Phoenix

KEY MESSAGES

- Record breaking lower desert high temperatures near or exceeding 100 degrees will be common through at least the middle of next week, with the hottest days being today and Saturday.

- Extreme Heat Warnings will remain in effect across the lower deserts through Sunday.

- The unprecedented afternoon heat will be dangerous, especially with any strenuous or long-duration outdoor activities without proper hydration and taking breaks in the shade, or air conditioning.

SHORT TERM /TODAY THROUGH SUNDAY/

Current midlevel water vapor imagery and 500 mb RAP analysis show the center of this strong ridge positioned over Southwest Arizona, with H5 heights reaching up to 594 dam. 500 mb heights of this magnitude are at the climatological max for this time of year and have been the main driver for these record breaking temperatures over the past several days. Today and tomorrow's afternoon high temperatures will be the hottest the region will experience during this early March heat wave. Across the lower deserts afternoon highs will be in the 102F-108F range. If today's forecasted high temperature of 106F is reached at Phoenix Sky Harbor, it would break the previous record of 96F set in 2017, by 10 degrees. Additionally, this would surpass even April's all time high recorded temperature of 105F set on April 22nd in 2012 and April 29th in 1992. Throughout the weekend H5 heights will lower slightly to between 582-585 dam by Sunday as the core of the ridge migrates eastwards. Temperatures will lower in response to hover between 96F-102F, still well above the seasonal normals for this time of year. That being said, the Extreme Heat Warnings will remain in effect across the lower deserts through Sunday. Ensure to follow proper heat safety precautions such as staying hydrated, taking adequate/frequent breaks, and staying indoors with AC if possible.

Lets take a break from talking about heat for one second. A 700 mb shortwave trough looks to develop by Saturday evening. This will lead to winds at increasing to around 20-25 mph, especially in portions of Southeast CA, and particularly in the SW corner of Imperial Valley.

LONG TERM /MONDAY THROUGH THURSDAY/

Of the next 7 days, Monday is shaping up to be the "coolest" (lower desert highs 94F-101F) thanks to a couple of factors. The ridge will not rebuild substantially until Tuesday over the Desert Southwest and lower level thermal profile will require stronger/sustained anticyclonic subsidence to warm further. Another factor is that guidance indicates something reminiscent of a Gulf Surge occurring Sunday night and possibly again Monday night, increasing moisture over a shallow layer near the surface. Dewpoint temperatures are shown increasing upwards of 45F-55F for the Yuma area and at times for the adjacent valleys (Imperial, Lower Colorado River, Lower Gila River). Dewpoints are forecast to increase at least into the 30s elsewhere across the lower deserts. It will be harder to realize widespread temperatures in excess of 100F especially on Monday thanks to these factors.

During the middle of next week, ensembles continue to advertise another significant yet more transient ridging feature building under an anticyclonically curved jet streak. Though the ridging will be lower amplitude compared to the current ridge, and anticyclonic subsidence will be shorter lived (likely peaking in its influence sometime Tuesday-Wednesday), H5 heights are forecast to rise into a 588-591 dam range - once again above CFSR climatological maximum values over a broad area. This will allow a gradual warming into the middle of the upcoming workweek, with coverage of 100F+ temperatures increasing. In summary, confidence continues to grow in a longer duration heatwave, with highs remaining between 15F-25F above daily normals and breaking daily records well into next week.

AVIATION

Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected through the forecast period. Winds will continue to follow familiar diurnal trends seen over the past 24 hours with speeds remaining aob 8 kts. Extended periods of calm and VRB conditions will be common, especially at the SE California terminals. Clear skies will dominate the region through Saturday.

FIRE WEATHER

Historic March heat and very dry conditions will continue through the weekend. Afternoon highs around 25 degrees above daily normals will be common today and Saturday, falling to around 20 degrees above normal by Sunday. Afternoon MinRHs between 5-10% will persist through Sunday, increasing slightly into a 10-20% range for portions of the Western Deserts early next week. Overnight recoveries will be poor, around 15-35% through Saturday night. However, MaxRH's improve to 40-60% Sunday night and Monday night primarily for valley locations in the western deserts like the Yuma area, lower Colorado River Valley, Imperial Valley, and lower Gila River Valley. Winds will be light today, mostly below 15 mph, but late afternoon and early evening breeziness will increase this weekend, with gusts locally to 20-25 mph.

CLIMATE

Daily record highs through the middle of next week:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 3/20 96 in 2017 99 in 2004 98 in 2004 3/21 97 in 2004 102 in 2004 100 in 2004 3/22 94 in 1990 98 in 2004 96 in 2004 3/23 93 in 1990 96 in 1990 93 in 1990 3/24 96 in 2025 97 in 2025 96 in 2025 3/25 99 in 2025 99 in 1896 99 in 2025 3/26 100 in 1988 99 in 1988 98 in 1988

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>555-559- 561.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ561>570.