textproduct: NWS Phoenix

KEY MESSAGES

- Record breaking lower desert high temperatures near 100 degrees will be common through the upcoming work week, with the hottest of the next 7 days likely today.

- 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 MONDAY/

Mid-level water vapor imagery and 500 mb RAP analysis show the core of this impressively strong ridge now over the vast portion of Southeastern Arizona. Even though the core is not directly over our region, very positive height anomalies remain over all of the CONUS, especially over Western CONUS and the Desert SW. These 500 mb heights are in the 99th to near max percentile of climatology, with even the 700 mb heights above the 97th percentile of climatology for today. This will lead to this afternoon's temperatures across the lower deserts to range between 102F-108F. This is almost identical to yesterday's temperatures, so yet again, we can expect previous record highs across the region to be broken by 5F-10F. By Sunday, heights aloft will decrease slightly to between 582-585 dam due to several shortwaves progressing over Canada and the northwestern states. This will help flatten the ridge over the Desert SW causing temperatures to cool 2F-5F for tomorrow and early into the workweek, with Monday looking to be the "coolest" day with only a ~40% chance of hitting 100F at Phoenix Sky Harbor. However, even with a slight drop, these temperatures will remain 15F-20F above normal for this time of year, and the Extreme Heat Warnings will remain in effect across the lower deserts through Sunday.

As the core of the ridge continues shifting to the southeast over the weekend, an approaching weak disturbance from the west will also begin to impact Southeast CA and Southwest AZ by this evening into Sunday morning. This disturbance will lead to an increase breezy conditions in these areas, with gusts likely between 20-25 mph, with locally higher speeds possible. Breezy conditions, with gusts near 20 mph in the late afternoon and early evening hours, will continue through early next week, predominately out in Southeast CA, and in the Imperial Valley.

LONG TERM /TUESDAY THROUGH FRIDAY/

During the middle of the upcoming workweek, ensembles remain in excellent agreement that another significant yet more transient ridging feature will build 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 587-590 dam range - once again above CFSR climatological maximum values for this time of year. This will allow temperatures to warm for the latter half of the workweek, with highs hovering in the upper 90s to lower 100s across the lower deserts. Latest probabilistic NBM output advertises IQRs of 4F or less for the forecast temperatures during this timeframe, yielding good confidence in this abnormal March heatwave sticking around and daily highs staying in record territory through at least the next 7 days.

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 during the TAF period. Winds will continue to follow familiar diurnal patterns at the Phoenix Metro terminals with speeds remaining aob 8 kts. At the SE California terminals, expect predominantly westerly winds at KIPL and southwesterly winds at KBLH. Intermittent gusts up to around 25 kts can be anticipated at KIPL this evening. Clear skies will give way to increasing high cirrus decks later this evening.

FIRE WEATHER

Record breaking heat and dry conditions will continue through next week. Afternoon highs around 25 degrees above daily normals will be common today, falling to around 15 to 20 degrees above normal by Monday. 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, but drying throughout the workweek. Overnight recoveries will be poor, around 15-35% areawide tonight. Overnight recoveries improve to 40-60% Sunday through Tuesday night primarily for valley locations in the western deserts like the Yuma area, lower Colorado River Valley, Imperial Valley, and lower Gila River Valley. Elsewhere, MaxRHs will range between 25-40% into the middle of the work week. Late afternoon and early evening breeziness will increase this weekend into early next week, with gusts locally to 20-25 mph in the Western districts.

CLIMATE

Daily record highs through the upcoming work week:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 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 3/27 98 in 1986 100 in 1986 99 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.