textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion

KEY MESSAGES

- Unseasonably hot conditions will continue to challenge daily temperatures records through the rest of the week and into the weekend.

- These hot conditions may be dangerous, especially for any strenuous outdoor activities without proper hydration and frequent breaks in the shade, or air conditioning.

- Temperatures should finally begin to back away from record territory by the end of the weekend as the high shifts east and cloud cover and shower chances increase.

SHORT TERM /TODAY THROUGH FRIDAY/

Ridging remains the dominant feature over much of the western CONUS with heights hovering around 588-590dm over the Desert Southwest. It is basically status quo with the forecast for today, continued hot and dry conditions, with the one exception being that temperatures will be a few degrees warmer compared to what was observed to start the week. With H5 heights once again around all- time records for this time of year, along with southerly/southwesterly flow inducing some warm-air advection, widespread triple digits will make their return for the lower deserts. Locations that do not reach the century mark can expect readings in the upper 90s.

By late today into Thursday, a tight area of low pressure, currently sitting off the California Coast, will inevitably move its way inland, helping to generate some breezy conditions for parts of the forecast area this afternoon and again Thursday. However, with the weak nature of this disturbance, the strongest gusts are only expected to reach upwards of 15-25 mph, with the higher end of that range favoring the highest ridge top areas. Otherwise, the remainder of the week looks to be calm as the ridge remains the dominant feature and even rebounds once again. Temperatures Thursday look as if they may cool a degree or two, at least for areas around the Colorado River Valley and westward, thanks to the lower heights provided by the passing system. Nonetheless, upper 90s to around the 100 degree mark will remain the common temperatures range through the end of the workweek.

LONG TERM /SATURDAY THROUGH TUESDAY/

Heading into the weekend, a potent cold front will dive south across the Plains with a strong surface high building in behind it. This will result in noticeable enhancement of our regional pressure gradient, generating breezy to locally windy conditions for areas primarily east of the Colorado River. The highest gusts, which may exceed 35 mph, will be focused over the higher terrain areas east of the Phoenix metro area, but gusts 20-30 mph look possible (50-60%) for lower desert areas of SOuth-Central and Southwestern Arizona. It appears likely (~80% chance) that some areas in the AZ high terrain experience gusts that reach Wind Advisory criteria. However, with the limited spatial and temporal scope of advisory level winds, no products will be issued at this time. If future guidance expands the areas of 40+ mph gusts, then it would not be surprising to see an advisory issued in the coming days. Temperature wise, the front half of the weekend will pick up where the previous few days left off as readings in the upper 90s to around 100 degrees will be common once more.

The back half of the weekend may yield a very welcome change as the high begins to shift further east, with the axis of this feature becoming centered over the Front Range and the Central Plains. As the high shifts, it will impart southerly flow over the region which will tap into to sub-tropical moisture, setting up an almost quasi- monsoonal pattern over the Desert Southwest. Models continue to suggest PWATs increasing to 200-250% of normal across the majority of Arizona by Sunday. This flux will, at the very least, bring in considerable cloud cover over the region, helping to decrease insolation and lowering our temperatures, albeit just by a bit. Some showers and perhaps some thunderstorms cannot be ruled out in association with moisture at these levels, especially out in eastern Arizona and along our higher terrain areas of Gila County, but with temperatures remaining well-above normal, it would take a decent amount more moisture to achieve higher probabilities and greater coverage of any precipitation. Another factor that will likely inhibit any widespread showers and thunderstorms will be a lack of forcing. Synoptic lift will be missing so any vertical development would have to rely solely on orographic influence. As of now, PoPs for our eastern most areas stand at 20-25%, with less than 10% chances for the lower deserts. Any hope of rainfall for lower elevation areas will have to fall any outflow boundaries moving off the high terrain, but with where potential storms may initiate, and the expected storm motion, that appears to be an unlikely outcome at this point.

Rainfall Monday cannot be ruled out just yet as elevated moisture looks to remain over the region. However, it looks as if the start of next week may suffer from a similar setup as Sunday with decent moisture but not enough supporting lift. Even though there are some ensemble members that indicate better instability on Monday, the best chances for showers and thunderstorms is only around 20% out where enhanced terrain features can induce precipitation development. There are signs of an approaching East Pacific trough approaching the West Coast toward the end of the forecast period. If this were to speed up at all and interact with lingering moisture, we could be talking about better rain chances in the coming days for the beginning of April.

AVIATION

Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under generally clear skies will persist throughout the TAF period. Winds will continue to exhibit the typical diurnal tendencies with speeds aob 10 kts with light and variable conditions likely, especially before the diurnal switchover.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns under mostly clear skies will persist throughout the TAF period. At KIPL, current light and variable winds will go southeasterly early this afternoon, shifting out of the west during the evening hours. At KBLH, winds will generally fluctuate between the south to southwest throughout the period. Overall speeds will be aob 12 kts, with some occasional elevated gusts during the afternoon hours at KBLH and evening hours at KIPL.

FIRE WEATHER

Record heat along with very dry conditions will continue through at least the start of the weekend. MinRH values will run generally around 5-10% over the next few afternoons before increasing closer to 10-20% Saturday-Sunday. MaxRHs will follow a similar uptrend with readings close to 20-40% the next few mornings before rising through the weekend. Winds through the end of the workweek should be generally light and follow diurnal trends, although some marginal breeziness (gusts 15-25 mph) will be observed this afternoon and once again Thursday. Stronger winds (gusts 25-35 mph) enter the picture late Friday into Saturday mainly, for areas east of the Colorado River. Higher gusts upwards of 40+ mph will be likely (~80% chance) for portions of the Arizona high terrain, but should be confined to the highest ridgetops. With very dry air in place, marginal breezes will lead to periods of elevated fire weather conditions through Friday. Even with the enhanced winds for Saturday, RHs should come up enough to limit critical thresholds for being met, but continued elevated, to near critical, conditions can be expected.

CLIMATE

Daily record highs through this week:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 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 3/28 95 in 2015 98 in 2015 98 in 2015 3/29 97 in 2015 100 in 1897 97 in 1969

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.