Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 262007 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 107 PM MST Tue Mar 26 2024 .SYNOPSIS...
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A weather system lingering across the region will continue to result in below normal temperatures and bring chances for showers and thunderstorms through this evening from Phoenix and across the higher terrain areas to the north and east. From mid to late week, high pressure will settle over the region resulting in dry conditions and a strong warming trend. Another stronger weather system will then bring more unsettled conditions with increased rain chances and cooler temperatures from Sunday into early next week.
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&& .DISCUSSION...
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A longwave trough extending from the central Plains through the western United States will continue to result in unsettled conditions today. A subtle shortwave riding along the western side of the trough resulted in scattered shower activity across the higher terrain areas east of Phoenix during much of the overnight into the early morning hours with another piece of energy upstream expected to help spark additional convective showers near the Mogollum Rim this afternoon. The northwesterly flow aloft will then carry these showers southeastward affecting mainly eastern Maricopa, Pinal and southern Gila Counties with more isolated activity possibly making its way into the Phoenix area. With the steep mid-level lapse rates still in place, instability parameters are sufficient to spark thunderstorms as well with the showers with CAPE values as high as 500 J/KG. Any stronger storm will be capable of producing gusty winds in excess of 30 mph as well as small hail. High temperatures today will continue to once again remain well-below normal with highs only topping out in the lower to mid 70s across the lower deserts. The weather pattern shifts starting on Wednesday as the trough exits to the east allowing a ridge of high pressure to build in, which will persist through the end of the week. With the ridge settling over the region, a drier air mass along with a strong warming trend are expected. High temperatures on Wednesday will warm into the upper 70s to low 80s across the lower deserts, with even warmer readings Thursday through Saturday with highs in the low to mid 80s. Attention will then turn to an upper-level low that is expected to reach the Pacific Northwest coast Wednesday into Thursday and then dive southward to be positioned off the California coast Friday into Saturday. As the upper-level low dives southward off the California Coast, it will be strengthening with 500 mb heights as low as 540dm, which is near the climatological minimum for heights fields at this level. Initially, the main hazard with this system will be gusty winds starting on Friday but then peaking on Saturday as the ECMWF EFI values rise to as high 0.6-0.8 across most of western and central AZ, meaning the majority of the members are showing highly anomalous winds for this time of the year. The other hazard with this system will then be the rainfall potential. A strong frontal band is likely to make its way from west to east across the region between Saturday night through the day on Sunday delivering moderate rainfall activity as well as isolated thunderstorm activity as the low gradually moves eastward. By early next week, as the cold core moves over Arizona, diurnally induced showers and isolated thunderstorms will be likely, especially across south-central AZ. Latest QPF amounts for the entire event at this time range from 0.25-0.50" across the western deserts to 0.50-0.75" across the lower deserts of south-central AZ with amounts of over an inch across the higher terrain areas to the north and east of Phoenix. Under the influence of the low, temperatures will be on a cooling trend beginning on Sunday and persisting through early next week with highs trending below normal once again.
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&& .AVIATION...Updated at 1730Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Breezy conditions will be the main aviation concern during the period. Gusts will develop this afternoon and hover around 20 kts out of the W. By this evening, Hi-res guidance is picking up on potentially multiple outflows, spawning from distant showers and thunderstorms, traversing the metro between 23-02Z. Where these outflows initialize will ultimately determine where more breezy conditions will emanate from, but current guidance indicates a NW`rly outflow impacting KDVT and KSDL before merging with another outflow which could lead to NE`rly gusts at KPHX and KIWA. Max gusts with these outflows may reach upwards of 25-30 kts. Rainfall activity today will be focused over the high terrain areas to the N and E, though any potential outflow interactions may spark some isolated shower activity around metro terminals. SCT-BKN low- cloud will lift and gradually scatter out as we go forward, though bases around 4-5 kft may linger into the early afternoon hours. Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions will be the main aviation concerns during the TAF period. Winds at IPL will follow diurnal trends with gusts upwards of 25 kts this evening. At BLH, winds will contain a W`rly component with occasional afternoon breeziness upwards of 20 kts before winds calm and become more variable by tonight. Mostly clear skies can be expected through tonight. && .FIRE WEATHER... Today will bring additional chances for mainly higher terrain light showers and a few isolated afternoon thunderstorms before high pressure settles over the region starting Wednesday. Winds today will be breezy at times, particularly in the afternoon, with gusts of 20-25 mph before diminishing into Wednesday. MinRHs today will range from 15-20% over the western districts to 25-30% over the lower deserts of south-central Arizona, and up to 50% over the Arizona high terrain. Drier and warmer conditions starting Wednesday will lower MinRHs across all of the lower deserts into the teens to around 20% with day to day afternoon breeziness persisting. Slightly above normal temperatures and dry conditions are then expected to last into the early part of the weekend before unsettled weather conditions move in by Sunday. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Lojero AVIATION...RW FIRE WEATHER...Kuhlman

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