451 FXUS65 KPSR 050555 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1055 PM MST Fri Apr 4 2025 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... A low pressure system centered over the forecast area will result in below normal temperatures and isolated to widely scattered showers mainly across the higher terrain of southcentral AZ through Saturday afternoon. From Sunday into early next week, the weather system will depart allowing a ridge of high pressure to begin building over the Desert Southwest. This pattern shift will resulting in a significant warming trend as highs steadily climb into the 90s to around 100 degrees across the lower deserts by the middle to latter half of next week. && .DISCUSSION... Latest visible satellite and local radar imagery depicts a closed upper-lvl low situated directly over southcentral AZ. Large scale lift along the eastern periphery of the low has resulted in widespread light shower activity mainly across the AZ high terrain. There are currently a few showers pivoting swd into the Phoenix Metro, however a lack of boundary layer moisture will keep much of this rain from reaching the ground. Despite the lack of rainfall, there is enough instability (ML CAPE 100-150 J/kg and DCAPE 400 J/kg) in place for potentially an isolated storm or two. Any stronger cell will be capable of producing gusty outflow winds and possible some brief small hail. Shower activity should wind down quickly after sunset due to the loss of heating with a quiet night anticipated thereafter. Temperatures will settle to the upper 40s to lower 50s across the lower deserts by Saturday morning. Throughout this weekend we will begin to see a pattern shift as the trough of low pressure weakens and shifts east of the region. As this occurs we will see a high amplitude ridge begin to build over the West Coast. On Saturday, the departing trough will still keep negative 500 mb hght anomalies in place over eastern AZ. This will result in temperatures remaining near to slightly below average across the eastern half of the forecast area whereas highs will be slightly warmer into the lower 80s along and west of the Colorado River. A trailing vort max on the back side of the departing trough is likely to provide lingering showers across E Maricopa and S Gila County on Saturday afternoon and evening. Farther west across SE California and SW Arizona, a tight pressure gradient will result in strong northerly winds. Gusts could reach as high as 25-35 mph for a few hours Saturday morning until the gradient relaxes by the afternoon. On Sunday, the upper-lvl trough will exit well to the east of our region, allowing the aforementioned upper ridge to build over the Desert Southwest. Rising hghts aloft will lead to temperatures warming back to around normal in the low to mid 80s across the lower deserts Sunday afternoon. Ridging aloft will become the predominant feature over the entire western U.S. from Monday onwards. H5 heights early next week are expected to rise between 580-582dm, or on the upper end of climatology for this time of year. Mostly clear skies and dry conditions will boost temperatures to around five degrees above normal on Monday as highs climb to around 90 degrees across the western lower deserts to the mid to upper 80s in the Phoenix area. Continued strengthening of the upper ridge will transpire through the middle of next week as H5 heights over our region are forecast to climb to between 585-588dm. Ensembles show forecast H5 heights likely peaking next Thursday at around 588dm which would be near record for the climatological period. As the high strengthens over our region Monday through Thursday, the atmosphere will heat up pushing highs into the lower 90s by Tuesday before peaking near 100 degrees for next Thursday and Friday. NBM deterministic forecast temperatures have shifted slightly lower during the latter half of next week, but given that forecast H5 heights are even higher than the March 24-26th event that saw upper 90s for highs, we should see highs a few degrees warmer. Eventually, a large Pacific trough is favored to shift farther to the south just off the West Coast by next weekend. If this occurs, it would flatten out the ridge over our region prompting a cooling trend by around next Saturday. && .AVIATION...Updated at 0555Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Breezy N-NNE winds gusting to around 18-20 kts are expected to weaken toward midnight. Thereafter, winds are favored to become more light and variable, favoring the E-NE at times. W-NW winds resume at the terminals by late morning into the early afternoon Saturday. Additional light showers/virga will be possible Saturday afternoon, which could create some gusty, erratic winds. FEW-SCT clouds aoa 9 kft will continue throughout the period with clearing skies during the overnight and morning period. Southeast California/Southwest Arizona including KIPL and KBLH: Winds at the terminals will continue mostly favor a N-NW component through the next 24 hours with a period of WNW winds at KIPL through the overnight hours tonight. Gusts will resume tomorrow morning starting around 16-17z, climbing upwards of 20-25 kts. Otherwise, mostly clear skies will continue with FEW clouds aoa 10 kft. && .FIRE WEATHER... Below normal temperatures and isolated to widely scattered showers across the eastern districts will continue through Saturday before a warming trend commences Sunday into early next week. Any showers that develop are not expected to produce wetting rainfall with only a few locations receiving anything measurable. As the weather system slowly departs ewd, there will be a period of breezy to locally windy conditions across SE California and the Lower Colorado River valley on Saturday where gusts could reach 25-35 mph. A gradual drying trend will transpire through this weekend as MinRHs lower to around 10-15% area-wide by Sunday. High pressure will settle back into the region by into early next week resulting in the return of above normal temperatures and seasonably dry conditions. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Salerno/Kuhlman AVIATION...Smith FIRE WEATHER...Salerno