408 FXUS65 KPSR 310553 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1053 PM MST Tue Dec 30 2025 .UPDATE...Updated 06Z Aviation Discussion. && .KEY MESSAGES... - An unsettled weather regime will result in a few rounds of light rain showers from late Wednesday afternoon through Thursday night. - Drier weather should return by the weekend with temperatures hovering near to slightly above normal. && .SHORT TERM /Today through Thursday/... Sharp upper level ridging has become established over the SW Conus ahead of an expansive cyclone spinning west of the Baja peninsula. Deep southerly flow between these features is promoting robust moisture advection above the H7 level reflected on satellite as a thick blanket of clouds progressing into the Southwest, and initiating the first vestiges of a top down saturation process. Little more than virga would be anticipated through Wednesday morning as dry air remains parked in the sfc-H7 layer, and ascent mechanisms are essentially absent under the influence of the upper level ridge. However, lower level moisture profiles will improve throughout the day Wednesday as the aforementioned cyclonic circulation begins opening and propagating towards the southern California coast imparting notable ascent and a period of unsettled weather. Forecast PWATs will increase to around 250% of normal by Wednesday morning before peaking around 300% of normal late Wednesday afternoon/overnight. Models remain consistent in depicting strong theta-e advection in a H8-H7 layer midday aiding in moistening the boundary layer via deep, albeit only modest isentropic upglide through a 300K-315K layer. This forced ascent will increase markedly Wednesday afternoon with models showing a band of light rain developing into southern Arizona and rapidly spreading north. Larger uncertainty continues with respect to the haste at which saturation becomes sufficient to produce measurable rainfall, however recent guidance and historical precedent under stronger theta-e surges suggests a rather abrupt conversion. Regardless, confidence is good that scattered light showers will advance through south-central Arizona Wednesday evening into the overnight with lesser confidence of measurable rain in the western CWA. At this time, the preponderance of model evidence indicates accumulation for most locations 0.00-0.20" with isolated instances of slightly higher amounts (likely concentrated in upslope areas). While rich boundary layer moisture with mixing ratios around 8 g/kg will remain abundant Thursday and certainly capable of supporting persistent orographically forced showers over higher terrain locations, a break in activity is likely across lower elevations awaiting the main shortwave and vorticity forced ascent arriving from southern California Thursday afternoon. Areal coverage of showers THursday afternoon and evening may become limited as the attendant shortwave rapidly weakens and lifts into northern Arizona while midlevels begin drying, however anomalous low level moisture will be available for any amount of lift. Similar to the initial round of showers Wednesday, rainfall amounts should be rather light with totals again under 0.25" for the majority of the forecast area. Rain chances will quickly translate east into higher terrain areas Thursday night as the vorticity center shifts into the four corners and general subsidence begins bleeding into the bulk of the CWA. && .LONG TERM /Friday through Monday/... Upper level ridging and drier air aloft will quickly work into the region by Friday, ending rain chances across the higher terrain by Friday afternoon. Gradual drying is expected to continue through the weekend as troughing remains positioned across the eastern Pacific into the Western U.S. There will likely be another couple of shortwaves moving through the trough through early next week, but the first one should miss our region to the north. By the time the second one potentially gets close to our region early next week, moisture should be much more limited resulting in little if any additional rain chances. Despite the unsettled weather pattern late this week into next week, temperatures are expected to stay quite mild. The NBM shows daily highs mostly in the upper 60s to the lower 70s with overnight lows staying at least 10 degrees above normal through Friday night. Eventually by early next week, overnight lows will dip lower with readings back into the 40s to lower 50s once some drier air moves back into the area. && .AVIATION...Updated at 0553Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Main aviation concern will be ceilings. Winds will stay mostly out of the east-southeast with a short period of southerly winds expected as the system approaches the terminals, with speeds remaining aob 10kts for the TAF period. By Wednesday evening (~23Z) -SHRA activity is anticipated, along with the aforementionedlower CIGS. CIGs will mostly be above VFR condition but look to just dip into MVFR late into the evening and through the over night hours into Thursday morning. BKN- OVC low to mid level clouds will be common. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period under BKN-OVC mid and high cloud decks. At both terminals winds will generally vary between north and west with speeds AOB 10 kts, becoming. By tomorrow morning, lower decks of clouds (050-100 at ~17-19Z Wednesday) will begin to fill in over the airspace and continue to lower heading into the afternoon with a period of VCSH conditions possible at both terminals heading into the afternoon. && .FIRE WEATHER... Slightly above normal temperatures and dry conditions will give way to a rapid increase in moisture Wednesday. Minimum humidity levels in a 20-30% range at lower elevations, and somewhat higher in far eastern districts today will increase closer to 25-40% Wednesday before peaking at 50-70% for Thursday and Friday. Enhanced north to northeast winds will be common again today, particularly across ridge tops of eastern districts where gusts of 20-30 mph will be possible through early afternoon. Speeds should relax by Wednesday as clouds and humidity levels increase. Periods of showers are then expected during the latter half of Wednesday through Thursday with overall light rainfall amounts for much of the lower deserts to 0.25- 0.75" in higher terrain areas. Somewhat drier conditions will work back into the region by the weekend, but humidities will remain elevated as temperatures remain 5-8 degrees above normal. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ SHORT TERM...18 LONG TERM...Kuhlman/18 AVIATION...Ryan FIRE WEATHER...Kuhlman