081 FXUS65 KPSR 300546 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1046 PM MST Mon Dec 29 2025 .UPDATE...Updated 06Z Aviation Discussion. && .KEY MESSAGES... - High pressure will result in dry and locally breezy conditions with temperatures slightly above normal through Tuesday. - An unsettled weather regime moving into the region during the middle and latter half of the week will lead to periods of increased light rain chances. - Drier weather should return during the weekend with temperatures still hovering near to slightly above normal. && .SHORT TERM /Today through Wednesday/... A Rex blocking pattern has become established over the East Pacific/western Conus with strong ridging folding into the Pacific NW while a deep cyclonic circulation spins well west of the Baja peninsula. Meanwhile, WV imagery depicts a more subtle vorticty center retrograding through central/southern California poised to become absorbed by the aforementioned southern gyre, and eventually providing the impetus for this system to eject into the SW Conus later this week. The current pattern configuration continues to promote strong sfc pressure rises from the Great Basin through high plains imposing modestly strong E/NE H9-H7 wind speeds. As a result, gusty winds with enhanced mixing have been noted through the lower Colorado River valley and ridge tops of south-central Arizona. This tight pressure gradient will result in deeper than usual mixing and translation of gusty winds to lower elevations, however will weaken over the next 36 hours. Otherwise, forecast confidence is very good that temperatures 4F-8F above normal will be common the next several days. On Wednesday, shortwave energy will begin propagating towards southern California as jet energy shifts to the eastern periphery of the cutoff low comprising the Rex block. While the negative height anomaly will be steady weakening as it opens and crests over a shortwave ridge, robust southerly flow will develop across northern Mexico eventually sending moisture northward into Arizona with PWATs quickly rising to 250-300% of normal by Wednesday evening. Upper level moisture (H7-H5 layer) will be first to spread into the Southwest creating cloudy skies and a top down saturation process. However, lower level moisture around the H8 layer will surge across the international border with notable theta-e advection increasing Wednesday afternoon. Larger synoptic scale forcing will initially be fairly weak, and the greater forecast uncertainty lies with the haste at which these top down and moisture advective processes can overcome the drier easterly flow and progress beyond just virga and sprinkles into accumulating rainfall. Most model guidance indicates this being accomplished very late afternoon, though historically this process can occur far more abruptly. Regardless, showers should readily blossom and expand through much of the CWA by early Wednesday evening, albeit with rainfall amounts likely limited, and potentially becoming more tied to orographic influences heading into the overnight. && .LONG TERM /Thursday through Monday/... The main forecast concern for the latter half of the week will be the evolution of this dramatic moisture increase and enhanced rain chances followed by a drying trend sometime later in the week. The peak of the combined forced ascent and moisture anomaly should occur Thursday with periodic rain chances through much of the day, and particularly pronounced north and east of Phoenix. Shower chances should diminish across the western deserts by Thursday evening, then throughout much of the Arizona zones during the overnight hours. Rainfall amounts are still a bit uncertain, but due to the overall weak forcing most lower desert areas should stay between 0.01-0.25" while some isolated areas and the more favored upslope areas north and east of Phoenix may receive 0.25-0.75". Upper level ridging is forecast to move over the region Thursday night into Friday with considerable drying occurring aloft. Some lingering light shower chances may stick around into Friday across the eastern Arizona high terrain, but this should result in little, if any additional accumulation. Guidance shows another upper level trough approaching the west coast of California later on Friday, but the current track is likely to mostly bypass the forecast area well to the northwest over the weekend. The NBM is still trying to suggest this may bring another round of rain chances, but that seems to be a stretch, so PoPs have been reduced Saturday and Sunday. Forecast high temperatures are expected to dip later this week, but readings are likely to stay 3-5 degrees above normal most days. Overnight temperatures will become quite mild starting midweek with lows mostly in the 50s due to the the cloudy skies. && .AVIATION...Updated at 0531Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns expected through the TAF period. Winds will maintain an easterly component throughout the TAF period, with speeds expected to generally be aob 10kts with the exception of elevated speeds and gusts tomorrow afternoon, similar to what we saw today. Currently no westerly shift is expected at any terminals tomorrow afternoon. SCT-BKN mid and high level clouds are expected through the period. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period. Winds at KBLH are expected to maintain a northerly component through the period, with speeds generally aob 10 kt, with some elevated wind speeds expected tomorrow afternoon. At KIPL, W to NW winds will prevail with speeds aob 10kts. SCT-BKN mid and high level clouds are expected through the period. && .FIRE WEATHER... Dry weather with slightly above normal temperatures will be seen early this week with minimum humidity levels in a 20-30% range. Enhanced north to northeast winds will be common through Tuesday, particularly across ridge tops of eastern districts where gusts of 20-30 mph are expected today. Moisture will begin to seep back into the region by Wednesday raising humidities and bringing rain chances late Wednesday and Thursday. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ SHORT TERM...18 LONG TERM...Kuhlman/18 AVIATION...Ryan FIRE WEATHER...Kuhlman