337 FXUS65 KPSR 191719 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1019 AM MST Thu Dec 19 2024 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Record to near record high temperatures are expected through Friday before a slight decrease in temperatures is likely starting this weekend. The dry conditions and well above normal temperatures will continue through early next week until a mostly dry weather system arrives around Christmas Day. The weather during the latter half of next week may be a little bit more unsettled, but overall dry conditions are likely to persist with daytime highs running a few degrees above normal. && .DISCUSSION... An unseasonably strong high pressure ridge is now positioned over much of the Western U.S., including the Desert Southwest. As H5 heights remain near 585dm today into Friday, record to near record highs are forecast for our area. Most lower desert locales are expected to top out in the upper 70s through Friday with much of the Phoenix area likely reaching or even topping 80 degrees. Daily records at KPHX are likely to be tied or broken today and Friday before temperatures begin to drop off slightly starting this weekend as the high pressure ridge gets tamped down a bit from a shortwave trough tracking across northern Nevada into Idaho. Skies will remain mostly clear into the weekend before some increased higher level cloudiness starts to impact the region by Sunday. The influence of the high pressure ridge will start to wain by early next week as the Aleutian Low shifts more southward just off the coast of California. This will allow for a more active weather pattern setting up over the eastern Pacific, affecting much of the Pacific Northwest and California through much of next week. For our region, this weather pattern will gradually push out the unseasonably warm high pressure ridge, but we are not expecting any atmospheric rivers (AR) to reach our area. The first AR hitting portions of Califonria on Saturday will largely push most of the moisture into the Great Basin leaving us with some higher clouds by Sunday. A second AR Sunday will essentially follow the first's path, while a third late Monday into Tuesday is likely to be a bit farther south into central California. For our region, the first two will largely go unnoticed with temperatures still reaching into the mid 70s through early next week with only some periodic high clouds. Guidance is still showing a stronger shortwave trough accompanying the third AR, likely at least passing through the northern portion of our region on Christmas Day. So far model guidance has not been showing very widespread precipitation chances for our region on Christmas, but there very well could be some shower activity that ends up affecting the Arizona high country. The trajectory of the system doesn't bode well for any good boundary layer moisture return, so it's quite doubtful the lower deserts would see any precipitation. Temperatures should also turn cooler with the passage of the weather system as highs are forecast to drop into the upper 60s to around 70 degrees across the lower deserts starting Christmas Day. && .AVIATION...Updated at 1719Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are expected through the TAF period. Light east winds are expected through most of the TAF period, with moderate confidence in a brief TEMPO westerly shift late this afternoon/evening. Periods of light and variable winds are expected at the terminals. SKC/FEW250 will prevail through most of the TAF period. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected through the next 24 hours. Overall wind speeds will remain light aob 7 kts, with the wind directions fluctuating between the west and north and with extended periods of variable to nearly calm conditions. && .FIRE WEATHER... No weather changes are expected through the weekend with dry conditions and well above normal temperatures persisting over the region. Expect overall light winds the next few days, but with some breezy easterly winds mainly in the morning across the eastern Arizona higher terrain. Low humidities are forecast over the next several days with MinRHs in the teens across the lower deserts to around 20% over higher terrain areas. The weather pattern next week is likely to become a bit more active, but with any weather systems again mostly bypassing the region just to the north. However, expect a gradual cooldown in temperatures during the latter half of next week and a slight rise in moisture levels. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Smith/Benedict FIRE WEATHER...Kuhlman