000 FXUS65 KPSR 021126 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 426 AM MST Sat Dec 2 2023 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... A cool air mass will linger across the region this weekend resulting in near to below normal temperatures and afternoon highs in the 60s across the lower deserts. A strong high pressure system will then spread over the region into early next week resulting in a quick warming trend and pushing high temperatures into the upper 70s starting Tuesday. Dry conditions and above normal temperatures will continue through at least next Friday. && .DISCUSSION... Broad upper level troughing remains positioned over the Southwestern U.S. with fairly dry northwesterly flow aloft over the Desert Southwest. Satellite imagery shows generally clear skies over the majority of the area early this morning and this should persist over the next 24-36 hours. Afternoon highs today will improve very slightly from Friday's highs, but will still fall short of normals by a few degrees. The cooler air mass will still remain in place into Sunday with the coolest nighttime temperatures likely occurring tonight with forecast lows commonly in the upper 30s to lower 40s for much of the lower deserts. This weekend will also present a strong atmospheric river hitting the Pacific Northwest with some of the higher level moisture eventually spilling southward through the Great Basin into portions of our region. By Sunday afternoon/evening, we should see some considerable high cloudiness moving into the area from the northwest, though this shouldn't prevent high temperatures from finally climbing back to normal readings Sunday afternoon. By Monday, a strong ridge of high pressure building to our west this weekend will finally displace the trough far enough east to allow for some significant height rises aloft and to continue the warming trend. Even though forecast H5 heights of near 580dm are expected on Monday, much of the warming aloft will not yet mix into the boundary layer and the high clouds could keep down insolation enough to only allow high temperatures into the lower 70s. Going into Tuesday and especially Wednesday, the full force of the warming from the high pressure ridge should be felt across our region while the high clouds are likely to push southeast of the area. The latest guidance has backed off slightly on the strength of the ridge over our region, but forecast NBM high temperatures still easily reach into the upper 70s starting Tuesday with at least around of 40% probability of Phoenix reaching 80 degrees on Tuesday and/or Wednesday. Later next week, a Pacific trough is forecast to reach the Pacific Northwest which will help to tamp down the ridge over the Southwestern U.S. starting Thursday, but any cooling should be subtle through next Friday. Ensemble guidance is fairly split on what to do with the Pacific trough going into next weekend with just over 50% of members showing the potential for a deep trough reaching our region at some point. However, most of the rest of the members show this trough mostly bypassing our region just to the north. Given these potential scenarios, it's safe to say we will see a cooling trend into next weekend, but it is too difficult to know what kind of precip chances it may present. && .AVIATION...Updated at 1125Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Light winds (aob 7 kts) will prevail through the TAF period, following typical diurnal wind directions, with W winds developing by 21-22Z. Periods of calm to very light and variable are anticipated. High level clouds will pass over during morning and afternoon. Otherwise, SKC will prevail. Southeast California/Southwest Arizona including KIPL and KBLH: Light winds (aob 5 kts) will prevail through the TAF period at both terminals. KIPL will see a light shift to the SE to E during the day, while VRB prevails at KBLH. KIPL will also see periods of light variability. High clouds will pass over this morning, with SKC prevailing thereafter. && .FIRE WEATHER... High pressure will slowly move into the region over the next few days resulting in a gradual warm up and temperatures back to normal on Sunday. Drier air will also filter in from the west pushing humidities lower as MinRHs drop to 25-30% on Sunday. Winds this weekend will be very light while somewhat following typical diurnal pattern. Much warmer and even drier conditions are expected for at least the first half of next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Benedict FIRE WEATHER...Kuhlman