FXUS66 KPDT 272339 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 445 PM PDT Fri Sep 27 2024 Updated Aviation Discussion .SHORT TERM... Tonight through Sunday night...Overall, quiet weather is expected through the period. Generally dry southwesterly flow will be over the Pacific Northwest tonight into Saturday. The flow will turn more westerly Saturday night into Sunday as a weak upper level trough moves by to the north. However, short wave energy and a cold front will move across the area on Sunday. The only impacts from these features are expected to be gusty winds cooler, temperatures and enhanced fire concerns. Dry northwesterly flow move back in behind the departing system. High temperatures on Saturday will range from the upper 70s to mid 80s in central oregon. This is about 10 to 15 degrees above normal, especially in central Oregon. The ECMWF EFI is keying in on some of these high values, especially over central and eastern Oregon with values generally ranging from 0.6 to 0.8. Monday looks to be a cool morning with lows in most areas in the 30s. This will be about 5 degrees below normal in most areas. Since it has been relatively warm, will also have to watch for possible freeze headlines, especially across some of the higher valleys of eastern Oregon and central Oregon. The gusty winds on Sunday look to mainly be in the 20 to 30 mph range, though there could be some gusts as high as 35 mph, and possibly to 40 mph in the Kittitas Valley. The ECMWF EFI shows values of 0.6 to 0.7 across the Simcoe Highlands and Oregon Columbia Basin, with some embedded 0.8 across the Basin. Additionally there is a larger swath north of our area with some 0.6 to 0.7 extend into the Kittitas Valley. The NBM probabilities of wind gusts >=39 mph are 60 to 80 percent across the Simcoe highlands and Oregon Basin on Sunday and 70 to 100 percent across the Kittitas Valley. Probabilities of winds >=48 mph are 30 to 50 percent in the Basin and 50 to 70 percent in the Kittitas Valley. .LONG TERM... Monday through Friday...Models are in pretty good agreement through Wednesday, but they begin to diverge thereafter on how meridional the pattern becomes by Friday. The cluster analysis shows most members (77%) agree there will be an upper level ridge along the coast on Monday, but one cluster (heavy ENS) hints at zonal flow developing quicker over the region. By Wednesday approximately 50% of members keep the upper level ridge pattern while the remainder show zonal flow. By Friday, all four clusters have their own solution but generally lean towards some form of a ridge (55%) or a trough (45%). As is pretty typical this time of year (transitional), models struggle to converge on a single solution beyond Day 5. The ECMWF and GFS ensemble means show the pattern transition more to zonal flow late Tuesday with a hint of the flow buckling as a weak trough digs off the coast late Thursday into Friday. This trough is expected to weaken further as it moves onshore with much of its energy remaining over Canada. In summary, a transitory upper level ridge should give way to general zonal flow from Tuesday through the rest of the extended with some weak embedded shortwaves. This pattern will lead to some periods of light rain over the Cascades, mainly the Washington side. NBM is hinting at more widespread precipitation occurring over the forecast area Friday night, but confidence is low given aforementioned cluster trends. However, confidence isn't high enough this far out to tweak rain chances lower. Relating to QPF, confidence is moderate to high (60-80%) the east slopes of the Cascades will see some light precipitation (generally less than 0.10 on an inch) on Friday, but low (15-20%) for the rest of the area. Daytime highs will generally hover around normal with Monday being the coolest day (about 5 degrees below normal). Earle/81 && .AVIATION...00Z TAFs...SCt-BKN cirrus clouds and light terrain driven winds will continue through early Saturday afternoon. The one exception will be at KDLS where NW winds are sustained around 10-13 kts at this time and will have similar winds on Saturday. RDM and BDN will also have slightly stronger NW winds after 21Z Saturday... NW around 10 kts gusting to 20 kts. Wister/85 && .PRELIMINARY POINT TEMPS/POPS... PDT 47 77 49 69 / 0 0 0 0 ALW 50 80 54 72 / 0 0 0 0 PSC 51 80 54 74 / 0 0 0 0 YKM 45 79 44 72 / 0 0 0 0 HRI 50 80 54 73 / 0 0 0 0 ELN 45 78 46 65 / 0 0 0 0 RDM 42 84 42 70 / 0 0 0 0 LGD 48 89 48 69 / 0 0 0 0 GCD 50 90 48 71 / 0 0 0 0 DLS 52 82 52 70 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...77 LONG TERM....81 AVIATION...85