823 FXUS66 KPDT 081750 AAA AFDPDT Area Forecast Discussion...Updated National Weather Service Pendleton OR 1050 AM PDT Fri Oct 8 2021 Updated aviation discussion .SHORT TERM...Today and Tonight...A long wave trough continues to impact the forecast area today with some showers over the eastern portion. This trough is split with the southern portion moving into California and sending some moisture across far eastern oregon this morning in the form of isolated to scattered showers. The northern portion is sliding down the coast and will consolidate with the southern portion to form a closed low over the Great basin on Saturday. The northern portion will have little impact to the forecast area other than some clouds. Overall the trough shifts eastward late tonight and Saturday allowing a temporary ridge of high pressure move into the region. Clearing skies will allow for some freezing temperatures in the upper John Day Basin so have issued a freeze warning for overnight through early Saturday. && .AVIATION...18Z TAFs...VFR conditions are expected for the next 24 hours. A few showers will continue through this afternoon from the Blue Mountains eastward but should not affect ALW or PDT. Most TAF sites will have FEW-SCT clouds at 7K-10K feet AGL today then skies will clear this evening and overnight. Winds will remain below 10 kts aside from DLS which will have northwest winds of 10-15 kts with gusts to 20 kts this afternoon. 83 && .PREV DISCUSSION... /issued 417 AM PDT Fri Oct 8 2021/ SHORT TERM...Today through Sunday night...A longwave trough with multiple embedded waves will be the primary influence of the weather across the PacNW for the next 24 hours. The forecast area is under a cyclonic flow aloft, and a strong wave riding down the backside of the trough will bring precipitation to western WA/OR but not have an effect for the east side of the Cascades. Any precipitation today and this evening will be mainly east of the Blue Mtns and east of John Day where scattered showers are expected. This is associated with an upper low over northern CA pushing moisture and instability to far eastern Oregon. QPF amounts of 0.1-0.3 inch are forecast, and the Wallowa Mountains could have a couple inches of snow in the higher peaks. The threat of thunderstorms is minimal and mainly over southeast Oregon. Skies will be partly cloudy today and temperatures will be near or slightly cooler than yesterday. The longwave trough will be forced eastward by an increasing westerly flow off the eastern Pacific. A drier northwest flow tonight will bring clearing skies and chilly conditions. No Freeze Warnings are planned at this time, as temperatures will be in the mid to upper 30s across the Columbia Basin. Central Oregon and the Grande Ronde Valley have already observed a hard freeze this season. The John Day Basin will be flirting with near freezing temperatures. The weak shortwave ridge will maintain dry conditions Saturday, and near seasonable temperatures will make for a pleasant day for outdoor activities. The next system to arrive Saturday night and Sunday will bring scattered to numerous showers over the mountains, but rain shadowing is likely off the Cascades with only isolated to scattered showers over most of the Columbia Basin down to central Oregon. Winds aloft will increase significantly on Sunday, and isentropic descent will bring 20-30 knot winds to the surface...possibly up to 40 knots. The NBM would support this with gusts at 30-35 mph in the meteograms at various stations in and around the Columbia Basin. QPF amounts are not impressive for Sunday and Sunday night with mostly up to 0.25 inch expected. Snow levels will fall to near 3500 feet Sunday night, but the precipitation will taper off overnight as well. However, some of the mountain passes may see light accumulations of snow for the first time of the season. The crest of the WA and OR Cascades could have 1-3 inches of new snow, including White Pass and Mt. Bachelor. Wister/85 LONG TERM...Monday through Friday...The long term will be mostly a troughy pattern through the work week as the deep low bringing the strongest shot of cold air across our region yet for this fall moves towards the Four Corners and then the Central US, followed by a pair of weaker troughs moving just north of us over the week before some ridging may finally settle in just beyond the long term forecast period. An upper level low will be over the CWA to begin the long term, deepening and descending towards the Four Corners region through Tuesday. The primary weather feature with this low will be the notably colder air associated with it, as much of the region drops below 40 degrees for overnight lows Monday into Tuesday. Freeze warnings will be likely for a notable portion of the CWA aside from the Columbia Basin/Gorge. Then, during the middle through end of the work week, a pair of weaker troughs associated with a low that's moving from the Gulf of Alaska into Canada, will move north of us. These should mostly bring precipitation that will cutoff at the Cascades, but some breezy to gusty winds may be possible Wednesday through Friday. Otherwise a steady increase in temperatures through the week is likely after the cool off, with highs on Friday about 5 to 10 degrees warmer than Monday. At this point in the forecast, ensembles are lining up well on the placement of the main low early next week, with the remaining question the strength and depth of the system as it moves towards the Four Corners. With multiple days of forecasts all but confirming our expected cooldown, it's unlikely major changes will occur and our first widespread freeze of the season should occur Tuesday morning. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 61 36 63 44 / 20 0 0 10 ALW 62 40 64 48 / 20 0 0 10 PSC 66 40 67 51 / 10 0 0 20 YKM 63 35 65 43 / 0 0 0 20 HRI 66 37 66 48 / 10 0 0 10 ELN 61 37 61 43 / 0 0 0 30 RDM 61 27 62 35 / 0 0 0 10 LGD 58 34 59 38 / 30 20 0 10 GCD 60 31 61 37 / 20 0 0 10 DLS 67 42 66 49 / 0 0 0 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Freeze Warning from 2 AM to 9 AM PDT Saturday for ORZ505. WA...None. && $$ SHORT TERM...91 LONG TERM....91 AVIATION...83