FXUS66 KPDT 241059 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 359 AM PDT Tue Sep 24 2024 UPDATED AVIATION DISCUSSION Aviation...12Z TAFS...VFR conditions are expected for this period. There will be smoke filtering into sites for KBDN during morning hours, which could bring MVFR or less CIG/vsby conditions. Winds will be less than 12kts for all sites during the day. However, winds could elevate for KBDN overnight up to 15kts. Feaster/97 && .PREV DISCUSSION... /issued 247 AM PDT Tue Sep 24 2024/ SHORT TERM...Today through Thursday night...Today will be warm and dry with light winds. Strong high pressure aloft and an inverted surface thermal trough will allow afternoon temperatures to climb into the 80s to lower 90s--about 15 degrees above seasonal average. A few record highs may be reached as well. The air mass is stable with strong low and mid-level inversions, therefore some of the colder valleys will be slow to reach their max temperature today and would actually be warmer if not for the strong inversions in place. It will be another quiet night tonight, although the upper level ridge will shift eastward and allow the upper flow to increase from the southwest. Bands of mid and high level clouds will also move across the area tonight. Weather concerns ramp up on Wednesday associated with a fairly organized cold front. Winds and blowing dust will be the two main concerns with the front. Models push the cold front east of the Cascades in the afternoon with the ETA along the Cascade Range between 1200-1400 PDT, across the Columbia Basin down to the southern Blue Mtns between 1400-1600 PDT, then the rest of the forecast area between 1600-1800 PDT. There is strong isentropic descent advertised by the deterministic models that could push winds aloft to the surface. There is an 850mb jet of 35-40kts and 700mb winds will be as strong as 50kts. ECMWF EFI has a large area of the Lower Columbia Basin down to Central Oregon in the 0.8-0.9 out of 1.0 for strong winds. The Columbia Basin and surrounding valleys are often susceptible to blowing dust around newly plowed fields in late September. Upon further review, highlights may be needed for winds and blowing dust. Confidence is high (80%) that patchy blowing dust will be observed but only 30% confidence that visibilities will fall below 1 mile for a large area. Will address the blowing dust concern in social media and weather graphics. Fire season is still upon us, and the hot dry windy product places some areas in the 90th to 95th percentile. RHs are not expected to be critically low to meet red flag criteria, but the Fire Danger Rating Areas are in the moderate to high category, so fire spread potential remains. Isolated thunderstorms are also forecast for northeast Oregon and southeast Washington Wednesday evening. The atmosphere will quickly destabilize ahead of the cold front, and a few storms are expected. CAMS gives about a 20% chance of thunder over the Blue Mountains and Wallowas. Storms that develop have a good chance of wetting rain but the probability of heavy rain is low (20%). Thursday and Thursday night will be met with a dry westerly flow. Seasonal average temperatures will return, and winds will be locally breezy. Any precipitation will be late Thursday night (40-60% chance) along the east slopes of the WA Cascades north of Mt. Adams ahead of a cold front over NW WA. Wister/85 LONG TERM...Friday through Tuesday...A zonal pattern will make its way over the PacNW through Saturday. Slight chance (20-30%) of showers occurring at the WA Cascades Friday morning, but could increase due to orographic lifting from the arrival of the cold front. Elsewhere will be low (<15% chance). Winds will be fairly light with occasional breezes up to 20 mph with increased westerly flow (30-40% probability). A transient trough will then continue passing through the PacNW Sunday before an upper ridge builds over starting Monday. Winds remain fairly light with lingering breezes around 20 mph or less (>40% probability). Though, models remain deviated for Sunday where the GFS and Canadian model both favor a shortwave trough passing through, but with the ECMWF being zonal. Tuesday, the ridge will break down as another shortwave trough arrives with a cold front inland of the forecast area. With orographic lifting and southwest flow, chances of evening showers could increase. But, confidence is low (20%). The GFS and Canadian models show the trough moving over to the forecast area whereas ECMWF favors a ridge. If the trough occurs, cooler temps and potential showers will continue. But if not, then a upper ridge builds over off the OR coast thus returning warm temps and dry conditions. Being said, this can make it challenging to forecast given the uncertainty. High temperatures will be mainly in the 70s through the long term period. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 88 58 83 47 / 0 0 20 50 ALW 91 64 87 50 / 0 0 20 50 PSC 88 62 86 51 / 0 0 10 40 YKM 88 55 81 40 / 0 0 30 10 HRI 91 60 85 49 / 0 0 10 40 ELN 88 57 77 43 / 0 0 40 20 RDM 91 55 80 40 / 0 0 10 20 LGD 86 58 87 47 / 0 0 20 60 GCD 87 54 85 47 / 0 0 10 30 DLS 93 59 78 50 / 0 0 30 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...85 LONG TERM....97 AVIATION...97