Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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557 FXUS66 KPDT 190926 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 226 AM PDT Thu Sep 19 2024 .SHORT TERM...Today through Saturday...A cutoff low centered over California continues to beget weak NW flow into our forecast area, making for dry conditions through the period. Only real sensible weather concern for the next couple of days will be an uptick in gap flows across primarily the Columbia River Gorge and the Kittitas Valley, where NBM probabilistic guidance depicts a 50-70% chance of gusts exceeding 40 mph both Thursday and Friday. This is due to a weak shortwave allowing for stronger NW winds aloft through the forecast area. Models, however, do not show winds extending very far beyond the Cascade Gaps, giving credence to the idea that these winds are primarily driven from aloft rather than via pressure gradient. There is a slight chance (15%) for the central Washington Cascades to see a weak orographic shower during the period, but any impacts are expected to be minimal. Otherwise, expect a clear and (relatively) warm day today, before temps trend more toward seasonal averages Friday and Saturday as the aforementioned shortwave allows for a (relatively) cooler airmass to advect into the Interior Northwest. May need to keep an eye out for overnight lows Saturday morning across our elevated valleys such as central Oregon and Wallowa County, as guidance does suggest overnight lows may flirt with freezing there. Evans/74 .LONG TERM...Sunday through Thursday...Ensemble runs remain in good agreement through the period but GFS and ECMWF deterministic runs are showing dramatic differences developing by days 6 and 7. Sunday will begin under a dry westerly flow but then switch to northwest flow behind the passage of a weak upper level trough through western Canada. This will be a dry trough passage other than a low chance of showers in the Washington Cascades. Main impact will be some locally breezy winds. A ridge of high pressure over the eastern Pacific Ocean with then push into the Pacific Northwest Monday and Tuesday lifting high temperatures to 5-10 degrees above normal. Wednesday and Thursday according to the ensemble runs should see the upper level ridge moving off to the east while an upper level trough from the Gulf of Alaska slowly pushes towards western Canada the Pacific Northwest. However, deterministic runs show the ECMWF holding the upper level ridge in place over the region longer with a slower progression of the Gulf of ALaska trough towards the Pacific Northwest. Meanwhile, the GFS sweeps the trough through the region rapidly Wednesday with a chance of precipitation followed by a westerly flow Thursday. The forecast reflects the ensemble version of events with some increasing low chance pops mainly along the Washington Cascades but there is a high degree of uncertainty based on the deterministic differences. && .AVIATION...12Z TAFs...VFR conditions expected over the next 24 hours under generally clear skies. Winds will be light through the morning then see increasing west to northwest winds 5-15kts through the afternoon and evening. DLS will see stronger winds at 10-20kts and gusts around 30kts. && .PRELIMINARY POINT TEMPS/POPS... PDT 77 47 69 41 / 0 0 0 0 ALW 79 51 71 44 / 0 0 0 0 PSC 81 53 75 46 / 0 0 0 0 YKM 81 47 75 41 / 0 0 0 0 HRI 81 52 75 44 / 0 0 0 0 ELN 76 50 71 43 / 0 0 0 0 RDM 77 42 71 36 / 0 0 0 0 LGD 78 45 68 40 / 0 0 0 0 GCD 78 44 72 37 / 0 0 0 0 DLS 79 53 73 48 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...74 LONG TERM....91 AVIATION...91