Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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138 FXUS66 KPDT 270131 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 630 PM PDT Thu Sep 26 2024 .SHORT TERM...This afternoon through Saturday night...Aside from likely (55-90% chance) rain showers along the Washington Cascade crest late this evening through tonight as a Pacific frontal system (warm front with trailing cold front) moves onshore and weakens, dry weather is forecast through the period. The frontal system will usher in locally breezy southwest to west winds along exposed ridges of the Simcoe Highlands and east slopes of the Washington Cascades overnight, but the probability of advisory- level gusts is low (30-40% chance). NWP guidance is then in excellent agreement in a dry, quasi-zonal mid-level flow for Friday, with the only noteworthy talking point being a warming trend and locally low afternoon RH. Saturday, the warming trend continues, especially across the Blue Mountains region as rising heights and southwesterly flow facilitate an unseasonably warm air mass (ECMWF EFI of 0.5-0.8 for maximum temperature). Low afternoon RH is also anticipated across the aforementioned area Saturday afternoon, but confidence in sustaining wind and RH Red Flag criteria is low (<30%). Late Saturday afternoon through Saturday night, westerly gap flow will increase in magnitude as cross-Cascade surface pressure gradients tighten in response to a mid-level shortwave trough passing across far northern Washington. Chances of precipitation are very low (5-14%) along the Washington Cascade crest. Plunkett/86 && .LONG TERM...Sunday through Thursday...An overall quiet pattern is expected through the extended period. On Sunday, the flow will be mainly westerly, but a very weak trough will move across the region. This feature will do nothing more than bring some low precip chances to the higher elevations of the Washington Cascades. Behind this trough, a dry northwesterly flow moves over the area with some ridging building in from the south. The next chance of precipitation arrives on Tuesday, again for the Washington Cascades, when a cold front and trough move across the area. The model guidance is in excellent agreement through Wednesday, but then begin to vary with respect to the timing and strength of the trough, with the ECMWF being a bit stronger and deeper with the trough. The GFS ensemble mean is in better agreement with its deterministic run at 500 mb than the ECMWF during the Wednesday time period, giving some more credence to its solution. There will be diurnal breezy winds Sunday, especially across the Simcoe Highlands, Columbia Basin and Kittitas Valley with winds around 30 mph, and possibly higher. NBM probabilities of wind gusts >= 39 mph generally range from 50 to 80 percent with the highest values in the Kittitas Valley. The ECMWF EFI also keys in on the winds and wind gusts during the Sunday time frame with values ranging from 0.5 to 0.7 mainly across the Columbia Basin and adjacent valleys. There will be diurnal breezes Tuesday and Wednesday as well with gusts generally around 20 mph, though there is considerable uncertainty on Wednesday depending on the cold front and trough, winds could end up being higher. && .AVIATION...00Z TAFS...Clear skies and winds less than 10 kts are expected through the TAF period. && .PRELIMINARY POINT TEMPS/POPS... PDT 49 77 47 77 / 0 0 0 0 ALW 53 80 51 81 / 0 0 0 0 PSC 55 80 50 80 / 0 0 0 0 YKM 46 77 44 78 / 0 0 0 0 HRI 51 80 49 80 / 0 0 0 0 ELN 49 74 44 78 / 10 0 0 0 RDM 43 78 43 83 / 0 0 0 0 LGD 48 80 48 88 / 0 0 0 0 GCD 48 82 50 90 / 0 0 0 0 DLS 54 79 51 81 / 10 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....77 AVIATION...85