Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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054 FXUS66 KPDT 281002 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 302 AM PDT Fri Jun 28 2024 .SHORT TERM...Today through Sunday...Water vapor satellite imagery tonight shows an upper trough departing into central MT, while a transient upper ridge sits offshore the PacNW. The upper trough passage earlier supported breezy winds across the forecast area, however those winds have been steadily decreasing tonight, and are expected to become light by the morning hours. Today, the transient upper ridge offshore will transit the PacNW as the trough to in MT continues east. The upper ridge will bring dry conditions with light winds across the region, while also facilitating a warming trend of 4 to 6 degrees as compared to yesterday afternoon`s temperatures. Upstream of the upper ridge, an upper trough associated with a low in the Gulf of Alaska will begin to amplify. Rounding this amplifying trough Saturday will be a shortwave impulse that will lift into southern BC by the late afternoon. This shortwave will bring a marine push through the Cascade gaps beginning Saturday morning, resulting in breezy winds with gusts 30-35mph developing through Kittitas valley, eastern Gorge, and portions of the Columbia Basin (confidence 70-85%). The upper impulse will also clip the central WA Cascades during it`s transit in the afternoon, resulting in only a slight chance (15-20%) of showers in this area. Though the ridge will have exit to the east, the Columbia/John Day Basins will see temperatures warm another 4 to 5 degrees Saturday afternoon, with all other locations only seeing a 1 to 2 degrees increase. Late Saturday into Sunday, the upper trough will push onshore, bringing slight chances(15-25%) of scattered showers across the Blues and Wallowas. An attendant cold front with the trough will push across the forecast area during the afternoon Sunday, increasing winds through the Cascade gaps and across the lower elevations. The typically breezy to locally windy areas of the Kittitas valley, Simcoe Highlands, OR Columbia Basin, and southern Blue mountain foothills will see a 70-85% chance of meeting or exceeding a 24-hr peak wind gust of 45mph. Otherwise, the cold front will tap into weak surface instability with modest low level lapse rates in Wallowa county, resulting in slight chances (~15%) of isolated thunderstorms in the afternoon. Lawhorn/82 .LONG TERM...Monday through Friday...The long-term period is expected to begin with an upper-level trough over the region on Monday, subsequently replaced by drier northwesterly flow aloft and rising heights as an offshore upper-level ridge likely (80-90% chance) propagates eastward beginning on Tuesday. Troughing to the north over the Northern Rockies will likely (90-100% chance) result in breezy to windy westerly winds through the Cascade gaps through Wednesday. While no Red Flag conditions are currently forecast, the combination of the aforementioned wind and low relative humidity in the teens to lower 20s will support areas of elevated fire weather potential. By Friday, over 80% of ensemble members are advertising some flavor of a big ridge in the vicinity of the PacNW. Solutions range from an offshore high pressure center (56% of members) to an inland-located ridge axis over the forecast area (25% of members). The unlikely solution (17-19% chance) for Thursday and Friday is another trough over the PacNW. The latter solution would result in much cooler temperatures relative to what is forecast. Moreover, it would support light precipitation for the Cascade crest and northern Blue Mountains. Given the favored ridging pattern, little to no precipitation chances (<10%) exist area-wide through the week. Moreover, thunderstorm chances are also low (<20%) through the period, and peak on Monday afternoon across the Blue Mountains. The anticipated warming trend through the week results in Moderate HeatRisk forecast for the lower elevations of the Columbia Basin and Blue Mountain foothills by Friday -- afternoon high temperatures have a 50-70% chance of exceeding 90 degrees, and a 5-15% chance of exceeding 100 degrees for our main population centers. Plunkett/86 && .AVIATION...Previous Discussion...06Z TAFS...All sites in VFR during this period with clear skies overnight then onset of some then high clouds Friday. Winds will continue to decrease becoming less than 10kts overnight and Friday. && .PRELIMINARY POINT TEMPS/POPS... PDT 81 55 84 57 / 0 0 0 10 ALW 83 57 87 59 / 0 0 0 10 PSC 85 59 88 62 / 0 0 0 10 YKM 82 57 85 57 / 0 0 0 0 HRI 85 57 88 61 / 0 0 0 10 ELN 80 55 81 55 / 0 0 0 10 RDM 80 50 80 50 / 0 0 0 0 LGD 78 52 83 55 / 0 0 0 20 GCD 81 52 87 53 / 0 0 0 10 DLS 85 59 85 61 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...82 LONG TERM....86 AVIATION...91