Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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836 FXUS66 KPDT 302143 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 243 PM PDT Thu May 30 2024 .SHORT TERM...Tonight through Saturday...The short term remains quiet, with no sensible weather concerns anticipated through the start of the weekend under a transient ridge that will give way to a quick moving and weak shortwave, with some mountain showers and our usual breezy but sub-advisory level winds possible at that time. Ensembles have a good agreement on the pattern over the next few days as a ridge makes its way onshore and then quickly moves eastwards as a weak shortwave trough sweeps across Saturday into Sunday. Under this pattern, a steady warming trend will occur thanks to the ridging, with temperatures steadily rising around 4 to 8 degrees tomorrow, with a smaller increase to possibly small decrease on Saturday as the front associated with the shortwave trough moves across the region. Meanwhile, conditions stay calm and clear most of tonight through Friday, but by Saturday overcast skies are expected with the passage of the boundary along with breezy winds. Winds with the passage of the system look to be fairly run of the mill for the region, strongest in the Kittitas Valley, Simcoe Highlands, and along the Columbia Gorge through lower Columbia Basin. The NBM projects a 45-90% chance of winds gusting to or in excess of 40 mph in these respective areas, but raising the threshold to 45 mph all but wipes out probabilities, keeping these conditions well below wind advisory criteria. Meanwhile, although some light showers in the mountains could be possible as this system passes, the probability for greater than or equal to a tenth of an inch of precipitation is zero everywhere except the northern Cascades, which only have a 20% chance at best. Overall, we remain generally quiet through the beginning of the weekend, a precursor to a bit more active pattern moving into next week. Goatley/87 .LONG TERM...Sunday through Thursday...Sensible weather concerns through the extended period will revolve around the passage of an upper trough and associated frontal system Sunday through Monday, bringing with it widespread rain chances and windy conditions. By Tuesday morning upper level ridging will build into the PacNW from the desert Southwest, starting a drying and warming trend that will extend through the late week. Sunday starts with a transient ridge quickly traversing the region ahead of an upper trough feature out in the northeast Pacific. Following on the heels of the ridge exit Sunday afternoon, a warm front associated with the upper trough will arrive to the Cascades by the afternoon. Light rain showers will push across eastern WA and OR Sunday evening with the warm front passage, and will pick up in intensity Sunday night through Monday morning with an associated cold front boundary passage. Monday afternoon into the evening, shower activity will continue across the eastern mountains and Cascades as the upper trough quickly slides across the PacNW. Overall, the rainfall associated with this system will be beneficial to the mountain and lower elevation regions, though periods of moderate to locally heavy rain can be expected with the cold front passage. Ensemble guidance points to an Atmospheric River as the culprit to the increased rainfall Monday morning. ECMWF and GFS ensemble mean solutions show a 150-200% of normal PWATS with the cold front passage, and GFS ensemble AR landfall tools show a 90-100% chance of IVT greater than 250 kg/m/s across southeast WA and northeast OR Monday morning. As for rainfall amounts through 5PM Monday: along the Cascade crest, northern Blues, and Wallowas NBM probabilities for 0.75 inches of rainfall is 55-75%; across the Cascade east slopes, Blue mountain foothills, and southern Blues NBM probabilities for 0.5 inches of rainfall are 45-60%; and across the remainder of the forecast area there is 45-60% chance for 0.25 inches of rainfall. Ensemble and deterministic guidance also indicate the cold front passage initiating isolated thunderstorms across the eastern mountains Monday afternoon(confidence 30-40%). Besides precipitation, the cold front passage and the follow-up from the upper trough will tighten pressure gradients across the region, resulting in windy conditions through the Cascade gaps and across the Columbia Basin. Most recent NBM QMD probabilities show a 70-80% chance of wind gusts greater than 45mph in the OR Columbia Basin, Simcoe Highlands, the Gorge west of the Dalles, and the eastern portions of the Kittitas valley. As for the rest of the lower elevations, NBM probabilities for gusts greater than 40 mph are between 55-70%. Tuesday through Thursday, 70-80% of ensemble members from the GFS, ECMWF, and Canadian ensemble suites are in agreement of an upper level ridge building into the PacNW from the desert southwest. While drying conditions are expected with ridging patterns, there are chances (25-45%) of rain showers across the WA Cascades Tuesday as weak shortwave impulses clip this area. Lastly, temperatures will be on a 5 to 9 degree increase each day, with a 65-80% chance that the lower elevations will exceed 80 degrees by Wednesday, and a 45-60% chance to exceed 90 degrees Thursday in the Lower Columbia Basin, eastern Gorge, and the Yakima valley. Lawhorn/82 && .AVIATION...18Z TAFs...VFR conditions to prevail at all sites through the period. Smoke impacts have lifted from sites RDM/BDN this morning, though low confidence (15%) if smoke impacts will return again late tonight. Winds will be light, less than 12kts, at most sites through the period. The exceptions will be at site DLS/RDM/BDN where winds of 12-15kts with gusts 20-25kts will be possible this afternoon. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 41 75 50 76 / 0 0 0 0 ALW 45 77 52 79 / 0 0 0 0 PSC 47 79 54 83 / 0 0 0 0 YKM 40 78 52 79 / 0 0 0 0 HRI 44 79 52 81 / 0 0 0 0 ELN 41 76 52 73 / 0 0 0 0 RDM 37 77 45 73 / 0 0 0 0 LGD 38 72 47 72 / 0 0 0 0 GCD 38 76 47 75 / 0 0 0 10 DLS 47 81 56 76 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...87 LONG TERM....82 AVIATION...82