FXUS66 KPDT 190515 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1015 PM PDT Mon May 18 2026 .KEY MESSAGES... - Scattered showers and isolated thunderstorms over Wallowa County today - Breezy to locally windy westerly winds through the Cascade gaps today and Tuesday - Warming and mostly dry Tuesday through the week && .DISCUSSION...Daytime heating has led to modest instability (surface-based CAPE of a couple hundred J/kg or less per SPC's RAP-based mesoanalysis and forecast soundings from the 12Z HREF/REFS) this afternoon across the Blues and Washington Cascades. While activity has been isolated elsewhere, scattered rain showers have developed across Wallowa County. Through evening, there is a slight chance (15 percent) of thunder across Wallowa County, with lower (5-10 percent) chances of rain showers and thunder for other parts of the Blues as well as the Washington Cascades. Tuesday through Saturday, warming temperatures and mostly dry conditions are forecast region-wide as an upper-level ridge of high pressure will likely (90-95 percent chance) build into the region from the Pacific and dominate the weather. A couple weak shortwaves passing through northwesterly flow aloft coupled with modest diurnally induced instability (surface-based CAPE of a up to a couple hundred J/kg from forecast soundings) may facilitate some isolated showers for the mountains through Thursday, but PoPs are low (10 percent or less). Breezy to locally windy westerly winds are forecast through the Cascade gaps today and Tuesday, but not anticipating a need for any wind headlines. In yesterday's discussion, mentioned the potential for westerly winds to meet advisory criteria on Thursday. Ensemble guidance has since trended towards a solution that would lead to a wind reversal to mostly light northeasterly (offshore) winds late Wednesday and Thursday as a shortwave digs south across the northern Plains and Rockies, just clipping the edge of our forecast area. Considering there is still some ensemble spread, will place confidence in this solution at medium (60 percent). Considerable uncertainty in the 500-hPa pattern is present in ensemble solutions by the weekend, with roughly 45-50 percent of the variance in solutions explained by timing differences among solutions regarding the arrival of a trough or closed low from the Pacific. The NBM has westerly winds returning to the region by late Friday, persisting through the weekend. Highest chances (10-40 percent) of reaching advisory-level winds have now been pushed back to Saturday and Sunday through wind-prone areas of the lower elevations, primarily the eastern Columbia River Gorge, north-central Oregon, the foothills of the Blue Mountains, and the Kittitas Valley. Of course, the magnitude of winds will be tied to the synoptic pattern, and given the uncertainty (see paragraph above), can't really talk about much confidence in forecast details yet. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...VFR conditions to prevail through the period. Winds will mostly be light, 12kts or less, and diurnally/terrain drive through the period. THe exceptions are site DLS/RDM/BDN, where winds will increase to 12-18kts with gusts to around 27kts at site DLS after 17Z; sites RDM/BDN will see gusts around 15-18kts develop after 19Z. Lawhorn/82 && .Preliminary Point Temps/PoPs... PDT 42 72 45 73 / 0 0 0 0 ALW 46 72 50 73 / 0 0 0 0 PSC 44 77 48 79 / 0 0 0 0 YKM 44 75 47 79 / 10 0 0 0 HRI 44 75 48 77 / 0 0 0 0 ELN 41 68 43 73 / 0 0 0 0 RDM 30 72 37 74 / 0 0 0 0 LGD 36 68 40 70 / 0 0 0 0 GCD 34 70 38 73 / 0 0 0 0 DLS 45 73 49 78 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... WA...None. OR...None. && $$ DISCUSSION...86 AVIATION...82