textproduct: Pendleton

KEY MESSAGES

- Lower (<20 percent) chances of showers and thunderstorms Sunday and a 20-30 percent chance of showers Monday with a (<20 percent) chance of thunderstorms mainly from the Blue Mountains eastward. - Increasing winds later Monday into Tuesday.

DISCUSSION...issued at 200 PM PDT Sat Aug 15 2026

Southwesterly flow remains over the Pacific Northwest. Low pressure will move from near British Columbia to well off the Oregon and California coasts by Monday afternoon. This will allow for a more split flow pattern to develop early next week, which should keep things dry. A ridge will build back over the area by midweek, with a return to southwest or south flow possible thereafter.

The showers and thunderstorms that affected portions of the Columbia and Blue Mountain foothills earlier have weakened and were moving out of the area. Additional showers and thunderstorms were expected to develop mainly from the Blue Mountains eastward this afternoon. Any thunderstorms could contain gust winds and abundant lightning. A Red Flag Warning remains in effect for mainly the eastern Oregon Mountains through this evening.

The model guidance is in reasonable agreement that thunderstorm activity on Sunday will be significantly less and further east. While isolated activity can not be ruled out, especially over Wallowa County, it does not appear to be widespread enough to warrant any kind of additional headlines. Activity could possibly be a bit higher on Monday, but looks to be mainly over Wallowa County.

As we go from Monday into Tuesday, a split flow develops and winds will increase across the area. There will be some gustiness developing Monday evening, but the better chances are Tuesday afternoon across the Cascade gaps, Kittitas Valley, Simcoe Highlands, Columbia Basin and Gorge. Winds could gust 20 to 30 mph in these areas. RH values will also decrease from Monday into Tuesday. NBM probabilities of wind gusts >= 25 mph are >70 percent in these areas. However, with the exception of the Kittitas Valley, NBM probabilities of wind gusts >=39 mph are less than 40 percent. Will need to see how these winds evolve over the next few days to see if any headlines will be needed, but fire weather concerns will at least be elevated.

The midweek period looks dry before the south or southwest flow returns and an upper low comes into play as well. All of these features could bring additional chances of precipitation by the end of the week.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

VFR conditions are forecast at all sites through the period. Winds will become breezy at DLS again Sunday afternoon. Elsewhere, lighter winds are forecast, albeit with some afternoon gustiness, especially at RDM/BDN. Precipitation chances are very low (10 percent or less) at all sites on Sunday.

FIRE WEATHER

For Sunday and Monday, thunderstorm chances will be less (<20 percent) and mainly confined to these same areas, though chances could be a bit higher on Monday than Sunday. At this time, there are no plans to extend the Red Flag Warning or issue another one for Sunday due to the lower probabilities and much less areal coverage. Current thinking is no headlines will be needed for Monday either, but will reevaluate that with each subsequent model run.

The next concern then becomes gusty winds later Monday into Tuesday, which could be in the 25 to 30 mph range, coupled with decreasing humidities. Fire weather concerns will be elevated, but will need to see how things do or don't come together for any weather headlines.

Preliminary Point Temps/PoPs

PDT 56 88 57 89 / 10 0 0 0 ALW 62 89 63 90 / 20 0 0 0 PSC 57 93 60 93 / 0 0 0 0 YKM 60 91 61 93 / 10 0 0 0 HRI 60 91 61 92 / 0 0 0 0 ELN 58 86 59 89 / 10 0 0 0 RDM 49 87 51 88 / 10 0 0 0 LGD 54 89 57 91 / 20 10 0 10 GCD 54 91 56 91 / 0 0 0 0 DLS 63 89 61 92 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until noon PDT Monday for WAZ026-522-523. OR...Air Quality Alert until noon PDT Monday for ORZ041-503-505-506- 508>511.