Weston, OR 97886 Weather

Key messages

- Near- to below-normal temperatures into next week.

- Periodic showers today, mainly along the Cascade crest. Medium-high (30-70%) chance of precipitation for central/eastern Oregon and southeast Washington over the weekend.

- Low chance (30% or less, except for freeze-prone areas) of a season-ending freeze for the eastern Columbia River Gorge Saturday and Monday.

Discussion

Not too much of a change in satellite imagery since yesterday's discussion. Water vapor imagery shows a large, quasi-stationary low-pressure system located just offshore of the Pacific Northwest. Middle and high cloud cover has increased since yesterday, and this appears to have helped put a damper on notable fog formation early this morning. Radar reveals little in the way of returns over the forecast area.

Ensemble NWP guidance is in excellent agreement that a shortwave currently visible just off the southwest Oregon coast will round the aforementioned upper-level low later this morning and induce low chances (30% or lower) of showers for the Oregon Cascade crest and medium chances (30-70%) of showers for the Washington Cascades. Farther east, dry conditions are forecast.

Over the weekend, the low is expected (95% confidence) to transition to an open-wave trough and move inland. While chances of precipitation have trended downward slightly, they are still medium-high (30-70%) across the majority of central/eastern Oregon and southeast Washington Saturday afternoon through Sunday morning. The best chance of significant precipitation will be over Wallowa County where the NBM places a 30-60% chance of 0.25" and 10-30% chance of 0.50" of QPF through Sunday.

Ensemble solutions are coming into a better concensus with regard to when the trough will exit to the east and upper- level ridging will build in from the Pacific; specifically, ensemble means suggest the trough will slide east late Sunday afternoon into Sunday night, and an amplified upper-level ridge will be overhead by Monday morning. Given clearing skies and dry conditions, this presents the best chance, albeit low at 30% or less, of a season-ending freeze for the eastern Columbia River Gorge. Freeze-prone portions of the Gorge do have somewhat higher chances of freezing, but at this time confidence remains too low to issue any watches.

Uncertainty in the 500-hPa pattern then grows Tuesday through the remainder of the week. Aside from a very low chance (5-15%) of precipitation on Tuesday, mostly dry conditions are forecast to continue until Thursday when ensemble guidance hints at the return of some more active weather. Even then, chances of precipitation remain low (40% or less, highest for the Cascades).

Aviation

VFR conditions are forecast at all sites for the next 24 hours. While high-resolution model guidance shows low-medium (10-50%) probability of MVFR or lower CIGs/VSBYs this morning at BDN/RDM, and lower probabilities (20% or less) elsewhere, model guidance has been more pessimistic with CIGs/VSBYs compared to what has been observed. Thus, have opted to forgo any mention of sub-VFR conditions in the 12Z TAFs. Otherwise, chances of precipitation are very low (10% or less), and winds of 12 kts or less are anticipated through the period.

.Preliminary Point Temps/PoPs: PDT 49 33 48 33 / 0 0 0 30 ALW 50 36 49 37 / 0 0 10 40 PSC 54 31 52 33 / 0 0 0 20 YKM 53 31 52 32 / 10 10 0 10 HRI 52 31 49 32 / 0 0 0 30 ELN 49 23 48 25 / 20 0 10 20 RDM 50 24 46 23 / 0 0 20 40 LGD 57 32 55 35 / 0 0 30 40 GCD 57 34 55 35 / 0 0 20 40 DLS 55 33 53 35 / 20 10 0 30

Watches, warnings and advisories

WA: None. OR: None.