Marine Weather and Tide Forecast for Boardman, OR

FXUS66 KPDT 231015 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 315 AM PDT Fri May 23 2025

SHORT TERM
Today through Sunday...Nighttime satellite imagery shows a band of cirrus lifting across southeastern WA while a stratus layer spills over the OR Cascades into central and north central OR. As for the rest of the forecast area, skies remain clear to partly cloudy.

A fairly weak upper shortwave trough will slide across the PacNW today, with what limited moisture it contains staying along the southern portions of the forecast area. A few isolated to scattered rain showers will develop over the higher mountainous terrain from east Grant county to the northern Blues and Wallowas this afternoon, but shower activity will quickly diminish by the early evening. Clearing skies will also result in weak surface based instability developing across these areas, resulting in a slight chance (~15%) in an isolated thunderstorm or two.

Upper level ridging will begin building into the region later tonight through early Sunday morning, resulting in a drying/warming trend with light winds. Temperatures will be warming about 5 to 10 degrees each day, with a 55-70% chance of the WA Columbia Basin and John Day Basin reaching 90 degrees by Sunday afternoon; chances drop off to 25-50% in the OR Columbia Basin. Otherwise, temperatures will be in the 80s in the lower elevations, with mid 60s to 70s in the mountains (70-80% confidence).

The forecast area will stay under the influence of the upper level ridge through at least Sunday afternoon, however, an upper level trough with an attendant cold front offshore will have already pushed the ridge axis east of the forecast by Sunday morning. The upper trough will continue to push towards the PacNW Sunday, placing the forecast area under a deep south to southwest flow aloft. Ahead of the trough, there is mod-high confidence (60-80%)
that CAPE values will increase to 300-700 J/kg across the OR Cascade east slopes, central OR, and the eastern mountains as well as strong to modest lapse rates in the low (0-3km) to mid (3-6km)
levels developing in these areas. Developing shower activity by Sunday afternoon will be able to tap into this available instability, resulting in isolated to widespread thunderstorms developing across the aforementioned areas, with light to briefly moderate rain showers developing across the remainder of the forecast area. Developing thunderstorms will be capable of gusty/erratic winds and small hail. The cross-Cascade surface pressure gradient will strengthen in response to the approaching cold front Sunday afternoon, resulting in breezy winds 15-25mph with gusts to around 35mph developing through the Cascade gaps and spilling into portions of the Columbia Basin Sunday afternoon and evening (confidence 70-80%). Lawhorn/82

LONG TERM
Monday through Thursday...Sensible weather concerns through the extended period will revolve around an upper trough and cold front passage Monday, with upper level ridging building over the region into the midweek.

Ensemble guidance is in good agreement that an upper trough and attendant cold front will continue to push across the PacNW through Monday night. While more widespread Sunday, shower activity will be confined to the Cascade crest and the eastern mountains throughout Monday, while isolated thunderstorm activity would be confined mainly to the higher terrain of the eastern mountains (confidence 55-70%). Shower activity will diminish through Monday evening as the trough exits to the east and upper level ridging builds into the PacNW from the south.

The upper level ridge will continue to build across the region Tuesday into Wednesday, resulting in a drying and warming trend during this period. However, early Wednesday through Thursday, ensemble members begin depicting a developing a weak broad trough to the south that will ride up the western CONUS shoreline into the PacNW. That said, ensemble members struggle with timing, position, and intensity of this feature as soon as Tuesday night.
In fact, about 10-15% of cluster members favor a this feature arriving to the region by Wednesday afternoon with light showers developing across the eastern mountains. The remainder of solutions depict the upper trough arriving to the PacNW and producing showers between Wednesday night to as late as Thursday afternoon. Confidence in the deterministic forecast during this period is low (20-30%), however, confidence is moderate (40-50%)
that shower activity will develop across the Cascade crest and eastern mountains by at least Thursday. Lawhorn/82
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