Marine Weather and Tide Forecast for Yakima, WA

FXUS66 KPDT 300955 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 255 AM PDT Wed Apr 30 2025

SHORT TERM
Today through Friday...Water vapor imagery tonight shows the axis of an upper shortwave trough moving southeast of the region currently, while an upper level ridge builds offshore.
As of writing this, the forecast area us under mostly clear skies, though decks of cirrus are moving southeast across portions of the WA Columbia Basin and developing off the Cascade crest.

By the morning hours, the aforementioned upper level shortwave trough will cross into the northern Rockies, allowing the upper ridge in the eastern North Pacific to approach the PacNW throughout today. The upper ridge will move inland later this evening, and continue to move east across the forecast area where it will exit by Friday afternoon. During this period, the upper ridge will facilitate a drying trend across much of the region, while temperatures will see a warming trend that will peak Friday afternoon. In fact, there is around a 50-80% chance that temperatures in the Yakima valley, Lower Columbia Basin, and portions of the Blue Mountain foothills will breach the 85 degree mark Friday afternoon, with a 60-90% chance that other lower elevation locations (including central OR) will see 80 degrees or higher.

By Friday afternoon, an upper level trough with a surface cold front will have arrived to the PacNW coast as the upper ridge takes its exit to the east. Out ahead of the trough/cold front, a deep southerly will result in increasing instability from the OR Cascades to Ochoco-John Day Highlands Friday afternoon. Shortwave impulses will be riding up the front of the trough Friday afternoon as well, initiating showers across the OR Cascade crest and central OR through the early evening. These showers will also be able to tap into high low level lapse rates as well as the increasing instability to result in a slight chance (<20%) of isolated thunderstorms developing into the evening hours. Breezy west to northwest winds (gusts 25-40mph) will also be developing through the late afternoon into Friday night through the eastern Gorge and the Kittitas valley as pressure gradients tighten in response to the approaching cold front. Friday night, showers will continue to develop along the Cascade crest/east slopes, central OR, and the Ochoco-John Day Highlands as shortwave impulses continue to ride up the upper trough and the cold front arrives to the Cascades.

LONG TERM
Saturday through Wednesday...Sensible weather concerns through the extended forecast will revolve around the passage of an upper trough over the PacNW that will bring shower activity through Sunday afternoon. A broad upper low will develop in the Gulf of Alaska, placing the region under a dry southwest flow aloft into middle of next week.

Shower activity will expand eastward Saturday morning as a cold front boundary sweeps across the forecast area while the trough axis moves inland. In the lower elevations, shower activity will diminish behind the cold front passage, with most lower elevation locations seeing dry conditions develop by the late afternoon.
Ensemble guidance is in good agreement that the upper trough will transition into an upper low Saturday night into Sunday morning, with the low continuing to move into the Desert Southwest throughout Sunday(confidence 60-80%). This evolution of the trough will result in rain and high mountain snow shower activity diminishing across the Cascades Saturday night, and the eastern mountains by Sunday afternoon (confidence 60-70%). Through Sunday afternoon, there is a 50-70% chance that the Cascade crest/east slopes and the eastern mountains will see 0.2 inches of rainfall with less than a 40% chance of half an inch of snow above 5kft.
There is good agreement that the combination of the cold front passage and the trough passage will keep tightened pressure gradients across the forecast area Saturday and Sunday, resulting in wind gusts 35-45mph through the Kittitas valley and the Gorge, and gusts 20-35 across portions of the Columbia Basin, north central OR, central OR, and the Blue mountain foothills.

Ensemble cluster guidance is in good agreement that the upper closed low will continue to stay southeast of the region Sunday afternoon through Monday, while upper level ridging will develop over the PacNW(confidence 50-65%). By Tuesday morning, the ridge axis will push east as a broad upper low develops in the Gulf of Alaska, placing the PacNW under southwest flow aloft through Wednesday (confidence 40-60%). Under this pattern, conditions will remain mostly dry(confidence 50-70%), though cannot rule out around a 15% chance of showers along the Cascade crest each afternoons and early evening (confidence 20-25%). Ensemble cluster guidance also indicates a slight warming trend into the middle of next week, with widespread lower elevation chances between 40-70% of meeting or exceeding 75 degrees Monday and Tuesday afternoon. Lawhorn/82
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