textproduct: Pendleton

KEY MESSAGES

- Widespread rain shower chances and isolated thunderstorms across the forecast area Monday into Tuesday

- Breezy lower elevations winds develop Tuesday through Wednesday

- Increasing potential for drying and warming trend into next weekend

DISCUSSION

Today: A transient ridge currently traversing the PacNW has brought dry conditions across the area, with satellite showing scattered cumulus fields across portions of the Cascades, Columbia Basin, and eastern mountains. Breezy to locally breezy conditions (10-25 mph with gusts to around 20-35mph) continue across the lower elevations this afternoon as a tightened cross-Cascade pressure gradient remains. Dry conditions and breezy winds will persist through the remainder today and into early Monday.

Monday through Wednesday: The transient ridge over the region will push northeast tomorrow as a shortwave trough dives into the PacNW from the Gulf of Alaska. Rain showers will develop across the Cascade crest Monday morning as the shortwave pushes inland, then quickly spread north and east as the trough axis swings across the region through the remainder of the afternoon and evening. Weak surface based instability developing across the eastern OR mountains Monday afternoon will also result in isolated thunder chances. In the Columbia Basin, breezy winds will develop with and just ahead of the main line of showers Monday afternoon and early evening, though any wind gusts look to remain below 35mph.

Tuesday, shower activity will retreat mostly to the mountain areas and Blue mountain foothills as northwest flow aloft develops behind the trough axis exit. Weak instability will develop across far northeast OR and southeast WA late in the morning and afternoon Tuesday, resulting isolated thunderstorms developing. However, thunderstorm activity is expected to diminish late in the afternoon as the trough lifts into MT and southern Alberta. Otherwise, breezy to gusty conditions (15-30mph with gusts up to 40 mph) will develop in the lower elevations throughout Tuesday. There is a 60-80% chance of gusts exceeding 45mph in the Kittitas valley, OR Columbia Basin, OR Blue mountain foothills, across the Horse Heaven Hills, and areas northeast of Dayton.

By Wednesday, ensemble guidance solutions favor the trough sliding further east and upper level ridging developing over the northeast Pacific. As the ridge further develops throughout Wednesday, shower activity will diminish across much of the PacNW, and breezy to locally breezy winds will continue across the lower elevations.

Thursday through Saturday: Ensemble guidance has come into better agreement since yesterday in the evolution of the upper level ridge offshore. About 75% ensemble members now favor the upper ridge amplifying and moving closer offshore the PacNW Thursday into the weekend. While the upper ridge may not be fully over the PacNW, the region will come under the influence of a warming and drying trend through the end of the weekend. Afternoon temperatures are advertised to warm into the mid to upper 80s by Saturday, with NBM probabilities showing a 35-50% chance of hitting 90 degrees across portions of the Columbia Basin/Gorge, and the Yakima valley. That said, it is worth noting that the remaining ~25% of ensemble members favor an upper ridge further offshore, which would allow shortwaves rounding an upper low in central Canada to clip the PacNW, producing light rain showers in the WA Cascades, northern Blues, and Wallowas. Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Dry and sunny conditions prevail through today and overnight. A system bringing in rain showers and an occasional isolated thunderstorm will move in late tomorrow morning. Not expecting any chances for the TAF sites themselves, but light to moderate rain showers will move in around 17Z for the Central Oregon and DLS sites. Was less confident that the rest of the sites will see rain showers before the 00Z TAF period ends, but have put in PROB30'sat 22Z for PDT, ALW, and PSC. All sites have a slight chance (5 to 15 percent) of developing temporary MVFR conditions, that can bring visibilities >6SM and lower cloud decks below 3000 feet. Heavier showers could bring some breezier conditions in the outflow of the rain system.

Preliminary Point Temps/PoPs

PDT 44 70 48 67 / 0 40 90 70 ALW 48 73 52 67 / 0 20 90 90 PSC 45 74 48 73 / 0 20 70 40 YKM 46 69 47 71 / 0 50 80 10 HRI 45 72 47 71 / 0 30 70 30 ELN 40 64 44 64 / 0 50 90 40 RDM 40 64 43 64 / 0 80 70 10 LGD 40 71 46 63 / 0 20 100 100 GCD 40 69 44 65 / 0 50 90 60 DLS 50 67 52 68 / 0 70 90 50

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.