textproduct: Pendleton

KEY MESSAGES

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

- Breezy lower elevations winds develop tonight through Wednesday

- Drying and warming trend late week through the weekend

DISCUSSION

Today through Wednesday: Satellite imagery this afternoon shows a shortwave trough with an attendant surface low just offshore the PacNW, with cloudy conditions across much of the region. Area radar shows the western half of WA/OR covered in showers, with shower activity extending to the east slopes of the Cascades, eastern Columbia River Gorge, and central OR.

A shortwave trough and surface low will continue to swing across the PacNW today through tonight. A rain shield will spread north and east from the Cascade crest through the remainder of this afternoon and evening, with isolated to scattered showers developing overnight. CAMs continue to indicate weak surface based instability developing across the eastern OR mountains this afternoon will also result in low chances (5-15%) of isolated thunderstorms. In the Columbia Basin, breezy winds will develop ahead of the precipitation late this afternoon, with wind gusts generally remaining less than 35 mph.

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 the WA Cascade crest, far northeast OR, and southeast WA late in the morning and afternoon Tuesday, resulting in a slight chance (15-20%) of isolated thunderstorms. However, thunderstorm activity is expected to diminish late in the afternoon as the trough lifts into MT. Otherwise, widespread breezy southwest to west winds (15-25 mph with gusts up to 40 mph) will develop tonight through tomorrow as a cold front boundary passage tightens pressure gradients across the forecast area. In the lower elevations, the strongest winds (sustained winds 25-35 mph with gusts up to 50 mph) are expected to develop across portions of north central OR, the eastern Columbia River Gorge, Simcoe Highlands, OR Columbia Basin, OR Blue Mtn foothills, and the Kittitas valley.

By Wednesday, the trough will slide further east of the region while upper level ridging will develop over the northeast Pacific. Any lingering shower activity over the mountains will diminish by the afternoon as the region comes under the influence of the upper ridge offshore. breezy to locally breezy winds will continue into Wednesday evening, but will become light Wednesday night into Thursday.

Thursday through Sunday: Late in the work week through the weekend, there is great agreement amongst ensemble guidance in warmer and drier conditions developing as upper level ridging continues to build offshore the PacNW. That said, uncertainty does grow in the amplitude and position of the ridge offshore. While ensemble cluster solutions all keep the region dry through this period, about half of the members keep the upper ridge further offshore with a northerly flow into the intermountain PacNW. These solutions also favor a shortwave trough to clip the region, which would increase winds in the lower elevations and bring elevated fire weather concerns. The other half of solutions keep the ridge axis much closer with northwest flow over the region. This solution would keep the trend of light winds, but would favor increased warming across the forecast area over the weekend. Speaking of temperatures, the NBM shows a 40-60% chance of areas of the Columbia Basin/Gorge and Yakima valley reaching 90 degrees Saturday, with a widespread 40-75% chance of 90 degrees across most lower elevation locations Sunday. Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

VFR conditions expected through the period. That said, a weather system moving through the region will bring rain impacts to all sites by this afternoon and evening, with a prob30 chance of showers continuing into overnight hours at sites DLS/PDT/ALW/YKM/PSC. Winds will become breezy tonight at sites PDT/RDM/BDN/ALW/PSC, with winds increasing to around 15kts with gusts around 25kts. Winds will increase at sites DLS/YKM around 15Z. There is moderate confidence (55-70%) that winds at sites DLS/PDT/PSC are expected to increase late tomorrow morning and in the afternoon to 15-25kts with gusts around 35kts. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 49 67 42 69 / 90 20 10 0 ALW 52 67 47 69 / 90 50 20 10 PSC 48 73 44 75 / 90 10 0 0 YKM 48 70 42 74 / 80 10 0 0 HRI 48 71 44 73 / 80 10 0 0 ELN 45 63 39 65 / 100 30 10 0 RDM 43 65 32 69 / 50 10 0 0 LGD 46 63 41 64 / 90 60 30 20 GCD 43 67 37 67 / 90 20 10 0 DLS 53 68 49 70 / 90 30 10 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 2 AM to 11 PM PDT Tuesday for WAZ024-521. Wind Advisory from 8 AM to 11 PM PDT Tuesday for WAZ026. OR...Wind Advisory from 2 AM to 11 PM PDT Tuesday for ORZ041-044- 508. Wind Advisory from 8 AM to 11 PM PDT Tuesday for ORZ507. Wind Advisory from 11 PM this evening to 5 PM PDT Tuesday for ORZ510.