textproduct: Pendleton

KEY MESSAGES

- Upper level ridging over the region will bring a warming and drying trend across the forecast area, with high end moderate to major HeatRisk developing in and around the Columbia Basin

- Monsoonal moisture push with shortwave impulses will result in a return of isolated to scattered thunderstorm activity across central OR and the northeast OR mountains

- Upper level troughing offshore will produce breezy winds in the Cascade Gaps and Columbia Basin Thursday into the weekend

DISCUSSION

Satellite imagery tonight shows mid to upper level cloud cover spreading north and east across the forecast area, with regional radar showing very light returns from Deschutes county to Baker county. This cloud cover is associated with a shortwave impulse that is pushing into southern OR and is forecast to ridge overtop an upper ridge over the PacNW.

Sensible weather concerns through the middle of the week will revolve around a strengthening upper level ridge producing hot temperatures in and around the Columbia Basin; the upper ridge will shift east Wednesday into Thursday, allowing monsoonal moisture and shortwave impulses to move across the forecast area and produce isolated to scattered thunderstorm chances.

Through early Thursday, the PacNW will see an upper level ridge of high pressure gradually strengthen each day while deep southerly flow persists aloft. This will introduce increasingly hot temperatures across the lower elevations, with the brunt of the heating expected in the Columbia Basin/Gorge and adjacent foothills/valleys through Thursday. Portions of the OR/WA Columbia Basin and the eastern Gorge will reach the 100 degree mark as early as Tuesday afternoon, with the Blue Mountain foothills, Yakima/Kittitas valleys, portions of north central Oregon, and portions of the John Day Basin reaching 100 degrees Wednesday(confidence 70-90%). These temperatures will continue in most of these areas Thursday, however increasing winds through the Cascade Gaps late afternoon may limit heating through the eastern Gorge and the Kittitas valley (confidence 60-70%). Between elevated afternoon and overnight temperatures, HeatRisk values across much of the lower elevations will be in the moderate to major categories starting Tuesday, with increasing confidence (70-80%) that heat highlights will be needed.

From now through the middle of the week, ensemble and deterministic guidance depicts a monsoonal moisture push riding the southerly flow into the intermountain PacNW, with PWATs rising to around 0.75 to 1.25 inches by this afternoon. However, activity isn't expected to develop until Wednesday when the upper ridge begins to push east, allowing shortwave impulses to lift across the forecast area. On Wednesday, the main thunderstorm activity will be focused across central OR and the mountainous terrain from the Cascade east slopes to the Elkhorn crest. In these areas, MUCAPE will be between 500-1000J/kg, low level lapse rates 8-10 C/km, and 0-6km shear between 20-40kts. These conditions will be enough for thunderstorms to develop in the afternoon and become organized as they propagate north. By Thursday, similar conditions will be present along the WA Cascades, Blue Mountains, and Wallowa county. Expect at least small hail, gusty outflow winds, frequent lightning, and a few storms to produce heavy downpours.

Late Thursday through the weekend, there is good agreement amongst ensemble cluster guidance that weak upper troughing will develop off the coast of the PacNW while upper level ridging pushes east and south. Southwest flow aloft will push prevent monsoonal moisture from advecting into the region, resulting in drying conditions across the forecast area. The proximity of the upper trough Friday and Saturday will also result in breezy west to northwest winds(15-25mph with gusts 25-40mph) through the Cascade gaps and across the Columbia Basin. Confidence is moderate (45-65%) that peak winds will overlap with critically low RHs in portions of the Columbia Basin and Cascade Gaps Friday and Saturday, resulting in elevated fire weather conditions those days. By Sunday, there remains good agreement that the trough will retrograde into the northeast Pacific, resulting in weaker Cascade gap winds (confidence 40-50%). Lawhorn/82

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

VFR conditions prevail through Monday with winds generally 10 kts or less.

FIRE WEATHER

Conditions will remain hot and dry into the middle of the week, with hottest conditions in the Columbia Basin and adjacent foothills/valleys. A shift in upper level ridging to the east will introduce increasing isolated to scattered thunderstorm chances. Wednesday, chances will be focused across central OR and the eastern mountains. Chances Thursday will be focused along the WA Cascade crest, Blue Mountains, and Wallowa county. Thunderstorms will be capable of frequent lightning, gusty outflow winds, small hail, and brief heavy downpours. Winds will increase through the Cascade Gaps and Columbia Basin Friday and Saturday, and are expected to overlap with critically dry conditions. Expect elevated to critical fire weather conditions those days. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 88 62 96 66 / 0 10 0 0 ALW 91 67 99 70 / 0 10 0 0 PSC 92 64 100 68 / 0 0 0 0 YKM 92 67 99 70 / 0 0 0 0 HRI 91 64 100 70 / 0 0 0 0 ELN 90 65 97 68 / 0 0 0 0 RDM 87 59 94 62 / 10 10 0 0 LGD 92 63 97 66 / 10 10 0 0 GCD 92 59 96 63 / 10 10 0 0 DLS 92 69 101 73 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Extreme Heat Watch from Tuesday morning through Thursday evening for WAZ024-027>029. OR...Extreme Heat Watch from Tuesday morning through Thursday evening for ORZ041-044-507. Air Quality Alert until noon PDT today for ORZ050-502-503-505- 506-508.