textproduct: Pendleton

KEY MESSAGES

- Temperatures warming to above normal through early next week

- Uncertainty late Friday through early next week in potential for mountain shower and thunderstorm activity

DISCUSSION

Today through Friday: A weak shortwave exiting the area has lead to cloudy conditions across the eastern half of the forecast area tonight. Radar tonight does show very weak echo returns across portions of the Blues, though surface observations show nothing making it to the ground at this time. Across the remainder of the forecast area, winds have become light, with otherwise quiet conditions at the surface.

Today, an upper level ridge will build over the PacNW and persist overhead through early Friday (confidence 80-90%). The building high pressure aloft will result in drying and warming conditions across much of the forecast area. High temperatures will warm well above normal into the upper 70s to lower 80s across the lower and mid elevations by Friday afternoon.

The upper ridge will flatten and push east as an upper trough sets up offshore the PacNW the second half of Friday. Conditions will remain mostly dry across the forecast area, however increasing southerly flow with and embedded shortwave impulse will bring isolated shower chances to the Cascade crest late in the afternoon and overnight (confidence 55-65%)

Saturday through Tuesday: Ensemble cluster guidance begins in good agreement of the aforementioned upper trough digging south and transitioning into a closed low off the northern CA coast late Saturday. During this time, the trough/low will place a southerly flow into OR, allowing weak instability to develop over the eastern mountains and OR Cascades. This will lead to slight chances (15-20%) of isolated showers developing with a slight chance (~15%) of isolated thunderstorms as well.

Sunday through Tuesday, while overall agreement in the development of the closed low and it's eventual push inland is high amongst ensemble members of the ECMWF, GFS, and Canadian, there is disagreement surrounding the location of the low offshore, the extent of the low, and the timing of it's transit inland. Scenarios range from a smaller low further offshore that would keep central OR and adjacent mountain areas dry, while a larger low circulation and/or a low centered closer to northern CA would produce isolated to scattered shower chances with isolated thunderstorms for Sunday. Monday and Tuesday, there is moderate confidence (40-55%) that the low's passage inland will bring shower and isolated thunderstorm chances across portions of central OR and the eastern mountains, however there is low confidence (15-25%) in timing and location of best chances of showers/thunderstorms owing to timing differences in the low moving inland.

In addition to impacts from the closed low, ensemble cluster solutions depict upper level ridging developing poleward of the low, resulting in continued above normal temperatures for the inland PacNW. By Monday, there will be a 50-70% chance for high temperatures to exceed 90 degrees across portions of Yakima valley and the WA Columbia Basin. Across the remainder of the lower Columbia Basin, the Gorge, Kittitas valley, and the John Day basin there is a 45-70% chance of exceeding 85 degrees Monday afternoon. Lawhorn/82

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR conditions to prevail through period. Winds will be light, 12kts or less, at all sites. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 68 42 75 45 / 0 0 0 0 ALW 69 46 75 49 / 10 0 0 0 PSC 74 44 80 45 / 0 0 0 0 YKM 73 44 77 47 / 0 0 0 0 HRI 72 42 78 44 / 0 0 0 0 ELN 68 42 73 43 / 0 0 0 0 RDM 66 34 72 37 / 0 0 0 0 LGD 66 38 71 41 / 10 0 0 0 GCD 65 37 71 42 / 20 10 0 0 DLS 73 47 80 50 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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