textproduct: Pendleton

DISCUSSION

Current satellite and radar imagery show light showers across the forecast area with the Lower Columbia Basin and portions of the Foothills of the Northern Blues-OR having locally moderate rainfall with sporadic lightning.

Thanks to the upper shortwave and persistent atmospheric river, this will help influence in developing low-topped convection with the frontal system mainly over the eastern mountains during the early morning hours. This also puts that area in the Marginal Risk of severe thunderstorms, according to the Storm Prediction Center (SPC). The 00Z HREF guidance suggests a 10-20% probability for thunder over the eastern mountains early this morning. Also, the CAMs seem to favor a 30-50% prob for thunderstorms across the aforementioned area with the models (GFS, RAP, NAM) showing scant instability. That said, this may be enough to potentially support sporadic/sub-severe storms with scant lighting flashes.

In addition to the shortwave and atmospheric river, this high wind event will continue through this afternoon across most of the forecast area. This will remain driven by the strong low-level jet streak of 50-100 kts along with a surface pressure difference of 10- 20 mb between PDX (Portland) and GEG (Spokane). High Wind Warnings (from Columbia Basin to central OR) and a Wind Advisory (from John Day Basin, Grand Ronde Valley and Wallowas) will remain effective through this afternoon. Strongest wind gusts of 55-65 mph are expected along portions of the Blue Mountain foothills and slopes of the northern Blue Mountains. By late this afternoon, winds will then slowly decrease with lingering breezy winds over the Simcoe Highlands and portions of the Northwest Blues. We might see windy conditions return Thursday afternoon through Friday morning with gusts up to 35-45 mph across majority of the forecast area. Strongest winds of 55-65 mph will be over the crest of OR Cascades and higher terrains of central OR late Thursday evening into overnight hours with a slight chance (<30%) of gusts at 70 mph.

Tonight through Friday, mountain snow will develop as widespread precipitation continues due to the atmospheric river moving across the Pacific Northwest. There is potential for low-elevation snowfall with high chances (>70 percent) in the Grande Ronde Valley and John Day Basin, but snow levels will rise above 3 kft in those low- elevation areas Thursday morning onward in the wake of a warm frontal system, limiting duration of snowfall. However, the WA Cascades will likely see additional snowfall up to 1 inch through Wednesday night into Thursday with a moderate chance (50-60%) for blowing snow.

River Flood Watches and Flood Watches remain in effect due to anticipated rising river levels through the week. Feaster/97

AVIATION...12Z TAFs

Strong winds will prevail for much of the day as a strong cold front moves through the region. The rain threat will wind down by late morning at the latest, but most sites will continue to see strong W/SW winds with gusts up to 45 kts and locally as high as 60 kts. Cigs will gradually clear through the day as colder, drier air moves in, becoming mostly clear save for some light low to mid clouds by the evening, before skies become bkn-ovc around 20 kft overnight heading into Thursday. Winds are largely expected to be at their worst between 12-15z, before dying down by around 00z. 74

PRELIMINARY POINT TEMPS/POPS

PDT 53 36 55 39 / 50 20 100 90 ALW 53 39 55 41 / 70 10 100 90 PSC 56 38 51 40 / 20 10 100 80 YKM 49 34 45 31 / 30 30 100 80 HRI 55 38 54 39 / 20 20 100 90 ELN 43 30 40 26 / 60 40 100 80 RDM 45 29 57 37 / 50 50 100 90 LGD 51 31 45 37 / 100 20 100 100 GCD 51 30 50 41 / 90 50 100 90 DLS 50 38 48 40 / 70 70 100 100

PDT WATCHES/WARNINGS/ADVISORIES

OR...High Wind Warning until 4 PM PST this afternoon for ORZ041-044- 507-508-510-511.

Wind Advisory until 4 PM PST this afternoon for ORZ049-050-505.

Winter Weather Advisory until 10 AM PST this morning for ORZ502- 503.

Winter Weather Advisory until 4 PM PST this afternoon for ORZ509.

WA...High Wind Warning until 4 PM PST this afternoon for WAZ024- 026>029-521.

Flood Watch through Friday afternoon for WAZ522-523.

Winter Weather Advisory until 10 PM PST this evening for WAZ522- 523.