textproduct: Pendleton

DISCUSSION

A stationary front draped across the PacNW in combination with a moist southwest flow aloft continues to bring showery precipitation across the forecast area this early afternoon. Satellite and radar imagery over the past few hours have shown an Atmospheric River beginning to shift southeast, with the main band of steady precip focused over southern portions of Oregon. Meanwhile, more showery light precip bands are developing along portions of the Cascade crest, the Lower Columbia Basin and adjacent valleys/foothills, and the northern Blue mountains. Currently, only light snow showers are developing along the WA Cascade Crest, while light rain and high mtn peak snow showers are developing along the OR Cascade crest and eastern mountains, where snow levels are generally over 6kft.

Today through Wednesday Afternoon: Showery precipitation will continue across the forecast area through Wednesday morning, shifting from north to south through the overnight hours. This is due to a mostly offshore trough closing off into a low, with the inland portion (over BC), pinching off into a broad shallow trough that will drop southeast of the region by late Wednesday morning. With the main AR to the south of the forecast area, showers will remain light across the lower elevations, with only a 15-40% chance of an additional 0.25 inches of rain in the lower elevations (70-80% chance of at least 0.1 inches) this afternoon through early tomorrow afternoon. As for the mountains, snow levels will gradually drop to pass level (3kft to 4kft) across the OR mountain zones as the shortwave forces a cooler airmass into the PacNW tonight. This will result in snow amounts of 0.5" to 3 inches across the passes, WA Cascades, and Southern Blues, with amounts closer to 3 to 5 inches in the interior northern Blues, Elkhorn crest, OR Cascade crest, and the Eagle Caps (confidence 65-85%).

Other than precip, breezy west to southwest winds (15 to 25mph with gusts 25 to 40 mph) will develop across forecast area as an area of surface low pressure develops over the upper portions of the Columbia Basin.

Drier conditions will settle into the region by Wednesday afternoon as upper level ridging builds across the northeast Pacific, raising 500mb heights across the PacNW.

Wednesday Night through Friday: There is good agreement amongst ensemble and deterministic guidance that the PacNW will be under a northwest flow aloft as ridging continues to build over the Northeast Pacific. This will result in mostly dry conditions across the forecast area through Friday night. That said, upslope forcing along the WA Cascade crest will be strong enough to wring out any lingering moisture in the flow aloft and produce light snow flurries, with daily snow amounts anywhere from a trace to one inch at Snoqualmie and White passes.

Afternoon breezy winds (15 to 25mph with gusts 25 to 40 mph) will continue to be a daily occurrence across mainly the WA Cascade east slopes/crest, and the Columbia Basin and adjacent valleys/foothills. There is strong agreement amongst ensemble and deterministic model guidance that a surface low will linger across northern WA through Friday, with high pressure developing west of the Cascades and over the Sawtooth mountains in ID.

Saturday through Monday: Through early next week, ensemble cluster guidance indicates that a closed low undercutting the upper ridge in the Northeast Pacific will slowly push east towards northern CA and southern OR. As it approaches, the southern portions of the forecast area will see light rain/snow develop as early as Saturday afternoon, with light precip persisting into early next week(confidence 50-70%). Otherwise, dry conditions will prevail across the remainder of the forecast area. Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Rain showers, mist and low CIGs will continue impacting most sites, which could result to MVFR conditions or lower. KRDM/KBDN will remain VFR, but are expected to deteriorate to MVFR around 02Z and 07Z, respectively. Conditions for KDLS, KRDM, KBDN, KYKM, and KPSC could improve around later this evening into Thursday morning. Winds will be less than 12kts, however guidance do show KDLS/KPDT gusting at 20-30kts for late Thursday morning through afternoon. Feaster/97

Preliminary Point Temps/PoPs

PDT 34 47 30 54 / 80 10 0 0 ALW 35 48 33 53 / 80 30 0 0 PSC 33 52 33 55 / 50 0 0 0 YKM 27 49 28 52 / 40 0 0 0 HRI 34 51 30 55 / 60 0 0 0 ELN 26 42 29 46 / 40 10 10 10 RDM 31 46 21 52 / 60 10 0 0 LGD 36 46 25 51 / 90 40 0 0 GCD 37 44 23 49 / 80 40 0 0 DLS 34 48 32 53 / 60 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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