textproduct: Pendleton

DISCUSSION

Satellite and radar imagery tonight show an upper shortwave moving into the PacNW after an earlier stalled frontal boundary and it's associated surface low have exited the region. Widespread rain/high mountain snow has now become mostly light mountain snow showers, with patchy low to mid level cloud cover across the lower elevations.

Today: The aforementioned shortwave will continue to bring light to moderate snow across the Cascades and eastern mountains with a few scattered light rain showers across portions of the Columbia Basin and Blue Mountain Foothills. By this evening the shortwave will have moved east of the region, taking with it the precipitation chances across our mountain zones. Through this evening, there is mod-high confidence (65-85%) in an additional 1 to 4 inches across the Cascade crest, Northern Blues, and the Eagle Caps, while confidence is low (15-20%) in greater than 4 inches of additional accumulations in the northern Blues. Otherwise, breezy winds with gusts mainly 20-30 mph will develop across wind prone areas in the lower elevation zones and exposed ridges late this morning into the afternoon hours.

Tuesday through Thursday: Deterministic and ensemble guidance has come into better agreement of upper level ridging building to the north of the forecast area late today into the first half of Tuesday. This will result in mostly dry and mild conditions to start off the mid week. A weak inversion developing Tuesday morning may result in spotty low stratus/patchy fog developing across the Columbia Basin and adjacent valleys. By late Tuesday, the ridge will push east as a trough with two defined lows develops offshore. One of the lows will move inland and become an open wave across northern CA and southern OR late Tuesday night through Wednesday. Shortwave impulses swinging out of the low during this period will bring light snow to portions of central OR, Ochoco-John Day Highlands, and the Strawberrys/Elkhorns/Wallowas.

By late Wednesday, the trough axis will exit the region, allowing a transient ridge to move over the PacNW with dry conditions prevailing through Thursday.

Friday through Sunday: By early Friday, ensemble cluster solutions show a trough dropping out of the Gulf of Alaska and setting up offshore the PacNW. Over the weekend, the trough will swing inland with increasing precipitation chances across the forecast area. While confidence is mod-high(65-80%) in the troughing, ensemble cluster solutions show uncertainty in the position and timing of the trough passage early Saturday through Sunday. While the simple majority (~60%) of ensemble cluster solutions favor light to locally moderate snow in the mountains, the remaining solutions (~40%) favor moderate to heavy snow accumulations in the Cascades and northern Blues throughout the weekend. In the lower elevations, there is at least moderate confidence (40-60%) of light rain during the daylight hours, with lower confidence (20-35%) in light snow or a rain/snow mix developing in the overnight hours through the weekend. Lawhorn/82

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

An upper weather system moving through the area will bring improved CIGs across the region by this afternoon. Site ALW may see periodic CIGs down to 2.5kft, while site YKM may see CIGs down to 100ft with vsby dropping to 2 miles. Otherwise, vsby/CIGs will improve to VFR conditions after the morning hours. Winds will increase to 12-15kts at sites DLS/KPDT/ALW/PSC this morning through the afternoon, with light winds elsewhere. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 30 46 30 42 / 0 0 10 10 ALW 32 47 33 42 / 0 0 10 10 PSC 30 50 31 49 / 0 0 0 0 YKM 28 46 28 48 / 0 0 0 0 HRI 29 48 31 46 / 0 0 0 0 ELN 27 42 27 45 / 0 0 0 0 RDM 23 46 25 42 / 0 0 10 10 LGD 26 46 28 45 / 0 0 20 30 GCD 26 46 28 44 / 0 0 30 30 DLS 34 48 33 50 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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