textproduct: Pendleton

DISCUSSION

Rest of today through Sunday: Zonal flow is setting up over the PacNW this afternoon behind the exit of a surface cold front and shortwave trough. Precipitation has tapered off across much of the area during this transition, however snow showers have developed along the WA Cascade crest, with shower activity gradually dipping south along the northern OR Cascade crest. Shower activity along the Cascade crest will increase throughout the remainder of this afternoon and through the overnight hours as a shortwave embedded in the zonal flow moves over the region, bringing with it a period of moderate to heavy snow accumulations into the Cascades and the northern Blues. Winter storm warnings will remain in effect through tomorrow morning for the Cascade east slopes as additional snow accumulations of 6 to 10 inches falls over this area, while winter weather advisories will continue through this evening and into the overnight hours as the shortwave brings another 2-6 inches in the northern Blues as well.

Saturday, zonal flow will continue across the PacNW and result in snow showers mainly the WA and northern OR Cascade crest, with drier conditions across the remainder of the area throughout the day. By Sunday, zonal flow aloft will become more southwest as a trough swings out of the Gulf of Alaska, resulting in another round of moderate to locally heavy mountain snow accumulations, a light rain/snow mix then rain between 2kft to 4.5kft, and rain in the remainder of the lower elevations.

Monday through Thursday: Ensemble guidance is in good agreement through next week that upper level troughing will develop offshore in the wake of the trough passage Sunday, with a general troughing pattern persisting through the end of the period. That said, disagreements do arise in the timing in the arrival/passage of embedded shortwave troughs, leading to low confidence (25-40%) in the details of precipitation amounts next week. That said, confidence is moderate-high (55-80%) that snow levels will remain low enough across the forecast area for each passing system to bring mountain snow with a rain/snow mix in high desert valley areas (e.g. Redmond-Bend areas) throughout the week. Of particular note, ensemble cluster guidance is in good agreement of snow levels lowering to the surface across the Blue mountain foothills, Yakima/Kittitas valleys, and the portions of the Columbia Basin Tuesday night through Wednesday morning, resulting in the potential of snow in these areas (confidence 40-65%). That said, each cluster solution depicts varying snow accumulation amounts in these areas, with one solution (29% of members) showing at least 2 inches across most of the lower elevation areas outside of the Lower Columbia Basin of WA, while the other solutions are anywhere from a few hundreths to 1 inch. Other than snow impacts, a handful of members (~10% of members) from the GFS and ECMWF ensemble suites are hinting at strong winds (20-30 mph sustained winds with gusts 35-50mph) developing across the forecast area Wednesday as a surface low swings across Oregon. Confidence is at least moderate (45-65%) that the forecast area will see breezy conditions develop as the surface low impacts the region. Lawhorn/82

AVIATION...00Z TAFs

Mostly dry conditions across the sites persist with predominately VFR status. Slightly breezy at some locations, especially PDT, RDM, ALW, PDT with 15 to 25 mph gusts, with brief periods of 30 mph. Winds will remain somewhat breezy through the period, but will slightly weaken as we head into the later evening hours. YKM has PROB30 chances from some light snow showers from 14Z to 18Z with MVFR conditions (that being the only sub-VFR period currently forecasted out of all sites). Otherwise, CIGs will remain high thanks to daytime mixing and stronger winds.

PRELIMINARY POINT TEMPS/POPS

PDT 31 47 30 48 / 10 10 10 50 ALW 35 47 33 47 / 20 20 10 50 PSC 34 50 30 46 / 0 10 0 30 YKM 27 46 27 41 / 10 20 10 30 HRI 33 50 30 46 / 10 10 0 40 ELN 24 38 24 36 / 30 40 30 40 RDM 23 45 25 49 / 10 0 20 60 LGD 25 38 27 42 / 20 10 20 70 GCD 23 41 29 46 / 10 0 30 80 DLS 35 46 32 43 / 60 50 30 60

PDT WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory until 10 PM PST this evening for ORZ502.

Winter Storm Warning until 10 AM PST Saturday for ORZ509.

WA...Winter Weather Advisory until 10 PM PST this evening for WAZ030.

Flood Watch through late tonight for WAZ522-523.

Winter Storm Warning until 4 PM PST Saturday for WAZ522.