textproduct: Pendleton

KEY MESSAGES

- Active weather pattern through the weekend with mostly rain across the region, and light high mountain snow developing by Sunday

- Breezy to locally gusty southerly winds across portions of central and northeast OR will continue through the weekend

- A train of upper low pressure systems will bring progressively cooler conditions across the forecast area, with light to locally moderate mountain snow accumulations, and potentially a dusting in portions of central OR

DISCUSSION

Water Vapor satellite imagery this afternoon shows an upper level low offshore Vancouver Island the PacNW, while visible satellite shows mostly cloudy conditions across the PacNW, with areas of clearing around Grande Ronde valley and Wallowa county. Meanwhile, radar shows embedded rain bands starting to cross the Cascade crest, with light returns from Yakima to the Redmond/Bend area. Southerly breezy winds have developed throughout the morning across portions of central and northeast OR as well, with some areas near the WA Blue mountain foothills reporting gusts as well.

Today through Saturday: The approaching upper low offshore the PacNW has not only resulted in a strengthening pressure gradient from central OR to the Blue mountains, but is also pushing a strong (45-65kts) 850-700mb jet streak east across central OR to northeast OR. This has resulted in areas of breezy winds with gusts 40-50 mph developing across these areas today, with winds expected to continue into the evening hours.

Other than winds, the approaching upper low will push the band of rain along the Cascade crest east through tonight, with light showers in the lower elevations and moderate to locally heavy showers across most mountain areas. 24-hr probabilities for 0.25 inches through Saturday morning are generally between 50-85% across the eastern mountains and the Cascade crest/east slopes. As for most of the lower elevations (except the Lower Columbia basin of WA), the probability of 0.1 inches is between 40-65%. Light Cascade mountain precip will continue into Saturday with dry conditions elsewhere while a transient ridge follows the exit of the upper low.

Sunday through Thursday: Next week is expected to start off with yet another upper level trough developing in the northeast Pacific that will push across the region through Tuesday. Ahead of the low will be a cold/occluded frontal boundary that will push a band of precipitation across the region throughout Sunday, with the frontal boundary stalling across far eastern OR/WA Sunday night into Monday morning. Monday, the upper trough will drop into the PacNW, pushing whats left of the frontal boundary into the northern Rockies, with precipitation mainly limited to the Cascades, Blues, Elkhorn crest, and the high terrain across Wallowa County. During the peak precipitation on Sunday, snow levels will mainly be above 6kft in the mountains, resulting in any snow accumulations being limited to the Cascade peaks, with a rain/snow mix down to around 5kft. Behind the frontal boundary, snow levels will drop to around 4kft, resulting in light snow developing along the Cascades throughout Monday, with rain transitioning into snow along the eastern mountains late Monday morning into the late afternoon. In addition to lowering snow levels, temperatures will cooling region-wide through Monday, with moderate-high confidence(55-75%) in afternoon high temperatures in the mid 40s to low 50s.

Tuesday through Thursday, ensemble cluster members are in good agreement that a transient ridge will slide into the PacNW Tuesday with dry conditions, then yet another upper trough will drop into the PacNW late Tuesday night into Thursday. There is increasing uncertainty in regards to timing/positioning of the trough late Wednesday into Thursday, but impacts amongst ensemble solutions remain similar during that period.

For Tuesday, while the ridge is overhead conditions will remain dry, however temperatures will remain cool as a cold airmass remains over the region. By late Tuesday night, the next round of precipitation will arrive to the Cascades, then push east across the region as the trough pushes inland. There is moderate confidence (50-60%) that snow levels will lower down to around 2-3kft Tuesday night and Wednesday morning, then increasing to around 3-3.5kft by Wednesday afternoon and evening. This will result in a light dusting (~0.1 inches) of snow in some lower elevation locations (confidence 35-50%) Wednesday morning, while there is moderate confidence (40-60%) in 3 to 4 inches of snow accumulations across the Cascades and eastern mountains through Wednesday night. Late Wednesday into Thursday, forecast confidence is low (15-20%) owing to positioning disagreements of the upper trough as it continues to cross the PacNW. Solutions from the ensemble cluster members range from light mountain snow continuing, to light mountain snow and light low elevation rain, to no precipitation during the Wednesday night to Thursday period. Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

DLS/PDT/RDM/BDN: Mostly VFR conditions expected to prevail through the period. A system moving into the region will bring rain impacts to all sites, with rain expected between 20Z-03Z at sites DLS/RDM/BDN, and between 03Z-08Z at site PDT. At site PDT, there is moderate confidence (45-65%) that southerly winds post precip will bring IFR or lower vsby/CIGS to site PDT tonight. Breezy southerly winds 12-20kts with gusts up to 30kts will impacts sites RDM/BDN through 01Z, and site PDT between 00Z to 08Z. Winds will remain light through the period at site DLS. Lawhorn/82

YKM/ALW/PSC: The advance of an upper level low towards the forecast region will bring precipitation and some lower visibility conditions across south-central Washington. Remaining morning fog and localized wind shear (20kt WS at ALW through 0400z) is giving way to overcast conditions with rain showers to light rain expected to spread eastward across the state after 2100z. In the wake of these showers, patchy fog or mist may develop at ALW and YKM, and should clear out as winds increase into the early morning hours and diurnal heating takes place.

Preliminary Point Temps/PoPs

PDT 40 61 42 57 / 80 0 10 80 ALW 44 59 46 55 / 80 0 0 80 PSC 38 61 40 58 / 60 0 20 70 YKM 36 57 38 54 / 80 0 50 30 HRI 39 61 41 58 / 80 0 20 70 ELN 32 50 34 48 / 70 0 60 30 RDM 31 53 36 51 / 20 10 20 60 LGD 37 55 38 48 / 90 10 0 90 GCD 35 53 36 49 / 90 10 0 90 DLS 40 56 43 52 / 50 20 60 80

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 7 PM PST this evening for WAZ029. OR...Wind Advisory until 7 PM PST this evening for ORZ049-050-507- 508. Wind Advisory until 4 PM PST this afternoon for ORZ510-511.