textproduct: Pendleton

KEY MESSAGES

1. Heavy snow Thursday night into Friday morning for the East Slopes of the WA Cascades. WINTER STORM WARNING REMAINS IN EFFECT UNTIL 5 AM PDT SATURDAY

2. Heavy snow for the Northern Blue Mountains WINTER STORM WARNING REMAINS IN EFFECT UNTIL 5 PM PDT FRIDAY ABOVE 4000 FEET

3. Breezy winds will continue over the weekend

DISCUSSION

Current radar and satellite show the significant rain shadowing along the OR Cascades keeping central and north central OR dry. However, the WA Cascades are seeing returns as the atmospheric river and upper level cold front continuing to push in from the west- northwest. Radar also shows returns over the northern Blue Mountains as the AR continues to push across the WA portion of the region. CW3E shows firm agreement that the axis of the AR will continue to traverse across the region through Friday night before essentially dying out.

An AR will continue to push IVT values of 250-500 kg/m/s into the region through Friday, resulting in persistent moderate to locally heavy precipitation rates across the Cascade crest and Northern Blues. Snow levels have hit the peak and NBM shows snow levels to begin to decrease through the rest of the day. Ground observations show a clear line of temperature difference as the cold front begins to already push over the Cascades. This cold air will continue to bring snow levels down and turn the precipitation from a wintery mix to snow. NBM raw ensembles show 70-90% probabilities that another 1 to 2 feet of snow will accumulate over the next 24 to 48 hours over the WA Cascades.

Current web cams along the Blues show there to be rain falling currently along the I-84 corridor but snow falling at the higher elevations like Tollgate. Ground temperatures along the I-84 corridor are still above freezing but are expected to continue to decrease once the cold front passes later this evening. NBM shows snow levels along the Blues to reach below 4000 feet. NBM raw ensembles show 60-80% probabilities of seeing over 6 inches of snow accumulations through Friday morning.

Winds will also remain elevated through the weekend as zonal flow aloft takes over. Sustained west winds of 10-15 mph are expected with 35 mph gusts. There will be localized areas that will see gusts to 35 mph, but those are mainly along the ridgetops and some higher elevations such as the Simcoe Highlands of Klickitat and the Ochoco-John Day Highlands. Confidence in the winds remaining through the weekend is high (70-90% confidence).

After the weekend, AR CW3E ensembles are in relatively firm agreement that the leading edge of an upper level ridge will traverse into the PacNW. This will bring warming conditions to the region and increase snow levels drastically. CW3E also shows firm ensembles agreement that another, but weaker, AR will roam around the axis of the ridge bringing more precipitation. Precipitation will begin as rain/snow before transitioning to mostly rain. This rain on snow plus warming temperatures will bring rises to some area rivers. For more information see the hydrologic outlook.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Deteriorating ceilings in expanding precipitation is anticipated overnight and into midday Friday. VFR ceilings will drop into the MVFR range in rain showers by 12-15z at YKM/DLS/PDT. A few locations could see those levels dip to around the IFR category of 1000ft between 12z and 18z (PSC/ALW). Look for wind shear in the lowest 2000 ft up to 45kt near the RDM, DLS and PDT overnight.

Preliminary Point Temps/PoPs

PDT 42 54 38 48 / 80 80 90 60 ALW 42 51 37 48 / 90 100 100 70 PSC 41 52 38 54 / 80 80 80 30 YKM 36 53 30 49 / 80 80 70 10 HRI 43 56 40 53 / 80 80 80 30 ELN 33 43 29 42 / 80 80 60 20 RDM 38 58 38 50 / 20 20 50 30 LGD 43 56 40 47 / 90 80 100 90 GCD 43 58 42 48 / 50 30 70 80 DLS 43 59 39 52 / 90 90 90 30

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning until 5 PM PDT Friday for WAZ030-523. Winter Storm Warning until 5 AM PDT Saturday for WAZ522. OR...Winter Storm Warning until 5 PM PDT Friday for ORZ502.