textproduct: Pendleton

DISCUSSION

Current radar and satellite imagery show high clouds moving across most of the forecast area with partly clear skies over portions of the Lower Columbia Basin and eastern OR mountains (the Wallowas and Northern/Northwest Blues). A closed low over the west coast is bringing light snow showers along the OR Cascade crest. However, the snow showers will weaken by early morning.

As the troughing pattern continues moving across the PacNW, mountain snow will linger through Friday morning. A Winter Weather Advisory will remain through 10AM PST today for the East Slopes of the OR Cascades with snow accumulations up to 5 inches. With the 25th-75th percentile and NWP guidance favoring the downward trend of snowfall totals (>1 inch, <20% probability), the advisory could end early than expected. We will continue monitoring the OR Cascades and reassess any changes if need be. The remaining mountain areas will have light snow through Friday (>1 inch, 20-40% prob). The lowlands may see snow accumulations up to 0.05 inch, but chances are low (<30%).

The upper ridge will then arrive late Friday through Sunday morning. Most of our forecast area will enter in a dry period Saturday through early Sunday morning, but with the approaching frontal system clipping the WA/OR Cascades. Light snow may develop over the WA/OR Cascades with snow accumulations exceeding 1 inch (20-40% prob) with possibly light rain/snow mix for the lowlands. With the west-southwesterly flow aloft, sustained winds of 12-15 mph with gusts of 20-40 mph are possible late Saturday morning through Sunday (50-80% prob). Active weather conditions will persist Monday onward with lower elevation rain and mountain snow. Winter Weather headlines could be considered for the WA/OR Cascades Monday with high-end snowfall totals (5-10 inches for WA Cascades and 2-6 inches for OR Cascades). Being 4 days+ out, confidence will be low (15-30%) at this time. Feaster/97

UPDATE

Winter Weather Advisory over the Oregon Cascades has been cancelled as the threat has ended. Lingering light snow showers will continue through the day with 50-60% probabilities of another 1-2 inches over the next 12 hours.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

MVFR or lower conditions forecast through the period. A weak upper level weather will bring light snow or rain/snow chances across most sites through the period, starting with sites RDM/BDN/YKM where light snow is currently being reported. Expect another round of light snow at sites RDM/BDN after 21Z. Otherwise, PROB30 groups for light precipitation have been included at sites PDT/ALW after 6Z, site PSC after 4Z, and site YKM after 23Z. Expect CIGs and vsby to deteriorate as light precipitation develops, especially with light snow impacts. Site DLS will be under MVFR CIGs through 20Z, with VFR conditions favored through the remainder of the period. There is a low chance (<20%) that CIGs may drop to or below 1kft after 06Z. Winds will be light, 12kts or less, through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 25 41 25 48 / 40 10 0 0 ALW 27 41 27 47 / 40 40 0 0 PSC 25 44 26 49 / 20 10 0 0 YKM 21 39 25 42 / 20 0 0 10 HRI 26 45 25 48 / 30 10 0 10 ELN 18 35 22 38 / 20 10 0 20 RDM 16 39 22 43 / 10 0 0 10 LGD 21 38 24 40 / 50 40 0 0 GCD 21 37 22 42 / 50 10 0 10 DLS 27 44 30 45 / 20 10 10 30

PDT WATCHES/WARNINGS/ADVISORIES

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