textproduct: Pendleton

UPDATED AVIATION...06 TAFs

VFR conditions will prevail through the day Saturday for all sites. However, KDLS/KPDT could see low clouds early Saturday evening that may bring MVFR conditions (<30% confidence. Breezy to windy conditions will be the main concern for all sites from the tightened surface pressure gradients due to this system. Low-Level Wind Shear (LLWS) is forecasted with winds exceeding to 40-50kts between 250 and 280 degrees by 2000ft AGL, but may decrease during Saturday morning hours (30-40% confidence). Those KDLS, KPDT, KYKM, KALW, and KPSC will have sustained wind of 15-25kts with gusts at 20-30kts overnight through most of the day Saturday. These aforementioned sites should gradually improve around early Saturday evening as the winds weaken. KRDM/KBDN will also gusty winds up to 30kts before decreasing between 14Z and 17Z. Feaster/97

DISCUSSION

Rest of Today through Sunday: Wet conditions will continue through this weekend as an upper ridge offshore continues to guide a weak to moderate atmospheric river into the PacNW.

By this evening, a cold front boundary will be in the process of crossing the forecast area while accompanied by a shortwave trough aloft. Cooler air with the cold front will mainly bring temperatures near to below freezing across mountain areas mainly above 4kft to 5kft. That will result in moderate to locally heavy snowfall across the WA Cascade crest, with high confidence that White Pass will see 8 to 12 inches of snowfall through tomorrow evening. The interior of the northern Blues will also see some moderate snow accumulations, though confidence is only moderate (50-60%) in snow amounts exceeding 6 inches above 5kft.

Breezy to windy conditions are also anticipated to develop across the forecast area starting later this afternoon. A low level jet (45-60kts) associated with the incoming shortwave trough will move over the forecast area, with moderate to high confidence (55-85%) that winds will mix down and impact many of our lower elevation areas across north Central Oregon, the eastern Gorge, and the Columbia Basin & adjacent valleys/foothills. Atypical for this setup and wind direction, strong west to northwest winds are also anticipated to develop through the Wallowa valley tonight through tomorrow. In the aforementioned areas, expect sustained winds of 25-40mph with gusts 40-55mph, while some ridges along the east slopes of the Cascades can also anticipate wind gusts between 50-75mph through tomorrow afternoon.

A brief precipitation break will develop for the lower elevations Saturday while light to moderate snow and/or rain will continue across the mountains under northwest flow aloft. By Sunday morning, another front and shortwave passage will ramp up precipitation chances during the day, with light to locally moderate snowfall above 4kft in the mountains, and light rain elsewhere.

Monday through Thursday: Overall, ensemble guidance is in good agreement of a progressive pattern consisting of several shortwave and frontal systems parading through the PacNW Monday through Thursday. ECMWF and GFS ensemble systems are also in a great agreement that these systems will be accompanied by a prolonged AR with IVT values peaking between 500 to 750 kg/m/s filtering into eastern OR/WA for at least a 48 hour period early to mid next week. What that translates to is a moderate to high confidence in (60-80%) heavy precipitation amounts at least across the Cascade crest and east slopes, as well as the Northern Blue mountains and the Wallowa mountains. That said, ensemble guidance is in disagreement over the timing and positions of the incoming systems each day, which results in a low confidence (20-40%) in the exact amounts of QPF that each area will see. But to provide an idea of the potential QPF amounts, the NBM gives the WA Cascade crest a 30-70% chance of at least 5 inches of QPF over a 72-hour period ending Thursday morning, and a 15-30% chance along the OR Cascade crest. Meanwhile in the northern Blues, likely owing to much of the precipitation falling out over the Cascades and west, NBM only shows a 20-50% chance of 2 inches of QPF, which drops to a 10-20% chance for 3 inches through Thursday morning. Due to the warm/mild nature of the incoming AR/airmass, much of the precipitation will be falling as rain across the mountain areas, which translates to rises along area rivers and streams. Of note, current river stage forecasts from the Northwest River Forecast Center place many rivers originating or along the WA Cascade east slopes into action stage by the middle of next week. Lawhorn/82

PRELIMINARY POINT TEMPS/POPS

PDT 40 51 38 52 / 30 40 40 80 ALW 41 50 40 51 / 50 50 50 80 PSC 41 55 39 52 / 10 10 10 70 YKM 38 55 34 50 / 40 20 20 70 HRI 43 55 39 53 / 10 20 20 70 ELN 35 48 32 44 / 60 40 30 70 RDM 32 49 31 54 / 30 20 10 50 LGD 38 46 33 44 / 80 70 70 80 GCD 34 45 32 47 / 50 40 40 80 DLS 47 55 44 54 / 70 60 70 90

PDT WATCHES/WARNINGS/ADVISORIES

OR...Wind Advisory until 10 AM PST Saturday for ORZ041-044-507-508- 510.

Wind Advisory until 1 PM PST Saturday for ORZ050.

WA...Wind Advisory until 10 AM PST Saturday for WAZ024-521.

Wind Advisory until 7 AM PST Saturday for WAZ026>029.

Winter Weather Advisory until 7 PM PST Saturday for WAZ522.