textproduct: Pendleton

DISCUSSION

Winter Weather advisories have been issued today for East Slopes of OR Cascades, Upper/Lower Slopes of WA Cascades and Simcoe Highlands through 10PM PST with North- Central OR ending at 4PM PST. The NBM probability of 6hr snowfall suggests a 50-70% prob for exceeding 2" over OR Cascades, Simcoe Highlands and WA Cascades (mainly White Pass) with 20-40% prob for North-Central OR exceeding 1". The 75th-25th percentile seemed to have a minimal spread for the North-Central OR, WA/OR Cascades and Simcoe Highlands. The HREF guidance also reveals a downward trend in the snow totals, suggesting that these advisories could end earlier than expected. We will continue monitoring those areas and see how things materialize.

Other than that, the upper ridge will continue to slowly break down over the region through this weekend. The frontal system associated with a closed low over the Pacific Ocean will approach along the WA/OR Cascades with light precipitation and spill into other areas (North Central OR, Simcoe Highlands, and Foothills-Southern Blue Mountains of OR). Low elevations may see light rain over the weekend, but mainly up to 0.10" (10-30% chance).

Additionally, sustained southerly winds of 15-25 mph with gusts of 35-45 mph will develop over the eastern mountains through this weekend (50-80% prob). The models remain consistent with the tight surface pressure gradients with these winds being driven by the south-southwesterly flow from the high terrain of Central OR to the Wallowas. That said, this led to issuing wind advisory for the Grande Ronde Valley until 10PM PST today. There is also an High Wind Watch in effect for the Grande Ronde Valley and Foothills-Northern Blue Mountains of OR through Sunday evening (10PM PST). The HREF guidance looks to be favorable for this wind event with the NBM probability of 24hr Max 10m Gust having 30-60% prob for gusts exceeding 50-50 mph for the those wind-prone areas.

Models remain in good agreement with the persistent active pattern Monday onward with mountain snow and low elevation rain (>70% confidence). Variances in timing and amplitude of the system associated with shortwave approaching our region from British Columbia could impact the forecast and will be monitored. The clusters seem to show the same amplitude issue starting Tuesday into next week as well. Regardless, all models and ensembles are aligned with the incoming precip for next work week. Feaster/97

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

VFR conditions are expected for the most part, through the period. There are a few exceptions, however. DLS is having some light snow and MVFR, but radar shows that decreasing through the afternoon. ALW had some LIFR CIGS. The latest observation showed them breaking out. Not sure they will not resume some lower conditions before breaking out once and for all later this morning or early this afternoon, but the trend is definitely upward. Otherwise, all other sites should be VFR.

Winds will generally be 10 kts or less at all sites, except BDN and RDM where gusts to around 25 kts are expected.

Preliminary Point Temps/PoPs

PDT 34 55 39 58 / 10 20 50 40 ALW 35 55 40 57 / 10 30 60 60 PSC 29 52 37 55 / 20 30 60 50 YKM 28 46 34 47 / 50 60 70 80 HRI 30 54 37 56 / 10 20 60 40 ELN 27 41 31 42 / 50 70 70 90 RDM 30 52 36 54 / 10 30 50 40 LGD 32 48 37 50 / 10 20 40 40 GCD 29 50 37 51 / 10 10 20 30 DLS 32 46 39 50 / 50 80 90 90

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 10 PM PST this evening for WAZ521>523. OR...Wind Advisory until 10 PM PST this evening for ORZ049. High Wind Watch from this evening through Sunday evening for ORZ049-507. Winter Weather Advisory until 10 PM PST this evening for ORZ509. Winter Weather Advisory until 4 PM PST this afternoon for ORZ510.