textproduct: Pendleton

DISCUSSION

Fog continues to impact the areas this afternoon, after having improving visibility in central Oregon, the foothills of the Blue Mountains have experienced sub one quarter mile visibility all morning. There had been a slight improvement based on webcams in the Cabbage Hill/Deadman Pass area as rain showers have moved through the area winds around noon. However as the rains passed the conditions again deteriorated with a sustained upslope wind component. A dense fog advisory has been issued as well for that area of the Oregon Northern Blue Mountain Foothills through midnight.

NBM 25th to 75th percentile snowfall is 6 to 8 inches respectively, and providing fairly high confidence for advisory level snow at the Santiam pass level ending sometime Tuesday. Winter Weather Advisories will be posted for the period from midnight Tonight through Tuesday night, for the eastern slopes of the Oregon Cascades, and from 4 am Monday through the end of the afternoon on Wednesday for the Northern Blue Mountains of Oregon and Washington.

The atmospheric river trends southward into CA and the sw US, which doesnt favor higher moisture content, which is reflected in the declining PWAT values though the week. Countering this is the invasion of much colder air aloft where 500 mb temps go from -25C to -35 C Monday Night into Tuesday anchoring over the region for the remainder of the week driving snow to liquid ratios higher to the 15 to 20:1 range through the mountain zones. Snow ratios drop to under 1000 ft by the Wednesday night, promoting chances for snow accumulations as well in some of the highland valleys, and areas away from the foothills, and continue to crash to near the surface even in the Columbia Basin. This should lead to at least a rain snow mix chance for most of the low lands by Thursday.

Additional snows are anticipated for the Wednesday and Thursday time frame, and additional advisories may be needed. The uncertainty is high with respect to afternoon and even overnight temperatures heading into the middle of the week. While the NBM does cool highs to the upper 30s by Thursday afternoon through the River Gorge and across the Lower Columbia Basin , the colder members of the ensembles would suggest even highs in the upper 20s across the foothills of the Blues. Russell/71

AVIATION...00Z TAFS

Variable conditions across all sites, with VFR at KRDM/KBDN, MVFR at KPSC/KYKM/KDLS, and IFR at KPDT/KALW due to reduced ceilings of 600 feet. Ceilings are expected to improve slightly this afternoon before dropping to LIFR levels (300-400 feet) along with 1/2SM visibilities for KPDT/KALW. These LIFR ceiling levels are also anticipated to occur for KPSC overnight into Monday morning as light rain approaches and begins mid-morning. Light rain will be widespread and drop ceilings and visibilities to IFR levels for KDLS/KYKM mid-morning on Monday as well. Fog is also likely to return for KRDM/KBDN with a light rain/snow mix through the early morning hours. 75

Preliminary Point Temps/PoPs

PDT 34 44 27 44 / 30 90 60 30 ALW 37 46 30 45 / 40 90 70 50 PSC 35 46 29 48 / 30 80 30 10 YKM 32 43 24 42 / 10 60 10 10 HRI 36 46 28 47 / 30 80 40 10 ELN 28 39 22 37 / 10 50 20 30 RDM 30 44 22 38 / 30 60 20 30 LGD 33 49 25 40 / 30 90 90 70 GCD 33 47 24 38 / 20 80 80 70 DLS 38 45 29 44 / 30 80 40 50

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 4 AM Monday to 3 PM PST Wednesday for WAZ030. OR...Winter Weather Advisory from 4 AM Monday to 3 PM PST Wednesday for ORZ502. Dense Fog Advisory until midnight PST tonight for ORZ507. Winter Weather Advisory from 10 PM this evening to 10 PM PST Tuesday for ORZ509.