textproduct: Pendleton

DISCUSSION

An upper level ridge of high pressure will continue to build into the western CONUS today and will peak over the region on Tuesday before gradually being pushed eastward on Wednesday. This high pressure will bring dry weather, but the potential for low clouds and fog will persist through midweek. Additionally, with the strong high and light winds, air stagnation could also become a concern.

Except for central Oregon, temperatures will be about 5 degrees below normal through Wednesday.

As the high moves eastward, a more south to southwest flow will develop during Wednesday. This flow will allow for moisture to move in from California by Thursday.

There are still some model differences between the guidance as to when the moisture arrives, with the deterministic ECMWF bringing moisture in by Wednesday night and the other guidance mainly waiting until Thursday.

QPF during this time looks to be fairly light, probably no more than a few hundredths to perhaps 0.10 to 0.20 inches over the mountains. Some guidance suggests, there will be a lull on Friday before low pressure moves north off the Pacific Northwest coast and swings a trough through with another shot of precipitation later Friday into Saturday. Once again, this precipitation will be mainly in the mountains. During this time QPF could be 0.25 to 0.30 inches over the mountains and only a few hundredths most elsewhere.

Low chance (30 to 40 percent) pops will remain over the mountains Saturday into Sunday with dry weather expected for the remainder of the area as yet another system could bring additional moisture.

Total liquid equivalent QPF from midweek through the weekend looks to be around 0.50 inches in the Blue Mountains and 0.75 to 1.00 inch along the crest of the Cascades. NBM probabilities of 0.05 inches of liquid equivalent precipitation during any one 24 hour period are never more than 40 to 50 percent in the Washington Cascade crest and no higher than 10 to 20 percent in the lower elevations.

Snow levels Thursday morning will range from 2000-3000 feet over the Washington Cascades to 3500-4000 feet over the Blue Mountains and Eastern Oregon Mountains to 5000-6500 feet over the Oregon Cascades. By By Thursday afternoon, snow levels will rise to between 3000 to 4000 feet in the Washington Cascades, 4500-5000 feet in the Blue Mountains and the eastern Oregon Mountains and over 6000 feet in the Oregon Cascades. Snow levels will continue to rise further through Friday until the trough moves onshore, at which point they will begin to fall. By Saturday night into Sunday morning, snow levels will be back to below 3000 feet in the Washington Cascades and below 4000 feet virtually everywhere else.

So, for most of the period, mainly rain will be expected, except at the higher elevations, during the Saturday into Sunday period some light accumulations of snow could be seen in the mountains.

AVIATION

12Z TAFS...VFR conditions are expected through the day today and into early tonight, with light winds, generally less than 10 kts.

For the overnight tonight period into Tuesday morning, guidance suggests, that fog could start to develop, especially at PDT/ALW/YKM/PSC. Not all of these sites may see it but some may. and there also could end up being low clouds as well. For right now, will indicate MVFR VSBYS in fog, but it could end up being lower depending on how things develop. Moderate confidence (40-60 percent) at best.

PRELIMINARY POINT TEMPS/POPS

PDT 34 21 35 21 / 0 0 0 0 ALW 34 24 34 24 / 0 0 0 0 PSC 34 22 35 21 / 0 0 0 0 YKM 36 21 36 21 / 0 0 0 0 HRI 34 23 34 21 / 0 0 0 0 ELN 32 21 34 20 / 0 0 0 0 RDM 42 20 44 21 / 0 0 0 0 LGD 38 26 41 29 / 0 0 0 0 GCD 43 25 46 26 / 0 0 0 0 DLS 38 26 37 26 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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