672 FXUS66 KPDT 021558 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 758 AM PST Wed Jan 2 2019 .UPDATE...A ridge of high pressure has continued to dominate the areas weather with dry conditions but will slowly push to the east allowing for a disturbance to approach the two state area later today. The disturbance will spread mid and high level clouds to the region and snow showers are expected to develop along the wa cascades this afternoon. The challenge overnight will be with the timing of the warm air advection that is expected by Thursday morning. Otherwise minor changes were done to temps and sky cover and now the present short term forecast appears on track while afternoon highs climb into the upper 30s to lower 40s with 30s in the mountains. && .PREV DISCUSSION... /issued 309 AM PST Wed Jan 2 2019/ SHORT TERM...Today through Friday...An upper ridge over the area is beginning to flatten as a weather system approaches the Pacific Northwest. The area will have increasing cloudiness today though any precipitation will be light and confined to the Washington Cascade crest. The system will be riding over the ridge and only making slow progress tonight. The warm front of the system will bring a chance of light rain as far east as Ellensburg by early Thursday morning then across the Washington portion of the area on Thursday. The big concern will be freezing rain in the Kittitas and Yakima valleys Thursday morning. Snow levels will be rising to 5000 to 6000 feet, so precipitation below that elevation will be rain. However, in the Yakima and Kittitas Valleys, temperatures will be below freezing for at least part of the morning and this will lead to rain freezing to surfaces. Precipitation amounts will just be a few hundredths of an inch and should melt in the afternoon. Will hold off on any winter weather highlights there for now as confidence isn't quite there and amounts will be lighter than the usual criteria. Winds will increase and become breezy in the mountains and especially the Grande Ronde Valley Thursday and will remain so through Friday. Thursday night the warm front will lift north out of the area and the cold front of the system will begin to cross the Cascades. A chance of rain and snow will be confined mainly to the mountains with snow levels starting out at around 5000 feet Thursday and falling to around 3500 feet over most of the area Friday though the Blue Mountains eastward will have snow levels around 3500 feet. Most of the area will just see a few hundredths of an inch though the Cascades will have up to a third of an inch Thursday night and around a tenth of an inch on Friday. Temperatures today will be in the 30s though Central Oregon will reach the lower to mid 40s. Friday and Saturday will be in the mid to upper 40s with mid 30s to lower 40s in the mountains. Perry LONG TERM...Friday night through Wednesday...Any lingering mountain snow showers become increasingly sparse through the evening Friday. Saturday and Sunday the area will be under the influence of an upper low in northern California, opening to a wave over much of the Pacific Northwest. Under westerly flow the lower elevations will be largely rain shadowed and with minimal moisture support any snow accumulations in the mountains will be rather limited. Colder air in the upper Treasure valley along with increasing winds aloft will support some enhanced winds in the Grande Ronde Valley and Blue Mountains foothills through the weekend, but don't think these will reach advisory criteria. Will see some better potential for widespread precipitation, possibly significant precipitation in the mountains Monday into Tuesday as fetch of Pacific Moisture noses in from the south as a warm front spread north over the region. With strong warm air advection snow levels will be rising rapidly from around 1500 feet through 5000 feet. Surface wind fields do suggest some cold air damming against the Washington Cascades, so could see snow lingering long enough to warrant some winter highlights over the east slopes. May also see a switchover the freezing rain prior to becoming all rain, but too early to get a good feel for exactly how the thermal profiles will evolve. Both thermal gradients from the upper Treasure valley to the Columbia Basin and winds aloft will be stronger than on the weekend and would expect some more significant gusts, possibly nearing warning criteria in the Grande Ronde Valley and Blue Mountain foothills Monday into Tuesday morning. May also see some stronger winds aloft mixing to the surface off the higher terrain via mountain wave action in central Oregon. The cold front associated with this system passes through Wednesday with precipitation becoming confined to the mountains once again along with a brief uptick in winds region wide with cold frontal passage. Peck AVIATION...12Z TAFs...Some local reductions in visibility in mist will be possible near YKM/PSC this morning along the rivers, but do not think visibility will drop below VFR at the terminals. Will start to see mid/upper level cloudiness return late this morning as the ridge begins shifting off to the east in advance of the next system Thursday. May see some downslope winds developing off the Blues this evening with some gustiness at ALW by Thursday morning. Winds remain light at the remaining terminals. Peck && .PRELIMINARY POINT TEMPS/POPS... PDT 40 31 46 36 / 0 0 10 10 ALW 40 32 48 37 / 0 0 20 20 PSC 36 31 45 37 / 0 10 20 10 YKM 39 31 42 33 / 0 10 30 40 HRI 38 31 45 35 / 0 0 10 10 ELN 39 29 40 32 / 10 20 50 50 RDM 45 28 49 34 / 0 0 10 10 LGD 35 28 34 32 / 0 0 20 10 GCD 36 25 42 32 / 0 0 10 0 DLS 41 33 44 36 / 0 10 30 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until 4 PM PST this afternoon for ORZ041- 505-506-509>511. WA...None. && $$ 97/