254 FXUS66 KPDT 161056 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 256 AM PST Mon Dec 16 2019 .SHORT TERM...Today through Thursday...Freezing fog/low stratus is widespread through the upper Columbia Basin of WA. Southerly winds in central OR and through the Blue Mountain foothills are preventing fog from encroaching south. These winds may ease or shift slightly allowing fog to develop through the Blue Mountain foothills and Columbia Basin of OR before morning. In the meantime, longwave ridge axis will set up over the area today while longwave trough off the western US coast deepens. Ridge axis will assist in maintaining sharp surface temp inversion. Due to this and generally light winds, fog and stratus will be slow to mix today, if at all. Currently expecting some brief clearing late in the day before another night of widespread freezing fog. Dense fog advisories may be needed if mixing fails to occur at all or if fog layer deepens tonight. Ridge shifts east Tuesday night and begins to open the region up to deep S/SSW flow aloft. Encroaching trough will tighten a southerly pressure gradient that is expected to elevate winds in Central OR and the Blue Mountains Tuesday and Tue night. As usual, there is particular concern for gusty conditions in the Grande Ronde Valley where winds are expected to be 35-40mph. Though moisture and cloud cover will begin overspreading the area Tuesday into Tue night, much of the initial precip will remain along the Cascade crest and westward given the flows orientation along the mountains. As precip chances increase, snow levels support snow for the Cascade and Blues and rain for the majority of the Columbia Basin. Initial precipitation may be mixed for the Kittitas and Yakima valleys as narrow tongue of warm air advects over the area in advance of the landfalling low. clark .LONG TERM...Thursday through Monday...Rather active and wet period is likely for the end of the week into the weekend. Surge of moisture will arrive early Thursday bringing good chances for lower elevation rain and mountain snow. Snow levels Thursday morning will range from ~1200 feet in the Washington Cascades as well as Blue/Wallowa Mountains to near 3500 feet in the Oregon Cascades where a few inches of snow is expected. By Thursday afternoon, warmer air will rapidly move into the Oregon Cascades and Columbia Basin of Oregon & Washington with snow levels increasing to 5500-6000 feet. The exception will be across the Washington Cascades where minor cold air damming will keep snow levels between 2500-3500 feet. With a continued stream of moisture over the Washington Cascades, winter weather headlines may be needed for the latter half of the week. While snow levels will gradually increase, subfreezing overnight low temperatures are likely across the Yakima/Kittitas Valleys as well as portions of the lower Columbia Basin in Washington and will allow for slight chances of freezing rain both Thursday and Friday morning. A warm front gradually lifts north through the area Friday night into Saturday morning bringing slowly diminishing precipitation chances through the weekend. The most likely areas to see continued precipitation chances through the day Monday will be along the Cascade crests as well as higher terrain of central and northeast Oregon. Richards && .AVIATION... && .PRELIMINARY POINT TEMPS/POPS... PDT 41 25 37 23 / 0 0 0 0 ALW 40 28 35 25 / 0 0 0 0 PSC 36 25 34 24 / 0 0 0 0 YKM 32 22 34 23 / 0 0 0 0 HRI 37 23 35 24 / 0 0 0 0 ELN 32 22 32 22 / 0 0 0 0 RDM 39 21 40 23 / 0 0 0 0 LGD 36 24 35 23 / 0 0 0 0 GCD 39 23 37 23 / 0 0 0 0 DLS 37 25 37 27 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ 91/75/76