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737 FXUS66 KPDT 062154 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 154 PM PST Fri Dec 6 2019 .SHORT TERM...Tonight through Sunday. Upper low centered offshore this afternoon with a frontal boundary and jet moving into the Pacific northwest. Fairly solid cloud cover evident on satellite and expect it will remain cloudy overnight into Saturday. Inversion continues to result in areas of low clouds and fog across the Columbia basin and adjacent valleys. This has lasted through the day in some locations and should continue tonight. Models continue to overspread the region with rain and higher elevation snow this evening continuing into Sat. Snow levels should be around 4-5000 feet. Pressure gradients bringing gusty south winds to the Grande Ronde valley. Expect 20-45 mph winds through Sat afternoon then decreasing after frontal passage. The upper low will merge with another system moving south through BC on Sat. Rain and higher elevation snow will continue through the night and into Sunday morning before ending. The departing system will result in northwest upslope flow over the Blues through the day where precipitation will linger. Several inches of snow accumulation are likely above 4-5000 feet. Colder air aloft Sunday with the upper low along with increased winds aloft Sat should help erode the inversion and fog. It will likely return Monday with upper ridge building back. 94 .LONG TERM...Sunday night through Wednesday afternoon...A high pressure ridge will build into the region Sunday night, bringing with it drier settled conditions. Temperatures will be milder, with highs in the 40s and lows in the 20s and 30s. With the ridge persisting over the region Monday and Tuesday, conditions will be favorable for freezing fog to form Monday night into Tuesday in the Lower Columbia Basin. A weak shortwave trough will break down the ridge starting Tuesday afternoon and move across the region Wednesday. Only low chances of mountain snow and lower elevation rain is associated with this system. Winds are not expected to become significant during this period. Lawhorn .LONG TERM...Wednesday night through Saturday...An upper ridge will give way to a weather system that will move into the region Wednesday night and Thursday. This system will spread mainly rain (snow levels sloping upward from 2500 to 4500 ft from north to south) across the forecast area with a warm front. Warm air advection will bring in warmer air and rising snow levels to around 4500 to 6000 feet from north to south by Thursday afternoon. The entire forecast area will see some precipitation out of this. There could be some mixed precipitation in some of the colder valleys in the northern CWA (Mainly the Yakima and Kittitas Valleys) Wednesday night at the start. If there is enough cold air trapped in these valleys east of the WA Cascades there could also be some freezing rain. At this time though, confidence is low and will not mention freezing rain yet in the forecast. After Thursday, the atmosphere remains mild with snow levels being nearly steady, or even rising a little more by Saturday. There will be a continued chance of rain each day (snow in the higher mountains) through Saturday as a series of waves move along a nearly stationery warm front over the forecast area. The long range models show the pattern remaining progressive with frequent weather systems through Saturday. Winds will be mostly light except for locally breezy conditions on the ridge tops. 88 && .AVIATION...00Z TAFs...Periods of IFR/LIFR conditions will continue at KPDT and KALW, but most other areas will break out the fog and low clouds by late this afternoon to mostly VFR or occasionally MVFR conditions. Visibilities at KPDT and KALW will be down to a quarter of a mile with CIGs less than 100 feet AGL at times this afternoon. This evening expect to see improvement as a weather system moves into the region with increasing westerly winds and clouds which will help to mix out the low level inversions and the stratus/fog. Winds will be mostly light at all TAF sites through the next 24 hours. 88 && .PRELIMINARY POINT TEMPS/POPS... PDT 32 46 35 43 / 40 50 50 40 ALW 30 46 37 43 / 30 50 50 30 PSC 30 42 34 44 / 30 40 30 10 YKM 32 41 31 44 / 60 40 30 0 HRI 31 43 35 44 / 40 40 30 10 ELN 32 40 31 43 / 60 40 30 0 RDM 34 48 31 46 / 60 60 50 20 LGD 35 41 34 41 / 60 60 60 60 GCD 33 44 33 41 / 70 60 60 40 DLS 35 44 36 48 / 60 50 40 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until noon PST Saturday for ORZ049. WA...None. && $$ 94/83/88/88