Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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315 FXUS66 KPDT 011127 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 427 AM PDT Wed May 1 2024 Updated aviation discussion .SHORT TERM...Today through Friday...Satellite and radar imagery tonight show an upper trough continuing to pull a band of light to moderate showers across northeast OR, while a drier northwest flow is setting up across western and central PacNW. While in the lower elevations this band has produced mostly rain, the northern Blues and Wallowa county can expect to see light snow accumulations of 1 to 2 inches through the remainder of the nighttime hours. Today, conditions will dry out across the forecast area as a dry northwest flow aloft sets up on the backside of the departing upper trough. That said, a weak plume of moisture is expected to wrap-around an upper low centered over southern Saskatchewan, resulting light snow showers over Wallow county and the northern Blues this afternoon. Otherwise, breezy west to northwest winds will develop through the Cascade gaps into the Columbia Basin, with strongest winds of 20-25mph and gusts up to 40mph possible through the Kittitas valley. The next system in the form of an open wave in northwest flow aloft will dive across OR around midnight, and exit the area by Thursday evening. There is good agreement amongst global and hires short term guidance that the open wave will keep much of the rain and mountain snow showers across the OR side of the forecast area, though the south central WA Cascades will see very light snow showers. The heaviest precipitation is expected to impact the OR Cascades as the wave tracks over the region, with HREF probabilities indicating a ~80% chance of 4 inches of snow above 4.5kft-5kt. Further east, the HREF shows the Ochoco-John Day Highlands having a 45-55% chance of 2 inches of snow; the remainder of the northeast OR mountains will see only up to an inch of snow (confidence 70-80%). Behind the open wave exit late Thursday, a transient ridge will slide into the PacNW bringing another brief period of dry conditions. By Friday afternoon, guidance shows an occluded frontal system pushing into the PacNW ahead of a closed developing in the northeast Pacific. Ahead of the front, the combination of the transient ridge then southwest flow aloft will result in warm air advection across the PacNW, pushing snow levels to between 6kft-7kft Friday afternoon and night. This will result in mostly rain showers with snow showers over the higher crest areas along the Cascades. Rain showers will spread east in the overnight hours Friday into Saturday. Only other notable phenomena will be breezy winds switching to the south and southeast across the forecast area ahead of the upper closed low and occluded frontal system Friday. Lawhorn/82 .LONG TERM...Saturday through Wednesday...Ensemble and deterministic models are showing better agreement for the weather pattern over the weekend before uncertainty increases Monday through Wednesday. Saturday will see a closed low off the PacNW coast moving SE and into SW Oregon by the afternoon and evening then into the Great Basin on Sunday. This will slowly push a cold front across the forecast area Saturday and into Sunday. The slow moving nature of the front and the path of the low will allow moisture wrapping around the low to advect back into the forecast area Saturday night and Sunday. This could provide some meaningful precipitation amounts as the 48 hour NBM probabilities indicate a 40-70% chance of half an inch of rain over the eastern mountains under this pattern and possibly around an inch for some mountain locations. River level forecasts show some rises on the main stem rivers as a result of this but as of now none are expected to reach bankfull. The low moves off into the Rockies Monday leaving the PacNW under a northwest flow. This is where the uncertainty begins to increase as timing of features in the flow become more apparent. Most likely scenario will be for small shortwaves to continue providing occasional showers Monday through Wednesday especially over the mountains. Snow levels will be down to 3000 to 4000 feet so could see some accumulation snow impacting travel over the higher passes. && .AVIATION...12Z TAFs...VFR conditions across all TAF sites today before another system arrives tonight mainly impacting central Oregon with some possible MVFR conditions. Winds will generally be less than 10kts but DLS could see winds gusting around 20kts into the evening before decreasing. && .PRELIMINARY POINT TEMPS/POPS... PDT 58 35 60 36 / 0 10 20 0 ALW 61 37 64 40 / 0 0 20 10 PSC 65 41 67 42 / 0 0 10 0 YKM 63 37 66 37 / 0 10 20 0 HRI 64 40 66 39 / 0 10 20 0 ELN 58 34 63 36 / 0 0 0 0 RDM 55 34 54 33 / 0 60 40 0 LGD 53 31 56 32 / 20 0 30 10 GCD 54 34 56 33 / 0 30 50 20 DLS 61 42 66 42 / 0 40 20 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...82 LONG TERM....91 AVIATION...90