FXUS66 KPDT 100527 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1027 PM PDT Fri May 9 2025 .UPDATED AVIATION...06Z TAFs...VFR conditions continue to prevail. Winds will remain up to 12 knots for most sites. Sites near the mountain gaps and other higher elevations, such as DLS/BDN/RDM, are forecasted to receive gusts up to 20 knots in the late morning/early afternoon hours. Cloud decks and VIS remain well above VFR standards throughout the period. && .PREV DISCUSSION... /issued 848 PM PDT Fri May 9 2025/ UPDATE... Latest satellite imagery showed mainly high clouds over the area. With mostly light winds expected, have made some downward adjustments to lows in several areas based on current observations and latest guidance. Otherwise, current forecast looks on track. PREV DISCUSSION... /issued 232 PM PDT Fri May 9 2025/ SHORT TERM...Tonight through Sunday Night...This afternoon a large upper trough remains off the British Columbia/Pacific Northwest coast while a ridge in centered over the Rockies. This is promoting a southwest flow over our area. Moisture aloft in this flow is sending scattered to broken high cirrus over the area and this will continue into tomorrow. This cloud cover along with a warm air mass under the ridge will give us a relatively warm night with lows in the mid 40s to lower 50s in the lower elevations and in the lower to mid 40s in the mountains. On Saturday, the trough will expand over our area as the ridge shifts further east. A wave will be moving through the trough and this will send a weak cold front into our area in the late afternoon and Saturday night. Saturday will see increasing clouds and temperatures about 3 to 5 degrees cooler than today with temperatures in the mid to upper 70s in most lower elevations though some warmer Columbia Basin locations will reach into the lower 80s. The mountains will be in the upper 60s to mid 70s. The approaching front will bring breezy west to northwest winds of 10 to 20 mph while the Cascade gaps will have northwest winds of 20 to 30 mph with gusts to 35 mph. NBM probabilities give a 30 to 40 percent chance of 35 mph gusts in the Columbia Gorge and Kittitas Valley. The front will bring light showers to the Cascades and eastern mountains in the late afternoon and evening with amounts of just a couple hundredths of an inch. Heavy cloud cover will help keep temperatures from dropping too far and will be a couple of degrees below tonight. Sunday and Sunday night will see the trough move to the coast line and this will keep cool and showery conditions over the area. The bulk of the rain will be over the eastern mountains with a quarter to half inch expected while the rest of the area will get no more than a tenth of an inch. Models are indicating enough instability for isolated thunderstorms from the Ochoco-John Day Highlights the Blue Mountains and into Wallowa County. CAPE values of 150-400 J/kg, low level lapse rates of 7-8 C/km and shear of 40-50 kts are expected to be present, so have a slight chance of thunderstorms in the late afternoon and early evening. Winds will pick up again in the afternoon and evening though not as strong as Saturday, with winds of 10 to 20 kts in most areas and 15 to 25 mph in the Columbia Gorge and Kittitas Valley. Temperatures Sunday will drop 8 to 13 degrees from Saturday with highs in mid 60s to lower 70s and in the mid 50s to lower 60s in the mountains. Perry/83 LONG TERM...Monday through Friday...Models are in fairly good agreement in having unsettled weather over the area Monday through Wednesday then becoming quieter Thursday and Friday as a trough departs and a ridge expands out of the eastern Pacific over our area. Model agreement erodes by Friday as to the timing and strength of a shortwave that flattens the ridge and moves through our area. The Extreme Forecast Index indicates only a few mildly unusual weather aspects in the Long Term period. It has values of 0.68 to 0.74 for wind speeds and wind gusts in the Cascade gaps Tuesday and Wednesday afternoon and winds of 20 to 30 mph with gusts to 40 mph are expected those afternoons without reaching wind advisory levels. It also has a value of 0.84 for QPF over central Oregon into the eastern mountains Monday and that appears to be the rainiest day. It also has a value of 0.68 for snow over the eastern mountains though at this time of year, it wouldn't take much snow to reach that level. The trough will slowly move across the area Monday and Tuesday keeping cool and showery conditions each day. The brunt of the rain will continue to be over the eastern mountains with a tenth to a quarter of inch there Monday and up to a tenth of an inch Tuesday. Elsewhere, amounts will just be a few hundredths each day. Instability shifts east and a slight chance of thunderstorms will be confined to Wallowa county Monday afternoon. There will continue west to northwest breezy winds each afternoon of 20 to 30 mph with gusts 40 mph in the Cascade gaps and 10 to 20 mph elsewhere. Temperatures each day will remain in the 60s to lower 70s with 50s in the mountains. Models develop some differences Wednesday as to the timing of the trough departing to the east and as a ridge begins building in from the eastern Pacific. Showers with very light rain amounts will be tapering off along the Cascade crest and over the northern Blue Mountains and Wallowa County. Temperatures will begin to increase and will be 3 to 5 degrees warmer than Monday and Tuesday. Pressure gradients will continue to support breezy to windy conditions in the afternoon and early evening, similar to Monday and Tuesday. Thursday, the ridge develops a northwest flow over and this will give us dry weather with temperatures warming about 5 degrees to the upper 50s and 60s in most of the area though the Columbia Basin will be unchanged in the upper 60s to mid 70s. Winds will be much lighter with only the Cascade gaps reaching 15 to 25 mph. On Friday, models have substantial disagreements about a wave moving out of the Gulf of Alaska and it is unclear if will flatten the ridge and move through the area Friday or Friday night. The NBM has a slight chance of rain over the mountains with the rest of the area dry and that seems like the best compromise. Temperatures are little changed from Thursday. Perry/83 && .PRELIMINARY POINT TEMPS/POPS... PDT 51 77 50 66 / 0 0 10 60 ALW 55 77 53 66 / 0 0 20 60 PSC 44 83 50 70 / 0 0 10 40 YKM 50 79 48 70 / 0 0 0 20 HRI 47 80 51 69 / 0 0 10 50 ELN 45 73 44 65 / 0 0 0 20 RDM 46 78 43 64 / 0 0 0 30 LGD 49 79 48 66 / 0 10 10 70 GCD 50 82 47 69 / 0 10 10 60 DLS 52 74 50 67 / 0 0 0 30 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ UPDATE...77 SHORT TERM...83 LONG TERM....83 AVIATION...95