Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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070 FXUS66 KPDT 161146 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 445 AM PDT Sun Jun 16 2024 Updated Aviation Discussion .SHORT TERM...Today through Tuesday night...Models are in excellent agreement on the evolution of the 500 mb pattern the next few days. The GEFS ensemble moves a developing upper low over SRN BC across Oregon and Washington tonight and Monday morning leaving broad troughiness in its wake for Monday night through Tuesday night. For this afternoon and evening as the upper low develops/ approaches there will be a 30-60% chance of showers and a slight chance (10-20%) of TSTMS along the east slopes of the Cascades. Thermodynamic profiles from NAM forecast soundings show steep low to mid level lapse rates and surface based CAPE of around 500 J/kg. This evening scattered to numerous showers (30-60% POPS) will develop over central Oregon and then move NE across the E/NE mountains overnight. QPF amounts are forecast to be .10-.15 inches on average. Light snow of 1-2 inches is expected at elevations above 5000 feet. On Monday the upper low will move east of the region with the bulk of the remaining showers confined to the northeast mountains and Wallowa County...with a 10-15% chance of TSTMS. A cold front will cross the area which will cause west-northwest winds to increase in the Cascade gaps. Strongest winds are forecast to be in the Simcoe Highlands north of he Columbia River and in the Kittitas Valley. The NBM probabilities of wind gusts exceeding 45 mph is 40-70%. All 50 of the ECMWF ensemble members are predicting max wind gusts exceeding 40 mph at KELN on Monday but none are forecasting 50 mph. Thus the potential need for wind highlights is moderate on Monday (40-50% chance). On Tuesday there will just be a slight chance of showers along the Washington crest and Wallowa County (15-20% chance). Otherwise it will be dry. It will be chilly today with high temperatures 10-15 degrees below normal, but it will warm up each day so that by Tuesday it will be just 3-5 degrees below normal for high temperatures. Low temperatures below freezing can be expected in the mountain valleys Monday and Tuesday morning. .LONG TERM...Wednesday through Sunday...Models are in good agreement with the synoptic pattern through Saturday, but differences begin to emerge for Day 8 (Sunday). A dry forecast is in store during this time with the exception of a few showers along the east slopes of the central WA Cascades next weekend. The biggest weather impacts over the forecast area will be the temperatures that are more typical for late July rather than late June on Friday and Saturday. Models have consistently advertised a weak marine push late Saturday that will result in increasing wind and elevated fire weather. The PacNW will be under a weak WSW flow aloft through the end of the week. It will be mostly dry but cannot rule out that sprinkles or an occasional orographic shower will develop over the mountains. Winds will predominantly be light and terrain driven, but there is a chance of localized gusts around 20 mph (40% confidence) or 25 mph (20% confidence). An inverted surface thermal trough building east of the Cascades Thursday night through Saturday will cause temperatures to climb to 10-15 degrees above seasonal average. The experimental HeatRisk product shows minor to moderate heat. Will there be 100 degrees during this time? NBM would suggest `no` based on the 10% or less probability. The probability of 90+ degrees from the NBM is 60-80% across the Lower Columbia Basin, the Yakima Valley, and portions of the John Day Basin. Forecasters will keep an eye on the thermal trough moving into ID and allowing cooler marine air to seep through the Cascades late Saturday. With forecast max temperatures in the 90s and forecast RHs in the teens, the increase in wind will elevate fire weather concerns. Confidence for the marine push on Saturday is around 30%. The forecast for Sunday will show cooler and breezy weather with a 20% chance of showers along the WA Cascades. The ensembles differ on the amplitude and position of an offshore trough, and 50% of the GEFS members maintain a westerly flow across the eastern Pacific and the PacNW. Differences are not major but are signs of inconsistencies that extend into the long range forecast for early next week. Wister/85 && .AVIATION...12z TAFs...Winds have diminished, and today`s winds will be less than yesterday but gusts 20-25 kt at DLS, RDM, BDN and PDT in the afternoon. Otherwise, high level clouds will increase with bases AOA 15 kft until 21Z. After 21Z, mid-level clouds will increase for SCT-BKN 6-10 kft and high level clouds above. Light rain will be in the vicinity of RDM, BDN, PDT and ALW. Wister/85 && .PRELIMINARY POINT TEMPS/POPS... PDT 65 43 67 43 / 0 40 30 10 ALW 68 45 71 46 / 0 30 40 10 PSC 71 48 74 48 / 10 20 10 10 YKM 68 43 72 43 / 30 20 10 0 HRI 71 46 73 47 / 10 30 20 10 ELN 65 45 68 45 / 30 20 10 0 RDM 60 35 61 34 / 20 30 10 0 LGD 62 40 60 39 / 10 50 50 20 GCD 64 38 60 37 / 20 70 50 10 DLS 68 50 68 48 / 20 10 10 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Freeze Warning until 9 AM PDT this morning for ORZ050. WA...None. && $$ SHORT TERM...78 LONG TERM....85 AVIATION...85