FXUS66 KPDT 020513 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1013 PM PDT Sat Jun 1 2024 .AVIATION... 06Z TAFS...VFR conditions and dry weather are expected overnight, then -RA will overspread the area on Sunday. DLS will likely see some MVFR conditions later Sunday afternoon/Sunday evening, and MVFR coan't be ruled out in other locations, especially if there are periods of moderate or heavy rain, but confidence is low (<30%) in the lower conditions for the other sites at this time. Winds have increased at PDT and ALW to around 30 kts at PDT and 20 to 25 kts at ALW, but these winds should decrease overnight. BDN and RDM will gust between 25 and 30 kts on Sunday. The other TAF sites should be 10 kts or less though some local gustiness can't be ruled out, especially around heavier rain. && .PREV DISCUSSION... /issued 435 PM PDT Sat Jun 1 2024/ AVIATION...00Z TAFs...VFR conditions expected over the next 24 hours. Breezy winds should lessen by the nighttime hours, becoming 10 knots or less most sites, but will pick back up tomorrow for Central OR sites (BDN/RDM) during the morning. Cloud decks remain mid to high level through the overnight hours, but will drop to around 5k feet tomorrow as precipitation begins to move into the region. Rain should overspread the region tomorrow morning into the early afternoon. Goatley/87 PREV DISCUSSION... /issued 246 PM PDT Sat Jun 1 2024/ SHORT TERM...Tonight through Monday...Satellite and radar imagery this afternoon show scattered cloud cover across the forecast area, with the central WA Cascades reporting any precip in the last 3 hours. While there are light radar returns moving across the area, the surface has been too dry for any precipitation to reach the ground. Through this evening, a weak shortwave trough and attendant surface cold front will continue to push east across the PacNW, producing light mountain showers and breezy conditions through the lower elevations. A brief dry spell with light winds will follow the exit of this coupled system tonight, though cloud cover will increase in the pre-dawn hours tomorrow. Active weather once again returns by mid tomorrow morning as an upper trough with leading frontal boundaries pushes into the PacNW from the northeast Pacific. Rain bands will spread across eastern WA/OR throughout Sunday and continue well through Monday morning as the warm and cold fronts sweep across the region. These showers will also be supported by an accompanying Atmospheric River that will bring PWATS between 0.75-1.25 inches (around 200% of normal) across the region, with GFS and ECMWF ensemble mean IVT values between 500-750 kg/m*s. This will translate to rainfall accumulations between 1.25-1.75 inches across the Northern Blues, Cascade crest and upper slopes, and the Wallowas from 5AM Sunday to 11AM Monday; 1 to 1.25 along the Cascade lower slopes and immediate foothill locations along the Northern Blues; 0.5 to 1 inches across the northern Blue mountain foothills, Wallowa/Grande Ronde valleys, and portions of the southern Blues; 0.1 to 0.25 inches across the remainder of the areas with locally higher amounts approaching the Cascade east slopes and the foothills of the Blues (confidence 60-80%). While rainfall may be heavy at times across the mountain locations, area rivers and streams have been low enough to abate the concern for flooding, however, smaller streams and areas of poor drainage could see localized flooding across portions of the eastern mountains and Wallowa county. There will also be potential for isolated thunderstorms to develop across the eastern mountains and Wallowa county Monday, with GFS and NAM guidance showing most unstable CAPE between 250-750 J/kg and 0-3km shear between 30-50kts over these areas. The main threats with any developing cells will be heavy rainfall, small hail, gusty winds, and frequent lightning. Besides rainfall, the cold front boundary and subsequent trough passage Monday will also tighten surface pressure gradients along the Cascades. This will result in windy to gusty conditions developing through the Cascade gaps and into the lower elevations late Monday morning through the evening. Sustained winds of 20-30 mph and gusts up to 45mph will be possible across the lower elevations, with higher values across the Simcoe Highlands, OR Columbia Basin, and the Kittitas valley. NBM currently shows a 80-95% 24-hr probability of max sustained winds reaching 30 mph and gusts reaching 45 mph across the OR Columbia Basin, Simcoe Highlands, and portions of the Kittitas valley. While probabilities are high, will wait for high-res guidance before potentially issuing wind advisories in the aforementioned areas. Lawhorn/82 LONG TERM...Tuesday through Saturday...A period of weather more akin to summer looks to be in store for the region later this work week, however model discrepancies continue to hinder forecast confidence. Guidance consistently depicts a broad ridge establishing itself over the PacNW by the midweek, but where this ridge axis ultimately centers itself remains up in the air, as just a slight eastward shift in its position would invite SW flow aloft into the forecast area, and thus a cooler temperature forecast as well as a chance for thunderstorms. The long-advertised Atmospheric River that will make for a wet forecast in the short term will start to relent early Tuesday, before high pressure slides in by Wednesday. Even this close in the long term, however, the deterministic GFS and ECMWF diverge on how the high pressure ridge establishes itself, with the GFS favoring a more negative tilt and thus more SW flow over the forecast area, while the ECMWF has a bit of a flatter ridge, which would lead to a warmer forecast. Ensembles seem to lean more towards the ECMWF solution, but confidence levels on the temp forecast are around moderate (50-60%) based on deterministic model differences. NBM probabilistic remains bullish on the potential for warm temps by the end of the work week, broadly depicting a 60-80% chance for highs above 90 on Friday for our lower elevation zones, but that could very well chance should the GFS solution start to win over in the forecast over the coming days. Forecast confidence is low (<30%) after Friday, as guidance exhibits wide variability. Ensemble clusters waver between enhanced SW flow and continued ridging. The former solution is what the NBM is currently leaning towards, which would result in shower and thunderstorm chances across the forecast area, while the latter would mean more heat for the forecast area. A bit of a tricky forecast thus far, but fortunately precip chances look to be limited until at least next weekend. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 52 69 54 66 / 10 60 100 80 ALW 55 71 57 68 / 10 60 100 90 PSC 58 71 59 73 / 10 60 80 50 YKM 51 68 50 69 / 10 70 80 40 HRI 56 72 56 71 / 10 50 70 60 ELN 49 65 50 65 / 10 70 80 50 RDM 46 68 53 63 / 10 40 70 50 LGD 47 69 54 63 / 10 40 100 100 GCD 46 71 55 66 / 10 30 100 90 DLS 56 67 58 66 / 10 70 90 60 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...82 LONG TERM....74 AVIATION...77