Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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839 FXUS66 KPDT 200918 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 218 AM PDT Thu Jun 20 2024 .SHORT TERM...Today through Friday... Bottom Line Up Front 1. Dry conditions with isolated dry thunderstorms along the eastern mountains. 2. Hottest day will be Saturday with moderate heat risk. With the northerly flow in place and the daily run of a surface thermal trough, dry conditions will prevail through the period. However, looking at some of the CAMs models, there will be some instability moving across the eastern mountains. Model derived sounding are showing MUCAPE values well above 400 J/kg with lifted indexes of -1 to -4, lapse rates of 8.5 C/kg and bulk shear nearing 40 kts. PWATs are moderate with 0.50-0.65 inches available. Given the ingredients as well as daytime heating and orographic lift, one can not rule out the possibilities of some isolated thunderstorms over the eastern mountains tomorrow afternoon (less than 25% probabilities). Not only are the ingredients available along the eastern mountains, but CAMs models show there are decent amounts of MUCAPE (250 J/kg) along the WA Cascades. However, probabilities of isolated thunderstorms along the eastern slopes are less than 10%. Models are in firm agreement with the upper level flow being from the northwest with a strong surface thermal trough making its way into the region. Models show Saturday to be the day with the strongest trough set up which will bring temperatures above Normal. EFI shows temperatures to be well above normal temperatures with over 70% of the raw ensembles putting the majority of the region in low to mid 90s with some isolated areas in the Basin in the high 90s. NBM is showing a moderate heat risk across the majority of the Basin as well as through the Gorge and portions of the southern Blues with very isolated locations seeing high risk. If you are out and about this weekend, please plan appropriately. For more information go to www.weather.gov/heat. Bennese/90 .LONG TERM...Sunday through Thursday...A dry cold front will result in gusty winds on Sunday. Models have consistently advertised this for at least several days now, so the confidence is high that it will be breezy to windy. The NBM probability of gusts >= 22 kts is over 90% for most of the forecast area and the probability of gusts >= 34 kts is 70-100% in the Lower Columbia Basin, eastern CR Gorge, Simcoe Highlands, and the Kittitas Valley. For gusts >=41 kts, the probabilities are around 80% for the Kittitas Valley, 30% for the eastern CR Gorge, and 15% or less elsewhere. Confidence is also high that the relative humidity will be in the teens for areas in and around the Lower Columbia Basin and across south central and southeast Oregon. All of the mean ensembles are showing dry air aloft behind the front...less than 10% at 700mb. The primary weather concerns for Sunday will be fire weather, and highlights may be needed as we approach the weekend. The westerly flow aloft across the eastern Pacific and the PacNW will begin to buckle in response to a deep closed low developing off the Gulf of Alaska. By Tuesday, a large trough will develop between 130-150W, and the westerly flow over WA/OR will back to the southwest. Models are not hinting at any convection and all show very weak or no surface-based instability. However, there is some elevated instability looking at the GFS with mid-level theta-e decreasing with height and DIV Q aloft. Usually, these are signs of isolated high based storms. For now, will not mention thunderstorms for Tuesday until confidence improves. At this time, confidence is only 15%. There are differences in the model progs for Wed-Thur, but nothing significant. Main difference is the amplitude of the trough as it moves inland, but less than 25% of the ensembles from the GEFS, ECMWF, and GEPS advertise a flat trough. The rest are showing a fairly organized trough over WA/OR Thursday. Therefore, Thursday is forecast to be a little cooler with 20-35% chance of showers along the Cascades and the eastern mountains. Wister/85 && .AVIATION...12Z TAFs...VFR conditions expected over the next 24 hours. Winds 10 knots or less except BDN/RDM tomorrow afternoon when gusts between 10-20 knots possible. SKC overnight but high level clouds will move over, generally SCT to BKN at 20-25k feet. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 87 54 89 56 / 0 0 0 0 ALW 91 57 92 60 / 0 0 0 0 PSC 92 57 94 60 / 0 0 0 0 YKM 88 56 93 59 / 0 0 0 0 HRI 93 56 95 60 / 0 0 0 0 ELN 86 54 90 59 / 0 0 0 0 RDM 83 50 88 53 / 0 0 0 0 LGD 83 53 85 54 / 0 0 0 0 GCD 85 50 89 55 / 0 0 0 0 DLS 92 61 94 63 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....85 AVIATION...87