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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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825 FXUS66 KPDT 152345 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 444 PM PDT Thu Aug 15 2024 Updated aviation discussion .SHORT TERM...Today through Saturday Bottom Line Up Front 1. Thunderstorms today and through this evening 2. Thunderstorms again Saturday The upper level shortwave trough has been causing some wrap around convection and showers this afternoon. Current radar shows quite a few cells popping up over the eastern mountains and putting out some lightning and rain showers. Ground observations show that some isolated locations have seen near 0.04 inches of rain with some of these cells as well as some lightning accompanying them. These storms will continue through the remainder of the afternoon and early evening bringing more rain chances as well as thunderstorms. The thunderstorms will stretch from central OR along the central and eastern mountains. A RED FLAG WARNING remain in effect along the aforementioned areas for abundant lightning through 11 PM tonight. Friday the models show a brief break form all the action before another round of thunderstorms roll through on Saturday and will primarily be along the east slopes of the Cascades. Models show another upper level low parking itself just off shore while its leading edge shimmies up along the Cascade crests Saturday. This will allow some added moisture to influx across the Cascades as well as increased instability. Model derived soundings from the CAMs shows relatively high MUCAPE values beginning to crest into the 700-800 J/kg with a LI of -4 to -6, mid level lapse rates over 8.5 C/km and effective bulk shear nearing 45 kts. These ingredients coupled with the southwest flow and orographic lift, thunderstorms will likely form along the crests and portions of the eastern slopes on Saturday. Primary concerns for thunderstorms on Saturday will be the amount of rain associated with them. Model derived soundings show PWATs over 1 inch which could lead to heavy downpours with these storms (50-70%). Raw ensembles show 30-50% chances for near 0.50 inches. Models are also showing these storms could be slow movers so they could train over the area and if near any recent burn scars, could cause flash flooding. Due to this fact, a flash flood watch is in effect for the eastern slopes of the Cascades Saturday afternoon through late Saturday night primarily concerns being over the many burn scars across the area (i.e. Retreat Fire, Williams Mine fire as well as some of the larger burn scars from 2021 and 2022). Bennese/90 .LONG TERM...Sunday through Thursday...The 500 mb pattern during the extended period will be dominated by an upper low remaining more or less stationary off the PACNW coast held in place by a full latitude blocking ridge centered over the SWRN states. The GFS does break down this ridge a bit Wednesday into Thursday by moving a shortwave across the nrn tier of states including the PACNW but this is not supported by the ensemble clusters which for the most part keep the upper low intact offshore. This will set up a swly flow aloft pattern across the region with relatively benign conditions. It will be warm but not hot with probabilities of reaching 90 degrees for high temperatures peaking at 20-30% in the Columbia Basin on Sunday then less than 10% areawide the remainder of the forecast period. Aside form some low pops (30% or less) along the Washington Cascade Crest, chances for rain will be less than 15% through the period. There is always some concern that a shortwave embedded in the flow could spark thunderstorms but the NBM probabilities of thunder are 10% or less each day. Weak marine pushes are also likely each day in this flow pattern but the latest suite of model guidance indicates that the probability of needing wind highlights is rather low (10-20%). 78 && .AVIATION...00Z TAFS...General VFR conditions will prevail through the forecast period with some mid level CIGS at 6-12 kft AGL through tonight for PDT and ALW along with a chance of showers through this evening and a 10% chance of some lightning. chance) at KBDN and KRDM tonight. Winds will generally be less than 10 kts overnight except for DLS where some 10-20kts winds will last into the evening. && .PRELIMINARY POINT TEMPS/POPS... PDT 54 82 54 90 / 10 0 0 20 ALW 59 86 58 96 / 20 0 0 10 PSC 63 87 59 96 / 20 0 0 10 YKM 54 84 54 90 / 30 0 0 40 HRI 60 86 57 94 / 10 0 0 20 ELN 56 84 54 91 / 10 10 0 30 RDM 46 81 49 82 / 10 10 10 50 LGD 49 83 51 92 / 50 10 10 10 GCD 49 83 53 92 / 50 10 10 10 DLS 59 83 60 90 / 10 0 10 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning until 11 PM PDT this evening for ORZ611-640-642- 644-645. WA...Flash Flood Watch from Saturday afternoon through late Saturday night for WAZ522-523. && $$ SHORT TERM...90 LONG TERM....79 AVIATION...79