891 FXUS66 KPDT 210923 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 223 AM PDT Tue May 21 2019 .SHORT TERM...Today through Thursday...An upper level low pressure system along the Oregon coast this morning will move southeast across southwest Oregon today and then settle into the large upper level trough over the western United States forming a closed upper level low over the Great Basin. This low is currently creating a nearly stationary frontal boundary with precipitation across the forecast area stretching from southwest Idaho to western Washington. This boundary will persist through much of the day stretching from the east slopes of the Washington Cascades back into northeast Oregon producing a steady light rain. It will begin to weaken and fall apart late this afternoon and evening with the precipitation emphasis overnight shifting south across eastern Oregon as the flow aloft turns more easterly. Wednesday and Thursday the forecast area will be under a north to northeast flow feeding into the large upper level low centered over the Great Basin. Some weak instability over the region in this flow will result in some showers over the eastern mountains and the Cascades both days with showers tapering off in the evenings. There will be a slight chance of thunderstorms today over central Oregon and then along the east slopes of the Washington Cascades Wednesday and Thursday afternoons. .LONG TERM...Thursday night through next Tuesday...The weather pattern will remain unsettled and showery through most of the extended period. There will be a break or two in the weather between systems, but overall it will remain unsettled. On Thursday night and Friday there will be an upper low over the northern Rocky Mountains and an amplified upper ridge well off the coast. This will put a north to northeasterly flow over the forecast area. An upper low pressure system will drop down from BC and bring more rain showers to the CWA on Friday. There will also be enough instability for possible afternoon thunderstorms on Friday over southeast portions of the forecast area. This upper low will slide southward along the coast into northern California by Saturday. There will still be some wrap around moisture into the CWA in an easterly flow on Saturday as this low moves southward. Once again, there will be enough instability Saturday afternoon and evening for possible thunderstorms, if there is enough surface solar heating. The upper low will stall over California and keep and easterly flow over the forecast area through Sunday. Yet again, there will be enough afternoon instability due to surface heating for possible thunderstorms as well on Sunday. By this time, the longer range models really begin to diverge significantly with each other, and therefore made little change to the forecast after Sunday as a result of the uncertainty. However, it will still remain unsettled with showers on Monday...with possible thunderstorms again in the afternoon in southeast areas of the CWA. On Tuesday some drying will take place as an upper ridge tries to build over the region. Temperatures will be rather cool through Saturday and then there will be a warming trend from Sunday onward with temperatures climbing up back into the 70s to lower 80s in the lower elevations and 60s to lower 70s in the mountains by Tuesday. It will be breezy on Friday, mainly in north central Oregon and the eastern Columbia River Gorge, but the winds will become calm Friday night. Winds will then remain light after that through Tuesday. 88 && .AVIATION...12Z TAFs...A band of rain showers has developed in a southeast flow over the area from northeast Oregon northwest to Yakima County along the Cascade east slopes in a wrap around flow around a low pressure system along the Oregon coast. There could be brief periods of MVFR conditions under this band of rain due to lower CIGs and visibility in the rain. However, most of the time it will remain VFR. The band of rain will shift southward through the day and tonight with KRDM and KBDN receiving the best chance of precipitation tonight. There could be more periods of MVFR conditions at KRDM and KBDN tonight as a result. Winds will be light through the next 24 hours. 88 && .PRELIMINARY POINT TEMPS/POPS... PDT 61 46 71 46 / 80 30 10 10 ALW 64 47 73 49 / 90 30 10 10 PSC 68 51 78 53 / 70 10 0 0 YKM 67 50 76 53 / 70 10 10 10 HRI 66 48 76 49 / 70 20 0 10 ELN 66 48 72 50 / 60 10 10 10 RDM 59 41 66 42 / 60 70 40 20 LGD 57 44 64 43 / 90 60 20 20 GCD 56 43 62 42 / 70 60 20 20 DLS 67 51 76 53 / 40 20 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ 91/88/88