Scientific Forecaster Discussion

000 fxus66 kpdt 221642 afdpdt Area forecast discussion National Weather Service Pendleton or 942 am PDT Wed may 22 2019 Update...minor updates to the grids this morning. Upper-level low over the Desert Southwest will slowly meander north and east through tomorrow. Ridging is trying to build over the low and work into our region. Expect drying and warming conditions today through tomorrow. Still expect a chance of showers and isolated thunderstorms this afternoon/evening over the Cascades/blues/wallowas into central or as mid-level moisture continues to wrap around the northern periphery of the low. Expect highs in the mid 50s to mid 60s mountains and upper 60s to mid 70s in the valleys and basins. Tomorrow looks to be drier and warmer as the low works away from the region. Could still see an outside shot for a few showers/storms over the mountains. Highs in the upper 50s to 60s mountains and 70s to low 80s in the valleys and basins. With low off to the south, north to northeast winds will pick up this afternoon and again 10-20 mph with some higher gusts in central or. Friday into the weekend, another upper-level low is expected to drop south out BC, over the pacnw and settle over the Desert Southwest. This will bring a good chance for showers and thunderstorms, mainly over the mountains, along with cooler temps. Aviation...18z tafs...VFR conditions will prevail through the period. Mostly mid and high clouds are expected with a tendency for clouds to thin out a bit tonight. Some stratocumulus will persist into the evening at kbdn and krdm with the potential for vcsh this afternoon. Winds will be the primary concern with north winds at 15 to 25 kt and some higher gusts diminishing after sunset...becoming mostly light over night. 78 && Previous discussion... /issued 230 am PDT Wed may 22 2019/ Short through Friday...there is an area of showers moving across north central and northeast Oregon this morning in a wrap around flow around an upper low pressure system over the Desert Southwest. Expect this pattern to persist through tonight. There will be some instability this afternoon mainly along the Cascade east slopes where there could be a thunderstorm or two this afternoon and evening. Elsewhere expect isolated to scattered showers today over the eastern and northeast mountains. The showers will decrease and end by late tonight due to the loss of surface heating. The lower Columbia Basin and adjacent lower elevations should remain dry today. Thursday will be similar to today. The upper low over the southwest will begin to lift to the northeast. There will again be enough moisture and instability again in the afternoon for possible thunderstorms along the Cascade east slopes. With the upper low departing to the northeast the eastern areas of the forecast area will be mostly dry and as a result did not include showers on Thursday in the eastern areas of the County Warning Area. Then on Friday another upper low pressure system will drop southward from western British Columbia into the Pacific northwest. This system will bring a better chance of showers and especially afternoon thunderstorms over most of the forecast area. There could be a couple to a few strong thunderstorms on Friday, but most will not be strong. But the areal coverage will be much greater than today or Thursday. Temperatures will warm today to the upper 60s to mid 70s in the lower elevations, then warming further to the mid 70s to lower 80s on Thursday, but then cooling back down to the upper 60s to mid 70s on Friday. These temperature forecasts will be the result of more clouds today and Friday, but less on Thursday. It will be locally breezy through the period, mainly in the afternoons and evenings, and especially near any showers or thunderstorms. Winds will be mostly light by the late night hours each night. 88 Long term...Friday night through the beginning of the extended period, a potent shortwave will be dropping into the Pacific northwest and this will cause a strong deepening of the longwave trough beginning Saturday and continuing into Sunday before the trough begins to move eastward. The upper low will be over Washington and Oregon on Saturday and will drop into California by Sunday, and gradually push into the Great Basin by Monday. The guidance has some short term ridging by Monday behind the trough before another low may begin to drop down Tuesday or Wednesday. Guidance begins to diverge after Tuesday. With a large upper trough in place, expect unsettled conditions over the weekend, though it will not be rainy the whole time. With the proximity of the upper low, there is a chance of thunder especially Saturday and into Sunday. Best on the latest guidance, less confident into Tuesday. If guidance trends continue will likely remove thunder chances for Tuesday and possibly Monday in later forecasts. Temperatures should begin a slow warming trend after Saturday. && Preliminary point temps/pops... PDT 68 44 74 50 / 10 10 0 10 alw 73 49 79 55 / 10 10 0 10 psc 76 53 82 58 / 10 10 0 10 ykm 75 52 80 53 / 10 10 10 0 hri 75 49 81 54 / 10 10 0 10 eln 71 50 77 53 / 10 10 20 10 rdm 63 42 69 44 / 20 30 10 10 lgd 62 43 69 47 / 30 20 0 0 gcd 61 42 69 45 / 30 30 10 10 dls 76 53 81 54 / 10 10 10 10 && PDT watches/warnings/advisories... or...none. Washington...none. &&

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