Scientific Forecaster Discussion
000 FXUS66 KPDT 180928 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 230 AM PDT Wed Sep 18 2019 .SHORT TERM...Today through Friday...Closed upper low centered north of Astoria pushed a frontal band across the region last night and is currently positioned from Wallowa County southwest to Klamath County. The weak cold front will track to the southeast and over southwest Idaho this morning. There will be additional waves of moisture and energy rotating across WA/OR over the next 24 hours that will bring scattered to numerous showers. WSR-88D is showing 40-50 dBZ returns associated with one mid level wave traveling across north central OR at this time. All zones will have at least a chance of showers and a slight chance of thunderstorms today as the closed low weakens into an open trough and migrates across the region. Precipitation amounts will vary from a few hundredths to around a quarter of an inch. There will likely be small hail or graupel with some thunderstorms. Additional light snow can be expected above 7500 feet. The locally breezy winds observed yesterday are decreasing, and winds today will be relatively light. The upper level trough will be in no hurry to leave the region and will remain east of the Cascades tonight and most of Thursday. Showers will taper off from the west overnight, and precipitation on Thursday will mainly be in the eastern zones from the Blue Mountain Foothills down to John Day east to the Idaho border. This area may also observe isolated thunderstorms Thursday afternoon. The NAM was particularly bullish with QPF on Thursday with more enhanced wrap- around moisture, and believe the GFS is more realistic with the heaviest precipitation amounts around 0.1-0.2 inch in Wallowa County with lesser amounts elsewhere. The trough will finally travel into Idaho Thursday night, and showers will taper off in the eastern zones by early Friday morning. There will be isolated to scattered showers over Wallowa county late Thursday night and Friday, but dry conditions elsewhere. The forecast area will be on the east side of a shortwave ridge and under a northerly flow aloft on Friday. Skies will be party to mostly cloudy with locally breezy winds as surface high pressure builds with a fairly tight pressure gradient. Friday will be a little warmer compared to today and Thursday but still below seasonal averages with highs in the upper 50s to upper 60s in the mountains and mid 60s to mid 70s elsewhere. Wister .LONG TERM...Friday night through Wednesday...A northerly flow followed by an upper ridge will move into the region and the forecast area Friday night into Saturday. This will bring fair weather with dry conditions and warmer temperatures. However, the warmer temperatures will only be by a few degrees, but becoming near normal. Then on Sunday another upper trough and cold front will move down from the northwest into the Pacific NW bringing a chance of showers into the Cascades Saturday night and then across the rest of the forecast area on Sunday. Temperatures will cool down again on Sunday due to the clouds and precipitation. However, it will only be a few degrees below normal as the flow will generally be from the southwest. However, the upper trough axis will be over the CWA by late Sunday evening and the atmosphere will be more unstable. However, due to the timing of the trough axis late at night am not expecting any thunderstorm activity this time of year. Cannot rule it out, but will leave any mention of thunderstorms out of the forecast for now. Models are still in fair agreement at this point in time in the future. Then on Monday through Wednesday the models begin to diverge from each other, become greater with time. Most of them show another upper ridge building over the region. However, cannot rule out some showers due to the uncertainty in the models solutions through the latter extended period, especially over the Cascades and northeast mountains. Most areas will remain dry though. Temperatures will rise back to near normal again for Tuesday and Wednesday. Winds will be mostly light through the extended period. 88 && .AVIATION...12Z TAFs...Radar is showing an area of rain moving in from the west. This is mostly affecting TAF sites KDLS, and occasionally KPDT and KALW. It is not a solid coverage of rain and so the precipitation will be intermittent. CIGs could drop to MVFR at times in the precipitation along with the visibility. However, most of the time all TAF sites will remain VFR. Winds will be light through the next 24 hours at all TAF sites. 88 && .PRELIMINARY POINT TEMPS/POPS... PDT 67 49 67 50 / 50 40 30 10 ALW 70 52 70 53 / 50 40 40 10 PSC 72 53 74 54 / 20 30 10 0 YKM 68 47 72 51 / 40 30 0 0 HRI 73 52 73 55 / 30 30 20 0 ELN 66 46 70 52 / 60 30 0 10 RDM 61 41 64 43 / 80 50 10 10 LGD 60 45 61 46 / 90 70 50 10 GCD 59 44 62 45 / 90 70 60 20 DLS 68 51 72 55 / 70 20 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None.