Scientific Forecaster Discussion
000 FXUS66 KPDT 291730 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1030 AM PDT Wed Mar 29 2017 Updated aviation discussion .SHORT TERM...Today through Friday...A wet and windy period is expected over the next 24 to 36 hours as a system and trough crosses the area. The warm front with the system is over the area and rain has begun in most locations. This afternoon and tonight the cold front will follow the warm front and move through the area. Rain will be likely across the area through tonight, perhaps a little less so in the Columbia basin and Yakima and Kittitas valleys. Rain amounts will be significant with up to 1.5 inches in the mountains, up to an inch in Union and Wallowa counties, up to 2/3 of an inch in the Blue Mountain foothills and up to half an inch elsewhere. Snow levels will be high, so snow will be confined to above above 7000 feet. The abundant rainfall will lead to river rises and hydrology concerns will have to be monitored carefully. Right now the John Day River at Service Creek and the Grande Ronde at Troy are expected to reach flood stage and several others are expected to be above bankfull. On Thursday a trough will cross the area with a chance of rain and snow in the mountains and a slight chance of rain in the lower elevations. Snow levels will be down to 3500 feet due to the colder air coming in with the trough. Rain amounts will be much light with less than a tenth of an inch in the lower elevations and up to a quarter inch in the mountains. Rain will taper off Thursday evening and end overnight. Winds will be another concern today and especially on Thursday. Pressure gradients are tightening up and much of the area will have southwest winds of 10 to 20 mph today with 15 to 25 mph in the Southern Grande Ronde Valley. Winds will decrease overnight but pressure gradients will be even stronger on Thursday with much of the area having west to northwest winds of 15 to 25 mph. The Columbia Gorge and the Kittitas and Southern Grande Ronde Valleys look to be borderline for a wind advisory. Do not have enough confidence to put one out this early but anticipate that advisories might be needed for those areas. Friday an offshore ridge will build over the area for a sunny and dry day. Temperatures will be in the 50s as the warm front crosses the area today. Tomorrow highs will be in the mid 50s to lower 60s in the Columbia Basin with 40s and lower 50s elsewhere. Friday will be in the upper 50s to mid 60s with upper 40s to mid 50s in the mountains. Lows tonight will be in the mid 30s to mid 40s due to the heavy cloud cover but will drop to the mid 30s to around 40 with mid 20s to lower 30s in the mountains Thursday night. Perry .LONG TERM...Friday night through Wednesday. The extended starts off mainly dry as a ridge of high pressure moves across the area Friday night. A weak frontal band is shown by the models to move south into Oregon on Saturday with some showers by late day. The unsettled weather returns by Sunday as a trough of low pressure is expected to move through Sunday with lingering showers over the eastern portions of the forecast area on Monday. Models are then diverging with the GFS dropping a low into southern Canada, while the ECMWF has a stronger ridge on Tuesday. They do however come back into more agreement with a large low pressure area off the west coast which will keep the unsettled weather through mid week. Temperatures will be near to slightly below normal. 93 && .AVIATION...18z tafs. VFR conditions are generally expected with light rain for some sites through this afternoon. There may be some MVFR with the heavier showers and ceilings 050-070 with visibility lowering to 4-6SM at times. Winds will be 10-20kt. && .PRELIMINARY POINT TEMPS/POPS... PDT 56 41 53 35 / 90 80 40 20 ALW 57 45 54 40 / 90 80 50 20 PSC 58 44 60 38 / 70 40 20 0 YKM 60 39 61 35 / 60 30 20 0 HRI 57 43 58 37 / 70 60 30 10 ELN 54 37 52 34 / 70 40 20 0 RDM 59 37 51 26 / 60 70 30 10 LGD 55 40 51 36 / 90 90 70 30 GCD 59 39 50 33 / 80 100 80 20 DLS 57 44 58 40 / 80 60 20 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None.