Area Forecast Discussion
Issued by NWS Pendleton, OR

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000 FXUS66 KPDT 050535 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 935 PM PST Thu Mar 4 2021 Updated aviation discussion .SHORT TERM...Tonight and Friday...A deep upper level ,trough off the coast is keeping a cold front nearly stationary along the west coast. Most of the precipitation will stay west of the Cascades overnight. The front will slowly start moving eastward Friday afternoon increasing the chance of precipitation along the Cascades but stay dry across the rest of the forecast area until Friday night. Even then it looks like the precipitation will be light and spotty. Will begin seeing some increasing southerly winds overnight mainly across the higher terrain of eastern Oregon. A wind advisory has been issued for the southern Grande Ronde Valley but this looks like a low end advisory event. Increasing winds and a little bit of high clouds will help hold temperatures up in some areas overnight so adjusted temperatures up in the evening forecast update. .AVIATION...06Z TAFs...VFR conditions currently across all sites, and will continue through the period but expect some lowering ceilings Friday afternoon and evening as a cold front begins to move over the Cascades. Breezy winds are expected for central Oregon sites as wind gusts 20-30 kts out of the South. Locally breezy S/SE winds are likely at PDT and ALW, as sustained winds hover around 10- 15 kts and occasionally higher gusts. && .PREV DISCUSSION... /issued 246 PM PST Thu Mar 4 2021/ Updated Aviation Discussion. SHORT TERM...Tonight through Saturday night. Low pressure offshore with a cold front along the coast this afternoon. Ahead of this system a southwest flow aloft spreading mid and high level clouds over Washington and Oregon. This will continue through the evening and overnight. Temperatures will be milder than the past few nights with lows in the 30s to lower 40s. As the front moves onshore surface gradients will tighten with increasing southerly winds developing overnight across central and northeast Oregon. On Friday the frontal boundary will move to near the Cascades with rain in the afternoon. Elsewhere across the forecast area partly to mostly cloudy and warm with highs in the 50s and 60s. Breezy to windy over central and northeast Oregon. The upper trough and weakening front move through the region Fri night and Sat with a period of rain and higher elevation snow. Southerly winds will become westerly with locally breezy conditions. Cooler with highs only in the 40s to mid 50s. The next upper trough and front moving into the Pacific northwest Sat night with increasing clouds and precipitation reaching the Cascades by morning. 94 LONG TERM...SUNDAY THROUGH THURSDAY...The long term pattern is dominated by a deep trough slowly traveling south along the PacNW coast before moving onshore in CA midweek. This feature is coupled with persistent southwest flow aloft, allowing for moisture to spin up and around the system and develop upslope precipitation along the Cascades and northern Blues. The trough will also keep partly to mostly cloudy skies overhead as mild temperatures are expected with highs in the upper 40s to low 50s for lower elevations and low to mid-40s in the mountains, and lows near freezing for the Basin. As the system near the WA/OR coasts late Monday into Tuesday, precipitation chances will be heightened to allow for the best chance for low elevation rain, primarily during the afternoon hours on both days. As the system drops along the northern CA coast, drier air should infiltrate into our area late Tuesday into Wednesday to provide a slight dry period before the next system approaches from the northwest. Upper level flow will also be shifting from southwest to northwest by Wednesday afternoon/early evening to bring a return to upslope rain/mountain snow along the Cascades and northern Blues. A weak system looks to be forced south through central and eastern BC early Thursday, and will pick up some Pacific moisture on its way through the interior PacNW, allowing for mountain snow chances to increase - especially for the WA Cascades. The system will be dissipating as it near the CAN/USA border, so precipitation chances are mainly expected at elevation and primarily along the western slopes of the Cascades and Blues, with little making it to lower elevations. Snow levels should stay relatively consistent through the workweek, mainly staying between 2000-3000 feet. During frontal passages, Tuesday and late Wednesday into Thursday, snow levels will hover between 1000-2000 feet. No hydrologic concerns are currently expected due to low variability in snow levels and cloud cover through the long term. Models are in fairly good agreement on the offshore system until late Tuesday/Wednesday, where the GFS slows down the system as it moves onshore just south of the Bay Area, and the ECMWF keeps its earlier speed and because of that, pushes farther south and moves onshore along the USA/MEX border before continuing east. Observing ensemble cluster and phase space data, confidence is leaning slightly toward the ECMWF outcome. This would lead to a quicker and more southerly track of the system, resulting in faster drying behind the system and a more substantial influence from the offshore ridge FRI/SAT. 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 41 68 37 49 / 0 0 20 40 ALW 43 68 40 51 / 0 0 20 40 PSC 36 66 41 56 / 0 0 20 30 YKM 35 56 36 54 / 0 10 40 10 HRI 39 67 40 54 / 0 0 30 30 ELN 33 51 34 49 / 0 10 50 10 RDM 33 62 34 46 / 0 10 50 30 LGD 36 53 33 42 / 0 0 10 50 GCD 34 59 32 43 / 0 0 10 40 DLS 36 55 38 53 / 0 20 60 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 7 PM PST Friday for ORZ049. WA...None. && $$ SHORT TERM...91 LONG TERM....91 AVIATION...91

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