Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/24/16


Area Forecast Discussion
National Weather Service Pendleton OR
255 PM PST Thu Nov 24 2016 .SHORT TERM...Tonight through Sunday...Multiple wind warnings and advisories are in effect until 4 am PST Friday. A low pressure system will move up along the coast tonight and into British Columbia. This will tighten the southerly surface pressure gradient and lead to strong and gusty winds especially when coupled with a 50 kt low level jet. The strongest winds will be over central Oregon and along the Blue Mountain Foothills as well as the Grande Ronde and Wallowa Valleys. Winds should peak in the mid to late evening then slowly decrease overnight. Precipitation should be light and mostly confined to the Cascade East Slopes. Have recently cancelled the Winter Weather Advisory for the WA East Slopes. Snow levels have risen to 3000 feet and expect mostly rain through the evening. There could be a little snow returning overnight down to around 2800 feet but expect the snow amounts to be light. On Friday and Friday night expect scattered showers and snow showers with most of the activity over the mountains. QPF amounts will be light. Southerly pressure gradients will tighten again between 09- 18z Saturday and there is some potential for wind highlights during that time period especially near the base of the Blue Mountains and Grande Ronde Valley. For now increased the winds to near advisory level in these areas for further evaluation. With broad troughiness over the region into Sunday there will be a chance of rain and snow mainly in the mountains with snow levels 3000-3500 feet. 78 .LONG TERM...Sunday night through Thursday...A strong channeled vorticity maximum in the mid/upper levels with attendant dynamic lift rides over a mid/upper ridge of high pressure offshore and moves rapidly southeastward along a moisture plume and a frontal boundary into the interior Pacific Northwest late Sunday night with snow levels 2500-3000 feet thus producing chance category PoPs Sunday evening and then likely PoPs overnight in SE Washington and NE Oregon. Snow accumulations of 3-6 inches may occur with this system in the Blue Mountains from 10 PM Sunday evening until 10 AM on Monday morning. The disturbance exits the region Monday afternoon, yet orographic lift over the NE Oregon mountains will produce numerous snow showers in the mountains of NE Oregon and the Blue Mountains in SE Washington through Monday afternoon. Monday night and Tuesday a mod/upper level ridge of high pressure builds over the forecast area yielding sinking air aloft, which will yield a drier atmosphere at lower and mid levels for mainly dry conditions on Tuesday. Tuesday night into Wednesday expect increasing clouds associated with a strong negatively tilted mid/upper level trough moving out of the Gulf of Alaska and into the Pacific Northwest. Snow levels with the aforementioned trough Tuesday night/Wednesday will remain around 2500-3000 feet so mountains will receive some modest snow accumulations on the order or 2-4 inches at pass levels with higher amounts of 3-5 inches possible above 4000 feet. Precipitation with this system will be winding down and ending in the Lower Columbia Basin and the Kittitas and Yakima Valleys by Wednesday afternoon, although snow showers due to orographic lift are expected in the Blue Mountains, the Wallowa Mountains and the Elkhorn Mountains Wednesday night through Thursday afternoon with a low chance of snow showers possible at higher mountain elevations in northeast Oregon through Thursday night. Snow showers should end by Thursday evening elsewhere in the interior Pacific Northwest. Polan && .AVIATION...18Z TAFs...A Pacific storm system will push plenty of mid level clouds over central, south central and SE Washington as well as central and NE Oregon with cloud bases of 5000-10000 feet AGL, over the next 24 hours. KYKM may see brief periods of MVFR if ceilings lower to MVFR threshold this afternoon with passing showers; however, not confident enough to forecast BKN028 at this time. The other TAF sites will most likely only see vicinity showers, if any precip at all with VFR conditions. Surface winds at air terminals east of the WA/OR Cascades are a concern. A low level wind jet stream around 5000 feet above MSL will remain through the period over the Columbia Basin, the Yakima Valley, and the foothills of the Blue Mountains. Aircraft ascending into the low level jet or descending out of the jet may encounter sharp vertical wind shear resulting in jarring free air turbulence. Closer to the ground at air terminal elevations, the winds at KPDT, KALW, KBDN, KRDM and possibly KYKM could be a problem today into the evening and will need to be monitored closely. Forecast winds in the KYKM TAF may be a tad too fast and higher terrain south of KYKM may shelter KYKM from the higher wind speeds aloft associated with the aforementioned low level jet. Southerly downslope winds off the Simcoe Mountains, the east slopes of the Cascades and the Blue Mountains could result in gusts of 25-35 kts at times. There is also the potential at KRDM, KYKM and possibly KBDN for the development of rotor action in the lee of the Cascades. This rotor action can cause the wind over an airfield to become temporarily lighter and from a direction opposite to the main surface winds. This change in winds can result in increased low level mechanical turbulence. Timing of such conditions is not easy, but they will be included in TEMPO groups with amendments when noticed. Polan && .PRELIMINARY POINT TEMPS/POPS... PDT 40 53 38 49 / 10 30 20 40 ALW 43 54 41 49 / 20 40 20 40 PSC 44 53 41 50 / 20 20 20 30 YKM 37 50 35 47 / 30 10 40 30 HRI 41 54 37 49 / 20 30 30 40 ELN 34 46 32 44 / 40 10 60 40 RDM 35 48 33 45 / 10 30 30 50 LGD 39 47 37 48 / 10 40 20 30 GCD 38 46 36 47 / 10 50 30 30 DLS 41 51 40 49 / 30 30 30 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 4 AM PST Friday for ORZ049-050-507-508. High Wind Warning until 4 AM PST Friday for ORZ509-511. WA...Wind Advisory until 4 AM PST Friday for WAZ029. && $$ 78/99/99