FXUS66 KPDT 180559 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 959 PM PST Sun Nov 17 2024 Updated Aviation Discussion .SHORT TERM...Today through Tuesday...A particularly active period is in store for the forecast area, with everything from rain, heavy mountain snow, and strong winds slated for the next 72 hours. For today, a cold front is swinging through the forecast area, bringing with it gusty conditions, rain, and eventually, mountain snow. Yesterday's system provided us with a shot of warm air that lifted snow levels above our major mountain passes, but as this cold front moves through, colder, northerly air will rush in behind and drop snow levels down to around 2000 feet. A Winter Storm Warning remains in effect for our Cascades and northern Blues zones, with the expectation being that warning-level snow will primarily fall between the writing of this discussion and early morning Monday. Light snow will persist into the day Monday, but only expecting a couple of inches at best to fall at pass level between daybreak Monday and midnight heading into Tuesday. Elsewhere, rain showers will occur along the cold front, before drier conditions prevail across the lower elevations late tonight through most of the day Monday. Breezy winds will continue amidst this active pattern. Looking ahead to Tuesday, a potentially significant low pressure system is shaping up off the coast of the PacNW. Global models are suggesting that this low could have a central pressure as low as 945 mb, which is quite strong for the region. This low will circulate a warm front through the forecast area during the latter half of Tuesday, while keeping us in a persistent band of wet, SW flow aloft through the remainder of the work week. Warm fronts lifting through from the southwest are typically conducive for downsloping wind events, and given how strong this low looks to be, did opt to issue a High Wind Watch for the base of the Blue Mountains of Oregon, as well as central and north central Oregon. Don't think models are quite capturing the potential wind threat this far out, but would not be surprised if CAMs start depicting wind gusts exceeding 60 mph for these areas Tuesday night into Wednesday. Moisture advection will be robust with this low as well, particularly for the Cascades. Models are currently suggesting that the foothills of the Cascades, particularly in Washington, could see heavy snow exceeding 6 inches above 2500 feet, with several inches of snow potentially extending down toward Cle Elum and even into the Kittitas Valley. Much is still subject to change with the forecast over the next few days, but particular interest will be kept on the Tuesday night into Wednesday time period in terms of monitoring the potential for a significant weather event. Evans/74 .LONG TERM...Wednesday through Sunday...Southwesterly flow aloft will be dominant in the long term as a very strong low pressure system sits just offshore of the PacNW, bringing plentiful precipitation in the form of an atmospheric river with temperatures warm enough to keep most of the region as rainfall rather than snow, but with this will come concerns of localized persistent rainfall and possibly isolated flooding. Wednesday starts with a deep and stacked low from the surface to 500 mb just offshore of the US/Canada. Strong winds will have already been occurring overnight from Tuesday into Wednesday, with a high wind watch currently in effect from Central Oregon up through the foothills of the Blues. By later Wednesday morning winds will still be breezy, but should be relaxing by the beginning of the afternoon. With winds lessening, our main concerns with this system will become precipitation as the low continues to sit just offshore and spin moisture across the region daily. Southwesterly flow should help to bring rising snow levels though, above 4-7k feet by Thursday. This means the majority of falling precipitation will be rainfall outside of the highest elevations, limiting impactful winter conditions for us. That being said, some localized areas of flooding may occur as we see daily rain alongside melting of any snow that did fall prior to this. A widespread flood event isn't expected currently, as daily QPF amounts will be around 0.1-0.5 inch outside of the mountains, but the NBM does show a near daily 50-100% probability of QPF amounts of 0.1 or more for our entire CWA. Look for localized rises on rivers for our region to be possible due to this rainfall. Overall there is moderate to high confidence in the forecast. Ensembles are in very good agreement on the forecast pattern, indicating the stalled low will drive our weather pattern through most of the next week or so. Differences primarily arise right at the end of the period, when clusters show a very varying solutions on how quickly this system finally decides to move inland. Otherwise, any uncertainty will be in the exact placement of the moisture and the potential low-end (at least for our area) atmospheric river event, but ensembles agree we'll be sitting around 150-200% of normal PWAT values for this time of year, so expect a soaker come later next week. Goatley/87 AVIATION...06Z TAFs...VFR conditions to mostly prevail through the period, but precipitation impacts may bring conditions to MVFR or lower. Next round of precipitation to the region is expected to arrive around 12Z, with light snow at sites RDM/BDN turning over to a rain/snow mix after 17Z. Snow impacts may also bring vsby/cigs to MVFR or lower categories, but confidence too low to include at these sites. Otherwise, expect mostly vicinity showers at sites DLS/PDT/ALW through the period. Winds of 12-17kts with gusts up to 25kts will develop at most sites after 17Z, though persistent winds will continue at sites ALW/PSC through 00Z. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 33 45 28 46 / 70 30 20 10 ALW 36 47 30 47 / 80 50 30 20 PSC 39 50 34 48 / 30 10 20 10 YKM 26 47 24 41 / 20 10 20 30 HRI 36 49 31 50 / 40 10 20 20 ELN 26 43 22 39 / 40 20 20 40 RDM 27 41 24 44 / 70 50 20 10 LGD 27 38 21 37 / 100 60 40 20 GCD 26 38 20 41 / 90 60 50 30 DLS 35 49 31 46 / 60 50 50 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Winter Storm Warning until 10 PM PST Monday for ORZ502-509. High Wind Watch from Tuesday afternoon through Wednesday morning for ORZ507-508-510-511. WA...Winter Storm Warning until 10 PM PST Monday for WAZ030-522. && $$ SHORT TERM...74 LONG TERM....87 AVIATION...82