244 FXUS66 KPQR 312221 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 221 PM PST Tue Dec 31 2019 SYNOPSIS...Rain will spread across the area this evening and overnight. As a cold front drops southward later tonight, rain transitions to showers by Wednesday morning. A much cooler airmass will move over the area on New Year's Day, with showers in the lower elevations and snow in the Cascades. Showers decrease on Thursday with perhaps a mainly dry period for Thursday night into Friday as a warm front lifts north of the region. But, rain and cooler temperatures return Friday night and persist through the weekend. && .SHORT TERM...Tonight through Friday...Radar imagery shows precipitation shield is slowly shifting southward, fueled by IVT in excess of 600 kg/ms currently impinging on the north OR/south WA coast. Models depict this IVT/AR to gradually weaken after 00Z, with precipitation advancing southward through entire CWA. As upper level shortwave moves through the Gulf of Alaska this evening and tonight, cold front over the PacNW is pushed southward restoring a New Year's Day airmass far more typical of early January. Snow levels begin a steady fall overnight, and drop to about 3500 feet by this time tomorrow. With moist westerly flow, sustained orographic precipitation appears favorable for the Coast Range and Cascades. Given the steep low-level lapse rates and about 100 J/kg CAPE, expect to achieve snow advisory amounts between 6-10" at the Cascade passes. Will even add a slight chance of thunderstorms to the northern grids per SREF guidance; although, confidence is low since the convective cloud tops of most member profiles are not quite cold enough for electrification. Aforementioned cold front lifts back northward as a warm front Thursday morning, and depending on the timing, the potential for a partly-to-mostly dry and mild break from Thursday afternoon into Friday appears likely. This break will be short-lived though, as another trough restores a cool and showery airmass for the weekend. DRB .LONG TERM...Friday night through Tuesday...Model/ensemble consensus shows a moist, progressive westerly flow during the extended period. The first shortwave arrives Friday night, followed every 36 to 48 hours thereafter. Freezing levels and precipitation amounts appear seasonal during this time. Although heavy precipitation is not expected, snow levels this weekend between 2500-3000 feet should be favorable for accumulation above 3000 feet and building the Cascade snowpack. This cool and occasionally wet pattern looks to continue through at least Tuesday. DRB && .AVIATION...Generally VFR conditions across the area with mixture of MVFR and IFR conditions along the south Washington and north Oregon coast. A warm front continues to slided towards the south through the evening. Within the postfrontal air mass expect MVFR conditions to develop inland, and IFR conditions along the coast. By 00Z Wednesday much of the area should be MVFR or lower. Gusty south winds along the coast through the evening, with gusts 35-40 kt, with the possibility for isolated gusts up to 45 kt. Inland areas likely to experience 25-30 kt gusts through the evening. There is a slight chance of thunder starting around 09Z Wednesday for areas north of KUAO, this slight chance also includes the coast north ok KONP. KPDX AND APPROACHES...Expect VFR to hold through the late afternoon. Conditions likely to fall into MVFR around 00Z Wednesday, with the possibility of IFR after 03Z Wednesday. Slight chance of thunder starting around 14Z Wednesday. /42 && .MARINE...A warm front will continue slowly moving south through the evening. South to Southwest wind gusts to 25 to 30 kt through late this evening, with the potential for some isolated gusts up to 35 kt. After looking at the most updated guidance as well as an afternoon scatterometer pass over our waters showing that winds are slightly weaker than expected, have adjusted the Gale Warning currently issued to match better with updated information. The wind backs to west and subside below 35 kt tonight. However, solid small craft advisory wind speeds will continue through Wednesday night. Another warm front approaches the waters Thursday. Operational models are showing some variance into the weekend. It should be noted that Gale force winds will be possible starting Thursday afternoon through at least Friday evening, but timing and duration are questionable. Seas currently around 11 to 13 ft, but they will build to 14 to 16 feet this evening and 18 to 20 ft by late Tuesday night. Latest model guidance continues to show an abnormally long- period swell set within our waters. This secondary swell is forecasted to be around 4 ft at 25 seconds, but reach 10 ft at 20 seconds by early Wed morning. The combination of this longer period swell and the pre-existing 14-15 second swell will result in wave heights around 20 ft or higher. Models show the two swell sets eventually becoming a dominant 18-20 second swell by late Wed morning. There will be a high likelihood for sneaker waves along the coast through at least Wed night. There is the potential for another round of 20-ft seas late in the week and into the weekend, but there is much lower confidence due to the large model discrepancies. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...High Surf Advisory from 10 PM this evening to 10 PM PST Wednesday for Central Oregon Coast-North Oregon Coast. Winter Weather Advisory from 6 AM Wednesday to midnight PST Wednesday night for Cascades in Lane County-Northern Oregon Cascades. WA...High Surf Advisory from 10 PM this evening to 10 PM PST Wednesday for South Washington Coast. Winter Weather Advisory from 6 AM Wednesday to midnight PST Wednesday night for South Washington Cascades. PZ...Gale Warning until 7 PM PST this evening for coastal waters from Cape Shoalwater WA to Cascade Head OR out 60 NM. Small Craft Advisory until 10 PM PST Wednesday for Coastal waters from Cascade Head to Florence OR out 10 NM-Columbia River Bar-Waters from Cascade Head to Florence OR from 10 to 60 NM. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest oregon and Southwest Washington from the Cascade crest to 60 nm offshore. This area is commonly referred to as the forecast area.