FXUS66 KPQR 050520 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 919 PM PST Mon Mar 4 2024 Updated aviation discussion... .SYNOPSIS...Showers continue across NW Oregon and SW Washington through tonight, slowly tapering off everywhere except for Lane County. A rough of widespread precipitation will affect Lane County tonight through early Tuesday, bringing additional snow above 1000-1500 ft. Mostly dry weather returns Tuesday through Friday with the potential for fog and frost in the evening through early morning hours. Wet and warmer weather is expected to return later Friday into the weekend with widespread rain and mountain snow. && .SHORT TERM...MONDAY AFTERNOON THROUGH WEDNESDAY...Radar imagery shows showers continuing across NW Oregon and SW Washington this afternoon. Longwave troughing remains over the West Coast as a cut off low forms over the eastern Pacific around 140W/40E. A shortwave moving through the PacNW today is what has brought renewed showers across the region along with continued cold air. There is still a 15-20% of thunderstorms through this evening for locations west of the Cascades with soundings indicating CAPE around 200-300 J/kg and 0-6 km shear 30-40 m/s. Most instability is elevated so strong thunderstorms are not likely, but stronger cells could have small hail or graupel. Some lightning has been observed throughout the day over the coastal waters west of Manzanita and Tillamook. North of Lane County, scattered showers will diminish overnight. Light snow showers may continue in the Coast Range and Cascades north of Lane Cane after the Winter Weather Advisory expires at 4 pm today, though additional accumulations will be light. A cold front will move through southern Oregon tonight into early Tuesday, generally in southern Douglas county just south of our forecast area. This will bring a push of widespread precipitation into Lane County overnight with another round of snow for the Cascades and foothills above 1000-1500 feet. Snow amounts of 2-4 inches are possible between 1500-2000 feet with 4-9 inches above 2000 feet through 4 am Wednesday. A Winter Weather Advisory remains in effect for elevations above 1500 feet. A dusting to up to an inch is possible down to 1000 feet, and about a 10-20% probability of non-accumulating snow down to 500 feet and even the valley floor. If the front ends up stalling farther north, closer to the Lane/Douglas county border, there is a less than 10% probability of accumulating snow of 1-3 inches down to 500 feet and accumulating snow less than an inch down to the valley floor. Ridging begins building over the eastern Pacific Tuesday into Wednesday as the longwave troughing currently over the PacNW begins shifting into the Intermountain West and the cut off low shifts south off of the California coast. Conditions will turn mostly dry Tuesday except for a 10-20% chance of an occasional shower along the coast, Coast Range, and Cascades. Skies will begin clearing by Tuesday night, which combined with the PacNW remaining on the lee side of the trough will allow for colder low temperatures Tuesday night into Wednesday morning. NBM indicates a near 100% chance of all locations falling below freezing and a 50-70% chance of lowland valleys falling below 28 deg F Wednesday morning. Expect widespread frost as well as the potential for fog across the lowlands Tuesday night into Wednesday morning. Low temperatures Thursday morning will still be on the cold side, though a few degrees warmer than the previous morning. -HEC .LONG TERM...THURSDAY THROUGH MONDAY/...Ensemble guidance is in very good agreement that the upper level ridge axis will move east over the PacNW Thursday into Friday, bringing continued dry weather and a bit of a warming trend to the area. Daytime temperatures are forecast to warm a few degrees Thursday and another 5 or so degrees by Friday, with highs topping out in the mid 50s across the lowlands Friday. Enjoy this brief period of dry weather because ensembles indicate another weather system is slated to move through the West Coast late Friday into Saturday with the potential for additional precipitation Sunday into Monday. This will be a warmer weather system with more warm, Pacific moisture associated with it, meaning snow levels will remain higher with no low elevation snow expected at this time. Ensembles become less certain on a solution for Sunday into early next week, though they all indicate at least some precipitation continuing into Monday. -HEC && .AVIATION...Current radar imagery as of 05z Tue show lingering showers across the region as a broad upper level trough moves eastward through the Pacific Northwest. Terminal observations also show a mix of MVFR/VFR cigs. Expect this mix of MVFR/VFR cigs (mostly MVFR) to continue through Tuesday morning with showers gradually diminishing tonight. Light and variable winds tonight will become northerly Tuesday as surface high pressure builds. After 19- 21z Tue, predominately broken VFR cigs will prevail across the region through the evening with dry conditions. *Note: The observations out of KONP are generally limited to wind and pressure at this time. Periodically cloud cover, vis, and present wx are reported but are unreliable. PDX AND APPROACHES...Decreasing showers tonight with predominately MVFR cigs and intermittent VFR cigs through Tuesday morning. After 21z Tue, cigs improve to VFR with dry conditions. Winds remain around 5 kt or less through the TAF period and turn more northerly tomorrow as surface high pressure builds. -Alviz && .MARINE...Showers and a few thunderstorms will be possible into the evening before instability wanes. Onshore winds around 10-14 kts will continue into the evening before riding builds in from the northwest and shifts winds to the north through Wednesday night when a weak front approaches the area. A stronger front will approach the area later this week and will increase SW winds Friday into Saturday. Seas around 7-8 ft will subside to 5 ft or lower by Wednesday evening. Conditions should remain quiet into Friday. /Batz && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until 4 PM PST this afternoon for Central Coast Range of Western Oregon-Coast Range of Northwest Oregon-Northern Oregon Cascade Foothills. Winter Weather Advisory until 4 AM PST Tuesday for Cascade Foothills in Lane County. Winter Weather Advisory until 4 AM PST Tuesday for Cascades in Lane County. WA...Winter Weather Advisory until 4 PM PST this afternoon for South Washington Cascade Foothills-Willapa Hills. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland