FXUS66 KPQR 110500 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 900 PM PST Mon Feb 10 2025 Updated Aviation Discussion... .SYNOPSIS...Overall mostly dry conditions are expected the next few days as temperatures plunge into the middle of the week, especially during the overnight hours. The majority of our concerns through this period will revolve around the abnormally cold overnight conditions locally exacerbated by east winds through the Columbia River Gorge and Cascade gaps. We continue to closely monitor the arrival of large-scale winter weather event on Thursday which likely brings a mix of snow, sleet, and freezing rain to the region through at least Friday. Forecast confidence is only moderate Thursday onward but should improve further the next few forecast cycles as additional high resolution guidance becomes available. && .SHORT TERM...Now through Wednesday night...Mid-level water vapor imagery clearly shows an upper-level shortwave trough progressing southward into the Pacific Northwest from Canada this afternoon, and once this passes through Oregon this evening, it will aid in pushing a rather cold airmass into the region by Tuesday. It’s worth noting the passage of this feature has already begun to stir-up some isolated to scattered snow shower activity over the Cascades, Coast Range, and portions of SW Washington. There’s chance (20-30%) this activity does drift over the I-5 corridor north Portland this evening before ending overnight; just something to remain aware of. Little to no impacts are anticipated. Otherwise, easterly flow through the Columbia River Gorge increases in earnest overnight into Tuesday facilitating well below normal temperatures overnight temperatures through at least Thursday or Friday. Tonight, temperatures throughout the lowlands see a 60-90% chance of low temperatures below 25 degrees, particularly in inland valleys outside of the Portland/Vancouver metro. with the increase in Gorge winds the apparent (feels like) temperature likely dips below this 25 degree threshold as well with even lower temperatures in the Cascades. Thus, a Cold Weather Advisory in effect through Tuesday morning for all of western Oregon. Tuesday night looks to be slightly colder with near universal ensemble agreement in temperatures throughout the CWA below 25 degrees in addition to stronger easterly winds headed into Wednesday morning exacerbating impacts in and around the Columbia Gorge/Cascades. For now, most of the Willamette Valley, Oregon Coast, and central Oregon Coast range and Cascades will fall solidly within the thresholds for a Cold Weather Advisory. Guidance indicates the north Oregon Coast range, Willapa Hills, east Portland Metro through the Gorge/Hood River Valley, and Cascades foothills are on the cusp of meeting our Extreme Cold criteria, so have opted to issue a Extreme Cold Watch for these aforementioned locations. Forecast confidence is very high(90%) those areas will hit the Advisory criteria at a minimum and we’ll continue to assess just how cold temperatures and wind chill values will drop over the next 24-36 hours. Beyond the cold and as alluded to earlier, strong easterly gusts can be expected through the Columbia River Gorge from tonight into the middle of the week with the TTD-DLS pressure gradient peaking near -7 to -10mb late Wednesday night into early Thursday morning due to an approaching area of low pressure off the coast. The magnitude of the cross-Cascade pressure gradient has increased a touch since yesterday and winds were adjusted higher to mach. Peak winds, especially during this latter portion of the period, are expected to gust into the 35-45 mph range for the east Portland/Vancouver Metro (highest around and east of I-205) in addition to gusts of 50-65+ mph for exposed areas around the east of Troutdale like Crown-Point and Corbett. At the moment these winds look to decrease during the extended period on Friday but there is some measure of uncertainty that winds could remain easterly through the weekend which (spoilers) would continue to adversely impact the Columbia River Gorge. Given the low overnight temperatures and gusty winds, there will be an enhanced risk for hypothermia and frostbite for those without adequate shelter and winter clothing. -Schuldt .LONG TERM...Thursday through Sunday...This is where the fun begins. Both deterministic and ensemble guidance are in relatively good agreement showing an upper-level trough and an associated surface low approaching the coast come early Thursday morning during which time it will aim a warm frontal boundary and band of stratiform precipitation at the region. Current timing would bring a west to east oriented swath of light snow/wintry mix to Eugene early Thursday morning followed by the Portland area by the midday/afternoon hours although confidence in this timing is only low to moderate currently - slight changes in the exact track/speed of the low pressure progression could adjust the timing +/- 6 hours. As is sometimes the case for our winter weather set-up, it’s not a matter of whether we’ll be cold enough, but moreso how much moisture is able to swing northward while fighting the cold/dry airmass near the surface. Going forward through Thursday night into Friday, warming air aloft gradually chips away the the sub- freezing temperatures just above the surface resulting in a south to north change over to ice-pellets/sleet then freezing rain for the lowlands. The closer your location to the Columbia River Gorge, the later this transition will occur due to a constant stream of cold air attempting to fight the warming temperatures. For spots like Eugene and Salem the switch to a wintry mix should be rather quick, likely by Thursday afternoon or early evening. So with this in mind, the lowlands in general shouldn't expect to see too much snow accumulation partially due to a lack of QPF coinciding with the cold temperatures both at the surface and aloft; from about Salem northwards through SW Washington, there is only a 20-45% chance of accumulations of 1 inch or more from 4am Thu to 4am Sat. South of Salem, freezing rain looks to be more prevalent, with snow being less of an issue. Obviously with a greater depth of cold air in the Columbia River Gorge and Upper Hood River Valley, there a better chance for snow accumulation; 40-60% chance for 3 inches or more during that same period. However, until wet get closer to the event and larger suite of high resolution guidance becomes available for the Thursday-Friday time period take these probabilities with a grain of salt since models struggle locally resolving warm air overrunning scenarios. A northward shift in the storm-track would allow for greater QPF availability and thus greater impacts. The bigger concern at the moment for the vast majority of the region is freezing rain, particularly Thursday evening through Friday. As mentioned precipitation likely begins as mostly snow, but as the warm front overruns the cold airmass freezing rain accumulation becomes increasingly likely. The LREF (comprising the raw ENS, GEFS, and GEPS) depicts a 40-80% chance of accumulating freezing rain in the Willamette Valley and adjacent foothills/valleys, with the best chance in the central Willamette Valley between Eugene and Salem, and within the coast range valleys. Should the worse case scenario occur, (LREF 90th percentile) ice accumulation of a 0.25-0.60 inches would be possible across a large chunk of the region. Overall confidence in the timing and exact amounts/locations is rather low, and we'll be carefully monitoring model runs in the next few days. Potential for winter precipitation through Friday should be taken into consideration if making travel plans in the middle of next week. Most ensemble members are showing a decrease in precipitation near the end of next week, with possibility of more moisture on Sunday or Monday. In some scenarios the low level flow never truly turns onshore which means there is a chance the Columbia River Gorge and Hood River Valley may be dealing with freezing rain into early next week. -Schuldt/JLiu && .AVIATION...With high pressure persisting over the area, expect widespread VFR conditions throughout the airspace. A weak thermally induced trough will briefly build within the Willamette Valley through the TAF period, resulting in easterly winds within the Columbia River Gorge. Expected these easterly winds to bring gusts up to 25-30 kt at KTTD and 20-25 kt at KPDX through most of the TAF period (mostly tonight and tomorrow afternoon for PDX). As for other terminals, expect winds generally under 10 kt through the TAF period, with the exception of some terminals seeing winds up to 12 kt during afternoon hours (18Z to 00Z). PDX AND APPROACHES...Expect VFR conditions and winds around 8-12 kt through the TAF period, with highest sustained winds and gusts up to 20-25 kt early tonight and tomorrow afternoon into the early evening. LLWS may be possible tonight until around 18Z Tuesday, but looks to be more speed shear than directional. ~Hall && .MARINE...Conditions remain relatively benign until at the middle of the week as high pressure will maintain northerly winds. Seas also remain around 4 to 6 ft. However, a pattern change is on the horizon as an upper level trough will cause the aforementioned high pressure to weaken. This will result in cold, offshore winds developing for all waters starting Tuesday afternoon/evening. In addition to the offshore winds, a building westerly swell from an approaching low, will result in seas building towards towards 7 to 9 ft on Thursday and 12 to 14 ft by Friday. This low pressure system could support Small Craft winds with a 60-80% probability starting Wednesday evening through Thursday. Also, temperatures will be at or below freezing overnight through the following morning, likely starting (70%-80% probability) Wednesday night and continuing through at least Friday morning. These conditions could result in ice developing on surfaces due to freezing spray and/or freezing precipitation starting Wednesday night/Thursday morning. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Cold Weather Advisory until noon PST Tuesday for ORZ101>128. Cold Weather Advisory from 7 PM Tuesday to noon PST Wednesday for ORZ101>103-105-107>111-114>118-126>128. Extreme Cold Watch from Tuesday evening through Wednesday morning for ORZ104-106-112-113-119>125. WA...Cold Weather Advisory until noon PST Tuesday for WAZ201>211. Cold Weather Advisory from 7 PM Tuesday to noon PST Wednesday for WAZ201-202-204>206-211. Extreme Cold Watch from Tuesday evening through Wednesday morning for WAZ203-207>210. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland