FXUS66 KPQR 112010 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 1210 PM PST Tue Feb 11 2025 Updated aviation discussion. .SYNOPSIS...Overall mostly dry conditions are expected Tuesday and Wednesday daytime hours as overnight temperatures continue to remain quite cold through the workweek. 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...Drier conditions are expected through the short term until Wednesday night, with increasingly offshore flow. Easterly flow through the Columbia River Gorge is already beginning to increase, with gusts up to 25-30 mph presently. Expect increasingly cold temperatures throughout the area as winds continue to bring in the arctic airmass currently east of the Cascades. Beginning Wednesday morning, the TTD-DLS pressure gradient begins increasing up to -7 to -9 mb, allowing for much stronger easterly gusts. Winds will peak Wednesday, with gusts in the east Portland metro area up to 35-45 mph. Even higher gusts can be expected at exposed areas along the Gorge, Potentially up to 55-65 mph Wednesday (and Thursday as well). Early indications are that winds should begin to weaken on Friday, but uncertainty exists regarding when exactly easterly flow will weaken. Possibility exists that easterly flow remains throughout the weekend as well, with continued probability of winter precipitation as a result (see the long term discussion). While easterly winds continue, 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. Temperatures remain depressed while easterly flow is ongoing as cold air continues streaming in through the Columbia River Gorge. Low temps Tuesday morning will be well into the 20s, with temperatures already below 30 degrees throughout the Willamette Valley as of 3am Tue. 60-90% chance of temperatures below 25 by the end of the night, particularly in rural routes, inland valleys, and the foothills. Cold Weather Advisory still on track through Tuesday morning as a result. Tuesday night looks slightly colder still, with potentially temperatures into the upper teens for cold pockets throughout the Willamette Valley and Columbia lowlands. Chances of temperatures into the upper teens (sub 20 degrees) are around 40-70% for the central and southern Willamette Valley between Corvallis and Eugene, east Portland metro, Coast Range, and Cascade foothills. These areas still see potential for an Extreme Cold Warning, and the Extreme Cold Watch remains in place as we evaluate the potential on Tuesday night. This will mostly come down to how much wind chill will affect these areas, which would make or break the difference between a Cold Weather Advisory or an Extreme Cold Warning. /JLiu .LONG TERM...Thursday through Monday...Continued agreement in a winter precipitation event beginning Wednesday night, pushing south to north and reaching the Portland metro area on Thursday morning. Still some slight disagreement in the exact timing +/- around 6 hours, but generally expecting precipitation to begin somewhere between Wednesday night to midday Thursday. Placement of the low continues to show agreement that the low will arrive at the central Oregon coast, allowing offshore flow to continue sustaining a cold surface airmass. Combined with a warm nose overriding due to the warm front, there is the right upper air setup for freezing rain and sleet. Early precipitation late Wednesday night looks to be a mix of snow and freezing rain as the warm nose won't have had time to fully set in, but this slowly transitions moreso over to freezing rain by afternoon/evening on Thursday. 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 20-40% 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 we 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. Freezing rain remains the primary impact, with the bulk of potential accumulations expected Thursday afternoon onwards. 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, highest in the Coast Range and central/southern Willamette Valley. A more reasonable scenario (LREF mean) has closer to 0.1-0.2 inches throughout much of the Willamette Valley, though once again slightly higher in the Coast Range. 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...High pressure will keep conditions VFR through the next 24 hours. Offshore flow will persist with speeds generally being driven by topography. In areas that are east-west channeled, like the Columbia River Gorge, winds will be more elevated. Around KPDX, KTTD, and K4S2 between 1000-3000 ft AGL, winds will range from 20-35 kt from the east. While speed shear will be present, due to a lack of directional shear, did not include in the TAFs. Through the lower elevation terminals in the Willamette Valley, winds are more northerly at the surface and easterly aloft, but speeds are not of concern. Below freezing temperatures will return after 02-04Z Wednesday. Due to conditions being so dry at the surface, no fog is expected in the next 24 hours, but exposed surfaces will be quite cold. PDX AND APPROACHES...VFR through the next 24 hours with localized speed wind shear below 3000 ft. Winds from the east from the surface to 3000 ft AGL but with a lack of directional shear, have omitted from the TAF. Temperatures will fall below freezing after 03-4Z Wednesday. -Muessle/HEC && .MARINE...Fairly benign weather through Wednesday as high pressure lingers over the region. Expecting seas of 5-6 ft at 12 seconds, and wind gusts less than 20 kt through Wednesday afternoon. Starting early Thursday, a strengthening low pressure system will near the coast. Thus far, it appears to make landfall around Newport. Will see an increased easterly wind with the approach, especially around Tillamook and the Columbia River Bar. Early Thursday morning through the early afternoon, guts up to 30 kt possible, and up to 35 kt around Clatsop Spit. The concern is how widespread these wind speeds will be as they appear to be focused in the coastal gaps. However, cannot rule out more widespread gusty winds and potentially Small Craft Advisory conditions in the outer waters. The easterly flow will aid in combating the background westerly swell so not expecting significant wave rises until early Friday behind the front. On Friday, seas will build to 10-13 ft at 18 seconds before easing to near 8 ft on Saturday. As previously mentioned, the incoming low pressure system will increase easterly flow which will cause temperatures to decrease. Expecting freezing conditions along moorages overnight Wednesday, Thursday, and Friday. With the added precipitation, cannot rule out freezing rain, snow, or even freezing spray if the winds are high enough from the east. Confidence is low as to whether any ice will form. -Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Cold Weather Advisory until noon PST today for ORZ101>128. Cold Weather Advisory from 7 PM this evening to noon PST Wednesday for ORZ101>103-105-107>111-114>118-126>128. Extreme Cold Watch from this evening through Wednesday morning for ORZ104-106-112-113-119>125. WA...Cold Weather Advisory until noon PST today for WAZ201>211. Cold Weather Advisory from 7 PM this evening to noon PST Wednesday for WAZ201-202-204>206-211. Extreme Cold Watch from this 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