Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
422 FXUS66 KPQR 050544 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 944 PM PST Tue Feb 4 2025 .SYNOPSIS...Stronger push of moisture tonight into Wednesday, combined with colder overnight temperatures, may create slushy lowland accumulations and defined snow above 500 feet. Afterwards overnight temperatures will remain colder through the end of the week, around 25-30 degrees in the valleys and along the coast. Further precipitation becomes lighter through the rest of the week so impactful accumulation is not expected. && .SHORT TERM...Now through Wednesday night...Widespread snowfall, becoming impactful in some areas, expected Wednesday morning as a defined front pushes through the region on Tuesday evening. Showers are beginning to move inland with most of the precipitation falling along the coast and Coast Range. Snow is already beginning to fall in Tillamook and in Newport, OR. The coast will see a 60-90% chance of snow accumulations over 1 inch Tuesday night and Wednesday morning, with a 40-70% chance of 2 inches or more. Temperatures are slightly warmer than the previous night, so we may not necessarily see an exact rinse and repeat. However, snow is still likely, and will accumulate on roadways. The Coast Range sees much higher snow accumulation due to orographic lift, with 85%+ chance of 4 inches or greater. Given the cold air pool and the mass of cold air aloft mixing down, could see anywhere from 4-10 inches of new snow which has sparked a Winter storm Warning for the Coast Range and Willapa Hills through Tue to 7pm Wed. For lowland and inland locations (Willamette Valley, SW Washington lowlands), it becomes much more complicated. The onshore southwesterly flow could produce lower accumulations due to precipitation shadowing, or higher amounts due to warmer and moister air moving over colder air at the surface. Precipitation will begin as rain tonight, but temperatures will continue to drop behind the front from earlier today. A weak easterly flow is bringing in lower temperatures a the surface which should become cold enough for snow to mix in from beginning around 12-3 AM Wednesday. For these lowland locations under 500 feet (excluding the coast), expecting around an inch of slushy snow. Most of the Willamette Valley (including Portland) sees around a 40-60% chance of accumulations over 1 inch between 10pm Tuesday and 10pm Wednesday. Slightly better accumulations at the West Hills and other areas of higher terrain, up to around 2 inches possible there. Slushy accumulations are expected to impact Wednesday morning`s AM commute, and care should be taken while traveling, particularly in hilly or elevated terrain. A Winter Weather Advisory has been issued from midnight to noon Wednesday for lowland areas as a result. The southern Willamette Valley sees the highest uncertainty, as breezy southerly flow beginning Wednesday morning could bring warmer air into those areas. Depending on how strong this southerly flow will be, we could end up with much less or even no accumulations in the southern Willamette Valley if it warms quickly enough. Otherwise, accumulations will be similar to the rest of the Willamette Valley and Columbia lowlands. Overall for the lowlands, there is low confidence in the exact locations of snowfall, and exact accumulations. There is high confidence that folks will see some kind of snow - whether it is slushy or sticks - with locally higher amounts under heavier showers. Confidence is also high that temperatures will warm enough during the day that snow will melt. Precipitation reaches the Cascades last, but orographic lift and colder temperatures allow for much stronger snowfall above 2500 feet or so. Current conditions show somewhere between 6-12 inches at the Cascades, including all mountain passes. As such, a Winter Weather Advisory has been issued for the south Washington and north Oregon Cascades, from midnight tonight through Wednesday night. Of note, currently watching potential for higher snowfall as model runs are slightly increasing QPF each run. Currently looking at 20-40% chance of the Cascades seeing snowfall about 12 inches, which would reflect warning- level snow. Will carefully be observing following model runs as we get closer to snow beginning. -Muessle/Liu .LONG TERM...Thursday through Monday...Model runs continue to show moisture on Thursday and beyond mostly shifting further south, reducing potential for impactful snow. Only around a 10-20% chance in the Willamette Valley and Columbia lowlands for accumulating snow between Wed 10pm to Thu 10pm. Each night afterwards shows some minor potential for snow to mix in, but precipitation remains too weak for any real impactful accumulations anywhere but the mountains. Temperatures continue to remain quite cold, in the upper 20s to around 30 in the lowlands from Wednesday night through early next week. Thursday night looks like the coldest night during this period, with NBM showing a 40-50% chance of low temperatures Friday morning below 25 degrees in the Willamette Valley. Good model consensus that cold temperatures remain with us through next week as well, with current guidance indicating lows remain in the upper 20s early next week. Still relatively low confidence in moisture next week; snow remains a possibility for all areas next week, with very high uncertainty in precipitation. -JLiu && .AVIATION...A broad area of low pressure offshore maintains cold and showery weather with southwest flow and generally VFR conditions. Showers will increase through 09Z Wed starting out predominately as rain, then slowly transitioning into periods of -SN/-SNRA. Showers will result in increasing probabilities of MVFR/IFR conditions, along with a 15%-25% probability for intermittent LIFR conditions. Visibilities may also decrease with more intense snow showers through 18Z-20Z Wed. Widespread accumulations of 1-2 inches expected, with up to 3 inches in elevated terminals like KMMV, and K4S2. Due to the showery nature of the precipitation there could be a wide discrepancy of snow accumulations across the lowlands including chances for precipitation to stay as just rain. Around 18Z-20Z Wednesday, expect predominately VFR and MVFR conditions through the remainder of the TAF period. Snow showers will also transition back to rain showers around the same time. Southerly winds generally below 10 kt with light east winds through the Gorge. Coastal locations could see southerly gusts up to 25 kt starting around 20Z Wednesday. PDX AND APPROACHES...Mainly VFR with occasional drops to MVFR in passing showers. Showers increase in coverage after 06Z-08Z Wed, with chances for MVFR conditions increasing to 60%-70% probability along with a 15%-25% probability for intermittent IFR/LIFR conditions. While probability for accumulating snow is low, there is around a 30-40% chance of up to 1 inch of snow over the next 24 hours. Snow that does fall will be slushy, and will struggle to accumulate. Southeast winds expected around 4-7 kt. /42 && .MARINE...A broad area of surface low pressure lingers offshore of the Pacific Northwest today. Light to moderate southerly breezes continue through tonight across the coastal waters, while the sea state remains dominated by a mid period northwest swell which has decayed to around 4 to 5 ft. Southwest winds are expected to increase on Wednesday as a relatively weak but compact low moves closer to the coast. Winds could gust as high as 25-30 kt across the central Oregon coastal waters. This will also likely bring an uptick in short period seas which could briefly push combined seas into the 8 to 10 ft range. Therefore, have issued a Small Craft Advisory through Wednesday evening. Benign conditions follow on Thursday with seas subsiding again to around 4 to 5 ft through the end of the week. The flow is expected to turn more northerly by Friday as low pressure moves toward central California. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until noon PST Wednesday for ORZ101>105. Winter Storm Warning until 7 PM PST Wednesday for ORZ106-107. Winter Weather Advisory until noon PST Wednesday for ORZ108>112-114>118. Winter Weather Advisory until 4 AM PST Thursday for ORZ113-119- 123>128. Winter Weather Advisory until 1 AM PST Thursday for ORZ120>122. WA...Winter Weather Advisory until noon PST Wednesday for WAZ201- 202. Winter Storm Warning until 7 PM PST Wednesday for WAZ203. Winter Weather Advisory until noon PST Wednesday for WAZ204>207. Winter Weather Advisory until 4 AM PST Thursday for WAZ208-211. Winter Weather Advisory until 1 AM PST Thursday for WAZ209-210. PZ...Small Craft Advisory from 4 AM to 10 PM PST Wednesday for PZZ252-253-272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland