FXUS66 KPQR 311822 AAA AFDPQR Area Forecast Discussion...Updated National Weather Service Portland OR 1122 AM PDT Thu Oct 31 2024 Updated Aviation... .SYNOPSIS...Cold front moves inland today bringing widespread showers, high precipitation rates and accumulation, and snow to the mountains. Winter Weather Advisories and Winter Storm Warnings remain in effect through Friday afternoon. Strong southerly winds late tonight into Friday morning with a 30-50% chance of gusts greater than 30 mph. Rain continues through the weekend though will be lighter && .SHORT TERM...Now through Saturday night...A storm system continues to push inland today which is bringing widespread showers to the region. This morning, radar has indicated heavy showers and gusty winds along the coast of Pacific County as thunderstorms train over the area. With this convective pattern, cannot rule out some rotation in the clouds and even a water spout or two over the ocean. Will continue to see showers through the day with variable rainfall accumulations. Will be difficult to nail down an exact rainfall accumulation forecast for the next 24 hours, but there is high confidence in the coast, Coast Range, and Cascades seeing the highest amount of precipitation. There is a wide spread of possibilities for rain with the higher resolution models being significantly higher than the NBM. The NBM is a bit more moderate so trended towards the 50th percentile with the 90th along the coast and Cascades based on isentropic lift. Over the next 24 hours there is nearly a 100% chance of 1 inch of rain along the coast, and an 80% chance of great than 1.5 inches. The 90th percentile (wettest solution) is nearly 2.75 inches of rain ending at 5 AM Friday. Similar probabilities for the Cascades. Given the westerly to southwesterly flow aloft, the Willamette Valley will see less due to a weak rain shadow. With that said, there is around a 10-20% chance of 1.5 inches of rain or more in the next 24 hours. Snow is the other concern today in the Cascades above 3500 feet. Based on a snow ratio of 10:1 (mid-slopes) up to 13:1 (volcanos), snow amounts too will vary with up to 10 inches at the lower elevations, and up to 2 feet at the highest peaks. The Winter Storm Warning remains in effect for the Willamette National Forest, while the other portions of the Cascades remain under an advisory. This is mainly due to the lack of high snow amounts from 3500-5000 feet. Late tonight into Friday morning the low pressure system that has been spinning in the northeast Pacific will get very close to the shoreline. This low is supported aloft by a 115 kt jet streak at 250 mb, and a 100 kt jet streak at 500 mb. These features, and an increasing pressure gradient between Portland and Eugene will cause winds to become predominately southerly and increase significantly. The coast will experience the highest winds with gusts up to 40 mph possible (40-55% chance) from Tillamook southward. The Willamette Valley too will see these gusty winds - especially from Salem southward. There is a wider spread of possibilities for winds here though. The HREF is trending much windier than the NBM with the Hi-Res ARW being the strongest of the solutions. With the HREF, there is around a 40% chance of gusts of 40 mph south of Salem, while the NBM has less than a 10% chance. Given the pattern, trended towards the HREF for sustained winds with gusts up to 30 mph inland. At this point, given the track of the low and the delicacy of it's location and timing, have decided not to issue any wind hazards at this time. Trending towards a peak wind speed time frame of Friday around 6 AM through noon. We will also see a surge of precipitation with the inland low movement. The increased winds and falling snow may reduce visibility along the mountain passes. Moving into the weekend, rain will persist due to several weak shortwaves passing through the flow of the dropping low. Saturday will be a low PoP/high accumulation scenario with strengthening onshore flow. Ridging is forming over the Pacific though which will become a deciding factor later in the forecast. One thing to note is that there are some high surf concerns for the coastline today. Based on the current and forecast wave heights, waves will be just below thresholds. Therefore, there is a chance that we could see higher surf through the day. Be sure to keep your eye on the ocean if on the beaches, and stay off of jetties. -Muessle .LONG TERM...Sunday through Wednesday...Showers will persist on Sunday as the longwave trough associated with the decaying low shifts southeastward. All 500 mb clusters are in good agreement with this trough moving over the four corners region of the desert southwest by Monday morning, with broad scale ridging forming over the Pacific. However, there is much less certainty in the overall sensible weather with this pattern shift. Deterministic models are suggesting a continued showery pattern through Tuesday with low accumulations. Models though are coming into better agreement in regards to this ridge moving inland on Wednesday though. About 50% of the models show the trough becoming positively tilted, and an expansive ridge with warmer air push on Wednesday. If this pattern holds, will likely see a few days of dry weather next week. -Muessle && .AVIATION...Predominantly MVFR conditions with intermittent improvement to VFR at area terminals as of 18z Thu. Scattered to numerous rain showers expected to continue through the period as a broad low pressure system remains over the region. This will bring variable MVFR/VFR flight conditions and SSE winds around 10 kt at all sites, with stronger gusts at the coastal terminals. Removed PROB30 for thunder from coastal TAFs based on recent observed and model trends, but still a 10-20 percent chance of thunderstorms at these sites through the period. Thunder chances increase inland after 12z Fri, but not enough to warrant inclusion in the TAFs at this time. A compact surface low will develop and push towards the north OR Coast early Fri morning, bringing stronger south winds gusting to 20-25 kt at all sites 10-12z Fri continuing through the end of the TAF period. PDX APPROACHES...Primarily MVFR in numerous rain showers with cigs below FL020 through the period. Expect intermittent, short lived improvements to VFR through 03z Fri. S-SE winds increase after 12z Fri. Thunder chances remain around 10 percent through the period, but probabilities too low for inclusion in TAF at this time. /CB && .MARINE...A surface low located west of Vancouver Island will drop southeastward towards the waters off the Washington coast today. This should largely maintain a showery weather pattern with occasional wind gusts of 25-30 kt near and under stronger showers. In addition, there is at least a 20-30% chance of a thunderstorm impacting a given location through tonight. Confidence has increased in a second surface low developing within the aforementioned surface low that is expected slow/stall west of Vancouver Island. Hi-res models are in good agreement with this development and have the low tracking towards the southern and central ORegon coast late tonight into Friday morning. HREF probabilities for wind gusts to reach Gale criteria are around 40-60% for the central and southern zones between 5am and 1pm on Friday. Given the increasing probabilities, have issued a Gale Watch for the mentioned time frame. High pressure then slowly builds over the northeast Pacific this weekend into early next week, but remains far enough offshore, that the Pacific Northwest will remain susceptible to fast moving fronts crossing the waters. Models do hint at a disturbance moving across the waters late Saturday into Sunday but confidence is not high at this time. -Batz && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until 5 PM PDT Friday for ORZ126. Winter Storm Warning until 5 PM PDT Friday for ORZ127-128. WA...Winter Weather Advisory until 5 PM PDT Friday for WAZ211. PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210. Small Craft Advisory until 5 AM PDT Friday for PZZ251-271. Small Craft Advisory until 8 AM PDT this morning for PZZ252- 253-272-273. Hazardous Seas Warning from 8 AM this morning to 5 AM PDT Friday for PZZ252-253-272-273. Gale Watch from late tonight through Friday afternoon for PZZ252-253-272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland