National Weather Service Area Forecast Discussion for Long Beach, WA USA
000 fxus66 kpqr 010552 aaa afdpqr Area Forecast Discussion...updated National Weather Service Portland, OR or 952 pm pst thu nov 30 2023 updated aviation... .synopsis...a pair of atmospheric rivers will bring periods of heavy rain to the area through the weekend, heaviest saturday night through sunday. periods of heavy snow will also occur in the cascades for elevations above 3000 ft through saturday before snow levels rapidly rise above 6000-7000 ft saturday night. there is the potential for a third atmospheric river early next week, however uncertainty is high with this system. aside from dangerous travel conditions over the cascade passes, the main concern this weekend into early next week is the potential for river flooding and urban flooding. && .short term...through sunday...a very active weather pattern is in store for northwest or and southwest wa as a series of at least two, if not three, atmospheric rivers impacts the area this weekend into early next week and increases the chance of river flooding and urban flooding. focusing first on current observations as of 330 pm pst thursday, areas of light rain were being observed across southwest wa and northwest or as a weak pacific frontal system continues moving through the area. however, precipitation was falling in the form of accumulating snow in the cascades (mainly above 3000 ft), and in the central columbia river gorge, including stevenson and hood river. there have also been reports of very light freezing rain near larch mountain, resulting in a light glaze of ice on road signs but not on roads. models continue to suggest cascade snow will become heavy friday morning as an upper level shortwave trough and attendant surface front push eastward over the area and bring another round of enhanced moisture. periods of heavy cascade snow and blowing snow will then continue through saturday afternoon/evening before snow levels rapidly rise to above 6000-7000 ft saturday night (resulting in a transition to rain except on the volcano peaks). expect dangerous travel conditions for anyone attempting to travel over the cascade passes friday through saturday; a winter storm warning remains in effect to cover this threat. qpf/snow amounts have increased a bit and the cascades should now see 10-30 inches of snow above 3000 feet, except up to 40 inches possible above 4500 feet. winds will gust to around 50 mph at times, resulting in blowing snow and reduced visibilities. for the rest of northwest or and southwest wa, precipitation will fall in the form of heavy rain capable of producing river flooding and urban flooding. the period of heaviest rainfall is expected saturday night through sunday as a moderate atmospheric river takes aim at southwest wa and northwest or. forecast rain amounts and details regarding the flooding potential are discussed below in the hydrology discussion.-tk .long term...sunday night through wednesday night....the remnants of saturday/sunday`s atmospheric river will bring more rain sunday night, however rain amounts should be much lighter as the system falls apart over the area. snow levels will be approximately 6000-7000 ft by this point, and snow won`t be a concern anywhere but the volcano peaks. ensemble guidance is in strong agreement regarding yet another atmospheric river event on monday, but little confidence exists regarding its exact path. ivt values range from 600-900 kg/(ms), with a start time sometime during monday daytime hours. although confidence is low, ensemble guidance seems to generally indicate the path of this system being slightly north of our cwa. current nbm guidance indicates around a 50% chance of 24hr rainfall (mon 4am - tue 4am) exceeding 1", down to 20-30% in the southern willamette valley. the northern cascades, northern coast range, and willapa hills see 90-100% chance of >1" rainfall, while the southern cascades and coast range are closer to 30-40%. with heavy rainfall from preceding days, additional rainfall, and snowmelt runoff from rising snow levels, river flooding continues to be a concern along non-mainstem rivers sunday into early next week. see the hydrology discussion below for more details. yet another atmospheric river is possible tuesday into wednesday, bringing mild and rainy conditions and continued chances for river flooding. that being said, uncertainty remains high with this system as models struggle to resolve exactly where the axis of heaviest rainfall will occur. in addition to this system, the deterministic ecmwf and gfs runs are showing yet another possible system late wednesday night going into thursday morning, but many ensemble members aren`t displaying this feature. uncertainty remains high going into mid/late next week. -jliu && .hydrology...a series of at least two, if not three, atmospheric rivers will bring periods of widespread heavy rain to northwest oregon and southwest washington this weekend into early next week. the first system will also bring heavy cascade snow for elevations above 3000 feet through saturday evening before snow levels rapidly rise above 6000-7000 feet saturday night. this means mountain snowmelt will also be a contributing factor in regards to river flooding concerns sunday into early next week as rain will be falling over a fresh snowpack. the period of heaviest rainfall is currently expected to occur saturday night through sunday. total rain amounts for the entire weekend are expected to range between 3.0-5.0 inches along the coast, 4.5-6.5 inches over the willapa hills and oregon coast range, and 3-4 inches across the willamette valley, portland/vancouver metro, and interior lowlands of southwest wa. 4.0-7.0 inches of rain is expected over the cascades, cascade foothills, and western columbia river gorge. 2.5-3.5 inches of rain is expected for central columbia river gorge and upper hood river valley. additional rainfall will occur early next week, however uncertainty is high regarding exact rain amounts from monday onward. given the aforementioned rainfall amounts expected this weekend, river levels will be rising quickly. most rivers across northwest or and southwest wa have anywhere from a 20-40% chance of reaching at least minor flood stage, except for the mainstem columbia and willamette rivers where the chance of reaching minor flood stage is around 5%. in fact, coastal rivers have a 10-25% chance of reaching major flood stage; this includes the willapa river near willapa, the naselle river near naselle, the nehalem river near foss, the wilson river and trask river near tillamook, the nestucca river near beaver, and the siletz river at siletz. to view current and forecast river stages for any river gage location across southwest wa and northwest or, visit https://water.weather.gov/ahps2/index.php?wfo=pqr lastly, urban flooding is also possible this weekend, especially in low-lying areas with poor drainage. if you have gutters and/or storm drains that still need to be cleared out, now is the time. any motorists with travel plans this weekend should also allow extra time for their commute as hydroplaning will be a risk due to ponding of water on roads. -tk && .aviation...evening radar imagery shows scattered showers across the area as one front departs east of the cascades and another quickly approaches from offshore. variable mvfr/ifr cigs being observed across the area as of 06z, with calm winds helping to support a localized pocket of dense fog in the central valley from kmmv-kuao. expect this fog to lift and flight conditions to improve back towards mvfr as the next frontal system approaches. rain associated with this front should reach the coastal terminals 09-10z and the spread inland through 12z fri morning, accompanied by gusty south winds and predominant mvfr conditions. frontal precipitation will clear the area from west to east 15-18z fri, resulting in another period of post frontal showers and variable mvfr conditions through fri evening. ** the new aviation weather center website is live. the new website can be found at aviationweather.gov ** kpdx and approaches...variable mvfr/ifr conditions with fl008-012 cigs this evening in post frontal showers. next frontal system approaches the terminal 10-12z fri with steady rain, mvfr flight conditions and gusty s-sw winds. front will clear the terminal 15-17z fri and yield another round of post frontal showers with variable mvfr/vfr conditions through the end of the period. /cb && .marine...a cold front will continue to move through the waters tonight bringing strengthening southerly winds to small craft criteria through at least tonight. seas will build towards 7-9 ft by tonight/friday morning. friday and into the weekend, a series of progressively stronger systems will move through the waters, resulting in a very active weather pattern through the start of the upcoming week. for the friday system, winds could gust up to 45 kt across the waters; therefore, a gale warning has been issued from late tonight into friday morning, followed by hazardous seas across all waters as seas build towards 14-17 ft. saturday and sunday, there still remains a 50-60% chance of wind gusts exceeding 40 kt over the waters, with a higher probability for these winds on saturday night/sunday. in addition, seas will continue to build towards 15-19 ft starting saturday and remaining elevated through at least monday as the very active weather pattern persists. a brief break will be possible on tuesday/wednesday, but models show another system starting to impact the region by wednesday and that system could cause seas to build towards 18-20 ft. /42/alviz && .beach hazards...high sneaker wave threat saturday-wednesday. a high sneaker wave threat will be present along the or and wa coasts starting this saturday and continuing through at least next wednesday. the cause is a series of systems coming from the central pacific ocean and moving towards the pacific nw. expect wave heights to slowly build towards 14-18 ft with a dominant period of 15-18 seconds. it is important to not focus on the highest wave heights as a representation of peak sneaker wave threat; the period between the waves is almost more important as it represents the energy being carried by the swell. sneaker waves will drive up further on the beach, when compared to waves of similar height. this can potentially catch beachgoers off guard. in addition, waves can easily lift and move large logs on the beach and knock people/pets off of jetties. therefore, have issued a beach hazard statement along our cwa`s entire coast starting early saturday morning and through at least early wednesday morning. && .pqr watches/warnings/advisories... or...winter weather advisory until 4 am pst friday for cascades in lane county-northern oregon cascades. winter storm warning from 4 am friday to 10 pm pst saturday for cascades in lane county-northern oregon cascades. wa...winter weather advisory until 4 am pst friday for south washington cascades. winter storm warning from 4 am friday to 10 pm pst saturday for south washington cascades. pz...small craft advisory until 4 am pst friday for coastal waters from cape shoalwater wa to florence or out 10 nm-columbia river bar-coastal waters from cape shoalwater wa to florence or from 10 to 60 nm. gale warning from 4 am to 10 am pst friday for coastal waters from cape shoalwater wa to cape foulweather or out 10 nm-columbia river bar-coastal waters from cape shoalwater wa to cape foulweather or from 10 to 60 nm. hazardous seas warning from 10 am friday to 1 am pst saturday for coastal waters from cape shoalwater wa to cape foulweather or out 10 nm-columbia river bar-coastal waters from cape shoalwater wa to cape foulweather or from 10 to 60 nm. gale warning from 4 am to 7 am pst friday for coastal waters from cape foulweather to florence or out 10 nm-waters from cape foulweather to florence or from 10 to 60 nm. hazardous seas warning from 7 am friday to 1 am pst saturday for coastal waters from cape foulweather to florence or out 10 nm-waters from cape foulweather to florence or from 10 to 60 nm. && $$ www.weather.gov/portland interact with us via social media: www.facebook.com/nwsportland www.twitter.com/nwsportland
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