National Weather Service Area Forecast Discussion for Long Beach, WA USA
000 fxus66 kpqr 261109 afdpqr Area Forecast Discussion National Weather Service Portland, OR or 409 am pdt tue sep 26 2023 .synopsis...an upper level trough is beginning to move into the pacific northwest today, as monday`s cold front slowly moves east across wa/or. the steadiest precipitation has moved into the cascades, with post-frontal showers and a few thunderstorms likely to continue throughout the day. stronger thunderstorms from late morning through this afternoon may be capable of producing gusty winds and small hail. the next low will develop rapidly offshore today, move across the coastal waters tonight, then move onshore into washington early wed morning for another quick shot of wind and rain. cool fall weather will follow as an upper trough settles over the region late week, with showery weather persisting. && .discussion...today through next monday...forecast remains largely on track as an active early fall weather pattern persists over nw oregon and sw washington. since early sunday morning, the lowlands and cascades have generally received around 1 inch of rain, except for the hood river valley which has received about a half inch. the coast range has seen more, with the most being in western lane county where 3 inches have fallen on the 3 buttes fire. we have yet to hear of any debris flow issues, so thus far this appears to be a beneficial, soaking rain. peak wind gusts with the front were generally in the 35-45 mph range along the coast, with the strongest gust being 55 mph at the highly exposed weather station in garibaldi. largely easterly mslp gradients kept winds modest inland, with peak gusts 25-35 mph for the willamette valley. the very first hints of a baroclinic leaf and developing low pressure are presently occurring between 130w-140w, roughly due west of the mouth of the columbia river. this is as the core of the jet stream presently over the ne pacific noses east of 140w, with the development occurring in the left-front quadrant of the jet. with a sharpening baroclinic zone and strong q-vector convergence, the low appears to be in a fairly ideal position to develop rapidly over the coming 18-24 hours. forecast models do rapidly develop a low offshore this afternoon and evening, but most are keeping it weak and in the 995-1005 mb range, peaking before making landfall along the wa coast. still feel that given the ingredients in play, these models are underestimating the potential for development and that the low will eventually turn out to be in the 985-995 mb range. a couple of 00z href members agree now, showing a 988 mb low. regardless of strength and track, models show high confidence that the resulting low pressure will be compact. therefore strength and position will be even more important than usual for determining the wind threat with this system. with models and ensembles still showing a good deal of variation in strength/track despite being within 24-36 hours from now, we will need to monitor closely how the low develops/tracks today in order to get more clarity in whether or not damaging winds are possible late tonight/wed morning. for now, the most likely scenario appears to be gusts 45-55 mph along the coast and 30-40 mph for inland areas. href probabilistic guidance shows the chances of exceeding these ranges at around 20 percent, which essentially equates to the chance of needing a high wind warning along the coast and a wind advisory for the i-5 corridor and willamette valley. based on the thoughts above, would still say the chances are actually closer to 30-50%, but this is still insufficient to warrant issuing a warning. again, will need to monitor satellite/radar trends closely today to determine whether or not these probabilities are in the ballpark. as for qpf, the deterministic output from nbm v4.2 appears reasonable. with the deepest moisture having shifted east of the area, widespread heavy rain is not expected, nor or major hydrologic issues. for the southern half of the forecast area, 00z href means are generally 0.25-0.75 inch, with 0.50-2.00 inches across the northern half. lowest amounts will tend to be across the inland valleys, with the higher amounts in terrain, especially the coast range and particularly the willapa hills. href 90th percentile qpf shows 2-3 inches for the willapa hills and s wa cascades over the next 24 hours, which could threaten minor flooding on the grays river. otherwise, this appears to be another beneficial rain event as the region plays catch-up from the dry start to september. once the low moves onshore wed morning, we will transition to a cool/showery pattern that will persist as an upper level trough settles into the pac nw for the remainder of the week. with 00z eps 850 mb temperature inter-quartile range around +2 to +4 deg c for the late week period, we may flirt with wet snow reaching the cascade passes, but accumulating snows appear reserved for the higher ski resort elevations above 5500 ft or so. for the lowlands, it will feel like true autumn weather with chilly nights/mornings warming well into the 60s or lower 70s each afternoon. frost is not anticipated at this time, but given the air mass it is not difficult to imagine a situation where our cooler outlying valleys have frost if skies clear out wed night or thu night. cluster analyses beyond thursday suggest a high likelihood of another trough digging into the northwestern usa by next weekend, but it remains uncertain whether we will be under the trough and showery, or under cool but drier northerly flow on the western periphery of the upper trough. either way, temperatures appear likely to remain below normal through the upcoming weekend. weagle && .aviation...12z tafs: showers continue today in post-frontal air mass. isolated thunderstorms are possible through the day, generally west of the cascades. afternoon thunderstorm may produce small hail. flight conditions generally vfr but expect occasional mvfr cigs and visibilities with heavier showers. next system spreads rain and another round of breezy condition across the area as a fast moving low approaches the north oregon coast or south washington coast late tonight or early wednesday morning. kpdx and approaches...showers continue primarily vfr conditions. brief mvfr cigs & visibilities can be expected through the day. winds under 10 kt out of the southeast this morning, then veer to more southerly in the afternoon with gust 15-20 kt. winds then ease and back to southeast in the evening, then gradually increase overnight. /mh && .marine...a low near haida gwaii at about 975 mb will continue to weaken as it drifts northward over the next couple of days. of interest is a compact, fast moving system that will develop offshore an approach wa/or tonight. models are not in great agreement with the path of the low, but ensembles generally place the low somewhere on the central wa coast to north oregon coast at 5 am wednesday. this low is expected to produce gale force winds across the waters tonight into early wednesday morning. a hazardous seas warning in effect for all zones through early this evening before the gale warnings come into effect. seas are in the 16 to 20 ft range with a period of 13-15 seconds as of 2 am. seas will gradually subside, but the next storm will increase the wind waves again, though not too significantly due to its fast motion. the weather pattern remain active for the latter half of the week, but overall systems are expected to be much weaker, with winds turning westerly and seas subsiding below 10 feet late wednesday afternoon. && .pqr watches/warnings/advisories... or...none. wa...none. pz...hazardous seas warning until 8 pm pdt this evening 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 8 pm this evening to 8 am pdt wednesday for coastal waters from cape shoalwater wa to florence or out 60 nm. && $$ www.weather.gov/portland interact with us via social media: www.facebook.com/nwsportland www.twitter.com/nwsportland
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