National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --174FXUS66 KPQR 092133AFDPQRArea Forecast DiscussionNational Weather Service Portland OR232 PM PDT Sun Jun 9 2024.SYNOPSIS...
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Generally pleasant and benign weather is on tap for thenext few days. The weak upper trough responsible for areas of drizzlealong the coast earlier today will move east across the Cascadestonight. High pressure will follow with warm temperatures and plentyof sunshine for Monday. Another weak system may clip mainly the northcoast with drizzle or light rain Tuesday, then high pressure brings areturn to warmer and drier weather Wednesday and Thursday.Temperatures may dip below normal next weekend as most forecastmodels bring an upper trough onshore - potentially strong enough tobring more widespread rain to the region.
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Now through Wednesday...A weak upper trough deepenedthe marine layer enough for some measurable drizzle along the coastnorth of Manzanita this morning. The ASOS at Astoria airport reportedthe most precip with 0.05". Based on area webcams and the latestreports, it appears the drizzle has mostly come to an end. The marinelayer should become shallower as the upper trough moves east of theCascades and higher pressure in the mid-levels assists subsidence.The coast should see stratus either persist or return overnight, butthe inland intrusion should be considerably less robust Mondaymorning. Any morning clouds inland will quickly give way to sunshineand a warm afternoon. With 850 mb temps likely to reach +10 to +12deg C by Monday afternoon, most of our interior lowlands should climbinto the 80s. NBM probabilistic guidance tends to agree with general40-70% chances of reaching 80 deg F in the Willamette and Hood RiverValleys Monday afternoon. A greater northerly component to thelow-level flow should lead to drier conditions as well.The NE Pacific remains more active than usual for June, and this willcontinue to be the case Monday night/early Tuesday as another uppertrough moves into British Columbia, pushing the tail end of its coldfront into the Pac NW. This looks like a similar situation as today,where mainly north coastal zones may get brushed with some drizzle orlight rain. PoPs remain low, except perhaps in the Willapa Hillswhere most guidance has a little QPF Tuesday morning. High pressurequickly returns Tuesday afternoon, drying things out and leading to afairly seasonable and pleasant day Wednesday. Weagle
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Thursday through Sunday...By Thursday, ensemble membersagree on shortwave ridging over the region, supporting drierand warmer conditions. Our forecast undercuts NBM MinRH bothWednesday and Thursday as northerly flow should cause dewpoints todip well into the 40s or possibly even the 30s as temperatures warmup under the upper ridge. Essentially, our forecast used a MOS blendfor dewpoints then calculated the MinRH for both days. By Friday, theupper ridge begins to shift eastward as another trough near the Gulfof Alaska dips southward toward the Pacific Northwest. By Saturday,most ensemble members (65%) agree on troughing entering the regionwith below-average 500 mb heights. If this scenario pans out, then wewould see increasing chances for widespread precipitation along withpotentially below average temperatures. For now, the NBM`s 15-45%chance of PoPs across northwest Oregon and southwest Washington atthe end of the week look reasonable. -Alviz/Weagle
-- End Changed Discussion --&&.AVIATION...
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At 21z Sunday, satellite and surface weatherobservations depicted mostly clear skies across the area. Theexception was along and near the coast from KONP to KAST where amarine stratus deck continued impacting flight conditions. Cigswere ranging between 400-700 ft at KONP and 1000-1500 ft at KAST.The central OR coast (including KONP) will likely see a very briefimprovement to VFR conditions by 22z Sunday before a marinestratus deck redevelops towards 01z Monday. Chances for anysubstantial clearing at KAST are much lower (<25%) where MVFR cigsare likely to continue through the day before lowering to IFRSaturday night. Periods of light drizzle will also be possible atKAST Monday morning, similar to what was observed Sunday morning.Models still show a chance for an MVFR stratus deck to developnear the mouth of the Columbia River Gorge and backbuild into KTTDand KPDX towards 12z Monday. Probabilities for this to occur haveincreased to nearly 50% and forecast confidence has increasedfrom low to medium. As such, have decided to include broken cigsaround 1800-1900 ft at KTTD and KPDX beginning at 12z.PDX AND APPROACHES...Expect VFR flight conditions for the rest ofthe day and evening. However, probabilities for MVFR cigs around2000 ft have increased Saturday night, peaking near 50% towards12z Sunday. This stratus deck will likely develop over/near KTTDfirst before quickly backbuilding westward towards KPDX. Expectnorthwest surface winds between 5-10 kt Sunday afternoon/earlyevening with light and variable winds Sunday night/Monday morning.-TK
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Buoy observations from early Sunday afternoon showedsignificant wave heights at 9 to 10 ft with a dominant wave periodaround 13 seconds. This is a foot or two higher than what thelatest model guidance suggests. As such, the forecast has beenupdated to increase wave heights for the rest of Sunday afternoonthrough Sunday evening to better reflect observations. Theseobservations also meet criteria for a marginal small craftadvisory. In addition, northerly winds were gusting up to 20 kt.Therefore have decided to issue a small craft advisory for theinner and outer waters through 11 PM Sunday. Seas should fall backbelow 10 ft thereafter as high pressure strengthens and northerlywinds weaken. High pressure will strengthen even more Mondaymorning, bringing seas down to 4 to 6 ft.Still expecting a weak cool front to move eastward over thecoastal waters early Tuesday morning, bringing a brief shift tosoutherly winds. This front looks to be weak, only producing windgusts up to 15-20 kt. That said, westerly swell will increasebehind the frontal passage Tuesday afternoon/evening, likelypushing seas back up to 9 to 10 ft and producing marginal smallcraft advisory conditions.Small craft advisory conditions become even more likely onWednesday as a thermal trough deepens along the south Oregon coastand helps increase northerly winds over the waters. Currentlyexpecting wind gusts up to 25-30 kt on Wednesday (95% chance). Infact, cannot completely rule out marginal gale force gusts up to35 kt over the southern waters (40-60% chance). -TK
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OR...None.WA...None.PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ251>253-271>273.
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