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. --154FXUS66 KPQR 031047AFDPQRArea Forecast DiscussionNational Weather Service Portland OR346 AM PDT Mon Jun 3 2024.SYNOPSIS...
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Low pressure approaching Vancouver Island is pushing acold front across western WA/OR this morning. This is bringing an endto the steady precipitation early this morning, leaving scatteredshowers for the remainder of the day. Another disturbance is likelyto bring rain to much of SW Washington and portions of NW Oregontonight into Tuesday. Temperatures remain on the cool side of normalthrough Tuesday, but a strengthening upper level ridge will lead towarmer and drier weather later in the week.
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Today through Wednesday...Steady rain is coming to anend across SW Washington and NW Oregon early this morning as a coldfront moves onshore, pushing the deepest moisture and strongestforcing east and south of the forecast area. This system slightlyunderperformed expectations in terms of QPF, as rain arrived a fewhours later than expected Sunday and the rainfall rates weren`t quiteas high as they could`ve been given the moisture flux involved. Thatsaid, this was still an impressive rain event by early June standardswith most inland valleys recording 0.50-1.00" of rain, and 1.50-3.00"for much of the coast and higher terrain in our forecast area. A fewRAWS stations have seen more than 3 inches of rain from this event,with the big winner thus far being Cedar RAWS with 3.63" as of 210AM.Latest imagery from KRTX/KLGX Doppler radars suggest the showeractivity upstream is paltry, which is not surprising considering thelack of a significant cold pool aloft. 09z RAP analysis does show amodest cold pool moving onshore near Cape Flattery, with 500 mb tempsas low as -24 deg C in its core. However, the 500 mb temps expectedto advect into our area are milder, which will effectively cap anyshowers at 10-15 kft. Suspect there will be enough shallowinstability from the heating of the day to support scattered showers,but it is highly unlikely (though not impossible) they will be ableto grow tall enough to generate lightning. Given the moisture inplace, even these shallow showers will be capable of producing briefheavy downpours today - but these will be of the hit-and-missvariety.Looking farther west, GOES-West infrared imagery shows a baroclinicleaf associated with our next developing system near 47N/145W. It isnotable that the GEFS maintains an atmospheric river of nearly thesame strength as Sunday`s as this next system moves into western WAand northwest OR tonight into Tuesday, though the EC ensemble suiteis weaker. Regardless, the forcing will be considerably weaker thanSunday afternoon and evening, so QPF will be considerably less thanwith Sunday`s system. Given the deep moisture in place and despitethe weak forcing, the higher terrain of our northern zones stand tosee another decent shot of rain, with HREF means showing 0.75-1.50"and HREF 90th percentile QPF showing 1-2" with some bullseyes inexcess of 2 inches. The inland valleys are much drier, with HREFmeans showing 0.10-0.25" except for a band of 0.25-0.50" nearKelso/Longview. The overarching point here is that tonight intoTuesday will likely be wet for SW Washington and much of the Oregoncoast while the inland valleys are less wet with generally spottylight rain.High pressure begins to build into the Pac NW from the southwestTuesday night into Wednesday, which will be the beginning of the endof our unseasonable cool and wet pattern. Temperatures Wednesday willclimb closer to seasonal norms, and should be mostly dry aside fromsome morning clouds and spotty light showers. Weagle.LONG TERM...Thursday through Sunday...High pressure will strengthenover the Pac NW Thursday, as a warmer air mass bulges northward fromCalifornia. This will continue the warming and drying trend, withtemperatures potentially reaching the 80s as early as Thursday. Thisis supported by the NBM probabilistic guidance, which shows general50-80% chances of our interior lowlands reaching 80 degrees. Thisshould begin a prolonged period of above normal temperatures for SWWashington/NW Oregon.One development over the past 24 hours is that models and theirensembles have generally shifted the upper ridge axis east of theCascades, which should maintain some degree of onshore flow for thePac NW. This will likely keep the coast and coastal valleys coolerthan their inland counterparts through the upcoming weekend. Anotherdevelopment is the potential for shortwave energy to come into playSaturday, which will increase the potential for showers andthunderstorms across the Cascades. All in all, it appears the hottestmodel solutions from a couple days ago will not come to fruition, andthis is also reflected in the near complete removal of any chance ofreaching 100 degrees by NBM probabilistic guidance for Friday andSaturday. The NBM probs of reaching 90 degrees are generally 25-55%for the Willamette Valley Friday and Saturday, so our forecastgenerally has highs in the mid 80s to lower 90s both days for theinland valleys.Given the recent rain and the lack of any strong offshore flow goinginto this late week/weekend warm spell, there could be a touch ofhumidity, and nights will likely remain mild - especially in theurban centers.Weagle
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MVFR prevailing inland with a mix of MVFR and IFR atthe coast. As a cold front moves through this morning expect animproving trend starting around 12Z Mon. In the post-frontalshowers expect a mix of MVFR to VFR through the day. Next systemapproaches overnight with IFR conditions returning to the coast after09Z Tue. Inland remains predominantly VFR, but MVFR probabilitiesstart to increase to around 20-50% towards 12Z Tue.Breezy southwesterly winds continue today, then gradually ease inthe late afternoon and evening hours. Winds increase tonight atthe coast as the next front approaches. Expect southerly gusts30-40 kt at the coast after 06Z Tue.PDX AND APPROACHES...Post-frontal environment with showers andintermittent MVFR/VFR cigs, but HREF indicating MVFR chancedecrease through the day. Winds will be southwesterly 10-15 ktwith gusts to 20-25 kt through the afternoon, then easing in theevening. /mh
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In the post-frontal environment will continue gustywinds and steep seas today. Not much of a break as another frontmoves to the waters. High probabilities for gales HREF with goodagreement with deterministic models give high forecast confidenceto issue a Gale Warning for the zones north of Cape Foulweatherincluding the Columbia River Bar for later tonight into earlyTuesday. Small Craft Advisories continue for the zones south ofCape Foulweather through Tuesday afternoon.High pressure builds midweek for more settled conditions for theremainder of the week. Expect a summer type pattern with highpressure offshore with a thermal trough along the coast. This maybring northerly winds gusting to 25 kt at times to late in theweek./mh
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OR...None.WA...None.PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210-251-252-271-272. Gale Warning from 11 PM this evening to 8 AM PDT Tuesday for PZZ210-251-252-271-272. Small Craft Advisory until 5 PM PDT Tuesday for PZZ253-273.
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