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. --222FXUS66 KPQR 030455AFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR954 PM PDT Sun Jun 2 2024Updated aviation discussion....SYNOPSIS...A late season atmospheric river continues to pushinland this afternoon producing ample rain over the region. Somelocalized flooding possible, especially over the Coastal areasand Cascades. Rain will taper through Tuesday but another weakfront arrives on Wednesday morning. Strong high pressure buildsthrough the remainder of the week which will increase chancesfor very warm temperatures.&&.SHORT TERM...Now through Wednesday Night...Today has notnecessarily worked out exactly as forecast, but overall theimpacts will remain similar. The late season atmospheric riverhas been slow to transition inland this morning. By 1100 thisstorm was already expected to be producing heavy rainfall.However, the heaviest rains have just started falling around1300. They are robust though with over a half inch of rainfalling over the Coast Range within the last 3 hours. Radar andsatellite do not show a break in the rain anytime soon though soexpecting those accumulation amounts to continuously rise. Withthese precipitation rates and amounts, cannot rule out localizedriver flooding or urban ponding. A hydrological outlook as beenissued so please turn to that for more details. With the rain ongoing what will end up happening over the next 24 hours? Letsstart that analysis by looking aloft.At 250 mb (~35,000 ft) the jet stream the stronger winds arebeginning to move over the region which is supporting the rainthus far. As we move into Monday, the strongest winds (the jetstreak) will pass over northwest Oregon and southwestWashington. There, winds are around 110 kt and nearly zonal.Shifting to the mid-elevations (500 mb), this jet is coupledwith west to northwesterly winds around 110 kt as well. As wereach the surface, winds become more south to southwesterlyaround the trough that sits over the northeast Pacific. Withthe westerly flow aloft, the Coast Range and Cascades areorographically lifting the system and thus enhancingprecipitation in those areas. The southerly winds are makingtheir mark though as wind gusts are exceeding 20 kt in mostplaces, with the coast seeing the highest winds with peak gustsaround 40 kt.Behind this system temperatures will cool aloft, but notnecessarily significantly enough to increase chances forthunderstorms. 850 mb temperatures only lower to around 0 deg C(32 F) but we usually are looking for much cooler conditions forhigher thunderstorm potential. The NBM has suggested around a15% chance in southwest Washington, but with a fully saturatedatmosphere and really no forcing mechanism, those chances arelikely lower. On Monday night a shortwave trough and a weak warmfront pushes inland once again. Will see another round ofstratiform rain but it will quickly move and will not beimpactful. However if the atmospheric river from todayoverperforms, then the added precipitation could have an impacton more triggery and full rivers. High resolution models areshowing quite the precipitation accumulation spread. InPortland, the 6 hour rainfall totals, ending at 0400, range from0.05-0.11 inch, with the 90th percentile at 0.15 inch. InTillamook, the range is around 0.08-0.19 inch with the 90thpercentile around 0.25 inch. As you get into the Cascades, theGifford Pinchot Natl Forest could see rainfall totals as high as0.80 inch. Ultimately, this system will once again beorographically driven.Rain will ease through the day on Tuesday with a few lingeringshowers into the afternoon. Wednesday starts the first day ofthe drying and warming conditions that will round out theremainder of the week. -Muessle.LONG TERM...Thursday through Sunday...If you enjoy warm, clear,and dry weather, then the later half of the week is perfect foryou. We are starting off meteorological summer out right with abroad ridge of high pressure which encompasses most of the West.This high pressure system is turning out to be robust with highconfidence and consensus in the ensembles. Sensible weatherwise, Wednesday will be dry and clear but near normal for hightemperatures. Through the week into Saturday upper levelstemperatures too will rise. 850 mb temperatures during thistime frame will rise to around 20 degrees C by Saturday. Thiswill create a deep layer of warm air with little to no reprieve.Looking at high temperatures, values range from the mid 60salong the coast to the mid 70s inland. Upper Hood River Valleyand western Columbia River Gorge will trend warmer within theforecast area due to the proximity to a bulk of the warm air andthe very slight easterly downslope flow. This will be the trendover the next several days.As we transition into Thursday and Friday, the ridge will onlyintensify and temperatures will compound on one another; eachday will be warmer than the previous. The models have finallystarted to come together on this range as it once was a 20degree spread, and now is a 10 degree spread between the25-75th percentile. High temperatures could rise to near 90inland but heightened concerns occur with the overnighttemperatures. Specifically pointing to the Upper Hood RiverValley and the Columbia River Gorge near Carson, models areshowing around a 35% chance that low overnight temperaturescould be greater than 70 degrees F early Saturday morning.Combine that with dewpoint temperatures in the upper 50s to mid60s, overnight recovery could be less favorable. There stillremains some level of uncertainty though so be sure to continueto watch the forecast for more information on the heat risk latein the week. -Muessle&&.AVIATION...
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As of 0430z Mon, widespread rain continues across theregion with a mix of IFR/MVFR cigs along the coast and MVFR/VFR cigsinland. As the cold front pushes through around 09-12z Mon, expectsouthwesterly winds to pick up with gusts to 25-30 kt along thecoast and 20-25 kt inland. Post-frontal showers with a mix of high-end MVFR/low-end VFR cigs will prevail throughout the day tomorrow(Monday) across all terminals. Breezy southwesterly winds willcontinue tomorrow, but will slightly ease throughout the day. Notexpecting much impact to visibility tomorrow as shower activity isforecast to be light.PDX AND APPROACHES...After 10-12z Mon, expect a post-frontalenvironment with light showers and intermittent MVFR/VFR cigs.Winds will be southwesterly 10-15 kt with gusts to 20-25 kt. -Alviz
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A strong storm system, will continue to slowly moveeastward through the overnight hours. Current buoy and land basedobservations are showing south/southwesterly gusts up to 40 kt.Therefore, have extended the current Gale Warnings out through theearly evening. Afterwards, have a Small Craft Advisory for allwaters through Monday night for winds and/or seas. Will extend thecurrent Small Craft Advisory for the Columbia River Bar throughMonday night as well. Winds will subside by Monday night and becomenortherly. Currently, seas around 8-10 ft. Expect seas to buildtowards 10-12 ft on Monday.Winds will remain northerly, but will likely increase towards SmallCraft conditions by the middle of the week. Seas will also continuebuilding through the middle of the week towards 12-14 ft as anotherwesterly swell enter the waters. /42
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OR...None.WA...None.PZ...Small Craft Advisory until 11 PM PDT Monday for PZZ210-251>253- 271>273.
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