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. --479FXUS66 KPQR 010953AFDPQRArea Forecast DiscussionNational Weather Service Portland OR252 AM PDT Thu Aug 1 2024.SYNOPSIS...
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High pressure expands over the western US today,bringing much warmer temperatures, with inland highs of 95 to 100degrees. The warm weather appears likely to continue through nextweek. Weak disturbances in the upper level flow bring slight chancesof thunderstorms for the Oregon Cascades Saturday and Sunday.
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(Today through Wednesday)...A broad upper level ridgeof high pressure continues to build over the western U.S. todaywhile high pressure centered over the Southern Plains shifts westacross the four corners region through Friday. As the heat expandsover the region today, 850 mb temps are expected to spike up to 23-24 deg C this afternoon. Expect this to translate to near recordhigh temperatures of 95 to 100 deg F across the lowland valleys ofNW Oregon and SW Washington. There may also be record high minimumtemperatures tonight into Friday morning as lingering low-levelmoisture maintains higher humidities, especially in northern partsof the Willamette Valley, Clark County and through the ColumbiaRiver Gorge where dewpoints remain in the 60s. These warmerovernight temperatures would limit relief from the hot daytimetemperatures. The Heat Advisory goes into effect late this morningand will continue through this evening. Major HeatRisk is forecastfor these locations, which means that anyone without effectivecooling and/or hydration will be affected by this level of heat.Although upper level ridging continues to build over the area onFriday, stronger onshore flow will help moderate high temperaturessomewhat with morning clouds (Friday and Saturday) and lateafternoon/evening breezes. Expect a modest southerly wind reversaland marine push Thursday evening to work its way up the WillametteValley through Friday morning. 850 mb temps are likely to hoveraround 20 deg C through Sunday, so warm afternoons are expected tocontinue with high temps in the lower to mid-90s.We are also monitoring a small chance of thunderstorms for theOregon Cascades on Saturday and Sunday. A weak upper leveldisturbance currently over Baja California is expected to driftnorthward, dragging with it some monsoonal moisture and moving intosouthern Oregon by early Saturday morning. An upper level trough offthe northern California coast may develop into a cutoff low as itlifts northward through Sunday. This will maintain southerly flowover the region through the weekend. Therefore, the forecastreflects a 15-20% chance of thunderstorms, mainly over the Lane andLinn County Cascades.There is general agreement in the long term WPC cluster analysesthat above average 500mb heights holding over our area, but higheruncertainty with the strength and positioning of the ridge. Thiswill likely continue very warm temperatures and dry conditionsacross the Pacific Northwest. NBM shows a 70-90% chance that daytimetemperatures reach 90 degrees or hotter for interior lowlands Mondaythrough Saturday next week. The CPC day 6-10 Outlook indicatesbetter than an 80% chance for above normal temperatures during thisperiod. /DH
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Light and variable winds will continue until around18-20z when winds will increase to around 5-8 kts from thenorth/northwest. Generally VFR conditions for inland and coastallocations. However, a weak marine push south of Florence isslowly moving north toward Newport. This may bring a period ofMVFR/IFR (40-50%) conditions to KONP around 12z, lasting until18-20z when stratus shifts offshore. KAST could also see a periodof MVFR/IFR conditions but probabilities are lower between 12-16z.Patchy MVFR conditions are possible in the Willamette Valley(10%-20% probability) around 12-16Z Thursday. If any lower flightconditions do develop, conditions will likely return to VFRaround 17Z-20z Thursday.It should be noted that wildfires burning in the Central ORCascades (east of KEUG) as well as within the Columbia River Gorge(east of KPDX and KTTD) could result in some slant rangevisibility issues at times.PDX AND APPROACHES...VFR conditions expected to persist throughthe TAF period. There is a 10%-15% probability for MVFRconditions to develop around 10z. If any lower flight conditionsdo develop, conditions will likely return to VFR around 16-18zThursday. /Batz
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North/northwesterly winds persist into the weekend asridging remains in place across the Pacific NW. Gusts up to 25kts will be possible through around 5am, warranting a Small CraftAdvisory for the outer water zones. Seas 4-6 ft through theweekend. /42/Batz
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OR...Heat Advisory from 11 AM this morning to 11 PM PDT this evening for ORZ108>118-120>122.WA...Heat Advisory from 11 AM this morning to 11 PM PDT this evening for WAZ204>207-209-210.PZ...Small Craft Advisory until 5 AM PDT early this morning for PZZ271>273.
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