Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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639 FXUS66 KPDT 210948 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 248 AM PDT Sat Sep 21 2024 .SHORT TERM...Today through Monday...A flat ridge of high pressure will be over the region today providing generally clear skies, light winds and near normal high temperatures. Another weak upper level trough will pass through western Canada Sunday clipping the Pacific Northwest similar to the one that occurred on Friday. This will once again produce some locally breezy conditions along portions of the east slopes of the Cascades. Primarily the Kittitas Valley and eastern Columbia River Gorge where winds will be 15-25 mph with gusts into the 30s. Fire weather concerns will be elevated due to these locally breezy winds but humidities remain high enough that no Red Flag conditions exist. A low chance (15-20%) of some showers remain possible along the crest of the central Washington Cascades but otherwise the forecast area will remain free of precipitation with this trough passage. This will be followed Monday by another ridge of high pressure building into the region from the eastern Pacific but showing a little more amplitude than todays flat ridge. This amplitude will allow the ridge to persist over the region through the first of the week before the next stronger trough arrives on Wednesday. .LONG TERM...Tuesday through Saturday...The long term forecast remains mostly benign as high pressure ridging brings warm conditions to the front half of the forecast, with growing uncertainty in the later part of the period but should include a likely cool down alongside at least Cascade rain. The long term begins under high pressure ridging which will control the CWA through Wednesday morning. This will allow for mostly quiet conditions with Tuesday itself now expected to be the warmest day of the period. Highs for our population centers are expected to range in the mid to upper 80`s, with a chance at 90 degrees not out of the question for portions of Central Oregon, the Columbia Basin, and the foothills of the Blue Mountains. The NBM presents a probability of 20-50% at temperatures 90+ for Central Oregon on Tuesday, with the other aforementioned regions at generally less than 10% for the day; on Wednesday, those probabilities shift to the Columbia Basin and foothills of the Blues, where a 20-40% chance at 90+ will exist. That being said, Wednesday is when we begin to see a general cooling pattern that will stay with us through the end of the forecast period, as widespread highs come back down into the low to mid 80`s for the most part. In fact, only the Columbia Basin should be as warm as the previous day, with all other locations at least a few degrees cooler. This cooling trend will be activated by a pattern change in the form of the deep ridge shifting eastwards while several systems begin to spin down into the PacNW, but generally only grazing our area and keeping us in a cooler, zonal flow. The first system moves in on Wednesday during the afternoon and evening, and the second on Friday; in both instances, moisture should be locked on the lee side of the Cascades, with any showers that do make it over the peaks quickly falling apart before they can make it past the foothills. Meanwhile highs drop around 3-6 degrees on Thursday, and should continue to descend a few degrees each day, swinging us from above normal to back below normal by next Saturday. The end of the forecast period is a bit more uncertain however, as ensemble guidance begins to separate by that time. The majority of the ensembles though are either zonal with troughing both over Canada or offshore, or more trough-like in nature with Friday`s system causing our flow to shift more northwesterly, either of which would be cooler than any of the more ridge dominant ensembles which only account for roughly 20% of overall guidance. Therefore, there is moderate to high confidence in the overall forecast (60-70%), with our warm mid-week and cool weekend looking fairly likely. Each of these systems may also bring us gusty winds on Wednesday/Friday, but nothing out of the ordinary and below wind advisory criteria, breeziest through where else - the Cascade Gaps. Goatley/87 && .AVIATION...12Z TAFs...VFR conditions expected over the next 24 hours. Skies will be mostly clear, though some high clouds moving into the region, particularly for sites on the Washington side of the region, could be possible. Some lowered ceilings caused by smoke also possible at BDN/RDM, but with low confidence. Winds 10 knots or less all sites. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 70 44 77 50 / 0 0 0 0 ALW 73 48 79 54 / 0 0 0 0 PSC 75 51 81 57 / 0 0 0 0 YKM 75 47 81 52 / 0 0 0 0 HRI 74 48 81 54 / 0 0 0 0 ELN 75 47 77 52 / 0 0 0 0 RDM 71 40 78 45 / 0 0 0 0 LGD 70 42 75 47 / 0 0 0 0 GCD 70 40 76 46 / 0 0 0 0 DLS 79 50 82 56 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...91 LONG TERM....87 AVIATION...87