Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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354 FXUS66 KPDT 082350 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 450 PM PDT Wed May 8 2024 Updated Aviation Discussion .SHORT TERM...Tonight through Friday night...Quiet weather accompanied by a notable warming trend is forecast through the period as an amplified ridge of high pressure influences the region. Synoptically, the region is currently under northeast flow aloft, located between an amplified offshore ridge that is nosing into the PacNW and a broad closed low centered over the Great Plains. Tonight, cloud cover and precipitation chances will diminish across the region as wraparound moisture decreases. Ensemble guidance is in excellent agreement that a closed low will develop northwest of the Four Corners region tomorrow and retrograde over the Desert Southwest through Friday. This will set up a textbook Rex block over the West with the aforementioned amplified upper-level ridge building across the PacNW. The result will be warming accompanied by dry conditions and offshore- oriented pressure gradients. Locally breezy northeast winds are forecast tomorrow, especially along wind-prone ridges. The main tangible consequence of the ridge will be warming temperatures with a 5-10 degree warming each afternoon Thursday and Friday. Confidence is very high (70-99% chance per NBM probabilities) that Friday afternoon highs will exceed 80 degrees in the lower elevations (especially the Columbia Basin, Yakima and Kittitas valleys, and along the lower elevations of the Blue Mountain foothills). Raising the threshold, confidence is medium- high (50-80% chance) that Friday afternoon highs will exceed 85 degrees in the lower Columbia Basin and Yakima Valley. In the populated areas of central Oregon, chances of 80 degrees are lower (15-50%) and are highest for the Redmond area. Plunkett/86 .LONG TERM...Saturday through Wednesday...Models in pretty good agreement through the period. However, they do differ on the timing of a weak shortwave Sunday night into Monday and in the strength of a developing upper level ridge off the coast. The EOFs show the greatest variance (50+%) Tuesday and Wednesday. In fact, by Wednesday, the WPC cluster analysis shows 57% of the members believe in an upper level ridge off the coast while 43% depict a more zonal flow pattern. Depending on the pattern, we could be near normal or 10-15 degrees above normal by the middle of next week. In addition, the ensemble means are leaning towards more zonal flow by Wednesday. NBM is trending more to normal temperatures (slightly above normal at this time) as well which is not surprising given aforementioned discrepancies. The deterministic models are surprisingly in relative alignment with a weak shortwave moving through Sunday evening. The ECMWF shows another shortwave moving through the northwesterly flow Monday afternoon. The disturbances are so weak their only impact on our CWA should be an increase in cloud cover and slightly cooler temperatures. However, the Washington Cascade Crest may see some isolated showers on Wednesday if more westerly flow develops. In summary, the extended period will start off with an upper level ridge weakening but daytime highs still 10-15 degrees above normal Saturday and Sunday. Several shortwaves should continue to flatten the ridge with more zonal flow developing, dropping highs back down to 5 degrees or so above normal. Another amplifying ridge could develop (low to moderate confidence) over the eastern Pacific, but resulting in a "cooler" northwest flow pattern aloft for our CWA. There will be some hydrological concerns over the weekend as an upper level ridge continues to produce above normal temperatures over the area. This will provide ideal conditions for melting some of our winter snowpack. All rivers will see rises, but portions of the Naches River are expected to recede bankfull by Saturday or Sunday. Earle/81 .AVIATION...00Z TAFs...VFR conditions to prevail through the period. Periodic CIGS of few-bkn AOA 20kft AGL will impact sites through the period. Breezy winds between 12-15kts and gusts up to 20kts will continue at site RDM/BDN through 4Z, becoming less than 12kts the remainder of the period. Everywhere else winds will be 12kts or less, with winds mostly from the north tomorrow...except site DLS where winds will be from the east. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 40 73 46 79 / 0 0 0 0 ALW 42 78 49 83 / 0 0 0 0 PSC 46 81 52 86 / 0 0 0 0 YKM 42 80 48 85 / 0 0 0 0 HRI 42 79 49 85 / 0 0 0 0 ELN 43 78 49 84 / 0 0 0 0 RDM 34 71 40 79 / 0 0 0 0 LGD 37 71 43 77 / 0 0 0 0 GCD 33 72 42 77 / 0 0 0 0 DLS 47 80 52 86 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....81 AVIATION...82