Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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690 FXUS66 KPDT 040239 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 739 PM PDT Mon Jun 3 2024 .EVENING UPDATE...The wind advisory across the region has been cancelled this evening as widespread gusts have dropped below 45 mph. A few gusts may reach back into the low 40s, but the majority of the region remains below this threshold and should continue to decline through the nighttime hours. Have adjusted winds to account for this. Also made some slight adjustments to precipitation over the next 12 hours, but these were mostly slight changes, with the majority of the afternoon forecast remaining largely the same. Goatley/87 && .PREV DISCUSSION... /issued 436 PM PDT Mon Jun 3 2024/ AVIATION... 00Z TAFS...Breezy to windy conditions will decrease over most sites through the evening, with winds generally 15 kts or less during the overnight hours. WInds will increase again Tuesday afternoon and become breezy behind the passage of an upper level disturbance. Winds should gust in the 20 to 25 kt range. This same disturbance could bring some rain mainly in the morning hours. Have opted for mostly PROB30s and a few TEMPOs. Rain should be light enough for VFR conditions to prevail except, at DLS, where some MVFR conditions are forecast. PREV DISCUSSION... /issued 230 PM PDT Mon Jun 3 2024/ SHORT TERM...Tonight through Wednesday...Radar imagery this afternoon shows showers mainly across the WA Cascade crest, while water vapor satellite imagery shows an upper level trough moving across the PacNW. At the surface, much of the forecast area are currently under winds of 15-30 mph, with gusts 30-50mph. By this evening, the upper trough will have exit into ID and western MT, placing the PacNw under a west northwest flow aloft. While much of the forecast area will remain dry, the flow aloft will result in upslope showers across the Cascades continuing through tonight. Surface winds will also decrease this evening behind the upper trough exit, with light to locally breezy winds overnight. Tomorrow morning, an upper low in the northeast Pacific will swing a shortwave coupled with a weak surface cold front across the PacNW. This will result in an increase in shower activity across the Cascades early tomorrow morning, while light to moderate rain showers associated with the frontal passage will develop across portions of the eastern mountains and eastern portions of the Columbia Basin. Rain accumulations will be heaviest across the Cascade crest/peaks as well as the northern Blues, where 0.25-0.75 inches is anticipated. Along the foothills and eastern portions of the Basin, expect up to 0.1 inches with any showers that pass overhead. The cold front and shortwave passage will also result in pressure gradients tightening again across the intermountain PacNW, however, deterministic guidance shows the pressure gradient between Portland and Spokane only peaking up to 9mb. This would translate to winds mainly 15-25mph with gusts up to 40mph across central and north central OR, the eastern Columbia River Gorge, and the Columbia Basin and adjacent foothills/valleys. The breezy winds and mountain showers will persist into the evening, but will quickly diminish overnight. By Wednesday morning, dry conditions and light winds will return to the PacNW as a broad upper level ridge builds in from the Desert Southwest. Afternoon temperatures will be on the increase as well for Wednesday, with a return to upper 70s and low 80s across the lower elevations. Lawhorn/82 LONG TERM...Thursday through Monday...Models are in overall good agreement in the weather pattern in the long term period though small differences initially become larger next weekend into early next week and reduce confidence in temperatures and the possibility of thunderstorms Sunday and Monday. Model ensemble cluster analysis shows excellent agreement Thursday in having a ridge over the Rockies and a southwest flow over our area. Friday is similar though models begin to have differences in the strength of the ridge which would affect the warming temperatures slightly. On Saturday, the model strength differences increase due to uncertainty about troughs in the Gulf of Alaska and from Hudson Bay down into the eastern CONUS, though overall 500 MB heights are higher and temperatures should peak that day. On Sunday, models bring a trough towards the west coast with widely varying strengths for the trough. This does reduce the influence of the Rocky Mountain ridge over our area and should cool temperatures. Models then differ greatly on Monday with the trough becoming a barely noticeable feature as most of the energy goes far to our south and forms a cut off low off of Southern California or Baja California. 55 percent of the models have the weak feature over or area and the other 45 percent have a weak ridge offshore with flow mainly westerly in most of the model clusters. The main concerns in the long term period are the building heat Thursday into Saturday and then how temperatures begin to cool Sunday and Monday and also the extent of showers and thunderstorms Friday afternoon onward. Overall forecast confidence starts out good and becomes normal by Sunday and then below normal on Monday. Thursday will be a sunny day with temperatures warming 7-9 degrees in general, though only around 5 degrees in central Oregon. This will give us highs in the mid to upper 80s in the lower elevations and in the 70s and lower 80s in the mountains. This pattern will continue on Friday with highs in the Columbia Basin warming another 5 or so degrees and about 3 degrees in the rest of the area. This will warm the Columbia Basin to the lower to mid 90s and the rest of the area will be in the upper 70s and 80s. The Columbia Basin and Columbia Gorge have a 60-85 percent chance of reaching 90 degrees while the Blue Mountain Foothills and central Oregon have a 35-45 percent chance of reaching 90 degrees. The southwest flow aloft will bring some moisture into the area and heat will provide the instability for a slight chance of late afternoon thunderstorms over the Ochoco-John Day Highlands and the John Day Basin. On Saturday, with the ridge at its strongest, the Columbia Basin will warm a couple more degrees while elsewhere, increasing cloud cover will cool temperatures elsewhere a couple of degrees. While chance of reaching 90 degrees in the Columbia Basin remains at 85- 100 percent and at 40-60 percent in the Blue Mountain Foothills, chances of reaching 100 degrees are 20-25 percent in the Tri-Cities and Hermiston and 10 percent or less elsewhere. Increasing moisture and instability will bring a chance of rain showers and a slight chance of thunderstorms to the eastern mountains and the central Oregon Cascades with a slight chance of rain showers along the rest of the Cascade crest and the Blue Mountain Foothills. On Sunday, the ridge weakens and with a trough offshore, models bring a marine push through the Cascade gaps with the Columbia Gorge and Kittitas Valleys having westerly winds of 15 to 25 mph in the afternoon. This cools temperatures 5 to 8 degrees to the 80s with mainly 70s in the mountains. This will also lead to another slight chance of showers and thunderstorms mainly in the eastern mountains. Conditions become less certain on Monday, so have gone with temperatures a degree or so cooler than Sunday and once again have afternoon 15 to 25 mph winds in the Columbia Gorge and Kittitas Valley. Have also continued a slight chance of afternoon showers in the Northern Blue Mountains and Wallowa County. Perry/83 AVIATION...Previous Discussion...18Z TAFs...Rain showers have moved into the eastern mountains this morning, so do not anticipate showers at any TAF site this afternoon. SCT-BKN skies at 050-090 will become FEW-SCT this afternoon. After 00Z, a weak disturbance will move over the area with skies becoming BKN-OVC at 035-060. Showers are possible after 06Z, but have limited mention of -SHRA to KDLS, KPDT and KALW after 08Z-10Z. Have used periods of VCSH at other TAF sites due to low confidence. Strong west to southwest winds are expected to continue at 15-30 kts with gusts to 40 kts through this afternoon before decreasing after 03Z. Winds will begin increasing again at KRDM and KBDN after 15Z tomorrow morning. Perry/83 && .PRELIMINARY POINT TEMPS/POPS... PDT 48 71 49 75 / 30 20 0 0 ALW 51 71 51 77 / 40 40 0 0 PSC 55 75 52 79 / 30 20 0 0 YKM 48 73 44 77 / 20 30 0 0 HRI 52 75 51 80 / 30 20 0 0 ELN 44 68 43 74 / 20 30 0 0 RDM 46 73 45 79 / 10 10 0 0 LGD 46 71 48 76 / 30 40 10 0 GCD 47 76 47 81 / 20 10 0 0 DLS 52 70 52 78 / 40 40 10 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ EVENING UPDATE...87 SHORT TERM...82 LONG TERM....83 AVIATION...77