Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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608 FXUS66 KPDT 160505 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1005 PM PDT Mon Jul 15 2024 Updated Aviation Discussion .EVENING UPDATE...Satellite imagery this evening show mid to high level cloud cover spreading north across portions of central and northeastern OR. Very little change in the forecast this evening, as high pressure continues to build back over the region, while low pressure aloft begins to develop off the coast of northern CA. Only change to forecast was to extend the coverage of the Heat Advisories to the Simcoe Highlands, north central OR, and the southern Blue mountain foothills, as HeatRisk in these areas will be in the high end moderate to major categories starting tomorrow. Lawhorn/82 .AVIATION...06Z TAFs...VFR conditions to prevail through the period. CIGS will be mostly few-sct AOA 12kft AGL through this evening, and developing again by tomorrow afternoon. Smoke from area wildfires may periodically impact vsby at sites PDT/ALW after 10Z, lowering CIGS down to 6SM, though confidence in MVFR or lower conditions is low (15-20%). Winds will be light, less than 12kts, at all sites through the period. Lawhorn/82 PREV DISCUSSION... /issued 428 PM PDT Mon Jul 15 2024/ .SHORT TERM...Tonight through Wednesday night...High pressure will build back over the region from the south. Additionally, an area of low pressure will move from off the northern California coast Tuesday afternoon to near the Washington coast by Wednesday and weaken into an open wave. As this low/wave moves by it could touch off some thunderstorms, with the east slopes of the Cascades the most likely location. However guidance is mixed on thunderstorm potential further east, with some guidance showing at least some CAPE across the Basin. The ECMWF EFI is not all that excited about thunderstorm potential at all on the east side of the Cascades, with its values generally 0.5 or less. The HREF does have some thunderstorm potential across central Oregon late Tuesday afternoon, and then more potential toward morning further north. Based on the best available guidance so far, we will be issuing a fire weather watch for the east slopes of the Cascades, as this is where the guidance shows the best chance for thunderstorms. The biggest question overall is how widespread the thunderstorms will be. It is possible the the fire weather watch will have to be extended further east. The other weather concern is increasing heat, as high pressure builds northward. Temperatures will once again be in the 101-103 range in the Columbia Basin, Yakima Valley and Blue Mountain Foothills on Tuesday and probably a degree or so warmer on Wednesday, with Wednesday likely being the warmest day. Some guidance doest suggest Thursday will be just as warm, while other guidance suggests a bit cooler temperatures on Thursday. A heat advisory is being issued for the Columbia Basin, Columbia Gorge, Foothills of the Blue Mountains, Yakima Valley and Kittitas Valley. For the Gorge and Foothills of the Blue Mountains it will be in effect Tuesday and Wednesday everywhere else it will run through Thursday. HeatRisk values will be moderate to Major Tuesday, Major on Wednesday and Moderate to Major on Thursday. Probabilities of high temperatures >=100 degrees are >80 percent in most of these areas Tuesday and Wednesday and 80 to 90 percent in the Basin on Thursday, though much lower elsewhere. High temperatures during this time will be about 10 to 15 degrees above normal in the advisory area with overnight lows 5 to 6 degrees above normal. .LONG TERM...Thursday through Monday...Models are in excellent agreement in keeping a persistent upper level ridge over the western states through most of the long term period with only minor differences developing Sunday. Differences increase further on Monday when an upper trough approaches the Pacific NW coast and may flatten the ridge to our south. Heat will be the biggest concern through the long term and temperatures will remain well above normal with temperatures peaking next weekend. While hot and dry conditions with a southwest flow tends to favor thunderstorm development, models are showing limited moisture and instability, so the forecast has no showers or thunderstorms. Thursday and Friday, models are in excellent agreement in having a strong ridge centered over the Rockies with a southwest flow over the area. Temperatures on Thursday will be 95-105 in the lower elevations and in the 80s and lower 90s in the mountains. Model guidance suggests a modest marine push through the Columbia Gorge that will generate west to northwest 10 to 20 mph winds in the afternoon. Cooler air from the marine push will lower temperatures a few degrees on Friday to the low 90s to around 100 while the mountains will be mainly in the 80s. On Saturday, model clusters are in good agreement in having the ridge strengthen further and shift the ridge axis westward closer to our area. This will warm temperatures 3 to 7 degrees in the lower elevations to 100 to 105 with a few upper 90s in central Oregon. The mountains will be in the 90s. On Sunday, a few differences develop between model ensemble members with 65 percent keeping a very strong ridge centered over Idaho and Montana while the others show an upper trough approaching the coast and weakening the ridge. Model guidance shows a few degrees of cooling in central Oregon and over the Cascades but warms the rest of the area a couple more degrees. This will raise the Columbia Basin to 102 to 107 while central Oregon north to the Columbia Gorge will be in the upper 90s. The mountains will remain in the 90s. Model probabilities show a 70-90 percent chance of 100 degree temperatures in the Columbia Basin Saturday and Sunday with a 15 to 20 percent chance of 110 degrees in the eastern Columbia Basin and eastern Blue Mountain Foothills on Sunday. Overnight lows in the Columbia Basin will be in the mid 60s to lower 70s so heat relief will be modest. Heat highlights look probable given these temperatures next weekend. Differences increase Monday as 65 percent of the models keep a strong ridge over Idaho with some differences as to the location of the offshore trough. Those differences affect 500 mb heights over our area and therefore the temperatures. The other 35 percent have the trough overhead and a much weaker ridge moving off to the east. The NBM favors 3 to 6 degrees of cooling and have gone with that. This gives the Columbia Basin upper 90s to lower 100s while the rest of the area is in the mid 80s to mid 90s. Models also suggest another modest marine push Monday afternoon with 10 to 20 mph winds in the Kittitas Valley and Columbia Gorge. Perry/83 .FIRE WEATHER...Fire weather watches will be issued for the east slopes of the Cascades and nearby areas for Tuesday late afternoon/evening through Wednesday late afternoon/evening. These watches may be expanded eastward. Fire weather concerns are elevated elsewhere due to the continued hot and dry conditions and Haines indices of 5. Dry thunderstorm potential begins Tuesday afternoon in central Oregon and moves northward with time. Guidance has highest probabilities along the Cascades, but there is at least (20-30%) along the Columbia Basin on Wednesday. How widespread the lightning will be is the big question. && .PRELIMINARY POINT TEMPS/POPS... PDT 58 99 65 99 / 0 0 0 20 ALW 64 102 67 103 / 0 0 0 20 PSC 64 102 67 103 / 0 0 0 20 YKM 61 101 68 100 / 0 0 0 20 HRI 63 103 67 104 / 0 0 0 20 ELN 62 101 67 100 / 0 0 0 20 RDM 53 98 60 96 / 0 0 10 0 LGD 56 98 61 98 / 0 0 0 20 GCD 57 98 64 99 / 0 0 10 10 DLS 63 105 72 99 / 0 0 0 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Heat Advisory from noon Tuesday to 10 PM PDT Wednesday for ORZ041-507-508-510. Fire Weather Watch from Tuesday afternoon through Wednesday afternoon for ORZ610-611-639-640. Heat Advisory from noon Tuesday to 10 PM PDT Thursday for ORZ044. WA...Heat Advisory from noon Tuesday to 10 PM PDT Wednesday for WAZ024-029-521. Heat Advisory from noon Tuesday to 10 PM PDT Thursday for WAZ026>028. Fire Weather Watch from Tuesday evening through Wednesday evening for WAZ690-694-695. && $$ SHORT TERM...77 LONG TERM....83 AVIATION...82