FXUS66 KPDT 191018 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 318 AM PDT Fri Jul 19 2024 .SHORT TERM...Today through Sunday...The strong upper level ridge over the western USA will continue its grip over the region through Sunday for continued very hot conditions across the forecast area. The good news is the ridge weakens allowing an upper level trough to impact the Pacific Northwest first of next week ending the heat wave. For today, a weak short wave off the coast will lift northeast into Canada while clipping the Pacific Northwest. The main impact will be slightly suppressing the upper level ridge over the region with high temperatures only reaching around 100 in the Lower Columbia Basin. However, the upper level ridge will push northward back into the region on Saturday with lower elevations highs of 100-105 degrees. On Sunday high temperatures will peak at 100-110 degrees across the lower elevations and mountain valleys with probability of exceeding 110 degrees in the Lower Columbia Basin at 40-60%. Both days could see some record high temperatures in many location of the forecast area. Various Heat Advisories and Excessive Heat Warnings are in effect over the weekend. There is an upper level trough in the Gulf of Alaska that is slowly moving towards western Canada over the weekend. Models are showing that it lifts a shortwave near the northern California coast up the Pacific Northwest coast on Sunday. This could provide enough instability to trigger some convection (10-20% chance) across central Oregon Sunday afternoon and then spread north into the Washington Cascades in the evening. Winds will generally be light over the next couple of days. However, on Sunday the approaching upper level trough begins to increase the pressure gradient along the Cascades as cooler marine air floods into western Oregon and Washington. This will lead to a push of this cooler air through the Columbia River Gorge and lower gaps of the Cascades resulting in some increasing breezy conditions (10-20mph) in the late afternoon and evening. .LONG TERM...Monday through Friday... Key Messages: 1. Potential thunderstorms on Monday. 2. Locally breezy conditions through next week. The strong high pressure ridge over our region begins breaking down Monday as a low off British Columbia coast moves inland, bringing SW wind aloft. Potential thunderstorms are possible for late Monday through early night, mainly across the John Day Basin and eastern mountains (50% confidence). Most unstable CAPE values are 500 J/Kg or less with lapse rates above 7 C/Km, showing marginal instability. Mountain showers are also possible as the trough really starts to move in, but confidence is very low (<15%) due to limited moisture advection from persistent hot, dry conditions. Potential fire weather conditions remains to be advised with this ridge breakdown and incoming breezy winds. Given these conditions, this will facilitate gusty conditions with RHs remaining in the teens to lower 20s. Moderate HeatRisk will be across some portions of the lower elevations. With Major HeatRisk at Wallowa county including Yakima Valley, heat advisories and warnings have been issued for those areas through Monday. Locally breezy conditions (15-25 mph) will occur across the Columbia River Gorge, Simcoe Highlands, Yakima and Kittitas valleys through next week. Probability for wind gusts exceeding to 40 mph Monday is at 30-50%. High confidence for increased wind gusts in these areas as well as the ridge breakdown continues with a low pushing through. As the trough passes, breezy conditions will continue across the forecast area with wind gusts at around 20-30 mph. High temperatures will be in the 90s and 100s Monday with the ridge over the region. Driven by a low, the trough will bring cool temperatures into the 80s and 90s across the forecast area Tuesday through next week. Feaster/97 && .AVIATION...06Z TAFs...VFR conditions will persist through the forecast period, however, there will be some lingering high level haze. DLS remaining breezy at 15 kts while the remaining sites are below 9 kts. Bennese/90 && .FIRE WEATHER...Hot, dry and unstable conditions increase and peak over the weekend. With significant fires occurring in Oregon zones 642 and 644 there is a Fire Weather Watch in effect for Saturday through Sunday. There are concerns for elevated fire threat due to increasing winds late Sunday as the cooler air associated with the approaching trough beginning to push into the region. This will produce winds of 10-20 mph with RH values in the teens to lower 20s. This will be monitored for highlight needs at a later time. && .PRELIMINARY POINT TEMPS/POPS... PDT 97 60 102 64 / 0 0 0 0 ALW 100 64 106 67 / 0 0 0 0 PSC 101 65 105 67 / 0 0 0 0 YKM 99 63 102 68 / 0 0 0 0 HRI 101 63 106 66 / 0 0 0 0 ELN 95 61 102 66 / 0 0 0 0 RDM 93 54 101 63 / 0 0 0 0 LGD 95 58 102 62 / 0 0 0 0 GCD 98 59 105 65 / 0 0 0 0 DLS 97 64 106 70 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for ORZ041-044-049-050-502-503-505-507-508. Fire Weather Watch from Saturday morning through Sunday evening for ORZ642-644. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for ORZ506- 510-511. WA...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for WAZ024-026>030-521. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for WAZ523. && $$ SHORT TERM...91 LONG TERM....97 AVIATION...97