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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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068 FXUS66 KPDT 081035 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 335 AM PDT Mon Jul 8 2024 .SHORT TERM...Today through Wednesday...Water vapor imagery tonight shows the axis of a strong upper level ridge has moved inland, and is settled over western OR/WA at this time. Great agreement amongst ensemble and deterministic guidance that the upper ridge axis will transit the PacNW through Tuesday, where it will exit into ID/MT where it will ultimately stall across eastern ID and western MT Wednesday. Tuesday afternoon into Wednesday morning, a weak vort and jet max in the mid levels will lift across central and eastern OR, providing weak instability/uplift to the region, though moisture support will be weak with a fairly pronounced dry layer in the lower levels. All said, confidence in instability leading to isolated dry thunderstorm chances is very low(10%). However, there is a threat for hot, dry, and unstable conditions to lead to enhanced fire weather potential on new and existing fires across central and eastern OR Tuesday(confidence 40-50%). At this time, confidence not high enough to issue any fire weather highlights for the unstable conditions. The upper ridge will also flatten Wednesday as an upper trough in the Gulf of Alaska ejects into BC. This will introduce a cooling trend into the region, though HeatRisk will remain major across the Columbia Basin and adjacent valleys Wednesday. Surface pressure gradients will also tighten in response to this system, producing breezy winds through the Cascade gaps and into portions of central OR and the Columbia Basin. Little to no surface moisture will make it`s way into the intermountain PacNW, resulting in widespread RHs still in the teens. The combination of the winds and low RHs have warranted the issuance of Fire Weather watch for the Columbia Basin and the Kittitas valley Wednesday. More details will follow in the fire weather section. Excessive Heat warnings and Heat advisories will continue through Wednesday for widespread HeatRisk values in the major category, with localized areas of extreme categories in the Columbia Basin Tuesday. The peak of this heatwave is expected Tuesday as the upper ridge axis moves across the forecast area. In most lower elevation zones, chances of exceeding 105 degrees are between 65-95% Tuesday, while chances of exceeding or meeting 110 in portions of the Columbia Basin are 40-60%. On Wednesday, areas closer to the Cascades are expected to cool by about 5 to 7 degrees into the upper 90s to around 102. However, the Columbia Basin, Yakima valley, and the northern Blue mountain foothills will continue to see the hotter temperatures near 105, with chances of exceeding 105 between 60-90%. Lawhorn/82 .LONG TERM...Thursday through Monday...While the long-lasting ridge will lose its potency by Thursday and we`ll see a relief from widespread triple digits temps, the synoptic pattern in the long term still looks to support relatively hot conditions as well as heightened fire weather concerns via breezy winds through the Cascade Gaps, which could extend well into the Basin. Ensembles are in good agreement that by Thursday, the ridge will flatten out and a more zonal pattern will take its place, however these types of patterns are typically supportive of gap flows due to a favorable orientation of the winds aloft. NBM probabilistic guidance already showing several consecutive days of >70% chance of wind gusts exceeding 35 mph through our usual wind prone areas: the Columbia River Gorge, Kittitas Valley, Simcoe Highlands, and extending into the Oregon Basin. While this zonal pattern may support advection of more mild air through the Cascade Gaps via west winds, the dry synoptic pattern will allow high temps to remain well in the 90s for most of our lower elevation and valley zones, so RHs will likely (70-80% confidence) remain at critical levels well into the teens even as temps begin to cool after the peak of this ongoing heat wave. Much of the period is dominated by this dry zonal pattern, however should note that both the deterministic GFS and ECMWF try to bring in a SW trough through the region around the beginning of next week. Obviously a bit too far out to determine how much moisture would potentially accompany this system, but the potential for mountain showers and thunderstorms always exists with these SW lows. Given how dry the boundary layer will be through the period, however, dry thunderstorms could be a concern as well. Confidence in the forecast beyond Sunday, however, is low (<20%). && .AVIATION...12z TAFs...VFR conditions expected. Skies will be clear with winds light and terrain-driven less than 10 kts. Pilots should be prepared for the potential for High Density Altitude during this ongoing heat wave. Evans/74 && .FIRE WEATHER...A Fire Weather Watch is in effect from Wednesday afternoon through Wednesday evening for wind low relative humidity for fire weather zones OR641, WA690, and 691. A dry system passing to the north will produce breezy winds through the Kittitas valley, eastern Columbia River Gorge, and portions of the Columbia Basin. RHs will remain in the lower to mid teens across these areas Wednesday afternoon, and with a dry airmass in place, recovery above critical thresholds will be slow through the evening and possibly overnight hours. Breezy winds will continue into Thursday in the Kittitas valley, but RHs are expected to remain above critical values. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 102 64 107 69 / 0 0 0 0 ALW 104 69 108 72 / 0 0 0 0 PSC 106 69 110 72 / 0 0 0 0 YKM 105 68 108 70 / 0 0 0 0 HRI 107 66 111 70 / 0 0 0 0 ELN 103 67 106 68 / 0 0 0 0 RDM 102 61 105 61 / 0 0 0 0 LGD 99 62 102 66 / 0 0 0 0 GCD 101 62 105 64 / 0 0 0 0 DLS 110 71 112 72 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning until 10 PM PDT Wednesday for ORZ041-044- 505-507-508-510-511. Fire Weather Watch from Wednesday afternoon through Wednesday evening for ORZ641. Heat Advisory from noon today to 10 PM PDT Wednesday for ORZ049- 050-502-503. Heat Advisory from noon today to 10 PM PDT Tuesday for ORZ509. WA...Excessive Heat Warning until 10 PM PDT Wednesday for WAZ024- 026>029-521-523. Fire Weather Watch from Wednesday afternoon through Wednesday evening for WAZ690-691. Heat Advisory from noon today to 10 PM PDT Wednesday for WAZ030. Heat Advisory from noon today to 10 PM PDT Tuesday for WAZ522. && $$ SHORT TERM...82 LONG TERM....74 AVIATION...74