The occurrence of extreme hot and dry summer conditions in the Pacific Northwest region of North America (PNW) has been known to be influenced by climate modes of variability such as the El Niño-Southern Oscillation and other variations in tropospheric circulation such as stationary waves and blocking. However, the extent to which the subseasonal remote tropical driver influences summer heat extremes and fire weather conditions across the PNW remains elusive. Our investigation reveals that the occurrence of heat extremes and associated fire-conducive weather conditions in the PNW is significantly heightened during the boreal summer intraseasonal oscillation (BSISO) phases 6-7, by ~50–120% relative to the seasonal probability. The promotion of these heat extremes is primarily attributed to the enhanced diabatic heating over the tropical central-to-eastern North Pacific, which generates a wave train traveling downstream toward North America, resulting in a prominent high-pressure system over the PNW. The ridge, subsequently, promotes surface warming over the region primarily through increased surface radiative heating and enhanced adiabatic warming. The results suggest a potential pathway to improving subseasonal-to-seasonal predictions of heatwaves and wildfire risks in the PNW by improving the representation of BSISO heating over the tropical-to-eastern North Pacific.

众所周知，北美太平洋西北地区 （PNW） 极端炎热干燥的夏季条件的发生受到气候变化模式的影响，例如厄尔尼诺-南方涛动和对流层环流的其他变化，例如驻波和阻塞。然而，亚季节偏远热带驱动因素对 PNW 夏季极端高温和火灾天气状况的影响程度仍然难以捉摸。我们的调查显示，在北方夏季季节内振荡 （BSISO） 阶段 6-7 期间，PNW 中极端高温和相关的有利于火灾的天气条件的发生率显着增加，相对于季节性概率高出 ~50-120%。这些极端高温的加剧主要归因于热带中部到东北太平洋上空的非绝热加热增强，这产生了一列向下游向北美行驶的波浪列车，导致 PNW 上空有一个突出的高压系统。随后，脊主要通过增加表面辐射加热和增强绝热变暖来促进该地区的地表变暖。结果表明，通过提高热带至东太平洋 BSISO 加热的代表性，可以改善 PNW 对热浪和野火风险的次季节到季节性预测的潜在途径。