Weathercatch: What is a monster ridge and why does it make our weather hot?

<p><p>Six years ago this week, things were heating up. Again.</p></p><p><p>An enormous upper-level ridge of high pressure over the West Coast that produced record-high temperatures and severe drought during summer 2015 had finally weakened and shifted. But the second week of September, it came back.</p></p><p><p>Meteorologists coined it a “monster ridge,” a persistent, sprawling ridge of high pressure that behaved like a wall, blocking cold fronts and Pacific storms from entering the region.</p></p><p><p>Toward the tail end of that monster ridge, temperatures cooled and then skyrocketed. From Sept. 9-13, much of the Inland Northwest experienced above-normal temperatures in the 80s and 90s. In Spokane, the heat spiked just short of 90 degrees on Sept. 12. The city’s average high for that date is 75.</p></p><p><p>Sounds a lot like this year, doesn’t it? After all, we’re emerging from a summer scarred by extraordinary heat and drought conditions, followed by a cool-off in late August and a steep warm-up that began on Labor Day.</p></p><p><p>Yes, a monster ridge is behind our abnormally hot, dry conditions this year, but it’s a different beast than the one that dominated our weather six years ago.</p></p><p><p>That monster ridge impacted our weather not just for a few months but for a few years. Stretched along the entire West Coast from northern Washington to Southern California, it pumped warm, dry air inland from 2014 to 2016. Hardest hit was California, which suffered a horrific drought.</p></p><p><p>While the ridge shifted position from time to time – allowing cool air or a storm system to slip through – it wouldn’t subside. The high-pressure pattern was so freakish that the term used to identify it was changed from a monster ridge to the “ridiculously resilient ridge” by UCLA climate scientist Daniel Swain. Shortened to RRR, the atmospheric blocking phenomena most impacted Washington from 2015-2016.</p></p><p><p>Fortunately, the current ridge driving our region’s abnormal heat, drought and wildfires is smaller and less stubborn than the RRR. And it’s not nearly as high, which is important because the higher the pressure, the stronger the wall that keeps out cooler temperatures and drought-busting precipitation.</p></p><p><p>Also, we don’t have a super-charged El Niño weather pattern like we did in 2014-16, when the periodic warming of the equatorial Pacific Ocean released even more heat into the atmosphere on top of that generated by the RRR.</p></p><p><p>Overall, we’re much better off this year. Chances are, this particular monster ridge will scatter and disappear before long, leaving us to celebrate the arrival of much-needed rainfall. We have a resilient ridge, but it’s far from ridiculous.</p></p><p><p>Temperatures this weekend should run slightly cooler and more seasonal than the hot temperatures we experienced during the workweek. The classic September weather we love is in store: temperatures in the mid-to-upper 70s with generous sunshine and blue skies.</p></p>