An anomaly like this obviously has a non climate change cause. Major blips like this happen from time to time and then quickly fall back to more normal levels. Maybe an unexpected side effect of Hunga Tonga? Just one of many possible culprits.
Also....the scale of that graph greatly exaggerates how big a deal it really is.
This what I've been trying to explain to Jesse. If the troughs dig in right we can get quick hitting cold fronts quickly followed by cool and decent weather. The troughs that cause a solid week of gloom are what I hate.