It seems to be winter now, with highs mostly in the 40s (or the 50s, if we’re lucky) and overnight lows in the 20s and 30s. Wasn’t it in the 70s just yesterday? Somehow, it feels like we missed out on fall.
And the weather records confirm that feeling. The temperature at Wilmington, DE (the nearest weather station with detailed on-line records) reached 79 on November 11. But then, temperatures plummeted. The high was just 38 on November 20, and the low was 24 that night.
Temperatures have recovered a bit since then, but it’s still cold. The graph below tells the story of our November: the first 12 days were unusually warm, and then the cold set in.
Google tells me it wasn’t just our area or just this year: this is an increasingly common weather pattern. There’s a good writeup at Yahoo News. It seems that two factors are at play. The global warming trend is extending the summer weather, while arctic polar vortex events are happening earlier and extending farther south than previously.
It isn’t clear what’s causing the change in the polar vortex, but one theory is that the loss of arctic ice, and the ensuing warming of the sea in that area, is an important factor in destabilizing the polar circulation, causing southward excursions of cold air.
If this is a permanent change, we may find ourselves telling future generations about the pleasant fall weeks we once enjoyed.