Following up briefly on last week's post, I took a closer look at cloud cover and solar radiation data from the Fairbanks area, seeking to document the remarkable lack of sunshine in the last few months. All lines of evidence indicate that it has, indeed, been persistently and unusually cloudy in Fairbanks since mid-August. Here's a chart showing the daily solar radiation measured since summer at the high-quality CRN site just to the northeast of town:
Of course it's typical for rain and cloud to increase across much of Alaska in August (see this post), but the change this year was more pronounced than usual for the interior, and the weather remained generally cloudier than normal all the way through autumn.
For the 90 day period ending November 10, the CRN instrument measured less radiation than in any other year, with data going back to 2002. Interestingly, the last 3 years have seen the lowest solar energy in this short history, so it's a persistent anomaly that I strongly suspect is related to the remarkable North Pacific warmth of the last few years.
ERA5 reanalysis data provides a much longer history of estimated solar radiation for the same window, and it sends a similar message:
Of course most of the solar radiation in this autumn window occurs in the first month or so, while the sun still has some strength, so it's worth looking at cloud observations from the airport ASOS for a more evenly distributed perspective on cloudiness. Here's the result: this was the cloudiest autumn since at least the mid-1950s, if the cloud cover observations are to be believed (and there are certainly inconsistencies in the observing method over time).
To get a sense of the spatial extent of the recurring anomaly, here are solar radiation anomaly maps for the August-October window back to 2020, the last relatively sunny autumn in Fairbanks.
Again, the analysis for the whole seasonal period is focused on the earlier part of the window (mainly August) because of the annual cycle. However, the last 5 years have also been cloudier than normal in each month separately, so it's not just a late summer change. The maps below also show a similar trend in the Arctic - at least according to the ERA5 model data. It's not good news for autumn aurora watchers, or for those who enjoy clear and crisp weather at that time of year.
We indeed experience a maritime climate this summer-fall in Fairbanks, and perhaps mainland Alaska. Not much for clear days supported by anticyclones. Nor were there the typically widespread thunderstorms that plague the land some years. Now it's been arid with a finger's depth of snow in the valley. It'll be interesting to see what the coming stratospheric warming event and collapse of the Polar Vortex brings.
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