You’re sick of it. I’m sick of it. And you know what I’m talking about. It seems that we just can’t catch a break from Mother Nature.
Since April 1st, we have had only two stretches of three consecutive days without rain. One of them was April 1st through 3rd. And it has rained on most of our weekends.
Making matters worse is that all of us have received more than ten inches of rain since April 1st…between two and five inches above the long term average for the same period. Farmers are really struggling, and so are businesses who depend upon the weather cooperating.
Our sump pumps are really getting a workout…and those that failed have created an ocean in some basements.
Lake levels are at record highs, so shoreline areas are in a constant state of flood awareness. And the mosquito population is going to explode with all of the standing water.
So what in the world is going on?
As usual, this discussion starts with the jet stream, which is the band of strongest wind aloft. It’s the dividing line between warm and cold air, and is the storm track that guides low pressure systems across the country.
Since April, the jet has averaged a configuration as depicted below:
As you can see, there has been a dip (trough) in the west, and a rise (ridge) in the east. And there we are in-between. For weeks now, you’ve heard us talk about a front hanging around that just doesn’t seem to go away.
That’s because the front is parallel to the wind aloft. When the steering winds are aligned with the same orientation as the front, the front just doesn’t move very far.
Normally, those troughs and ridges are progressive. In other words, they move from west to east across the country. Every trough brings a front ahead of it. The front moves through, and then keeps on moving. But this pattern has remained largely intact for two-and-a-half months, and the fronts have become unwanted house guests that just won’t leave.
The big question is: what is causing this to happen?
There are many atmospheric and oceanic circulation patterns around the globe that impact the jet stream’s position.
The most famous are El Nino and La Nina. But there are many other important ones, such as the North Atlantic Oscillation, the Arctic Oscillation, the Antarctic Oscillation, the Pacific-North American Pattern, the Pacific Decadal Oscillation, and the Madden-Julian Oscillation.
Right now, we don’t have a clear picture of which, or what combination of these, are forcing the jet stream to stay the way that it is, but there’s one more important part of the story that needs to be considered: global warming.
The temperature difference between northern and southern latitudes is key to the jet stream’s strength (i.e., the strength of its wind). A direct consequence of Earth’s warming climate is that northern latitudes are warming much faster relative to southern latitudes (which was one of the earliest predictions, and has verified perfectly).
The reduced temperature difference is apparently weakening the jet stream, and this results in more pronounced troughs and ridges. And the deeper those troughs and ridges are, the slower they move.
Furthermore, the warming climate enhances evaporation of ocean water around the world. The increased water vapor in our atmosphere is what storms turn into precipitation, and this also results in more extreme precipitation events – ask anybody in the central Plains this spring about THAT.
So it’s very plausible that climate change is part of the reason we’ve had such an active and wet spring. But wait – there is actually some good news!
Long range computer models (called ensembles), suggest that we’ll finally transition to a more traditional summer pattern for July and August.
Take a look at the 90-Day temperature forecast issued for the June through August period by the Climate Prediction Center (CPC):
Notice how we are near the edge of above average area. If we have a cooler than average June, then this forecast means that we’ll need some above average temperatures in July and/or August to push three-month temperatures near or above average.
As for precipitation, take a look at this:
The CPC is projecting our June through August total precipitation to be not far from average.
Given how much rain we’ve had, we’d need some dry weather to get back closer to average.
So don’t write off the entire summer yet. It’s very likely that we’ll get back to some great summer weather. And for those of you with short memories (or weren’t born yet), you haven’t seen a truly crummy summer unless you lived through the Bummer Summer of 1992: following Mount Pinatubo’s explosive eruption the previous fall, the planet cooled, and we had an entire summer of this past week’s weather.
We even set some records for coldest high temperatures. We aren’t there yet.
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