Today is the first day of astronomical fall. The days are growing noticeably shorter, the leaves are already changing, and the morning air is crisp and energizing. It’s the most wonderful time of the year (only for some of us!), so naturally, summer has to linger and screw it up. Most of the United States will see warmer-than-normal temperatures for the next week or two thanks to a jet stream that’s stuck in heat mode.
As with all things, it’s safe to blame Canada for our current atmospheric logjam. They’re too quiet to be innocent. The above image is a snapshot from this morning’s run of the GFS model, showing the winds at the 250-millibar level, which is right around where the bulk of the jet stream lives.
By tomorrow evening, we’ll see large troughs of low pressure off the east and west coasts of Canada, and stuck in between these troughs will be a ridge of high pressure.
Ridges lead to very boring weather for those stuck under their influence—not much rain, calm winds, and warm temperatures. It’s a weather blogger’s worst nightmare.
With the exception of a few twists and turns, and occasional disturbances along the way, this pattern will largely stick around through next week, keeping almost everyone east of the Rockies (and not in the Carolinas) dry and comfortable to end September.
It’s going to be abnormally warm—and by quite a bit—in much of the country for the duration of Ridgepocalypse 2015: Fall of Doom. Models are painting high temperatures well above average for much of the central and eastern parts of the U.S. and Canada between now and the middle of next week. Some folks could see highs more than 15 degrees above average if it pans out.
Above you see the GFS model’s current thinking for temperature anomalies (in Celsius) on Saturday evening, with the most abnormal warmth painted across the northern Plains and south-central Canada. Advance a few days (to Tuesday afternoon), and you’ll see that the trend continues as it moseys southeastward.
Such large temperature anomalies aren’t exactly as bad as they sound, of course. It would suck in the dead of summer, yes, but this is late September, and average highs range from the 60s near the border to the 70s in the Midwest. The fact that you’ll be able to go without a jacket in North Dakota is noteworthy now. Welcome to fall.
The latest forecasts from the Climate Prediction Center reflect model trends, showing extremely high confidence in temperatures that are above average. These maps don’t show you forecast temperatures—dark red doesn’t mean you’ll roast—but rather the forecasters’ confidence in above- or below-average temperatures. Warmer colors equate to higher odds of temperatures coming in warmer than average for the duration of the period.
Forecasters are very confident that the Great Lakes and Ohio Valley will experience an extension of late summer for the next ten days, with lower (but still considerable) odds of comfortable warmth blanketing everyone except for Oregon and Washington.
What changes when you extend that period a little bit?
Not too much.
The more things change, the more they stay the same. The weather should get more interesting in a few weeks.