Astronomical Autumn begins tomorrow at 10:49 AM EDT. Meteorological Fall began a few weeks ago when the calendar turned from August to September. The first freezes have come to parts of the northern states this week as more evidence that Summer is ending. So, it seems a good time to look at some of the Autumn weather outlooks around the web. We have a lot of images to get to, so let’s get rolling…
The CPC is projecting above normal temperatures for much of the lower 48. The only projection for below normal temperatures is along the West Coast. By my count, there are only 4 or 5 states (can’t tell with Louisiana) that are not projected to be above normal in any part of the state. Generally speaking, only the states that border the Pacific Ocean (and Nevada) and the southeastern states are not given a reasonable chance to experience above normal temperatures.
As for precipitation, the best chances for above normal rain are in Arizona and along the Gulf Coast. The Northwest has the best chance for drier-than-normal conditions this Fall. At least according to the CPC. Accuweather disagrees…
They see the Pacific Northwest experiencing wet conditions in the early-to-middle portion of the season with this shifting a little southward later. Otherwise, there seems to be reasonable agreement with the CPC. Accuweather sees the warm conditions in the East, especially along the Canadian border. They also see the above normal precipitation along the Gulf Coast (although Accuweather slides this area of above normal precipitation up the Atlantic Coast into southern Virginia). The only other disagreement may come in parts of the west where Accuweather projects below normal temperatures in the northern Rockies.
If two outlooks are good, a third must be better… (well, not necessarily)
Clearly, this web site divides their forecast areas up and summarizes their projections within that area. (It’s not a really smooth graphic when northern Kansas is one degree below normal in November while the southern half of the state is one degree above normal.) The only reason I’m showing this is because it runs counter to the previous outlooks and, if it ends up being right… well, that would be hilarious. I’m not going to bother with their precipitation maps. You can check them out at the linked page.
If you’re wondering how long-range, seasonal weather predictions are made, it’s usually a combination of long-range climate models and analog forecasting. Analog forecasting involves looking at how seasons from years past with similar conditions are panned out. The conditions they look at are things like El Niño/La Niña and the Pacific Decadal Oscillation – indices that slowly develop over time and usually last in their state for the entire season (and longer). This year, there is a developing El Niño (although it seems like a weak El Niño right now) in the equatorial Pacific Ocean and the PDO is in its’ cold phase. Meteorologists will look at past years where there was a weak El Niño and cold PDO to determine if there’s a pattern in temperature and precipitation anomalies. If there seems to be a strong pattern in these analog years, forecasters will tend to put more stock in history than climate models. Otherwise, it will probably be a blend of the two, but with considerably less confidence. (Not that there’s ever great confidence in a seasonal outlook.)
We’ll check back at the end of the season to see how these outlooks performed.
Bonus Canadian Fall outlook!!….
I’m not sure how we’ll be able to check this for accuracy at the end of the season, but I’ll try. They seem to agree with some of the US outlooks with warmth along the eastern US/Canadian border and perhaps below normal temperatures along the Pacific coast. It appears they strongly disagree with Accuweather’s prediction of below normal temperatures in the northern Rockies. Of course, keep in mind that above normal temperatures in Canada during the Fall are still some cold temperatures – especially that pocket of above normal temperatures projected near the Arctic. I wouldn’t exactly throw on the swimming trunks and head toward the North Pole.