Joe Lundberg

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September in July From the Rockies to the Appalachians

July 30, 2014; 11:17 AM ET

Wednesday, 11:55 A.M.

Okay, where did summer go? Who took it away? I went out for my usual Tuesday evening group ride last night here in the State College, Pennsylvania, area, and it was NOT warm. I wore a long-sleeved Nike undergarment to keep my core AND arms warm on a cloudy, chilly evening (by July standards) with temperatures only in the mid-60s. And there were many others who dressed similarly! Just look at the highs from Tuesday across the Midwest, Great Lakes and Ohio and Tennessee valleys into the East:

Normal highs in most of this area are 80 or better and closer to 90 in the Tennessee Valley and parts of Virginia. So, as you can see, yesterday was much below average and compares very much to the middle and latter stages of September!

Where it is raining today in the eastern Rockies and parts of the southern Plains, high temperatures will be some 20 degrees or more below average, just stunning for the end of July. In fact, it would be more typical of October in some locations, like in Colorado down into Kansas, Oklahoma and North Texas, with highs just in the 60s and 70s.

This is all being caused on the grand scale by the deep upper-level trough of low pressure from Quebec and Ontario down to the Tennessee Valley and Deep South:

The feature that dumped heavy rain on Colorado yesterday afternoon into last night is, indeed, sliding across the southern Plains now and will reach the lower Mississippi Valley tomorrow with rain and thunderstorms. And where it's cloudy and rainy tomorrow, look for another day with temperatures far, far, far below average.

Around the Great Lakes, it will be another afternoon with temperatures held in check underneath this upper-level trough, though at least there's enough dry air around now that there will be some sunshine to bring the highs up from yesterday's levels. Still, the trough in and of itself represents an area with colder-than-average air aloft, so as the sun continues doing its work heating things up, the boiling point will be reached, leading to a scattering of showers and thunderstorms that will quickly bring temperatures back down to rather chilly levels for late July.

If you're expecting a quick rebound to something more akin to typical summer weather, especially in the heat department, well, think again. This trough, while weakening over the next few days, won't easily vanish. Here's the 12z NAM 500mb forecast for Saturday afternoon:

In fact, there's still plenty of blue on the maps for next week. Look at this chart, a forecast of the temperature departures for the period Aug. 6 through 13:

Even though this deep and wide trough clearly weakens this weekend and into next week, it doesn't simply vanish, and it isn't being replaced by any kind of upper-level ridge, either. There will be some ridging over the Rockies this weekend into early next week to promote some warming, but it's not going to last for very long, as still another disturbance will dig into the Plains states later next week to renew some degree of cooling in the Plains and Mississippi Valley.

At least in the East, the humidity will return this weekend, so in that regard it will feel a bit more like early August, though it will do so at the price of numerous showers and thunderstorms that may lead to some flooding. It will also keep the daytime highs down below normal until some drying tries to take place early next week.

If you really do like the heat, head west. The Northwest is hot and dry once again and will pretty much stay that way through the weekend with 90s and 100s common around much of Oregon and Washington. The Southwest, of course, is hot, but there will also be some afternoon and evening thunderstorms to contend with across Arizona in the coming days thanks to the summer monsoon. There, at least, the weather is much more typical of July, rather than September.

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About This Blog

Joe Lundberg
Joe Lundberg, a veteran forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.