Joe Lundberg

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Heat, Chill and Floods

July 14, 2014; 11:20 AM ET

Monday, 11:50 a.m.

The weather pattern across North America is decidedly amplified. There is a lot of north and south movement in the jet stream these days, and that's carrying a lot of heat pretty far to the north in western Canada. At the same time, there a blast of autumnal air entering the northern Plains and Midwest, a shot of cool and dry air that will make deep inroads into the southern tier of states the rest of the week. And before it reaches the South and East, it will generate a lot of showers and thunderstorms that will lead to areas of severe weather and flooding.

Let's start with the jet stream forecast for this evening, with the departures from normal superimposed on that graphic:

The two features that stand out the most are the upper-level lows from the Midwest to northern Quebec, and the strong ridging over the West and Northwest way up into central and western Canada. Look at some of the highs from Sunday:

I have witnesses to that heat over the interior of southern British Columbia over the weekend, as my coach Lindsey Miller was at a camp in Penticton in preparation for Challenge Penticton, the Ironman competition I'm entered into Aug. 24. I sure hope that ridge is down by then! At least in the short term there will be some changes in western Canada and the Northwest. While the blistering heat continues through the heart of the workweek, an upper level trough will come inland Thursday to first trim the heat in western Canada, then on Friday into the start of the weekend in the Northwest.

In contrast to all that heat, the Plains and Midwest are now undergoing a transformation to a much cooler weather regime. The upper level low will get about as far south as it is going to get late tonight and tomorrow morning over Lake Michigan, but the effect of the intense upper level low will be felt much beyond that point. In the end, it will drive a cold front off the Northeast and mid-Atlantic coasts late tomorrow night and Wednesday, and off the Southeast coast later Wednesday. It will even get down to the Gulf Coast, though it will be hard to imagine this front, even if does get to the Gulf Coast, having a significant reduction in the humidity levels in Florida. Regardless, it sets us up for a huge area with large negative temperature anomalies right at a time when the heat should be nearing its peak. Look at the projected anomalies for Wednesday:

You can rest assured that record lows will be set, and I'm pretty sure there will be a number of record low maximum temperatures set as well. Do be a little cautious, though, as that little feature rolling through the Northwest today? Well, that dives southeastward tonight and tomorrow, the out into Kansas and Oklahoma by Wednesday. That disturbance will ignite showers and thunderstorms, and they will probably prevent the coolest air from getting past the Red River Valley or all the way to the Gulf Coast. And as it cuts across the lower Mississippi Valley Thursday, the showers and thunderstorms will follow, and they may have an impact on temperatures across the South and into the East Friday into the start of the weekend.

Before that disturbance is even a thought over the horizon, the East will be sticky with a lot of showers and thunderstorms ahead of the cold front. Dew points are in the 70s in most places, and it's not going to take much to generate showers and thunderstorms, some of which will be severe, and some of which will produce flooding downpours.

Several inches of rain are likely to inundate parts of the mid-Atlantic and New England through tomorrow night, with some of that wet weather lingering right into Wednesday morning over eastern New England before somewhat cooler and less humid air takes over for the rest of the week. I say somewhat, because the intensity of the chill out in the middle of the country will fade by Wednesday and Thursday as the upper-level low opens up and lifts out to the northeast rather quickly.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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About This Blog

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