Dip in the jet stream to usher in refreshing air mass across the Ohio Valley, mid-South

 By Brandon Buckingham, AccuWeather Meteorologist

Published Aug. 17, 2020 6:07 AM

Residents across the Ohio Valley and mid-South have been all too familiar with hot and humid conditions this summer, but a break from the searing heat and humidity is in store this week as a cold front is set to sweep southward.

So far, August has featured temperatures much closer to climatological averages typically observed across the nation's midsection; a much-needed break from the heat that baked the region during the month of July. As daylight hours continue to decrease as we approach the autumnal equinox, most locales are currently at, or just past their hottest days (on average) of the year.

As temperatures begin to lower across the Northern Hemisphere, the atmospheric jet stream, which can be a driving force behind day-to-day weather has the ability to dip farther south, and in the coming days, it will do just that.

"This week, many locations in the Ohio Valley and mid-South will experience high temperatures 10-15 degrees lower than the warmest temperatures of last week," AccuWeather Meteorologist Mary Gilbert said.

Along with the lower temperatures, the air mass dragged southward by the jet stream will also feature a lower moisture content, resulting in much more tolerable humidity levels and largely dry conditions.

Prior to the arrival of cooler air however, a few showers and thunderstorms will be possible along a cold front that will sweep southward. During the day on Monday, places like St. Louis, Champaign, Illinois and Lafayette, Indiana, will be in the path of potential wet weather from the advancing cold front.

For the aforementioned cities, Monday may end up being the only day this week with rainfall in the forecast as a much drier air mass will get ready to settle in.

The threat for wet weather will then slide southeastward into the day on Tuesday, targeting portions of the mid-South. Cities next in line for a few scattered showers and thunderstorms include Louisville, Kentucky, as well as Nashville and Knoxville, Tennessee.

In the wake of this unsettled weather, a refreshing gift from Mother Nature is in store across the Ohio Valley and mid-South into midweek as cooler and drier air settles in. It is still August however, so "cooler" is somewhat relative here. With that said, many locales can expect high temperatures in the upper 70s to lower 80s during the afternoon.

The biggest form of relief will come during the overnight hours, as mainly clear skies can allow temperatures to fall into the 50s and 60s, allowing residents to open up the windows to let some fresh air inside.

"In conjunction with cooler daytime highs, cooler overnight lows will help to reduce the demand on area energy grids as many residents will be able to cool their homes by opening windows and turning off air conditioners overnight," Gilbert added.

The cooler air mass will continue to sink into the Deep South into midweek; however, the push of more refreshing air will not be quite as noticeable compared to areas farther north. Still, places like Huntsville, Alabama and Tupelo, Mississippi, who typically observe high temperatures in the lower 90s, can expect afternoon temperatures to remain limited to the upper 80s. Overnight low temperatures will also be a touch lower in these locales at midweek, dipping down into the middle to upper 60s.

The dip in the jet stream across the Deep South will help to play a role in producing wet weather for areas farther east into late week, as the steering winds aloft will aid in bringing a surge of moisture into the Southeast.

Well above-average warmth, like that currently being observed across much of the western United States, will remain at bay across the Ohio Valley and mid-South through the remainder of the week as the jet stream pattern is likely to remain relatively unchanged.

Temperatures will slowly rebound close to seasonable levels late week and into this weekend, and along with that, a return of wet weather will expand across the region by this weekend.

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