October has started off unseasonably cool and dry thanks to the weather pattern in the upper levels of the atmosphere. Take a look at the map below, showing the weather features at about 18,000 feet up. You'll see a large trough (or elongated low pressure system aloft) delineated by the dashed brown line extending through the eastern U.S. and a ridge (or elongated area of high pressure aloft) over the western U.S. We're on the backside of the trough, which is feeding cool Canadian air across the eastern U.S. Being on the back of th trough, our air at this level is feeding into the Mid-South from the northwest - what we in the business commonly refer to as "northwest flow." Typically, this will mean cooler a cooler airmass and the potential for fast-moving upper-level systems to dive around the backside of the trough and bring us some form of "weather." One of those is passing by this evening and bringing a few clouds, but nothing more due to very dry conditions below 18,000 feet.
The trough will continue to affect our weather for the next 36 hours or so, until the ridge to the west scoots east and lands overhead. Ridges aloft typically mean warmer weather and dry conditions. So, the forecast calls for warmer temps (back into the 80s) this weekend as the ridge moves in, with no rain in store. By the middle of next week, the next trough, shown on the map over the eastern Pacific, will move in and bring a chance for precipitation. Now you know how upper-level systems can affect our weather down here on the ground!