An incoming cool down drawn by a low pressure passing through the Northern Tier will foreshadow a more prolonged stretch of below average temperatures across much of the central and eastern US by the end of this month, just in time for meteorological fall. As that low pressure and its associated warm and cold fronts push through late-week, severe weather will also be a threat from the upper Midwest on Thursday to the Northeast on Friday.
Ahead of the cold front will be hot and humid conditions as high temperatures rise into the 90s across many areas of the Midwest, which is up to 20 degrees above average. Behind that front to the north and west will be the complete opposite: temperatures that are below average. Highs on Thursday across the Northwest and northern Plains will generally be 10 to 20 degrees cooler than normal. Some towns in the Dakotas and eastern Montana will even be as much as 30 degrees below normal, which translates to actual high temperatures into the 40s and 50s. Yep, fall is coming.
The front will push through overnight, allowing for cooler and drier air to ooze into the Midwest on Friday while the Northeast warms up ahead of that cold front. In the Northeast, temperatures will generally be in the 70s but up to the 80s in the eastern Great Lakes region, which is up to 25 degrees above average. Now contrast that behind the front where high temperatures will range from the 50s to 70s. That is generally 10 to 15 degrees below normal.
This cool down will not last too long, however. Temperatures will return back to normal to eventually slightly above average levels by the end of the weekend. On Saturday, conditions across the Plains, Midwest, and Northeast will be up to 10 degrees below average in most areas, which means highs will be in the very comfortable 60s and 70s.
Temperatures will then rebound on Sunday as the jet stream pattern briefly takes on a classic, zonal flow, which means upper-level winds will move from west to east, therefore allowing for near-seasonable conditions. Once you get into the Northwest and northern Plains, that’s where you’ll notice signs of the next incoming cool down. This one will likely last for an extended period of time, however.
Those cooler temperatures, which is associated with a trough, will gradually move east across much of the central and eastern US, first affecting the Plains early- to mid- next week, then the Midwest midweek, and finally the Northeast and Mid-Atlantic late-next week. The I-95 corridor and coastal areas of the Northeast and Mid-Atlantic should remain seasonable. Not only will there be cooler temperatures but also wetter weather, especially in the central US. Across the Southern Tier, there won’t be much of a cool down. Instead, temperatures will be above average to end the month and into the start of October thanks to an elongated upper-level ridge of high pressure.
How long will this cool down last? Likely through the start of October before temperatures return closer to normal, although there aren’t as many signals that point to a pronounced area of above or below average temperatures during the latter half of October.