If you’re looking forward to cooler Autumn weather, you’re in for a treat. Today and tomorrow, the Midwest and Northeast remain on the lookout for severe storms. But behind these storms is chilly air, bringing fall right to our doorstep as we close out September.
Some of the country has already experienced cooler temperatures through the beginning of this week, but a high pressure ridge aloft has brought much of the country back to more seasonable, possibly even warm, temperatures over the weekend and earlier this week. The circulation around this ridge has brought fuel to the Midwest and East in the form of warm, moist air. As a shortwave trough aloft moves across the nation it will clash with this high pressure, creating a line of severe storms along or ahead of the associated cold front. While these storms are to be taken seriously, we can at least look forward to what they bring behind them.
This morning, the battling upper-level pressure systems have formed a wave over the US. The high pressure crest sits atop New England, and the inflection point is essentially along the Mississippi River. The battling cold and warm air masses mirror this shape as well, with warmer temperatures in the east and cooler temperatures making their way in from the west.
This low pressure, and the cold air trailing behind it, will continue to move across the Midwest today, where unstable air will be pushed up by the passage of this cold front and form a line of severe, possibly tornado producing, storms. These storms, although annoying, do work to effectively cool down the atmosphere. As a storm roars up, it uses up most of the energy and heat from the warm air, cooling it as upward motion brings it higher into the atmosphere. When these storms are finished, what’s left to move in after them is cooler, drier air. This cold front associated with these storms is currently draped across Lake Huron down to Iowa. It will continue eastward today, bringing the severe weather threat along with it. This trough will deepen due to a jet streak over the Great Lakes and Ontario, enhancing upward motion and increasing severe risk later today for much of Illinois and Indiana.
This time tomorrow morning, the Midwest will have cooled considerably, with temperatures almost 15 degrees below average. This trough will continue to bring its cold air across the east while also bringing storms and severe weather threat with it. For Wednesday into Thursday, much of the Northeast can expect the same as these last two days. Storms ahead of this cold front will bring more autumnal temperatures for Thursday and Friday.
After this cool down, this trough is expected to remain over the US as its flow follows these lines of low pressure down from cold Canada. On Thursday, a strong jet streak will extend down into the Upper Great Plains from British Columbia, draping itself across the Midwest, Great Lakes, and Northeast. This will allow frigid air from the north to finally make its way down into the midlatitudes. By Friday afternoon, the Northern Plains will be blanketed by cold polar air. These cold temperatures will reach down even as far south as Kansas. Montana and the Dakotas can expect lows down in the 30s by the end of the week, which is absolutely frigid for this time of year.
As this trough and jet streak hang out over the northern US, cold air will be advected across the northern half of the country. The northeast won’t see most of colder frigid temperatures until this weekend, but temperatures certainly won’t be warm before then. Make sure you’re all bundled up and cozy because fall has officially arrived, and it doesn’t look like its going anywhere anytime soon.