Late autumn cold followed by a rise in temperature

The typical temperature rollercoaster of fall was already on display this month. The coldest air of the season last week was followed by a warm-up this past weekend. However, AccuWeather forecasters say even colder air is on the way this week.

The recent warm-up phase ensured that autumn foliage lovers had ideal weather for leaf peeping on Saturday. Unfortunately, rain started on Sunday and knocked some leaves off the trees.

This rain was associated with a cold front. In the wake of the front, gusty winds will shed more leaves from trees in locations that have reached or passed their peak.

The biggest change will be in the temperature range. Even though the calendar says it's mid-October, the cold air will be on its way about a month earlier than planned.

“We're seeing this situation in late fall, so it's an early taste of it,” said Tyler Roys, senior meteorologist at AccuWeather.

As the cold air moves over the relatively warmer Great Lakes, another aspect of late fall or early winter will occur.

“Lake-effect showers are expected downwind of the Great Lakes,” Roys noted.

Since it is still October, most showers will occur as rain. In higher terrain and away from the immediate influence of the lakes, at least some snowflakes may mix with the rain. This is particularly the case during the night and early morning hours when temperatures are typically at their lowest.

“Some of these showers could fall as a mix of rain and snow over inland areas of far northern Pennsylvania and southern New York, although snow accumulation is not expected on paved areas,” Roys explained.

With cold air masses and strong winds, AccuWeather RealFeel® temperatures are well below thermometer. For some it will seem like winter has already arrived.

The cold air will move further south and east on Tuesday. Places like Philadelphia, which were forecast to see temperatures rise to 80°F on Sunday afternoon, will not reach 60°F until Tuesday. A similar scenario is likely to unfold in Washington, DC. In both cities, residents and visitors alike have to quickly swap shorts and T-shirts for sweatshirts.

“For many, this could be the time when they are scrambling to make sure they have enough fuel and keep their furnaces on for the duration of this season,” Roys said.

Lake effect precipitation that began Monday will continue through Tuesday and likely Wednesday. Unlike Monday, much of the overnight rainfall on Monday, Tuesday and Wednesday will be confined to locations closer to the lakes. Similar to Monday, mostly rain is expected, although a mix of rain and snow will form in higher elevations and away from the lake shores.

The most widespread frost is expected to occur on Wednesday. By then, even people in the Southeast will experience temperatures that are below historical averages. During the morning hours, residents across the South like Charlotte, North Carolina and Atlanta may reach for their pumpkin spice lattes as AccuWeather RealFeel® temperatures dip into the upper 80s.

A high pressure area will form over West Virginia by Wednesday evening. The closer you get to this altitude, the clearer the sky becomes and the wind becomes significantly weaker. The combination of calm winds and clear skies creates ideal conditions for radiative cooling. This phenomenon occurs at night when heat built up during the day radiates back into space. With temperatures dropping, frost will be a problem Wednesday evening as far south as southern Alabama, northern Georgia and western South Carolina.

“This will end the growing season in some locations,” Roys warned.

For those unprepared for sustained relaxation, there is good news on the horizon. Warmer air will begin to move into the western Great Lakes on Thursday. From Friday through at least the weekend, temperatures in the Ohio and Tennessee valleys, New England, the Mid-Atlantic and the Southeast will be above historical average due to the northward moving jet stream and warmer flow around the anticyclone. Little to no rain is also expected.