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Forecast: A good chance for widespread frost

Issued September 10, 2018: Covering the period from September 12 to September 19

As we slowly slide into fall, it looks more likely that most, if not all, regions will see their first fall frost during this forecast period. Before you get all depressed, it doesn’t look like the shot of cold air will last long, as the models are pointing toward a return to more “summer”-like conditions over the second half of the month.

To start off this forecast period, the weather models show us in a fairly strong southwesterly flow. We will be stuck between a large area of warm high pressure over the eastern U.S. and a large cool area of arctic high pressure to our northwest. Between these two features, several areas of low pressure will develop and lift to the northeast, keeping us unsettled. The first of these features will slide off to our northeast on Wednesday, resulting in partly cloudy skies with daytime highs near 20 C and overnight lows around 10 C. Two more lows will quickly follow Thursday and Friday, bringing clouds and showers. Daytime temperatures will be a little cooler with the clouds, as highs are expected to be in the 14 to 18 C range and overnight lows around 7 to 10 C.

Each of these lows will slowly help to drag down the arctic high, so by the weekend we will begin to feel colder weather. Saturday looks to be a transition day with a mix of sun and clouds and temperatures more than likely falling during the day. If we do clear out by late Saturday, we will probably see the first widespread frost Sunday morning, as the weather models show overnight lows in the 0 to -2 C range, with the coldest temperatures over northwestern regions.

The arctic high looks like it will stick around for a few days, bringing sunny skies in the morning, a mix of sun and clouds in the afternoon, and clear skies at night. There is a good chance for more widespread frost on both Monday and Tuesday mornings before the high moves off to the east and we start to see southerly winds develop Wednesday. This should help boost our temperature back up to more seasonable mid-September values for the second half of next week.

Usual temperature range for this period: Highs, 13 to 24 C; lows, 2 to 11 C.

About the author

Co-operator contributor

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.

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