Orillia will enjoy a notably mild autumn day with fog lifting through the morning and a high close to 17 °strong> °C, but a sharp temperature swing is expected overnight with skies turning mainly cloudy and a low near 8 °C — followed by a plunge to around −5 °C by Monday night.
What to expect through the day
This morning's dense fog is forecast to break up as the morning progresses, giving way to sunshine and a warm afternoon. Environment Canada–based data driving the local forecast indicates a steady rise through the late morning and early afternoon hours, with the warmest conditions between about 2 p.m. and 5 p.m.
| Time | Temperature |
|---|---|
| 9 a.m. | 8 °C |
| 12 p.m. | 12 °C |
| 3 p.m. | 16 °C |
| 5 p.m. | 17 °C |
Evening and overnight
After the afternoon warmth, conditions turn mainly cloudy tonight with a risk of a few showers overnight and a low near 8 °C. Winds will be light to moderate, but a change in flow is expected on Monday with northwest winds increasing later in the day.
Early-week outlook and consequences
Monday brings a cooler profile: cloudy skies and a daytime high closer to 13 °C, with northwesterly winds becoming noticeable later in the day. The most significant change arrives Monday night when calm, clearish conditions allow radiational cooling and temperatures to fall sharply — a forecast low near −5 °C has been posted for Monday night.
- Daytime warmth will make outdoor activities comfortable today; expect sun and milder air.
- Fog this morning may reduce visibility for early commuters; allow extra travel time until visibility improves.
- Prepare for a large diurnal swing Monday night: frost is possible where temperatures drop to freezing or below.
These rapid swings between daytime warmth and near-freezing overnight lows are typical in the transition to late autumn and can affect sensitive plants, uninsulated pipes, and road surfaces. Gardeners should be cautious about tender plants, and motorists should be aware that shaded roads could develop frost or slippery patches early Tuesday morning.
Seven-day snapshot
The short-range forecast shows a variable pattern with mostly cloudy conditions and modest daytime temperatures through the rest of the week. A mix of sun and cloud returns intermittently with the chance of a few light showers later in the week. UV levels today are moderate, so brief sun exposure poses low to moderate risk.
| Day | Forecast high |
|---|---|
| Today | 17 °C |
| Monday | 13 °C |
| Tuesday | 8 °C |
| Wednesday | 12 °C |
| Thursday | 16 °C |
Practical advice: drivers should be alert for patchy fog this morning and possible frost on Monday night into Tuesday. Homeowners with vulnerable outdoor plants should consider protective coverings before the cold snap. Otherwise, the mild afternoon provides a good window for outdoor plans.
Weather remains changeable through the coming week, so continue to check updated forecasts and local advisories for any shifts in timing or intensity of precipitation and temperature extremes.
