A high pressure system will move into the St. Lawrence Valley area Tuesday night, bringing clear or partly cloudy skies into the area, the National Weather Service says.

The system will also bring mild or warm temperatures into the area through Wednesday, the service says.

An upper level low-pressure system will sweep through the area Wednesday night and into Thursday, possibly bringing showers or thunderstorms, the service says.

Scattered showers and cooler temperatures are expected to persist into the weekend, the service says.

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The full forecast follows:

• Tonight: Partly cloudy, with a low around 54. Southwest wind 3 to 8 mph.

• Wednesday: Sunny, with a high near 80. Light south wind becoming southwest 5 to 9 mph in the morning.

• Wednesday Night: Partly cloudy, with a low around 61. Calm wind.

• Thursday: A chance of showers, then showers and thunderstorms likely after 11am. Mostly cloudy, with a high near 73. Southwest wind 6 to 13 mph, with gusts as high as 25 mph. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.

• Thursday Night: Showers and thunderstorms likely before 8pm, then a chance of showers. Mostly cloudy, with a low around 58. Southwest wind 3 to 6 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

• Friday: A 40 percent chance of showers before 2pm. Partly sunny, with a high near 74. Southwest wind around 6 mph. New precipitation amounts of less than a tenth of an inch possible.

• Friday Night: A 50 percent chance of showers and thunderstorms after 8pm. Mostly cloudy, with a low around 57. Southwest wind 3 to 6 mph.

• Saturday: A chance of showers. Partly sunny, with a high near 72. West wind 5 to 11 mph. Chance of precipitation is 40%.

• Saturday Night: A 30 percent chance of showers. Partly cloudy, with a low around 53. Southwest wind 5 to 9 mph.

• Sunday: Mostly sunny, with a high near 73. West wind 6 to 8 mph.

• Sunday Night: Mostly clear, with a low around 51. Light southwest wind.

• Monday: Sunny, with a high near 78. Calm wind becoming west 5 to 7 mph in the morning.

• Monday Night: Partly cloudy, with a low around 55. Light and variable wind.

• Tuesday: Partly sunny, with a high near 78. Southwest wind 5 to 8 mph.