There is a storm system potentially heading toward the Boston region later in the week that may bring rain, but that “disorganized” and hard to predict weather formation won’t impact an otherwise perfect marathon Monday, according to the National Weather Service.

Though by Wednesday there’s a chance of showers forecast that could last all the way through the weekend, it will be quite a nice race day, according to NWS Meteorologist Kyle Pederson.

Temperatures Monday will be pushing toward the 70 degree range in areas south of Boston when the starting gun goes off for the start of the 128th Boston Marathon. There’s a high temperature of 65 degrees forecast for the city under sunny skies. Pederson said the wind may be “breezy” at times, but not bothersome.

“That’s about as nice as you get for this time of year,” Pederson said.

Temperatures are expected fall into the middle-40s overnight into Tuesday, with mostly clear skies forecast.

Tuesday should be slightly cooler, Pederson said, as more seasonable weather settles over the region and brings highs in and around Boston to around 65 degrees. Winds are again “breezy,” especially west of the city he said, with gusts of 20 mph possible. Overnight lows are predicted to fall toward the lower 40s, and could hit freezing in higher elevations, according to the meteorologist.

Wednesday should be partly sunny but still cooler with the high temperature expected to top out around 60 degrees, though Pederson said it should be less breezy. Clouds roll in after 9 p.m., when the National Weather Service predicts a 40% chance of rain in the greater Boston region.

“Rain chances start increasing Wednesday into Thursday,” Pederson said. “It’s a pretty disorganized system, so it’s a little uncertain how things play out.”

Showers are possible throughout the night, when temperatures fall to the mid-to-lower 40s.

More rain is called for Thursday, according to the Weather Service, with a 30% chance of showers predicted both before noon and after 3 p.m. Even when it isn’t raining, the day is expected to be mostly cloudy, with a high in the lower 50s and an around 15 mph wind.

Rain continues into Thursday night but tapers off after 11 p.m., according to the weather service. Overnight lows around 40 degrees are expected in Boston, with freezing temperatures possible in the Berkshires and northern Worcester County.

Yet more rain is possible on Friday, though the weather service currently predicts just a 30% chance of showers across the region. It should be slightly warmer, however, with an about 12 mph breeze, highs in the upper-50s, and overnight low in the middle-40s.

The weekend could be half wet, according to Pederson, with a 30% chance of rain possible on Saturday and highs in the middle-50s both Saturday and Sunday.

“It’s so far out, and such a disorganized-type system,” he said.

Jennifer Tullio of Sarasota, Florida, jumps for joy at the Boston Marathon finish line on Boylston Street, on Sunday. This will be Tullio’s 8th consecutive year running the marathon. However shortly after last year’s race she was diagnosed with breast cancer. Her hair now short from the medical treatment and still a bit weak, Tullio was asked about how she will do. “It won’t be pretty, but I’ll finish it.” (Photo by Jim Michaud / Boston Herald)