Temperature in Mt Prospect IL: Why Most People Get It Wrong

If you’ve lived in the Northwest Suburbs of Chicago for more than a week, you know the drill. You walk out the door in a heavy parka, and by noon, you’re looking for a place to stash your scarf because the sun decided to make a guest appearance. The temperature in Mt Prospect IL is famously fickle. It’s not just "Midwest weather"—it’s a specific brand of atmospheric chaos dictated by the village’s proximity to Lake Michigan and its spot in the sprawling heat island of the Chicago metro area.

Most people look at a weather app, see 40 degrees, and think they’re set. They aren’t.

Honestly, the numbers rarely tell the whole story here. Between the "lake effect" shifts and the wind tunnels created by suburban development, the actual temperature you feel while walking down Central Road can be ten degrees off from what your phone says. It’s a place where 25 degrees can feel like 10, and 85 degrees can feel like a steam room.

The Reality of Seasonal Swings in Mount Prospect

Mount Prospect doesn't do "mild" very well. We basically skip spring and fall most years, crashing headlong from a freezing January into a humid July. According to historical data from the National Weather Service, the average high in January sits around 32°F, but that’s a bit of a lie. You’ve likely experienced those weeks where the "Polar Vortex" dips down, and suddenly we're looking at lows of -18°F or worse.

On the flip side, July brings an average high of 84°F.
But wait.
The humidity is the real killer. Because we’re sitting on relatively flat terrain with plenty of moisture trapped in the soil and nearby forest preserves, the dew point often skyrockets. When that happens, 84 degrees feels closer to 95. You’re not just hot; you’re wearing the air.

Winter: More Than Just Snow

In January 2026, we've already seen how the mercury can dive. Just this week, the temperature in Mt Prospect IL hovered around 14°F with wind chills making it feel like 5°F. That’s the "bite" locals talk about. The wind speed in Mount Prospect averages around 18 mph during the winter months, which is significantly higher than the summer breezes. That wind isn't just a nuisance; it’s a heat-thief. It pulls the warmth right off your skin.

If you’re checking the forecast, look at the "RealFeel" or "Apparent Temperature." That’s the number that actually determines if your car is going to struggle to start or if your pipes are at risk of freezing.

Why the "Lake Effect" is a Wildcard

You’ve heard the term "cooler by the lake." Mount Prospect is about 15 miles inland from Lake Michigan, which is a bit of a geographic "no man's land." We are close enough to feel the lake’s influence but far enough away that we don't always get the cooling relief in the summer.

Sometimes, a "lake breeze" front will push inland. It might be 90 degrees at the Fashion Outlets in Rosemont, but by the time you drive back to Mount Prospect, the temperature has dropped to 78 because the lake air finally pushed through. It’s unpredictable. Meteorologists often struggle with these micro-fronts because they can stall out right over the Des Plaines River, leaving Mount Prospect in a pocket of heat while Des Plaines or Arlington Heights cools off.

Breaking Down the Monthly Averages

If you're planning a move or just trying to figure out when to turn on the HVAC, here is the rough breakdown of what to expect throughout the year:

• January & February: The deep freeze. Highs around 33°F, but lows frequently hit 18°F. This is peak "gray sky" season, with cloud cover nearly 60% of the time.
• March & April: The Great Tease. You’ll get one day that’s 65°F, followed by three days of 35°F and sleet. This is the wettest period for the ground, though June actually sees more rainfall volume.
• May & June: The sweet spot. Highs climb from 70°F to 80°F. June is technically the wettest month, averaging over 4 inches of rain, often coming in via massive thunderstorms that roll in from the west.
• July & August: The swelter. Highs average 84°F, but record highs have topped 100°F in the past. These are the months where the dew point makes or breaks your day.
• September & October: The decline. My personal favorite. The air clears up, the humidity drops, and you get crisp 60-degree afternoons.
• November & December: The slide back into winter. Temperatures drop fast, averaging 48°F in November and 37°F in December.

The Heat Island and Suburban Sprawl

Mount Prospect isn't a rural cornfield anymore. It’s a developed village with plenty of asphalt, rooftops, and concrete. This creates a "micro-heat island." During the summer, the temperature in Mt Prospect IL can stay higher at night than in more rural areas like Hampshire or Huntley. The concrete absorbs heat all day and radiates it back out at night.

If you live near the Metra tracks or the downtown redevelopment area, you might notice your outdoor thermometer stays a few degrees higher than someone living near the Burning Bush Trails Park or the Kensington Business Center. Trees matter. Areas with more canopy cover stay noticeably cooler during those August heatwaves.

📖 Related: Why Seeing 3333 Isn't Just a Weird Coincidence

Misconceptions About the Cold

One thing people get wrong? Thinking it’s always snowing when it’s cold. Honestly, the coldest days in Mount Prospect are usually the sunniest. When an arctic high-pressure system moves in, it clears out the clouds. The sun looks beautiful, but there’s zero insulation. That’s when you get those "diamond dust" days where ice crystals sparkle in the air, but the temperature is hovering near zero.

Actionable Tips for Navigating Mount Prospect Weather

If you want to stay ahead of the curve, don't just look at the high and low. Do these three things instead:

1. Check the Dew Point, Not Humidity: Relative humidity is a bit of a scam. A 90% humidity day in winter feels fine. A 70-degree dew point in July is a nightmare. If the dew point is over 65, prepare to be sticky. If it’s over 70, stay inside.
2. Monitor Wind Direction: In Mount Prospect, a North/Northeast wind usually means cooler, damp air from the lake. A Southwest wind is the "blowtorch" that brings the heat up from the Gulf and the Plains.
3. Prepare for the "Freeze-Thaw" Cycle: Because our temperatures fluctuate so much around the 32°F mark in February and March, potholes are a way of life here. If you see a week of 40-degree days followed by 20-degree nights, keep an eye on your tires and your alignment.

Mount Prospect is a great place to live, but the weather requires a certain level of mental toughness. You need a closet that holds a heavy down coat, a light windbreaker, and a breathable linen shirt—sometimes all for use in the same week. Keep an eye on the barometric pressure too; those rapid drops are what trigger the migraines and the sudden thunderstorms that characterize our wild Illinois summers.

To stay prepared for the next shift, ensure your home's insulation is checked before the November temperature drop and keep a survival kit in your car that accounts for extreme wind chills, not just snow.