If you’ve ever stood in a parking lot near the Herndon-Monroe Park and Ride and felt a random, bone-chilling gust of wind, you know that weather in Herndon VA is a moody beast. It isn't just "D.C. area weather." It’s its own thing. Being tucked into the Dulles Corridor means we get a weird mix of urban heat and open-field wind tunnels.
Honestly, the climate here is a game of four very distinct acts. You’ve got the humid soup of July, the "is it spring or winter?" confusion of March, and those glorious, crisp October days that make you forget the summer humidity ever existed.
The Winter Reality Check
January is the boss here. It’s the coldest month, period. You’re looking at average highs of 42°F and lows that dip to 26°F, but let’s be real—the wind chill off the Dulles runways makes it feel ten degrees colder.
Snow is a gamble. We average about 18 inches a year, but it never comes in a nice, even distribution. Most of it dumped in January and February. You’ll get three years of nothing but "wintry mix" (the local term for "slush that ruins your commute") and then a Nor'easter that shuts down the Town of Herndon for three days.
Basically, if the forecast mentions a "Polar Vortex," stay home. The 2026 patterns have shown these Arctic surges are getting more frequent, pushing frigid air deep into the Mid-Atlantic.
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Spring and the Great Pollen Fog
March is the windiest time to be in town. Average speeds hit around 15 mph, but the gusts are what get you. It’s also the start of what locals call "The Pollening."
Herndon is incredibly green. That’s great for aesthetics, but by May—our wettest month with about 5 inches of rain—everything is coated in a thick, neon-yellow layer of pine and oak pollen.
The temperature swings are wild. You might need a heavy coat at 7:00 AM for your commute on the Silver Line and be in short sleeves by 2:00 PM. It’s annoying. You just have to dress in layers.
Surviving the Summer Swamp
If you haven't experienced a Virginia July, imagine living inside a warm, wet sponge. That’s weather in Herndon VA in the summer.
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- Hottest Month: July, with highs hitting 87°F-89°F regularly.
- The Muggy Factor: Dew points peak in late July, making it feel "oppressive."
- Afternoon Storms: We get these massive, sudden thunderstorms that roll in around 4:00 PM. They’re loud, they’re fast, and they usually knock the temperature down ten degrees.
Air conditioning isn't a luxury here; it's a survival tool. Humidity levels average around 64% in the summer, but on a "muggy" day, the air feels thick enough to chew.
Why Fall is the Real Winner
September and October are why people live here. The humidity drops off a cliff. September is actually the clearest month of the year, with blue skies 64% of the time.
The highs sit in the 60s and 70s. It’s perfect. If you’re planning to visit Frying Pan Farm Park or walk the W&OD Trail, do it in October. The colors are peak, the air is dry, and you won’t be sweating through your shirt.
What Most People Get Wrong About Herndon Weather
A lot of people assume that because we’re inland, we don't have to worry about hurricanes. Wrong. We get "remnants."
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When a tropical storm hits the coast, Herndon often gets the tail end—meaning days of relentless, flooding rain and high wind risks. According to First Street data, Herndon actually has a "moderate" wind factor risk. We’ve seen sustained winds in historical events that can top 60 mph, which is more than enough to pull down the massive old-growth oaks that line our residential streets.
Also, the "January Thaw" is a real phenomenon. You’ll get a random 60-degree day in mid-January, everyone goes to the park, and then forty-eight hours later, it’s 20 degrees and snowing. Don't let the thaw fool you into putting away your salt melt.
Actionable Survival Tips for Locals
- The Sump Pump Test: If you have a basement in Herndon, test your sump pump in late March. April and May rains are no joke, and the water table here is higher than you think.
- Car Prep: Change your wiper fluid to a winter mix by November. The "blue stuff" freezes on the Dulles Toll Road when the temperature hits 15°F at 60 mph.
- Emergency Kit: Keep three days of water and a battery-operated radio. Power outages in the older parts of Herndon (near Elden Street) can happen during heavy ice storms.
- Tree Maintenance: Trim any branches overhanging your roof before the winter "ice" season starts in December.
Herndon is beautiful, but the weather requires a bit of respect. Whether you're dealing with the summer "swamp" or the winter "slush," being prepared is the only way to keep your sanity.
Check your local NOAA alerts frequently. The weather here changes faster than the traffic on 28.