What's the Weather Like in Baltimore During May?

May in Baltimore brings mild to warm temperatures, moderate rainfall, and frequent sunny days suitable for outdoor plans. Average highs reach 75°F, with lows around 55°F. Humidity begins to climb mid-month, and afternoon thunderstorms occur on roughly 8 to 10 days. Pack layers, an umbrella, and sunscreen; you'll need all three.

Temperature and Humidity Patterns

Early May still carries spring coolness. Mornings often fall into the 50s, and you'll want a light jacket for walking the Inner Harbor before 10 a.m. By late May, highs consistently reach the mid-70s, and humidity levels rise noticeably, making the air feel heavier than the thermometer suggests. The shift typically accelerates after May 20th.

This matters for planning. If you're visiting May 1 to 10, pack a sweater and long pants as backup. If you're here May 21 to 31, plan air-conditioned breaks into your itinerary, especially if you're walking Fells Point or Federal Hill for extended periods. The humidity jump is sharp enough that locals often refer to "pre-humidity May" and "actual May."

Rainfall and Thunderstorm Frequency

Baltimore averages 3.5 to 4 inches of rain in May, spread across multiple days. Unlike spring's steady rain, May brings afternoon and evening thunderstorms. These develop quickly, last 20 to 40 minutes, and clear just as fast.

The practical implication: check hourly forecasts (not daily ones) if you're planning outdoor activities between 2 and 7 p.m. The National Weather Service Baltimore/Washington office provides hourly updates at weather.gov. A compact umbrella fits in any bag, and most downtown hotels stock them if you forget. Actual rain that cancels plans happens on fewer than half of May days, but the possibility shapes your schedule.

Outdoor Activity Windows

Full sun and 70-degree temperatures make mid-morning (9 a.m. to 1 p.m.) the prime window for activities like the Baltimore Museum of Art's sculpture garden, walking Canton Waterfront Park, or exploring neighborhoods on foot. You'll see locals doing this consistently mid-May onward.

If you're planning a harbor cruise or open-air activity, aim for mornings. Afternoon heat and humidity build steadily after 2 p.m., and that's when thunderstorm cells form. Evening (after 7 p.m.) cools enough for comfort again.

Comparison to Other Months

May is warmer than April but cooler and less humid than June. The difference matters: June averages 7 to 8 inches of rain and sustained humidity that keeps nighttime lows above 60°F. April still sees frost risk and unpredictable cold snaps. May splits the difference, making it genuinely pleasant for the first half but transitioning toward summer heat by month's end. If you dislike humidity, early May is your window.

What to Pack

Layers work better than a single heavy jacket. Bring a button-up long-sleeve shirt you can tie around your waist, a lightweight sweater, and a rain jacket or compact umbrella. Sunscreen is essential; UV index reaches 7 to 8 by late May, and Baltimore's waterfront reflects intensity onto your skin. Sunglasses and a hat reduce glare and heat on your face during long walks.

For evening plans, a sweater or light cardigan is standard. Restaurant patios and rooftop bars (common in Fells Point and Canton) are popular in May, but temperatures drop 10 to 15 degrees after dark.

Pollen and Allergies

Pollen counts remain moderate in early May but rise sharply by mid-month as trees finish flowering and grasses begin their season. If you have seasonal allergies, antihistamines taken before 8 a.m. prevent afternoon symptoms. Local pharmacies stock Baltimore-branded and national brands at comparable prices.

Best Days for Planning

Clear days mid-May (typically May 10 to 20) offer the highest probability of no rain and comfortable temperatures. If your May visit is flexible, aiming for this window increases odds of uninterrupted outdoor time.