Historical weather data, all-time temperature records, and monthly climate averages for Williamstown, NJ. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5th in Williamstown typically lands in the mid-60s for highs, but the date has a wild range in its 122-year history — from a brutal 17° in 1908 to a shirt-sleeve 86° back in 1910. Today sits right at the seasonal pivot point where a frost is still possible but increasingly unlikely, with only a 1% chance of snow and about a 1-in-3 shot at rain.
Williamstown's weather has real teeth at both extremes — 107° in July 1901 and -25° in February 1934 represent a 132-degree swing in recorded history. A single August day in 1906 dumped 7.15 inches of rain, and a February 2010 snowstorm buried the area under 19 inches in one shot.
Summer is the main event here, with highs peaking around 87-88° in mid-July and staying in the mid-80s through August. If you're avoiding the heat, January and February are the coolest months, topping out in the low-to-mid 40s. The wettest stretch runs in early-to-mid August, when late-summer storms average over an inch of rain per week.