December in Allentown averages a daily high of 5.8°C with nights around -3.2°C. Expect roughly 11.8 wet days totalling 100.9mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Allentown is May–June.
Based on ALLENTOWN LEHIGH VALLEY INTERNATIONAL AIRPORT, PA US (5.8km), 1995–2024. 30 years of December data.