Fog is the main visibility concern in Allentown’s forecast, with possible development overnight and again Tuesday and Wednesday mornings. The National Weather Service Mount Holly forecast starts Monday near 36 degrees under clear skies, then calls for sunshine and light southwest winds to lift the afternoon high to about 66.
Fog Risks Give Way to Warmer Afternoons
The National Weather Service Mount Holly forecast says Monday’s clouds will decrease, with light southwest winds. Monday night should remain mostly clear, with a low near 40, though areas of fog could develop after 11 p.m.
Tuesday may start with fog before 9 a.m. Once it lifts, mostly sunny skies should return and temperatures could reach 69 degrees. Wednesday’s forecast also allows for morning fog, before 10 a.m., followed by a high near 73.
Rain Chances Rise Thursday
The dry stretch is expected to end Thursday, when rain is likely after 7 a.m. and the forecast precipitation chance is about 70%. Thursday night and Friday both look wet and mostly cloudy, with highs near 72 and 71 degrees, respectively.
The latest outlook adds detail on the late-week rain compared with Sunday's Allentown forecast. For outdoor errands or events, Monday through Wednesday offer the best window before rain becomes a concern.
Showers May Ease by Saturday
Friday night could still bring a chance of light rain. Saturday has a 30% chance of showers, then should turn partly sunny with a high near 67. Sunday is forecast to be cooler but mostly sunny, with a high around 62.
Climate Context and Thursday’s Rain Chance
The Pennsylvania 2025 State Climate Summary reports that annual average temperatures have increased more than 2°F since the beginning of the 20th century, with most warming in winter and spring; summer and fall have not warmed as much. It also states that annual precipitation has generally been above average since the 1970s, primarily because of increases in summer and fall precipitation; this long-term climate record does not explain or establish this week’s forecast. See the Pennsylvania 2025 State Climate Summary.
A 70% precipitation probability is not a guarantee of rain at every location. The National Weather Service says that probability applies to a particular forecast point and time period; for Allentown, the current forecast gives Thursday a 70% chance, with rain likely after 7 a.m. The National Weather Service’s explanation of precipitation probabilities defines measurable precipitation as at least 0.01 inch.
Drivers should watch for reduced visibility during overnight and early-morning fog, especially Tuesday morning. No active weather alerts are listed for the local forecast area.
