Long Arm Reservoir — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Long Arm Reservoir, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Long Arm Reservoir today is 17.6°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
⚠️ As of today, the minimum water temperature ranges from 60°F (15°C) to 65°F (18°C). The water is comfortable for most people, making it an ideal range for water sports enthusiasts. The temperature does not cause significant discomfort, and swimming will be pleasant for the majority. However, it's important to remember that prolonged exposure to the water can still lead to cooling, so it's essential to monitor the time spent in the water, especially for children or elderly people. It is important to note that these swimming tips and recommendations apply only in good weather. When the air temperature is below 68°F (20°C), and sometimes even below 77°F (25°C), swimming can be unpleasant even with relatively high water temperatures.
Water Temperature Chart Over the Last 30 Days
Table of Daily Sea Temperature Data
| Date | Current | Average | Forecast |
|---|---|---|---|
| OCT 5 | 20.6°C | 20.0°C | |
| OCT 6 | 19.9°C | 20.0°C | |
| OCT 7 | 19.3°C | 20.0°C | |
| OCT 8 | 19.4°C | 20.0°C | |
| OCT 9 | 18.6°C | 20.0°C | |
| OCT 10 | 18.6°C | 20.0°C | |
| OCT 11 | 18.5°C | 20.0°C | |
| OCT 12 | 18.2°C | 20.0°C | |
| OCT 13 | 20.0°C | 17.7°C | |
| OCT 14 | 20.0°C | 17.8°C | |
| OCT 15 | 20.0°C | 18.0°C | |
| OCT 16 | 20.0°C | 18.1°C | |
| OCT 17 | 20.0°C | 18.2°C | |
| OCT 18 | 20.0°C | 18.3°C | |
| OCT 19 | 20.0°C | 18.4°C |
* Current - Actual water temperature value
** Average - Average water temperature on this day in recent years
*** Forecast - Our water temperature forecast
Actual nearshore water temperatures may fluctuate by several degrees from the reported values, especially following heavy rainfall or extended periods of strong winds. Certain wind patterns can cause colder, deeper waters to rise and replace the sun-warmed surface water, leading to noticeable variations.
Our forecast is based on a proprietary mathematical model that considers real-time water temperature changes, historical trends, key weather patterns, wind strength and direction, and air temperature specific to each region. Additionally, we incorporate data from other resorts to enhance accuracy.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Min | Avg | Max |
|---|---|---|---|
| January | 1°C | 4°C | 7°C |
| February | 1°C | 4°C | 7°C |
| March | 1°C | 5°C | 10°C |
| April | 8°C | 12°C | 17°C |
| May | 12°C | 18°C | 24°C |
| June | 18°C | 21°C | 24°C |
| July | 19°C | 24°C | 29°C |
| August | 20°C | 23°C | 26°C |
| September | 21°C | 24°C | 26°C |
| October | 16°C | 20°C | 24°C |
| November | 7°C | 12°C | 17°C |
| December | 3°C | 7°C | 10°C |
Long Arm Reservoir: Water Temperature by Location
Long Arm Reservoir: Weather Forecast
October 13
October 14
October 15
October 16
October 17
October 18
Location & Local Information
Long Arm Reservoir, like many inland reservoirs in Pennsylvania, shows clear seasonal variation in surface water temperature. In winter the surface typically sits near freezing, roughly 32–40°F (0–4°C), with ice possible in sustained cold periods. Spring brings a steady rise, often into the 40–60°F (4–16°C) range as turnover and warming progress. By summer the upper layers commonly warm to comfortable swimming temperatures, frequently 68–80°F (20–27°C) on warm afternoons, while deeper water remains markedly cooler. In autumn the surface cools again, moving back toward roughly 50–65°F (10–18°C) as stratification breaks down. These ranges can vary year to year with weather, depth, and inflow conditions, and surface readings during heat waves can exceed the typical summer maximum.
Swimming access at Long Arm Reservoir depends on management rules rather than temperature alone. Many Pennsylvania reservoirs restrict or prohibit open swimming because they serve as water supply sources, to protect water quality, and for safety reasons such as variable depths, submerged hazards, and boat traffic. Where authorities do permit swimming, it is usually confined to designated areas and seasonal hours when surface temperatures are warmest. Visitors should consult local reservoir managers or posted signage before entering the water and be mindful of cold-water shock early and late in the season.