Will Water Freeze at 33 Degrees? The Exact Answer
No, water will not freeze at 33 degrees Fahrenheit. Pure water at standard atmospheric pressure freezes at exactly 32 °F (0 °C). At 33 °F, water is still above its freezing point and remains a liquid. The one-degree difference is enough to keep water from turning into ice.
Why 33 °F Isn’t Cold Enough
The freezing point of pure water is a fixed physical property: 32 °F at sea level Wikipedia. At 33 °F, water molecules still have enough thermal energy to prevent the crystal structure of ice from forming. If you place a glass of water in a room that is 33 °F, the water will stay liquid indefinitely.
Impurities change this. If water contains salt or other dissolved solids, its freezing point drops below 32 °F. Ocean water, with a salinity of about 3.5%, freezes at roughly 28.4 °F. So water at 33 °F could freeze if it is a very salty solution, but only because the freezing point has been lowered. For pure tap water or distilled water, it will not freeze at 33 °F.
The National Weather Service National Weather Service uses 32 °F as the threshold for freezing rain and frost advisories. They do not issue those warnings at 33 °F because that temperature is not cold enough for ice formation on roads or plants.
Pressure also affects the freezing point, though the effect is small. At higher altitudes, water freezes at a temperature slightly above 32 °F. On a mountain summit at 10,000 feet, pure water might freeze at about 32.1 °F. In practice, the National Oceanic and Atmospheric Administration NOAA uses 32 °F as the standard freezing point for weather forecasting because the pressure variation is negligible for most populated areas.
Water can sometimes stay liquid below 32 °F in a phenomenon called supercooling. If water is very pure and free of nucleation sites, it can remain liquid at temperatures as low as -40 °F before suddenly freezing. This does not change the freezing point itself; it just delays the phase change. So while water at 33 °F will not freeze, water at 30 °F might also remain liquid temporarily if it is supercooled.
Some outdoor thermometers have accuracy margins of ±2 °F. If a thermometer reads 33 °F, the actual temperature could be 31 °F or 35 °F. In the first case, water could freeze because the true temperature is below 32 °F. If you see frost on your car windshield and the thermometer says 33 °F, the sensor is likely off by a degree or two, or the surface temperature of the windshield dropped below 32 °F due to radiative cooling.
Key Takeaways
- Pure water freezes at 32 °F (0 °C) at standard atmospheric pressure. At 33 °F, it remains a liquid.
- Impurities like salt lower the freezing point, so salty water can freeze below 32 °F, but that does not change the freezing point of pure water.
- If you see frost or ice at 33 °F, the actual surface temperature is likely at or below 32 °F due to wind chill or evaporative cooling.
- For practical purposes, assume any temperature above 32 °F means liquid water unless the water contains dissolved substances that depress the freezing point.
