Weather Conditions

Understanding Weather Terms

The National Weather Service has supplied some definitions for several weather phrases common in Northern Arizona.

• Advisory: a weather event may threaten life or property if caution is not exercised.
• Blowing Snow: wind-driven snow that significantly reduces surface visibility to less than 7 miles.
• Breezy: sustained wind speeds of 15-25 mph.
• Chance: a 25-55% probability that one point in a forecast area will have precipitation.
• Flurries: light snowfall that generally does not produce measurable accumulation.
• Freezing Drizzle or Rain: the effect of drizzle or rain upon impact on objects that have a temperature of 32 degrees or below.
• Frost: a covering of small ice crystals that forms on or near the ground when temperatures approach or drop below 32 degrees.
• Hail: Precipitation in the form of balls or lumps usually consisting of concentric layers of ice. A thunderstorm is classified as severe when it produces hail 3/4 inch in diameter.
• Humidity: amount of water vapor in the atmosphere.
• Ice Storm: a freezing rain event that produces damaging ice accumulations of 1/4 inch or greater.
• Likely: a 55-75% probability that one point in a forecast area will have precipitation.
• Numerous: showers or thunderstorms with 55-75% area coverage.
• Rain: a nearly steady and uniform fall of liquid precipitation over an area for several hours.
• Scattered: showers or thunderstorms with 25-55% area coverage.
• Severe Thunderstorm: produces or exceeds either of the following: damaging winds of 58 mph, hail 3/4 of an inch in diameter or tornado.
• Shower: intermittent rain or snow.
• Sleet: solid grains of ice formed by the freezing of raindrops or the refreezing of largely melted snowflakes.
• Slight Chance: 1-25% probability that one point in a forecast area will have precipitation.
• Snow: steady fall of snowflakes for several hours over the same area.
• Snowpack: combined layers of snow and ice on the ground at any one time.
• Snow Showers: snow that stops and starts suddenly and is characterized by rapid changes in both intensity and visibility.
• Sustained Wind: wind speed determined by averaging observed values over a 1-minute period.
• Warning: indicates a hazard weather element is imminent or has a very high probability of occurrence.
• Watch: alerts the public to the possibility of severe weather, or some other hazardous weather element.
• Wind Chill: apparent temperature that describes the combined effect of wind and low air temperatures on exposed skin.
• Windy: sustained winds speeds of 20-30 mph.