Bad weather definitions
Severe weather
Severe thunderstorm warning
Issued when there is radar-based evidence or a reliable observer report that a storm is producing, or is expected to produce, wind gusts of 58 mph or greater, structural wind damage, and/or hail 1 inch in diameter or superior.
Vigilance of violent storms
It is issued by the Storm Prediction Center (SPC) when conditions are conducive for severe thunderstorms to develop over a wider region. Tornadoes are not expected in such situations, but the development of isolated tornadoes cannot be ruled out.
PDS watch for severe thunderstorms
PDS stands for “Especially Dangerous Situation” and is issued by the SPC when conditions are favorable for the development of severe high-end thunderstorms over a wider region. In this situation, the SPC considers it likely that multiple extreme weather events with significant wind damage will occur. Citizens should adjust their daily routine and listen for more updates when this watch is issued. Tornadoes are not expected in such situations, but the development of isolated tornadoes cannot be ruled out and widespread straight-line wind damage is likely.
Tornado Warning – Observed or indicated by radar
Issued when there is radar-based evidence or a reliable observer report that a tornado is imminent or in progress.
Tornado Warning – Noticeable
Issued when a reliable observer reports a tornado exists (ie, it is confirmed, not indicated by radar) and is doing considerable damage.
Tornado Warning – Catastrophic
Issued when a reliable observer reports a tornado exists (hence, it is confirmed, not indicated by radar) and is causing extreme damage that is considered catastrophic; complete destruction is possible.
Tornado watch
It is issued by the Storm Prediction Center when conditions are conducive for severe thunderstorms and tornadoes to develop over a wider region.
Tornado PDS Clock
PDS stands for “Especially Dangerous Situation” and is issued when the SPC deems a major outbreak of long-lasting, large, violent tornadoes likely. This is a high-end tornado watch. People in a PDS Tornado Watch are expected to change their daily routines to ensure they are aware of the weather and ready to act on short notice.
Significant weather warning
Released for severe thunderstorms that are below severe levels, but can still have some negative impacts. Usually released for threatened wind gusts of 40-58 mph or hail up to 1 inch in diameter.
Flooding
Flood Flash watch
Generally issued when there is a possibility of flash flooding or urban flooding over an area within the next 36 hours.
Flash flood hazard
Issued when a flash flood is imminent, usually within the next 1-3 hours. Usually issued based on observed heavy rainfall (measured or estimated by radar), but can also be issued for significant dam failures that have occurred or are imminent.
Flood Guard
Issued when there is a possibility of widespread general flooding over an area within the next 36 hours.
Flood warning for the river forecast point
Issued when a river gauge has passed, or is expected to pass, a predetermined flood stage.
Flood warning
Issued when flooding is imminent or occurs, usually within the next 1-3 hours, but not expected to substantially threaten life and property.
Absence of rainfall
Wind warning
Issued when sustained winds of 30 to 39 mph are expected for 1 hour or more.
Strong wind alarm
Issued when sustained winds of 40 mph or more are expected for 1 hour or more, or for wind gusts of 58 mph or more with no time limit. A High Wind Watch is issued when these conditions can be met 12 to 48 hours in the future.
Dense fog warning
Issued when fog is expected to reduce visibility to 1/4 mile or less.
Heat warning
Issued when daytime heat index highs are expected to reach or exceed 105°F for at least 2 consecutive days, with low temperatures in between of 75°F or higher.
Excessive heat warning
Issued when daytime heat index highs are expected to reach or exceed 110°F for at least two consecutive days, with low temperatures in between of 75°F or higher. An Excessive Heat Watch is issued when these conditions can be met 12 to 48 hours in the future.
Frost warning
Issued when low nighttime temperatures are expected to range from 33°F to 36°F in the growing season.
Freeze warning
Issued when low nighttime temperatures are expected to reach 32°F or lower during the growing season. They are usually issued to highlight the first frosts of fall or unusually late frosts in spring. A Freeze Watch is issued when these conditions can be met 12 to 48 hours in the future.
Air stagnation warning
Only released at the request of the Environmental Protection Agency (EPA), whenever atmospheric conditions are stable enough to cause air pollutants to build up in a particular area.
Dust blower warning
Issued when dust blowing is expected to reduce visibility by between 1/4 and 1 mile, generally in winds of 25 mph or higher.
Dust storm warning
Issued when dust blowing is expected to frequently reduce visibility to 1/4 mile or less, generally in winds of 25 mph or more.
Thick smoke warning
Issued when smoke is expected to reduce visibility to 1/4 mile or less.
Fire weather surveillance
Issued when 12 to 72 hours of future dry vegetation and conditions conducive to extreme fire danger are expected.
Red flag alert
Issued when dry vegetation and conditions conducive to extreme fire danger are expected, usually within 24 hours.
Winter season
Snow warning
Issued when 2 to 4 inches of snow accumulation is expected. A warning may still be warranted if minor accumulations will produce travel difficulties, especially at the start of the winter season.
Snow drift warning
Issued when blown snow is expected to occasionally reduce visibility to 1/4 mile or less in winds generally 25 to 34 mph. The event should last at least 3 hours.
Snow and snow drift warning
Issued when winds of 25 to 34 mph are expected to be accompanied by falling snow and blowing snow, occasionally reducing visibility to 1/4 mile or less. The event should last at least 3 hours.
Freezing rain/drizzle warning
Released for freezing rain when ice buildups are expected to cause travel problems, but not to exceed 1/4″.
Sleet warning
Issued to accumulate 1/4″ to 1″ sleet. Since sleet usually occurs with other types of precipitation, a winter weather warning will almost always be used in these cases.
Winter weather warning
Issued for a winter weather event where more than one hazard is present, but all precipitation is expected to remain below the advisory criteria. For example, it would be issued if 2 inches of snow was expected with a small amount of sleet mixing in at times.
Wind chill warning
Issued when wind chill readings reach -5°F to -19°F, with wind speeds approximately 10 mph or higher.
Wind chill warning
Issued when wind chill readings reach -20°F or colder, with wind speeds of approximately 10 mph or more. A Wind Chill Watch is issued when these conditions can be met 12 to 48 hours in the future.
Ice storm warning
Issued when a period of freezing rain is expected to produce ice accumulations of 1/4″ or greater or cause significant disruption to travel or utilities.
Heavy snow warning
Issued when a period of sleet is expected to produce ice accumulations of 1″ or greater, or cause significant disruption to travel or utilities.
Severe snow warning
Issued when snow is expected to accumulate 4 inches or more in 12 hours or 6 inches or more in 24 hours.
Winter storm warning
Issued for a winter weather event where more than one hazard is present and one of the warning criteria listed above is expected to be met. For example, it would be issued if 5 inches of snow was forecast in 12 hours, with some sleet mixed in at times. It is commonly issued for heavy snow with high winds of 25-34 mph which will cause the snow to blow and drift. A Winter Storm Watch is issued when these conditions can be met 12 to 48 hours in the future.
Blizzard warning
Issued for sustained winds or frequent gusts greater than or equal to 35 mph accompanied by falling and/or blowing snow, frequently reducing visibility to less than 1/4 mile for three hours or more. A Blizzard Watch is issued when these conditions can be met 12 to 48 hours in the future.
