Criteria for Watches Warnings and Advisories
Winter Weather Warm Weather Non-Precipitation Open Water / Tropical
WATCHES A Watch tells you that conditions are favorable and there is a pretty good chance that the event may happen. When a watch is issued begin making preparations for the upcoming event. Listen to your local media to know when warnings are issued. Watches are intended to heighten public awareness of the situation.
WARNINGS A warning means that a certain weather event is IMMINENT. Measures should be taken to safeguard life and property IMMEDIATELY
ADVISORIES Advisories are issued when events are expected to remain below the warning criteria, but still cause significant inconvenience. Most common in association with snow events.


WINTER SEASON WATCHES/WARNINGS/ADVISORIES


SNOW ADVISORY -- A Snow Advisory will be issued when 3-5 inches is expected to fall.

*Check with your NWS office for local snowfall requirements.

BLOWING SNOW ADVISORY -- A Blowing Snow advisory will be posted for events in which visibility is intermittently 1/4 mile or less.

FREEZING RAIN / FREEZING DRIZZLE ADVISORY -- This requires that hazardous driving conditions be taking place and/or up to 1/4 inch of freezing rain on tree branches and/or if power lines break.

WINTER WEATHER ADVISORY -- A Winter Weather Advisory will be issued if conditions warranting two separate winter advisories are met.

WINTER STORM WATCH -- A Winter Storm Watch may be issued when conditions are forecast to meet the criteria for more than one warning with in the next 36 hours. A watch for a single winter weather event does not exist, for example a Wind Chill Watch or a Heavy Snow Watch. Just the same, if a forecaster thinks there will be significant snow and ice tomorrow, he/she will issue a Winter Storm Watch.

WINTER STORM WARNING -- A Winter Storm Warning will be issued if conditions are forecast to meet the criteria for two separate warnings in the next 12-24 hours. Example: If you have Heavy Snow Warning conditions along with Wind Chill Warning conditions, a Winter Storm Warning will be issued.

BLIZZARD WARNING -- A Blizzard Warning will be issued when the following conditions are forecast to last at least 3 hours. Falling and/or blowing snow frequently reducing visibility to < 1/4 mile AND sustained winds or frequent gusts > 35 mph.

ICE STORM WARNING -- An Ice Storm Warning will be issued if freezing rain/drizzle is occurring with a significant accumulation of ice (more than 1/4 inch) or accumlation of 1/2 inch of sleet.

HEAVY SNOW WARNING -- A Heavy Snow Warning will be issued if 6 or more inches of snow is expected in a 12 hour period.



(WIND CHILL PRODUCTS AND FROST/FREEZE PORDUCTS ARE FOUND IN THE NON-PRECIPTATION SECTION).


WARM SEASON WATCHES/WARNINGS/ADVISORIES


TORNADO WATCH -- A Tornado Watch will be issued when conditions are favorable for the development of severe thunderstorms and tornadoes. The Storm Prediction Center (SPC) is the sole agency responsible for issuing a watch. A watch covers several thousands of square miles and generally lasts from two to six hours.

TORNADO WARNING -- A Tornado Warning is issued when a tornado has been reported to the NWS by spotters or the public, doppler radar detects strong low level rotation within a strong thunderstorm, or a combination of spotter reports of cloud features and doppler radar observations indicate a tornado may form at any moment. . There is imminent danger for people in the area warned. Issued by a local NWS office, the size of the warning area is generally the size of one or two counties and usually lasts less than an hour.

SEVERE THUNDERSTORM WATCH -- A Severe Thunderstorm Watch will be issued when conditions are favorable for development of severe thunderstorms. While not anticipated, tornadoes may occur in the watch area. The Storms Prediction Center (SPC) is the sole agency responsible for issuing a watch. A watch covers several thousands of square miles and generally lasts from two to six hours.

SEVERE THUNDERSTORM WARNING -- When a Severe Thunderstorm Warning is issued, severe thunderstorms are occurring and have been reported by spotters or detected by radar. The National Weather Service (NWS) defines a severe thunderstorm as having winds 50 kts (58 mph)or greater, and/or hail 1 inch or greater in diameter (about quarter-sized). There is imminent danger for people in the area warned. Issued by a local NWS office, the size of the warning area is generally the size of one or two counties and usually lasts less than an hour.

FLOOD WATCH -- A Flood Watch will be issued for situations related to widespread general flooding.

FLOOD WARNING -- A Flood Warning will be issued when inundation of a normally dry area near a stream or other watercourse is expected, OR unusually severe ponding of water expected.

RIVER FLOOD WARNING -- River Flood Warnings are initiated when a river at a gauge site is expected to, or has, exceeded flood stage.

FLASH FLOOD WATCH -- A Flash Flood Watch will be issued for serious situations in which life and/or property are in danger. Flash Flood watch covers flash flooding, widespread urban and small stream, and headwater flood events.

FLASH FLOOD WARNING -- A Flash Flood Warning will be issued in response to a few hours of locally heavy rainfall, a dam or levee failure, or water released from an ice jam rapidly flooding nearby land.

URBAN AND SMALL STREAM FLOOD WARNING/ADVISORY -- An Urban and Small Streams Flood Warnings or Advisories are issued when flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.

NON-PRECIPITATION WATCHES/WARNINGS/ADVISORIES


WIND CHILL ADVISORY -- Issued when wind chill values are expected to be in the -20 to -30 degree F range.

WIND CHILL WARNING -- Issued when wind chill values are expected to be -30 degrees or less.

*The values for the wind chill products are accurate for the Chicago area. Check with your local National Weather Service office for the warning/advisory criteria where you live.

HIGH WIND WATCH -- Issued when wind speeds are forecast to meet warning criteria with in the next 24-36 hours.

HIGH WIND WARNING -- Issued for sustained wind speeds of 40 MPH or greater lasting for 1 hour or longer, OR winds of 58 MPH or greater for any duration of time.

WIND ADVISORY -- Issued for sustained winds 31-39 mph for at least 1 hour; OR any gusts to 46-57 mph.

DENSE FOG ADVISORY -- Dense Fog Advisories may be issued for visibilities 1/4 mile or below. These Advisories will usually be posted for widespread events, not small local events such as valley fog in the summer.

HEAT ADVISORY -- A Heat Advisory will be issued when the Heat Index is expected to reach 105 with a nighttime low not below 80.

EXCESSIVE HEAT WARNING -- Excessive Heat Warnings will be issued with a maximum heat index > 115 with minimum 80.

* * Special heat warning criteria were established for the Chicago metro area after the disasterous July 1995 heat wave. Heat advisories are not issued for Chicago.

FROST ADVISORY -- A Frost Advisory will be issued when widespread frost is forecast during the growing season (reported air temperatures do not necessarily have to be below freezing for frost).

FREEZE ADVISORY -- A Freeze Advisory will be issued for widespread temperatures of 32 degrees Fahrenheit or colder are forecast during the growing season (frost may or may not occur).

OPEN WATER / TROPICAL WATCHES/WARNINGS/ADVISORIES


SMALL CRAFT ADVISORY -- A Small Craft Advisory is issued for sustained winds 25-33 knots AND/OR Seas > 7 feet within 12 hours

GALE WARNING -- A Gale Warning is issued for 1-minute sustained surface winds in the range 34 kt (39 mph or 63 kph) to 47 kt (54 mph or 87 kph) inclusive, either predicted or occurring not directly associated with tropical cyclones.

STORM WARNING -- A Storm Warning is issued for 1-minute sustained surface winds of 48 kt (55 mph or 88 kph) or greater, predicted or occurring, not directly associated with tropical cyclones.

TROPICAL STORM WATCH -- An announcement that a tropical storm poses or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A tropical storm watch should normally not be issued if the system is forecast to attain hurricane strength.

TROPICAL STORM WARNING -- A warning for tropical storm conditions including sustained winds within the range of 34 to 63 kt (39 to 73 mph or 63 to 118 kph) that are expected in a specified coastal area within 24 hours or less.

HURRICANE WATCH -- An announcement of specific coastal areas that a hurricane or an incipient hurricane condition poses a possible threat, generally within 36 hours.

HURRICANE WARNING -- A warning that sustained winds 64 kt (74 mph or 119 kph) or higher associated with a hurricane are expected in a specified coastal area in 24 hours or less. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force.

SPECIAL MARINE WARNING -- A Special Marine Warning is issued for a brief/sudden occurrence of sustained wind or frequent gusts > 34 knots, usually associated with thunderstorms.