Severe Weather Definitions

[AJE]

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.

Watches - A watch tells you that conditions are favorable and there is a good chance that the event may happen. When a watch is issued begin making preparations for the upcoming event. Tune in to for more information. 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.

Warnings

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.

Coastal Flood Warning - A Coastal Flood Warning is issued when moderate to severe coastal flooding is occurring or is imminent.

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

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.

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.

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

Frost Warning - A Frost Warning will be issued when widespread frost is forecast during the growing season (temperatures do not necessarily have to be 32 for frost).

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

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.

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 accumulation of 1/2 inch of sleet.

Lake Snow Warning - A Lake Snow Warning is issued when heavy lake effect snow is occurring, imminent, or has a very high probability of occurring within the next 12 hours. Lake effect snow usually occurs in narrow bands over limited areas, particularly in the Great Lake region. The snow is expected to accumulate at least 7 inches with strong winds producing high drifts. Lake effect snow squalls/showers can occur quite suddenly and cause blizzard-like conditions.

River Flood Warning - A River Flood Warning is issued when river flooding is occurring or imminent at one or more forecast points along a river.

Severe Thunderstorm Warning - When a Severe Thunderstom Warning is issued, tornadoes and/or severe thunderstorms are occurring and have been spotted or detected by radar. The National Weather Service (NWS) defines a severe thunderstorm as having winds 50 kts (58 mph) or hail greater than ¾" in diameter (about dime-sized). (A storm that spawns a tornado is obviously also considered severe.) 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. Stay away from windows, doors and outside walls. Put as many walls between you and the tornado as possible on the lowest floor of your building. If you do not have a basement, seek shelter in an interior bathroom or closet. Get under something sturdy. Protect your head. Stay away from mobile homes. Get out of your vehicle. If there is no safe shelter, lie flat in the nearest ditch or ravine with your hands shielding your head.

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.

Tornado Warning - When a Tornado Warning is issued, tornadoes are occurring and have been spotted or detected by radar. 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. Stay away from windows, doors and outside walls. Put as many walls between you and the tornado as possible on the lowest floor of your building. If you do not have a basement, seek shelter in an interior bathroom or closet. Get under something sturdy. Protect your head. Stay away from mobile homes. Get out of your vehicle. If there is no safe shelter, lie flat in the nearest ditch or ravine with your hands shielding your head.

Wind Chill Warning - Issued when wind chill values are expected to be -50 degrees or less.

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.

Watches

Coastal Flood Watch - A Coastal Flood Watch is issued when moderate to severe coastal flooding is possible.

Excessive Heat Watch - Excessive Heat Warnings will be issued when a maximum heat index > 115 with minimum 80 is expected to develop within a 24 to 48 hour timeframe.

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.

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

High Wind Watch - Issued when wind speeds are forecast to meet warning criteria with in the next 24-36 hours.

Lake Snow Watch - A Lake Snow Watch is issued when there is a possibility of heavy lake effect snow (accumulating 7 inches of more within a 12 hour period). Lake effect snow usually occurs in narrow bands over limited areas. The watch is issued at least 12 hours before the snow is expected to begin, however its occurrence, location, and/or timing is still uncertain.

River Flood Watch - A River Flood Watch is issued when river flooding is possible at one or more forecast points along a river.

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. Keep an eye on the sky for changing conditions and make preparations in case a weather warning is issued.

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. Keep an eye on the sky for changing conditions and make preparations in case a weather warning is issued.

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.

Advisories
Blowing Snow Advisory - A Blowing Snow Advisory will be posted for events in which visibility is intermittently 1/4 mile or less.

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.

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.

Freezing Fog Advisory - A Freezing Fog Advisory will be issued when fog is present with temperatures below freezing, and the fog is expected to cause a thin layer of ice to develop on bridges, overpasses, and other elevated roadways.

Freezing Rain 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.

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

Small Stream Flood Advisory - An Urban Flood Advisory is issued when flooding of low lying areas, creeks or small streams is either imminent or already occurring.

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

Snow and Blowing Snow Advisory - A Snow and Blowing Snow Advisory is issued when 3-5 inches of snow is expected to fall AND visibility will be intermittent for 1/4 mile or less.

Urban and Small Stream Flood Advisory - An Urban and Small Streams Flood Advisories are issued when flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.

Urban Flood Advisory - An Urban Flood Advisory is issued when flooding of streets, low lying areas or storm drains is either imminent or already occurring.

Wind Advisory - Issued for sustained winds 31-39 MPH for at least 1 hour or any gusts to 46-57 MPH.

Wind Chill Advisory - Issued when wind chill values are expected to be in the -35 to -50 degree Fahrenheit range.

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