National Weather Service United States Department of Commerce

Watch, Warning, and Advisory Definitions

 

Basic Definitions:

The National Weather Service issues a variety of products to keep our customers informed of unusual, inconvenient and hazardous weather conditions. A multi-tier concept is employed to accomplish this task with Outlooks, Watches, Warnings and Advisories to point out specific conditions.

 

Outlook:  Used to give considerable lead time that a hazardous event may develop in the next 7 days.
 
Watch:  Issued when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so.
 
Warning: Issued when a hazardous event is occurring or has a very high probability of occurrence. Warnings advise of a threat to life or property.
 
Advisory: Issued when a hazardous event is occurring or has a very high probability of occurrence. Advisories describe events that cause significant inconvenience.
 

 

                                                  
 

CONVECTIVE EVENTS - PRODUCT

THRESHOLDS

SEVERE THUNDERSTORM WARNING - SVR

Winds 50 kts (58 mph or implied by damage), and/or hail 1 inch or greater

TORNADO WARNING - TOR

Tornado occurring or developing

SEVERE THUNDERSTORM WATCH - WCN

Thunderstorms capable of Winds 50 kts (58 mph or implied by damage), and/or hail 1 inch or greater. Issued by SPC, 0-8 hours.

TORNADO WATCH - WCN

Thunderstorms capable of producing tornadoes. Issued by SPC, 0-8 hours.

SIGNIFICANT WEATHER ALERT - SPS

Winds 40+ mph (35 kts),  hail 1/2 inch or greater and/or frequent/continuous lightning

HYDRO & LAKESHORE EVENTS - PRODUCT

THRESHOLDS

FLOOD WATCH - FFA

Possible long duration flooding over a general area more than 6 hrs after main rainfall

FLASH FLOOD WATCH - FFA

Possible short/long duration flooding over a general area less than 6 hrs after main rainfall

LAKESHORE FLOOD WATCH - CFW

Possible flooding affecting homes, businesses, or roads along the lakeshore within the next 1-3 days

FLASH FLOOD WARNING - FFW

Flooding that produces life/property threat in 0-6 hrs

FLOOD WARNING - FLW

Flooding that lasts 6 hrs or more over a general area and/or affects mainstem rivers that is a threat to life/property

LAKESHORE FLOOD WARNING - CFW

Flooding affecting homes, businesses, or roads along the lakeshore within the next 0-48 hours

FLOOD ADVISORY- FLS

Inconvenience flooding in 0-24 hrs

LAKESHORE FLOOD ADVISORY - CFW

Flooding affecting beaches, docks, marinas, and watercraft along the lakeshore within the next 0-48 hours

MARINE EVENTS - PRODUCT

THRESHOLDS

SPECIAL MARINE WARNING - SMW

Winds (convective or non-conv) 34 kts for 2 hrs or less, hail 3/4 inch and/or waterspouts

GALE WARNING - MWW

Sustained winds 34 to 47 kts or freq gusts 38 to 47 kts expected within 24 hours

STORM WARNING - MWW

Sustained winds 48 to 64 kts or freq gusts 50 to 64 kts expected within 24 hours

HURRICANE FORCE WIND WARNING - MWW

Sustained winds 65+ kts expected within 24 hours

HEAVY FREEZING SPRAY WARNING - MWW

Heavy freezing spray is expected within 24 hours 

MARINE WATCH - MWW

Issued when warning criteria (except SMW) is expected within 72 hours

MARINE WEATHER STATEMENT - MWS

Winds (convective or non-conv) <34 kts,  hail <3/4 inch, and/or thunderstorms

LOW WATER ADVISORY - MWW

Water is expected to be several inches below chart datum for an extended period of time

     - Consider when an NPW is in effect for High Wind

     - Issue when Gale Warning is in effect for Saginaw Bay

     - Coordinate with WFO CLE for Michigan waters of Lake Erie

     - Water falls below 36" on Detroit River at Gibralter

SMALL CRAFT ADVISORY - MWW

Winds 22-33 kts and/or waves > 3 ft - Nearshore Waters Only

DENSE FOG ADVISORY - MWW

Widespread vsby 1 mile or less

COLD-SEASON EVENTS - PRODUCT

THRESHOLDS

WINTER STORM WARNING - WSW

 

Heavy snow: Heavy snow including lake-effect with winds less than 35 mph

     - 10 inches within 24 hours

     - 8 inches within 12 hours

     - 6 inches within 8 hours

☞ Mix: A combo of 2 or more of the following: heavy snow, sleet, freezing rain/drzl

Forecaster Discretion: Winter Storm Warn for lesser amts in shorter time pd w/ blwg snow

Heavy sleet: Sleet accums of 3+ inch in 12 hours or less

SNOW SQUALL WARNING - SQW

Snow squalls reducing visibility to 1/4 mile or less, for 15 minutes or more, on dry frozen highways

BLIZZARD WARNING - WSW

Sustained winds or freq gusts 35+ mph and falling/blowing snow with vsby near 1/4 mile or less

for 3 hrs (only blowing snow needed for ground blizzard)

ICE STORM WARNING - WSW

Ice accum over 1/4 inch in 12 hours or less

WIND CHILL WARNING - WSW

Wind chills or air temperature 25 below or colder

WINTER STORM WATCH - WSW

Issued when Warning criteria is expected 12-72 hours in the future

WINTER WEATHER ADVISORY - WSW

☞ Snow (including lake-effect):

     - >4 inches but <10 inches in 24 hours

     - >4 inches but <8 inches in 12 hours

     - >2 inches but <6 inches in less than 8 hours   

☞ Light freezing rain or freezing drzl with ice accum < 1/4 inch in 12 hr or less

☞ Mix: Mix of snow, sleet, freezing rain/drizzle

☞ Sleet: Sleet accums 1/2 to 3 inch in 12 hours or less

☞ Snow & blowing/drifting snow: Wind driven snow, blowing snow, intermittent vsbys 1 mile or less for 3 hours or more with winds 25 to 34 mph

Blowing snow: Blowing snow reducing vsbys to 1 mile or less with winds < 35 mph

WIND CHILL ADVISORY - WSW

Wind chills or air temperature 15 to 24 below for 2 or more hours

WINTER STATEMENT - SPS

- Warning/Advisory in effect: issued to highlight area of heaviest snow, sleet, or freezing rain/drizzle in next 2-4 hours

- No Warning/Advisory in effect: issued to highlight area of snow, or sleet, or freezing rain/drizzle causing localized travel impacts in next 2-4 hours

NON-PRECIP EVENTS - PRODUCT

THRESHOLDS

HIGH WIND WARNING - NPW

Sustained winds 40+ mph (35 kts) for 1 hr or more, or any gust 58+ mph (50 kts)

EXCESSIVE HEAT WARNING - NPW

A 3 hr period of Heat Index 105 or more; continue into the night with Heat Index around 80 or more. Can be issued at lower heat index values for consecutive days of excessive heat.

RED FLAG WARNING - RFW

Winds 15+ mph (20 ft level on NFDR sites), RH 25% or lower, temps 75+F, and critically dry fuels combine to produce extreme fire danger and/or fire behavior within 24 hours in coordination with governement land management agencies

FREEZE WARNING - NPW

During growing season, widespread temps of 32 F or less

RED FLAG WATCH - RFW

Issued when Red Flag Warning criteria is expected 24 to 48 hours in the future

NON-PRECIP WATCH - NPW

Issued when Warning criteria is expected 12-48 hours in the future

AIR STAGNATION ADVISORY - NPW

Major buildup of air pollution/particulate due to stable atmos. conditions (initiated by Michigan EGLE)

HEAT ADVISORY - NPW

A 3 hr period of Heat Index 100 or more; continue into the night with Heat Index around 80 or more. Can be issued at lower heat index values for consecutive days of excessive heat.

WIND ADVISORY - NPW

Sustained winds 30+ mph (26 kts) for 1 hr or more, or any gust 45+ mph (39 kts)

DENSE FOG ADVISORY - NPW

Widespread vsby 1/4 mile or less for 3 hours or more

DENSE SMOKE ADVISORY - NPW

Smoke producing widespread or localized vsby 1/4 mile or less

BLOWING DUST ADVISORY - NPW

Widespread/localized vsbys less than 1 mile for 3 hrs or more with sustained winds 25 mph

FREEZING FOG ADVISORY - NPW

Fog, usually with vsby 1/2 mile or less, freezing on cold objects with deposits resulting in

impact to commerce, transportation, people, etc.

FROST ADVISORY - NPW

During growing season, widespread frost (temps usually 33-37 F)

DENSE FOG - SPS

Vsby 1/2 mile or less