National Weather Service United States Department of Commerce

Dangerous Heat Continues Across the South for Memorial Day; Severe Thunderstorms Along the East Coast

A dangerous early-season heat wave over south Texas, the Central Gulf Coast, and southern Florida will persist through Memorial Day. At or near record daily high temperatures and heat index readings over 115 degrees are possible. Along the eastern seaboard, strong to severe thunderstorms are expected to develop this afternoon and linger into the evening hours. Read More >

APPENDIX A - NATIONAL WEATHER SERVICE PRODUCTS & CRITERIA 
(What to listen and watch for)


WARNINGS

The hazard (tornado, severe thunderstorm, flash flood, etc.) is imminent. The probability of occurrence is extremely high. Warnings are issued based on eyewitness reports or clear signatures from remote sensing devices such as radar and satellite. Lead-time for thunderstorm type events is generally 30 minutes or less. Lead-time for river floods, and winter storms can be 6 to 18 hours or longer.

When severe weather approaches your area, our forecasts become so short term that we are actually "warning" you that a potentially life threatening event is about to happen and to put your protection plan into action. When we issue a warning it means a certain weather phenomena is occurring or imminent.

WARNINGS

CRITERIA

TORNADO WARNING tornado is occurring or imminent
SEVERE THUNDERSTORM WARNING thunderstorm winds 58 mph and/or
hail ¾ inch are occurring or imminent
FLASH FLOOD WARNING short duration (less than 6 hours), intense flooding resulting from torrential rain, dam breaks or ice jams
FLOOD WARNING longer, more gradual flooding usually beginning after 6 hours of excessive rainfall or during spring snow run off
SMALL STREAM FLOOD WARNING short duration (less than 6 hours), intense flooding resulting from torrential rain
URBAN FLOOD WARNING short duration (less than 6 hours), localized intense flooding resulting from torrential rain in city areas which results in damage or closed roads
BLIZZARD WARNING winds 35 mph and falling and/or blowing snow reducing visibility to < ¼ mile lasting for 2 hours or longer
HEAVY SNOW WARNING
Snake River Valley below 3000 feet
4 inches in 12 hrs.... 6 inches in 24 hrs
HEAVY SNOW WARNING
Mountains generally 3000 feet and above
8 inches in 12 hrs.... 12 inches in 24 hrs
ICE STORM WARNING ice storm producing significant and possibly damaging accumulation of ice (usually ¼ inch
WINTER STORM WARNING heavy snow with another winter element (wind, freezing rain, wind chill, etc.)
HIGH WIND WARNING sustained winds 40 mph for at least 1 hour or any gusts 58 mph or more for any duration which are not associated with thunderstorm activity
FREEZE WARNING temperatures at or below 32 degrees over a large area during the growing season
WIND CHILL WARNING Wind chills at or below minus 20 degrees F with a wind of 10 mph or greater are expected.
FROST WARNING don't issue these
DUST STORM WARNING widespread visibilities < 1/4 mile and winds 30 mph or greater

 

WATCHES

When meteorologists have determined that conditions appear right for the development of the hazard and the probability of occurrence is usually greater than 60% a weather watch is issued. Watches generally cover larger areas than warnings. In the case of thunderstorms, less than 30% of the watch area may experience the hazard. However, with larger storms such as winter storms, the entire watch area may be affected. Severe thunderstorm and tornado watches are usually issued 1 to 2 hours before the event begins. The Storm Prediction Center in Norman, OK currently issues all Severe Thunderstorm and Tornado Watches. With flash floods, the length of time can be 3 to 12 hours. For river flood and winter storm watches, lead-times are usually 12 to 36 hours or longer.


The NWS issues watches up to 36 hours in advance of potentially hazardous weather, giving you plenty of time to plan ahead and protect yourself and your family. A Watch means conditions are favorable for certain weather phenomena to occur but it is not expected immediately. Go about your normal activities, but be aware of rapidly changing weather conditions and notify school emergency contact points for potential activation later on. A list of various watches appears on the next page.

WATCHES

CRITERIA

TORNADO WATCH conditions are favorable for tornadic development
SEVERE THUNDERSTORM WATCH conditions are favorable for the development of thunderstorm winds 58 mph and/or hail ¾ inch
FLASH FLOOD WATCH potential for short duration, intense flooding resulting from torrential rain, dam breaks or ice jams
FLOOD WATCH potential for longer, more gradual flooding usually beginning after 6 hours of excessive rainfall
WINTER STORM WATCH potential for a blizzard, heavy snowfall, ice storm and/or high winds
WIND CHILL WATCH potential for wind chill at or below -20°F with a wind of 10 mph or greater
HIGH WIND WATCH potential for sustained winds 40 mph and/or gusts 58 mph for any duration which are not associated with thunderstorm activity

 

ADVISORIES

An advisory is issued for weather that is expected to be a disruption to the normal routine and an inconvenience, but it is not expected to be life-threatening. Advisories are issued for 3 to 5 inches of snow, dense fog, minor street flooding, etc. The time frame is similar to that of a warning. A list of various advisories appear below.

ADVISORIES

CRITERIA

URBAN AND/OR SMALL STREAM FLOOD ADVISORY short duration (less than 6 hours), localized flooding resulting from torrential rain in city areas, non-life threatening
WINTER WEATHER ADVISORY a combination of winter weather (snow, wind, freezing rain, wind chill, drifting snow) that presents a hazard but does not meet warning criteria
BLOWING/DRIFTING SNOW ADVISORY blowing and/or drifting snow which causes reduced visibilities and/or significant travel problems
SNOW ADVISORY
below 3000 feet
Snow Accumulation 3-5 inches in 12 hrs 5 to 9 in 24 hrs
SNOW ADVISORY
Mountains generally 3000 feet and above
none issued -
FREEZING RAIN/DRIZZLE ADVISORY freezing rain event resulting in significant inconvenience and that could lead to life- threatening situations if caution is not exercised
WIND CHILL ADVISORY wind chill forecast of minus 35 degrees F or lower with a 10 mph or greater wind speed
WIND ADVISORY sustained winds 30 to 39 mph lasting for one hour or longer and/or wind gusts 45 to 57 mph for any duration which are not associated with thunderstorm activity
DENSE FOG ADVISORY widespread visibilities reduced to less than ¼ mile because of fog
BLOWING DUST ADVISORY widespread visibilities reduced to less than ¼ mile
because of dust or sand
VOLCANIC ASH ADVISORY whenever it occurs

 

STATEMENTS

Statements are issued to update current weather situations or highlight significant changes to come. Statements are also used to explain why watches, advisories, or warnings have been issued. Four special types of statements include:

  • Special Weather Statements - If strong or severe thunderstorms are expected, a statement is issued discussing this outlook (or potential). The Storm Prediction Center issues special statements when there is the potential for a severe thunderstorm or tornado outbreak.
     
  • Severe Weather Statements - These are follow-ups to severe weather Warnings. They highlight which warnings currently are in effect and detail any reports of severe weather that have been received.
  • Short-term Forecasts ("NOWCASTS") - These are short, concise statements discussing the movement of precipitation during the next few hours or even a shorter time frame (in the case of thunderstorms). They also highlight any other short-term changes, such as increasing cloudiness, drops in temperature, wind shifts, etc. During active weather, these could be issued hourly or even more frequently.
  • Public Information Statements - These statements provide information of special interest such as a summary of recent records set, weather safety information, special activities (weather related) that may be occurring, etc.

 

FORECASTS

General weather and hydrologic information issued daily (times given are listed in Pacific time).

  • 1 to 2 day forecasts are broken into 12 hour increments while the 3 to 7 day extended forecasts list cover a 24 hour period. Both are issued twice a day at roughly 4 AM, and 4 PM, with updates as needed. These zone forecasts are broken down into "zones" across Idaho based on related to climatology and topography. Figure 1 on the next page shows the different zones for Idaho. Special weather events are highlighted with headlines at the top of the forecasts such as ...

    "Severe Thunderstorm Watch in effect until 8 PM this evening"
    "Wind Advisory in effect until 4 PM this afternoon"
    "Flash Flood Watch is in effect until 8 AM Wednesday."
  • State Forecast Products are issued routinely at 400 AM and 400 PM. This product shows a more general forecast trend for three specific regions of Idaho including Northern Idaho, Southwest Idaho and Southeast Idaho.
  • Special hydrologic forecasts are issued during flood season usually around noontime.

NOTE: All of the above (Watches, Warnings, Statements, Advisories, Forecasts) are broadcast continuously on the NOAA Weather Radio.

However, the NWS Forecast Offices also issue other forecasts, such as Aviation Terminal Forecasts and Fire Weather Forecasts (for prescribed burning operations or wildfires). These products are not announced on the Weather Radio.

Spokane Weather Office Forecast Responsibility in Washington

31 Northeast Blue Mountains 37 Northeast Washington Mountains
32 Lower Asotin and Garfield Counties 38 Okanogan Highlands
33 Washington Palouse 41 Wenatchee Area
34 Moses Lake Area 42 East Slopes of Northern Cascades
35 Upper Columbia Basin 43 Okanogan Valley
36 Spokane Area 44 Waterville Plateau


Spokane Weather Office Forecast Responsibility in Idaho

1 Northern Panhandle Mountains 4 Central Panhandle Mountains
2 Coeur d'Alene Area 26 Lewiston Area
3 Idaho Palouse 27 Camas Prairie