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National Weather Service Weather Forecast Office

Denver/Boulder, CO

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"Reporting Severe Weather"

Spotters provide an invaluable service to their communities and to the National Weather Service.

Spotter reports help your community by assisting local public safety officials in making critical decisions to protect lives – when to sound sirens, activate safety plans, etc

Spotter reports also help the NWS in the warning process. Your report becomes part of the warning decision making process, and is combined with radar data and other information and used by NWS forecasters to decide whether or not to:

• Issue a new warning
• Cancel an existing warning
• Continue a warning
• Issue a warning for the next county
• Change the warning type (from severe thunderstorm to tornado, for example)

For your reports to be the most useful, they should be as detailed, accurate and timely as possible.  Use the guidelines below to help you make your report:

WHAT TO REPORT

Weather Events

Although reporting criteria may vary slightly depending on the spotter network and local needs, these are the events the National Weather Service would like to know about as soon as possible:

TYPE OF EVENT	WHEN TO CALL	NWS WARNING CRITERIA/ ADDITIONAL INFORMATION
TORNADO	Always Call - ALSO CALL 911	Tornado Warning Issued. Look for debris on the ground
FUNNEL CLOUD/ WALL CLOUD	Always Call	Look for organized, persistent, sustained rotation
HAIL	Call if Half-inch size or larger**	Severe Thunderstorm Warning Issued: 1 inch diameter or larger. Always report the largest size hailstone
WIND GUSTS	Call if 50 mph or higher	Severe Thunderstorm Warning Issued: Sustained 40 mph. Gusts to 58 mph or greater. Specify estimate or measurement
HEAVY RAIN/ FLOODING	1.0" rain/hr or greater for urban areas. 1.5" rain/hr or greater for rural areas. Also Call 911 for flooding.	Flash Flood Warning issued: Flooding that impacts roads, homes or businesses.
STORM DAMAGE	Always Call	Damage to structures (roof, siding, windows, etc) Damage to vehicles (from hail or wind) Trees or large limbs down Power/telephone poles or lines down Damage to farm equipment, machinery Or any other significant damage

**Quarter size hail (1.00 inch) is considered as severe weather hail.
Again, reports should provide as much detail as possible to describe the where, when, how, etc of the event.

Some commonly used hail sizes

Pea	.25 inch	Golf Ball	1.75 inch
Half-inch	.50 inch	Hen Egg	2.00 inch
Dime	.75 inch	Tennis Ball	2.50 inch
Nickel	.88 inch	Baseball	2.75 inch
Quarter	1.00 inch	Tea Cup	3.00 inch
Half Dollar	1.25 inch	Grapefruit	4.00 inch
Ping Pong Ball	1.50 inch	Softball	4.50 inch

General Guidelines for Estimating Wind Speeds

30-44 mph (26-39 kt)	Whole trees in motion. Inconvenient walking into the wind. Light-weight loose objects (e.g., lawn furniture) tossed or toppled.
45-57 mph (39-49 kt)	Large trees bend; twigs, small limbs break and a few larger dead or weak branches may break. Old/weak structures (e.g., sheds, barns) may sustain minor damage (roof, doors). Buildings partially under construction may be damaged. A few loose shingles removed from houses.
58-74 mph (50-64 kt)	Large limbs break; shallow rooted trees pushed over. Semi-trucks overturned. More significant damage to old/weak structures. Shingles, awnings removed from houses; damage to chimneys and antennas.
75-89 mph (65-77 kt)	Widespread damage to trees with large limbs down or trees broken/uprooted. Mobile homes may be pushed off foundation or overturned. Roof may be partially peeled off industrial/commercial/ warehouse buildings. Some minor roof damage to homes. Weak structures (e.g., farm buildings, airplane hangars) may be severely damaged.
90+ mph (78+ kt)	Many large trees broken and uprooted. Mobile homes damaged. Roofs partially peeled off homes and buildings. Moving automobiles pushed off the road. Barns, sheds demolished.

HOW TO REPORT

Your severe weather report should be detailed but concise, and should address the following questions:

WHAT did you see?

WHERE did you see it?   Report the location/approximate location of the event. Be sure to distinguish clearly between where you are and where the event is thought to be happening (“I’m 5 miles north of Mayberry. The tornado looks to be about 5 miles to my northwest”).

WHEN did you see it?   Be sure that reports that are relayed through multiple sources carry the time of the event, NOT the report time.

Any other details that are important - How long did it last? Direction of travel? Was there damage? etc.

If you are unsure whether to report or not to report, GO AHEAD AND REPORT IT.