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:
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:
Spotter networks usually work best when a central location (an EOC or warning point, for example) collects reports from the local spotter network, then relays a consolidated report to the National Weather Service. This reduces duplicate reports and makes the system flow smoothly.
In this type of network, communication between the spotter and the control point must be clear to avoid misinterpretation. As a report is relayed through multiple sources, the chances for error being introduced into the chain grow.
Look at this example:
"I am 3 miles north of Mayberry on Highway 78. I see a tornado about 5 miles to my northwest. It looks to be moving east along Highway 412"
Spotter report is relayed to another station, who relays it to the county warning point, who relays it to the NWS.
"There is a tornado in Mayberry"
Obviously, the report the NWS received is not accurate - the location and the time are incorrect.
Reporting Severe Thunderstorms and Tornadoes
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:
When to call
- Hail: A thunderstorm is producing hail (stones of ice) larger than a pea. Use coins to compare your hail size. A severe thunderstorm begins at penny size or .75 inches. Once hail becomes larger than coins, compare it to balls such as a golf ball (1.75 inches), tennis ball, softball, etc. On rare occasions, thunderstorms can drop enough hail to begin accumulating like snow. You might report that you have pea size hail but it is now 3 inches deep on the ground!
- Wind: A thunderstorm is causing winds to gust to 60 mph (50 kts) or greater. Estimating winds is difficult. We prefer a measured wind report using an anemometer. If you do not have one, report any wind damage such as to trees (large branches down, trees snapped or uprooted) or damage to property (shingles torn off, etc.) If considerable damage has occurred, if possible, report how large an area seemed to be affected or if you witnessed it, the events that you saw and heard.
- Tornadoes and funnel clouds: On rare occasions, thunderstorms will produce funnel clouds which sometimes touch down as a tornado over land or a waterspout over rivers, lakes, and the bay. A wall cloud is sometimes a precursor to severe weather. A funnel cloud appears as a pendant (or funnel) lowering from a thunderstorm cloud and it is spinning or rotating. Report this! If the rotating winds are touching the ground, it is a "tornado". The funnel cloud need not be visibly touching the ground for a tornado to be on the ground. Look for rotating debris rising up from the ground. Report this immediately!
- Damage: Any storm related damage should be reported. While it is best to have the report close to the event so we can use the information to assist us with issuing warning, the damage report is also important for publishing storm data and research purposes. Therefore, we want this information regardless of how old it might be.
Again, reports should provide as much detail as possible to describe the where, when, how, etc of the event.
| 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 |
| 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. |
Flooding, Flash Flooding and Heavy Rain
Types of Flooding
- Flash Flooding: Flash flooding occurs when torrential rains cause a sudden and dramatic rise in small streams and creeks causing them to flood out of their banks and over roads and bridges. It is the #1 weather killer in the country because people often try to drive through these flood waters and are trapped or swept away. Flash flooding can be a very localized event occurring from one thunderstorm. Flash flooding can also occur when a dam suddenly breaks. The dam may be manmade, or it could be an ice jam or a debris dam that backs up water and then suddenly lets loose.
- River Flooding: After a widespread heavy rain event or rain and snow melt event, the rivers rise out of their banks. Because it takes time for the rain to run into the small streams and then into the rivers. River flooding often occurs after the rain has stopped. People along the lower stems of large rivers may not see the flood waters until 1 to 2 days after the rain has stopped.
- Coastal (Tidal) Flooding: Tidal flooding can occur in the tidal portions of large rivers. Flooding usually occurs when strong and persistent winds such as with a nor'easter, tropical storm (such as Fran in September 1996), or hurricane affects the area. Persistent winds from the east to northeast push the water into the bay and rivers. While the wind lasts, each tide cycle is higher than the previous. A storm surge can occur as the center of the storm moves by and the winds are at their strongest. A storm surge is a sudden dramatic rise in the water level.
When to Call
- Measured rainfall: Call when you measure an inch or more of rain. Sometimes this area gets incredible rains. In a case like that, call as you measure each addition inch.
- Storm Total: Call or e-mail your local NWS office with your final, total measurement of rainfall when it is greater than an inch.
- Flooding: Call whenever flooding is observed. For example, you see a stream out of its banks or flowing across roads, bridges or property. Do not go near this water and do not try to cross it!
- River Spotter: If you live near a river and are interested in becoming a river observer for the National Weather Service, please contact your local NWS office.
Any other details that are important - How long did it last? Direction of travel? Was there damage? etc.
Page Last Updated, 05/08/09