St. Louis County R.A.C.E.S. and SKYWARN
"Taking the County by storm."
Severe Weather Reporting Criteria
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The National Weather Service, Central Region, has released a change of criteria to the Severe Thunderstorm Warning guideline:
As of April 1, 2009, the criteria for a Severe Thunderstorm Warning is 1 inch hail (the size of quarters) and/or 58 mph wind for several states in the midwest including Iowa, Illinois, Missouri, Wisconsin, and Minnesota. (Previously and for other parts of the county, the criteria was 3/4 inch (penny size) hail and/or 58 mph winds).
Background
The National Weather Service conducted a demonstration in the state of Kansas and adjoining County Warning Areas over the past four years, utilizing a hail size criterion for issuance of Severe Thunderstorm Warnings of 1” in diameter, rather than the historical ¾” threshold.
The basis for the change...
- Core partners shared concerns about the public becoming desensitized by numerous warnings being issued for marginal hail sizes. A Texas Tech research study, “Hail damage threshold sizes for common roofing materials” (Marshall, T.P., Richard F. Herzog, and Steven K. Smith, 2002:, 21st Conference on Severe Local Storms, San Antonio, TX) cited laboratory tests of numerous types of shingles. These tests showed hail damage to shingles and other roofing materials begins at 1-inch hail diameter.
- Customer responses in Kansas have indicated high satisfaction with adoption of the 1-inch hail criterion.
Expanded Implementation
Beginning in the spring to summer of 2009, this demonstration will expand to include 14 states in the central US, inlcuding Iowa, illinois, Missouri, Wisconsin, and Minnesota.
What does this mean for me?
The bottom line is...fewer Severe Thunderstom Warnings. And when Severe Thunderstorm Warnings are issued, the storms will have the potential to cause damage.
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With the change to the NWS guidelines, this was a good time to post items here we're frequently asked about when requesting spotter storm and/or damage reports. This page also works well as a reference area. If you have additions or questions, please feel free to send me mail at: shelleysh1@att.net.
How to submit a report:
If you're a licensed amateur radio operator, you can call in on 146.940 repeater. Give your callsign, location (closest major intersection) and spotter ID, along with the severe weather and/or storm damage information. It will be immediately passed on to the St. Louis National Weather Service (NWS) office.
If you are not an amateur radio operator you may report your severe weather observation or damage report several ways...
1. If you have internet access, you can report it directly to the NWS via eSpotter. You may register with eSpotter by going to http://espotter.weather.gov.
2. You can call the St. Louis NWS Office direct on their toll free number: (800) 852-7497.
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What to report:
Hail: Although 1" hail is now criteria for the NWS to call a Severe Thunderstorm Warning, they still would like to know about hail, regardless of the size. The occurance of hail, and its size, can sometimes be beneficial to the NWS in determining perhaps whether storm cells are gaining or losing strength, or for other reasons. So we continue to ask for all hail reports, even those less than 1". The following is a helpful chart to follow for measuring hail sizes:
Hail Size Conversion Chart
Pea - 1/4 inch
Penny - 3/4 inch
Quarter - 1 inch
Half Dollar - 1 ¼ inches
Walnut - 1 ½ inches
Golf ball - 1 ¾ inches
Egg - 2 inches
Tennis ball - 2 ½ inches
Baseball - 2 ¾ inches
Grapefruit - 4 inches
Softball - 4 ½ inches
Wind Speed of 58mph or Greater: Estimating wind speed can often be difficult, especially during a severe weather event when stress, excitement and tension levels may be running high. This is known as the "Set Effect" and can somewhat alter our abilities to measure things such as wind speed. In order to make estimates easier, the list below provides guidelines for wind speeds which can help in providing accurate reports.
25-31 mph - large branches in motion
32-38 mph – whole trees in motion
39-54 mph – twigs break off, wind impedes walking
55-72 mph – damage to chimneys and TV antennas, large branches broken and some trees uprooted
73-112 mph – removes shingles, windows broken, trailer homes overturned, trees uprooted
113+ mph – roofs torn off, weak buildings and trailer homes destroyed, large trees uprooted
Flooding and Flash Flooding: Heavy rains can create situations which require important reports from weather spotters. Flooding is dangerous and takes all too many lives every year! Listed below are the flooding and flash flooding reports the NWS would like to know about when we have both fairly short-term periods of very heavy rain and extended periods of rain.
- A rapid rise out of banks flow of a river or stream that poses a threat to life or property.
- Approximately six inches or more of flowing water over a road.
- Any amount of water in contact with, flowing into, or causing damage to an above ground building (does not include water seepage into basements).
- Three feet or more of ponded water which could pose a threat to life or property.
Tornadic Activity:
Wall Cloud: A wall cloud is formed in a supercell thunderstorm. It is a localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. Rotating wall clouds often develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Wall clouds should be reported immediately. Storm chasing can be very dangerous and is not something we encourage! We prefer spotters to report from the safety of their homes (basements).
Funnel Cloud: A true funnel cloud rotates, but has no ground contact or debris, and is not doing damage. If it is a low-hanging cloud with no rotation, it is not a funnel cloud. Caution: tornadoes can happen without a funnel; and what looks like "only" a funnel cloud may be doing damage which can't be seen from a distance. Some funnels are high-based and may never touch down. Still, since a funnel cloud might quickly become a tornado (remember rotation!), it should be reported.
Finally, if you do observe a tornado, report it after reaching a safe location. Your safety is the most important thing!
Reporting Criteria