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Used with permission, Jeff Koterba/Omaha World-Herald. |
Does your mother know the difference between the damage that can be done by 58 mph winds and 91 mph winds? I didn’t think so. Everyone knows that 91 mph is worse than 58 mph, but Mom probably doesn’t know how much worse. She’s not alone. And that’s part of the reason so many people were surprised by how much damage the June 29, 2012 derecho did.
When a thunderstorm produces winds of at least 58 mph the National Weather Service (NWS) issues a severe thunderstorm warning. The June 29 derecho produced a measured wind gust at Fort Wayne International Airport of 91 mph. What does NWS do when thunderstorm winds reach 91 mph? It issues … a severe thunderstorm warning.
Beginning April 1, 2013, the NWS Northern Indiana weather forecast office will join all other offices in the NWS central region in an experiment to test of a new type of storm warning. “Impact-based warnings” are designed to help people understand the difference between barely severe storms and storms like the one we had June 29, by indicating what the storms might do.
For example, at 3:09 p.m. June 29, NWS issued a severe thunderstorm warning for several northwestern Ohio counties (Example 1). It included the following text: “This storm has a history of producing destructive winds in excess of 80 mph. Seek shelter now inside a sturdy structure and stay away from windows!” Notice that the warning mentioned a wind speed and action to take but said nothing about what that wind might do.
Example 1: 2012 Severe Thunderstorm Warning
BULLETIN – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE NORTHERN INDIANA
309 PM EDT FRI JUN 29 2012
THE NATIONAL WEATHER SERVICE IN NORTHERN INDIANA HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR…
WESTERN ALLEN COUNTY IN WEST CENTRAL OHIO…
SOUTHERN DEFIANCE COUNTY IN NORTHWEST OHIO…
PAULDING COUNTY IN WEST CENTRAL OHIO…
VAN WERT COUNTY IN WEST CENTRAL OHIO…
SOUTH CENTRAL HENRY COUNTY IN NORTHWEST OHIO…
PUTNAM COUNTY IN WEST CENTRAL OHIO…
* UNTIL 400 PM EDT
* AT 304 PM EDT…NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DESTRUCTIVE WINDS
IN EXCESS OF 80 MPH. THESE SEVERE STORMS WERE LOCATED ALONG A
LINE EXTENDING FROM 27 MILES NORTHWEST OF ANTWERP TO 12 MILES
WEST OF PAYNE TO 24 MILES SOUTHWEST OF OHIO CITY…AND
MOVING EAST AT 65 MPH.
* LOCATIONS IN THE PATH OF SEVERE THUNDERSTORMS INCLUDE…
PAYNE…ANTWERP AND CONVOY…
PAULDING…VAN WERT AND OHIO CITY…
SPENCERVILLE AND DEFIANCE…
DELPHOS…OTTOVILLE AND CONTINENTAL…
ELIDA…
OTHER LOCATIONS IMPACTED BY THESE SEVERE THUNDERSTORMS INCLUDE
WORSTVILLE…TIPTON…MIDDLEBURY…MARK CENTER…BRICETON…SCOTT…
LATTY…HAVILAND…CECIL…CAVETT…THE BEND AND SHERWOOD.
PRECAUTIONARY/PREPAREDNESS ACTIONS…
DOPPLER RADAR HAS INDICATED SOME WEAK ROTATION WITHIN THIS LINE OF
SEVERE THUNDERSTORMS. SEVERE THUNDERSTORMS CAN PRODUCE TORNADOES WITH
LITTLE OR NO WARNING. IF A TORNADO IS SPOTTED…ACT QUICKLY AND MOVE
TO A PLACE OF SAFETY IN A STURDY STRUCTURE…SUCH AS A BASEMENT OR
SMALL INTERIOR ROOM.
THIS STORM HAS A HISTORY OF PRODUCING DESTRUCTIVE WINDS IN EXCESS OF
80 MPH. SEEK SHELTER NOW INSIDE A STURDY STRUCTURE AND STAY AWAY FROM
WINDOWS!
TO REPORT SEVERE WEATHER…CONTACT YOUR NEAREST LAW ENFORCEMENT
AGENCY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE
IN NORTHERN INDIANA.
&&
LAT…LON 4064 8404 4064 8410 4065 8411 4065 8421
4068 8422 4068 8437 4071 8445 4072 8445
4072 8449 4084 8480 4135 8472 4127 8400
TIME…MOT…LOC 1908Z 269DEG 58KT 4154 8487 4104 8487
4054 8487
WIND…HAIL 80MPH <.50IN
Example warnings courtesy Michael Lewis, warning coordination meteorologist, NWS Northern Indiana
Had impact-based warnings been in effect that day, the same warning would have included language like this: “Impact … damage to vehicles…buildings…roofs and windows. Trees uprooted and large branches up to 9 inches in diameter down.” (Example 2). Impact-based warnings will also tell us whether a storm is indicated by radar or actually observed by humans.
Example 2: Mock Impact-Based Severe Thunderstorm Warning
BULLETIN – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE NORTHERN INDIANA
309 PM EDT FRI JUN 29 2012
THE NATIONAL WEATHER SERVICE IN NORTHERN INDIANA HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR…
WESTERN ALLEN COUNTY IN WEST CENTRAL OHIO…
SOUTHERN DEFIANCE COUNTY IN NORTHWEST OHIO…
PAULDING COUNTY IN WEST CENTRAL OHIO…
VAN WERT COUNTY IN WEST CENTRAL OHIO…
SOUTH CENTRAL HENRY COUNTY IN NORTHWEST OHIO…
PUTNAM COUNTY IN WEST CENTRAL OHIO…
* UNTIL 400 PM EDT
* AT 304 PM EDT…A LINE OF SEVERE THUNDERSTORMS EXTENDED FROM 27
MILES NORTHWEST OF ANTWERP TO 12 MILES WEST OF PAYNE TO 24 MILES
SOUTHWEST OF OHIO CITY…AND MOVING EAST AT 65 MPH.
HAZARD…GREATER THAN 80 MPH WIND GUSTS.
SOURCE…TRAINED SPOTTERS.
IMPACT…DAMAGE TO VEHICLES…BUILDINGS…ROOFS AND WINDOWS. TREES
UPROOTED AND LARGE BRANCHES UP TO 9 INCHES IN DIAMETER
DOWN.
* LOCATIONS IN THE PATH OF SEVERE THUNDERSTORMS INCLUDE…
PAYNE…ANTWERP AND CONVOY…
PAULDING…VAN WERT AND OHIO CITY…
SPENCERVILLE AND DEFIANCE…
DELPHOS…OTTOVILLE AND CONTINENTAL…
ELIDA…
PRECAUTIONARY/PREPAREDNESS ACTIONS…
THIS STORM HAS A HISTORY OF PRODUCING DESTRUCTIVE WINDS IN EXCESS OF
80 MPH. SEEK SHELTER NOW INSIDE A STURDY STRUCTURE AND STAY AWAY FROM
WINDOWS!
TO REPORT SEVERE WEATHER…SEND REPORTS VIA TWITTER WITH THE HASHTAG #NWSIWX.
&&
LAT…LON 4064 8404 4064 8410 4065 8411 4065 8421
4068 8422 4068 8437 4071 8445 4072 8445
4072 8449 4084 8480 4135 8472 4127 8400
TIME…MOT…LOC 1908Z 269DEG 58KT 4154 8487 4104 8487
4054 8487
HAIL…<.50IN
WIND…>80MPH
The impact-based warnings experiment includes three forms of tornado warnings, based on the storm’s damage threat. Tornadoes with “considerable” and “catastrophic” damage threats will have new “tags” at the very bottom of the warnings, for example, “tornado damage threat … considerable” and “tornado damage threat … catastrophic.” Note that NWS has been including tags at the bottoms of warnings for the past three to five years (they’re highlighted at the bottoms of the example warnings above). The impact-based warnings experiment expands on these tags to enable users and automated systems to glean information more quickly.
A basic tornado warning will have no damage threat tag. It will include impact language such as, “Significant house and building damage possible.” The vast majority of tornado warnings issued by the Northern Indiana NWS office will look like this.
A “damage threat considerable” tornado warning will include impact language such as, “Major house and building damage likely and complete destruction possible.”
A “damage threat catastrophic” tornado warning will include impact language such as, “This is a life threatening situation. You could be killed if not underground or in a tornado shelter.” The NWS will rarely use the catastrophic language, saving it for storms like the 2011 Joplin, Missouri tornado.
More information about impact-based warnings, including example tornado warnings and a map of NWS offices participating in the experiment, is available on the NWS website.
When a warning is issued, it will be important to access the entire text of the warning. You can do so via NOAA Weather Radio, the Web and some email services. Make sure your friends and family also know how to get the full text of warnings, so they’ll benefit from the impact statements.
Impact-based warnings will make detailed, timely reports from SKYWARN storm spotters even more important. More than ever, NWS will need to know what storms are doing near you; exactly what they’re doing. Did tree limbs come down? How big? Did you see structure damage? Was it just a few shingles blown off or part of a wall blown down? And NWS meteorologists will need that information immediately, especially when a storm system moves as fast as the June 29 derecho did (60 mph). The tornado damage threat tags are especially dependent on spotter reports. Radar data alone is insufficient for NWS meteorologists to determine appropriate damage threat tags.
If we provide the information NWS needs, when it needs it, impact-based warnings could lead to fewer comments like one often heard after the June 29 derecho: “I had no idea it would be that bad.”
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