Re: more questions on wind
Posted by
Chris in Tampa on 5/21/2013, 10:55 pm
Here is more on the EF scale:
http://www.spc.noaa.gov/efscale/
Which links to this document:
http://www.depts.ttu.edu/weweb/Pubs/fscale/EFScale.pdf
They have a whole bunch of things they look at. Greg Forbes from TWC was involved in the EF scale. Last night he said it was an EF5 tornado. There was a large tank that had been thrown a very large distance. Also some blocks that seems to have been thrown a long way. He was also mentioning the trees that been brought down not only had the leaves all gone but some were debarked. Some of those things he had mentioned, though I forget which specifically, made him say it was an EF5. (the large tank was one of them, maybe it came half a mile, I forget the distance he thought it might be) Looking at the document above, debarking can occur at lower wind speeds though too.
That PDF document has a lot of information and graphs. You can see the one and two family residences and elementary school graphs for example. For the residences, for "Destruction of engineered and/or well constructed residence; slab swept clean" the expected is 200 mph wind, with a lower bound of 165mph and higher of 220 mph. I guess there was enough categories that were up around 200 mph. From the aerial damage there were a lot of homes that were completely gone down to the slab and some of those seemed to be well built.
I don't think a tornado is counted as if it was capable of dong EF4 damage had it moved quickly and did EF5 damage because it moved slowly and/or was very large and took longer to move over. I think it differs from hurricanes in that way. I think they just look at the damage and determine based on the damage what it was, not truly dependent on wind speed, but I'm not sure. I took a brief look a the document and it seems very focused on looking at the damage. So if a hurricane was treated the same way, Hurricane Frances would be rated worse than another hurricane that was exactly the same in every other way except the storm motion at landfall. I guess it makes sense if they did that way. Tornadoes don't usually last long and you do not have a whole lot of information on all of them. There movements can be very erratic. Trying to determine an approximate wind speed in addition to trying to be able to determine the motion, which could be whipping around back and forth as it moves along in the same general direction would be hard enough even if you had lots of eyes on it, which happens more and more with people chasing it, but I guess you needed a scale where no one could be there and you have no good radar data, but you can still compare it to other tornadoes. I guess just looking at the damage gives you that.
The Tornado Outbreak of May 20, 2013:
http://www.srh.noaa.gov/oun/?n=events-20130520
I just took a look at the map they posted and noticed it was at Briarwood Elementary that actually had the EF5 damage. From earlier paths it looked like Plaza Towers was more close to the center, but as they say with hurricanes it is not a point. Take a look at the Google Earth file they posted:
http://www.srh.noaa.gov/images/oun/wxevents/20130520/20130520-storm_survey_path_points.kmz
That white tank I think is actually the one Greg Forbes was next to last night.
Briarwood is where everyone did apparently survive, while EF4 was the rating at Plaza Towers. All preliminary I guess still, but Briarwood was newer and had safer areas and despite getting hit worse, there appear to be no deaths.
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE NORMAN OK
250 PM CDT TUE MAY 21 2013
...NWS DAMAGE SURVEY FOR 5/20/2013 NEWCASTLE/MOORE TORNADO EVENT -
UPDATE 3...
...NWS DAMAGE SURVEY HAS NOW RATED THE NEWCASTLE/MOORE TORNADO AS EF5...
.OVERVIEW...
THE NATIONAL WEATHER SERVICE DISPATCHED FOUR DAMAGE SURVEY TEAMS TO
THE PATH OF THE NEWCASTLE/MOORE OK TORNADO. NEW STATEMENTS WILL BE
ISSUED THROUGHOUT THE DAY AS THESE TEAMS REPORT FINDINGS. THIS
INFORMATION REMAINS PRELIMINARY AND THE INFORMATION HERE COULD
CHANGE.
.NEWCASTLE/MOORE TORNADO
RATING: EF5
ESTIMATED PEAK WIND: 200-210 MPH
PATH LENGTH /STATUTE/: 17 MILES
PATH WIDTH /MAXIMUM/: 1.3 MILES
FATALITIES: N/A
INJURIES: N/A
START DATE: MAY 20 2013
START TIME: 2:45 PM CDT
START LOCATION: 4.4 W NEWCASTLE /GRADY COUNTY /OK
START LAT/LON: 35.2580 / -97.6775
END DATE: MAY 20 2013
END TIME: 3:35 PM CDT
END LOCATION: 4.8 E OF MOORE OK /CLEVELAND COUNTY /OK
END LAT/LON: 35.3409 / -97.4007
SURVEY SUMMARY: EXPERTS SURVEYING IN MOORE HAVE DETERMINED DAMAGE IS
EF5 WITH MAXIMUM WINDS OVER 200 MPH. FOUR SURVEY TEAMS CONTINUE TO
INSPECT DAMAGE FROM THIS LONG TRACK TORNADO. INITIAL DAMAGE WAS
FOUND AROUND 4.4 MILES WEST OF NEWCASTLE...SOUTH OF TECUMSEH ROAD
ALSO KNOWN AS NW 16TH STREET AND EAST LAKE ROAD. THE TORNADO TRACKED
NE TO THE INTERSTATE 44 BRIDGE OVER THE CANADIAN RIVER AND THEN TOOK
A MORE EASTWARD TRACK THROUGH MOORE. TORNADO DAMAGE ABRUPTLY ENDS
0.3 MILES EAST OF AIR DEPOT ROAD AND N OF SE 134TH ST.
INITIALLY PRODUCING EF0 AND EF1 DAMAGE THE STORM INTENSIFIED VERY
RAPIDLY IN 4 MILES OR AROUND 10 MINUTES PRODUCING EF4 DAMAGE BEFORE
REACHING INTERSTATE 44. NUMEROUS INDICATIONS OF EF4 DAMAGE WITH SOME
AREAS NOW DETERMINED AT EF5 DAMAGE...THE HIGHEST CATEGORY ON THE EF
SCALE...WITH OVER 200 MPH WINDS.
ADDITIONAL INFORMATION SUCH AS MAXIMUM PATH WIDTH WILL BE UPDATED
AS THE TEAMS COMPLETE THEIR SURVEYS.
$$
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