Garrett’s Blog: How Strong Was Arkansas’ Tornado?

Debris hangs from a tree after a tornado hit the town of Mayflower, Arkansas

The National Weather Service – Little Rock – expects to find EF3 Tornado damage in the Mayflower or Vilonia along a damage path some 40 miles long. The damage survey may take several days to be completed but damage they’ve already seen is consistent with winds from 136-165mph.

The damage survey uses the Enhanced Fujita Scale to estimate wind speeds with 28 damage indicators. The enhanced version was put into practice in 2007 and reflects changes in wind engineers and how structures or vegetation respond to a 3 second wind gust.

These are the 28 Damage Indicators they’re evaluating. You can click on the “degree of damage” number on the right for a look at how each variable is evaluated.

DI No. Damage Indicator (DI) Degrees of Damage (DOD)
1 Small Barns or Farm Outbuildings (SBO) 8
2 One- or Two-Family Residences (FR12) 10
3 Manufactured Home – Single Wide (MHSW) 9
4 Manufactured Home – Double Wide (MHDW) 12
5 Apartments, Condos, Townhouses [3 stories or less] (ACT) 6
6 Motel (M) 10
7 Masonry Apartment or Motel Building (MAM) 7
8 Small Retail Building [Fast Food Restaurants] (SRB) 8
9 Small Professional Building [Doctor’s Office, Branch Banks] (SPB) 9
10 Strip Mall (SM) 9
11 Large Shopping Mall (LSM) 9
12 Large, Isolated Retail Building [K-Mart, Wal-Mart] (LIRB) 7
13 Automobile Showroom (ASR) 8
14 Automobile Service Building (ASB) 8
15 Elementary School [Single Story; Interior or Exterior Hallways] (ES) 10
16 Junior or Senior High School (JHSH) 11
17 Low-Rise Building [1–4 Stories] (LRB) 7
18 Mid-Rise Building [5–20 Stories] (MRB) 10
19 High-Rise Building [More than 20 Stories] (HRB) 10
20 Institutional Building [Hospital, Government or University Building] (IB) 11
21 Metal Building System (MBS) 8
22 Service Station Canopy (SSC) 6
23 Warehouse Building [Tilt-up Walls or Heavy-Timber Construction] (WHB) 7
24 Electrical Transmission Lines (ETL) 6
25 Free-Standing Towers (FST) 3
26 Free-Standing Light Poles, Luminary Poles, Flag Poles (FSP) 3
27 Trees: Hardwood (TH) 5
28 Trees: Softwood (TS) 5

An interesting side note, the original Fujita Scale actually had 12 levels and was based on the Beaufort Wind Scale. The wind speeds are only theoretical and thankfully atmospheric winds within thunderstorms don’t reach Mach 1 speeds.

300px-Fujita_scale_technical_svg

-Garrett



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