High Winds

Severe Thunderstorm Element: HIGH WINDS
Copyright Skip Voros, WD9HAS, Executive Director MASA Inc.

Damaging thunderstorm winds are another one of the life-threatening elements of severe storms. In 1995 approximately 38 people
were killed nationally and another 473 injured because of destructive winds. The financial losses were over 745 million dollars.
[In 1996 Wisconsin had one fatality and 12 injuries.]

Normally the straight-line thunderstorm winds flowing out from a storms downdraft do not exceed about 30 miles per hour. However
when such outflow winds reach 58 MPH (50 knots) or higher, the thunderstorm is then classified as severe.

Damaging thunderstorm winds have been termed Downbursts by the late and renowned severe storms researcher Dr. Ted Fujita,
and he further classifies these events as Macrobursts when the damage area is larger then 2.5 miles, or Microbursts when the
damage area is less then 2.5 miles. Downbursts can cause damage equivalent to a 'strong' tornado and are extremely dangerous
to aviation, especially aircraft taking off or landing.

In May of 1995 at the Grissom Air Force Base in Indiana, a downburst event was measured at 135 MPH. [On July 4th, 1977 one
the country's worst downbursts occurred in northern Wisconsin, winds reached more than 115 MPH and a damage swath over
150 miles long flattening hundreds of thousands of acres or forest land.]

Many wind storm survivors often feel consolation in saying they were in a tornado, when in fact downburst winds were in affect.
Downbursts are characterized by divergent, broad, and diffuse damage tracks, and a lack of rotation about a vertical axis. Aerial
surveys after the fact best reveal these facts.

WIND SPEED REPORTS

Without a fixed or portable wind speed indicator (anemometer) it is sometimes difficult to accurately judge wind speed. In a worst
case event when the storm spotter has little or no training on wind estimates, he should describe/report the winds effects on man-
made or natural objects: "A 12 inch tree trunk has been snapped, 8 inch tree limbs are across the road, numerous electric poles
have been snapped, a 4 foot brick chimney has been toppled, metal garbage cans are airborne, the 10x16 foot highway billboard
has been toppled," etc.

As a helpful aid to the SKYWARN storm spotter who is without a permanent wind speed indicator or is in a remote and unfamiliar
location without a portable anemometer is the chart produced by the National Weather Service issued January 6th 2003 in their
10-1605 directive.

WIND SPEED ESTIMATES BASED ON DAMAGE:

WIND SPEED	OBSERVATIONS
30-44 Mph	Trees in motion. Light-weight loose objects (e.g., lawn furniture) tossed or toppled.
45-57 Mph	Large trees bend, twigs, small limbs break, and a few larger dead or weak branches may brake. Old/weak structures (e.g., sheds, barns) may sustain minor damage (roofs, doors). Buildings partially under construction maybe damaged. A few loose shingles removed from houses. Carports may be uplifted, minor cosmetic damage to mobile homes and pool lanai cages.
58-74 Mph	Large limbs break, shallow rooted trees broken/uprooted. Semi-trucks overturned. More significant damage to old/weak structures. Shingles, awnings removed from houses, damage to chimneys and antennas; mobile homes, carports incur minor structural damage; large billboard signs may be toppled.
75-89 Mph	Widespread damage to trees with trees broken/uprooted. Mobile homes may incur more significant structural damage; be pushed off foundations or overturned. Roofs 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	Many large trees broken or uprooted. Mobile homes severely damaged; moderate roof damage to homes. Roofs partially peeled off homes and buildings. Moving automobiles pushed off dry roads. Barns, sheds demolished.
Note: All references to trees are for trees with foliage. Significantly higher winds may be required to cause similar damage to trees without foliage. Very wet soil conditions may allow weaker winds (30-57 Mph) to uproot trees. Storm spotters are not expected to be structural engineers and you can not judge wind speed strictly by damage alone. The quality of construction techniques and materials used greatly affect the end result.

All wind speed reports should be qualified, that is they are either an ESTIMATE of speed, or an actual MEASUREMENT of speed.
You never want to hear something like: "the winds are very strong, boy, its really getting bad." That type of report indicates the
spotter is responding emotionally and offers no useful information.

         "This is station/squad X2... ESTIMATED wind speed of 60 MPH" at hy. 83 and Miller road, Milwaukee County, at 4:06 PM," 
          or: "W9xxx... MEASURED wind gust of 72 MPH at........."  is the appropriate reporting format.

          If wind speed direction is requested, remember the direction is FROM which way the winds are blowing. Do not judge surface wind 
          direction by cloud movement....upper level wind fields often move at different directions than do the surface (ground level) winds. Check 
          with local spotter groups to determine their specific reporting criteria and reporting format.

THE "SET" EFFECT.....

Storm spotters must also keep in mind that during a severe weather event, Stress, Excitement, and Tension levels are running high.
This is called the "SET" effect, and it can alter your logic and reasoning abilities. Because of its presence, it is often very easy to
over estimate wind speed reports.....

                         A wind gust of 40 MPH during a fair weather day will not cause any great concern, but this same wind speed 
                         gust when experienced during severe weather  may seem like 55-65 MPH gust because of the SET effect.

When in doubt about your estimate, re-think it and try to remain calm and objective as possible. Your goal is to pass real time
observations with accuracy, speed, and professionalism.

Original copyright 1998 by Milwaukee Area SKYWARN Association, Inc., Non Profit & IRS 501c3 Tax Exempt.
Updated 2/8/03, 1/20/06, 11/4/08. Copy and paste is a plagiarism and a copyright violation. Ask permission to
use this material. Violators subject to criminal prosecution. Copyright 2008 MASA.

Severe Thunderstorm Element: HIGH WINDS Copyright Skip Voros, WD9HAS, Executive Director MASA Inc.

WIND SPEED REPORTS

WIND SPEED ESTIMATES BASED ON DAMAGE:

THE "SET" EFFECT.....

Severe Thunderstorm Element: HIGH WINDS
Copyright Skip Voros, WD9HAS, Executive Director MASA Inc.