Spotter Wind Estimates

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Nov 12, 2004
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Tallahassee, FL
Well I know that spotter hail estimates can't always be as accurate as people would like, but what about wind estimates? In my opinion thats harder to gauge because you don't have a handy reference system like objects to compare hail to. So my initial warmup question is how exactly do you estimate wind speeds? Prior experience? Look at surrounding obs and kind of interpolate your thoughts?

Thanks!
 
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Alex, here's the Beaufort Scale to estimate wind speeds:

25 - 31 MPH: Large branches in motion; whistling in overhead trees/wires.

32 - 38 MPH: Whole trees in motion.

39 - 54 MPH: Twigs break off trees; wind impedes walking.

55 - 72 MPH: Damage to chimneys; shallow rooted trees blown over. Limbs around 6" in diameter (average size wrist) break off trees.

73 - 112 MPH: Peels surface off roofs; windows broken; mobile homes overturned; moving cars blown off road.

113+ MPH: Widespread damage to homes and buildings.
 
Well thats partially what I based my table off of, but I needed to narrow it down a bit more. For instance the Beaufort Scale goes from severe threshold winds to hurricane force winds with nothing to narrow it down a bit. But yes, I did try to use that. :)
 
Here's another then...I'm not sure how old it is because some of the wording is odd.

Order is as follows:
Beaufort number); MPH; International Description; (Specifications)

0) <1 MPH Calm (calm; smoke rises vertically)

1) 1-3 MPH Light Air (direction of wind shown by smoke drift not by wind vanes)

2) 4-7 MPH Light Breeze (wind felt on face; leaves rustle; vanes moved by wind)

3) 8-12 MPH Gentle Breeze (leaves and small twigs in constant motion; wind extends light flag)

4) 13-18 MPH Moderate (raises dust, loose paper; small branches moved)

5) 19-24 MPH Fresh (small trees in leaf begin to sway; crested wavelets form on inland waters)

6) 25-31 MPH Strong (large branches in motion; whistling heard in wires; umbrellas used with difficulty)

7) 32-38 MPH Near Gale (whole trees in motion; inconvenience felt walking against wind)

8) 39-46 MPH Gale (breaks twings off trees; impedes progress)

9) 47-54 MPH Strong Gale (slight structural damage occurs)

10) 55-63 MPH Storm (trees uprooted; considerable damage occurs)

11) 64-72 MPH Violent Storm (widespread damage)

12) 73-82 MPH Hurricane (widespread damage)

http://spotterguides.us/basic/basic05.htm

Just a little way down the page you will find a wind speed estimate guide.
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That must be the updated version of the old one I have....thanks!
 
I think your asking for the impossible, short of having an anemometer and taking a direct measurement.

Why? Every twig, branch and limb is different. All lawn furniture is not made of the same material, or the same weight, or might be tied down. There are too many variables from any given item to another similar item.

Seriously, if it's that important to be that exact, you need an anemometer.

EDIT: And really, does a spotter report necessarily NEED to be that precise? You can always just report what you saw blowing around or damaged and let the forecasters factor that report into their warning decisions. Keep in mind it's storm spotting, not scientific research.
 
Seriously, if it's that important to be that exact, you need an anemometer.[/b]
And, if mounted on your vehicle, get it out of the wind envelope of your vehicle. Usually this means at least 2-3 feet above the roof. Otherwise, the wind estimates will be off, and most likely higher than the actual wind.
 
Indeed it would be nice to have a more narrowed down "visual scale" but let's face it, it's hard enough to get many spotters to stop reporting it's dark with light rain right after the net control just announced they only wanted tornado reports right now. heh

As for me personally, I always sucked at visually estimating wind and hail sizes, thus one of the main reasons I have a weather station on the chase vehicle and carry a steel ruler. Then I can confidently give a MEASURED report.

EDIT: Second what Greg said, you gotta get that thing up in the air. Those little cheap magmount wind speed indicators will give you bad readings at times.
 
I have a hand-held anemometer that I use whenever I need it. Most chase days, it sits in my car, unless I feel inclined to measure the inflow speed, etc. I tend to use it most during the squall line chases, when I plop myself in the path of the gust front, put on the rain suit, and hold the anemometer high.

As far as guestimating? I don't really even try too much. I think most chasers could give a decent wind estimate +-10 mph, and most spotters could probably do +- 15 mph. I'm not knocking the spotters, but I think wind speed estimation comes from a lot of practice/experience, and chasers tend to have more experience around high winds (RFD, etc) than non-mobile spotters. It is common, however, for most wind reports to be overestimates (sometimes, gross overestimates). IMO, this is a perseption issue -- 70mph winds "look" a lot worse than 35 mph (worse than most would say to be "twice" the speed). I think people see this during hurricanes and tropical storms a lot. "Man, the winds MUST have been at least 110-120mph! I've never seen anything like it"... Well, how often do people REALLY see 70-80mph winds? Not often, that's for sure.

Of course, being around high wind events doesn't do anything unless you know what the actual speed of the wind is so you can file it, along with what it "looks" like, away in your mind. As David noted, every situation seems different, so it'd be tough to get a really good estimate anyway.
 
This is one thing that has bothered me for years.
In most spotter guides, they state what the tree's limbs should look like when a certain wind speed is reached, such as 60mph wrist sized limbs break off trees. However, A branch that has zero leaves, like the case right now in most area, will not be broken at the same wind speed as one which has leaves. This can throw off measurements based on trees and tree limb damage greatly.

As stated earlier, the best way is to own an anemometer. When i bought my hand held i thought it was the best buy i have made since my vid. cam. and still think so today.
 
Spotter wind estimates are a known weakness, often VASTLY overestimated. I tell spotters to try to use Beaufort scale information to make their estimates. I know I usually make an initial estimate and knock off 10-15 mph for what is likely to be the actual wind.

I remember a story from (I think) our MIC about a national WCM conference where several attendees were asked to enter a wind tunnel and let the operators know when they thought the winds reached severe criteria. Most everyone indicated severe winds at only 40-45 mph, and these are the professionals.
 
In my limited experience, I have found that I get the most accurate results when I watch the debris, blowing rain, etc. and track it with my eyes like it is a car travelling at that speed. Most of us can guess the speed of a travelling car pretty well. You can actually practice this just by watching cars on the road. This method plus your experience will give you good results.

I know it sounds crazy, (and it probably is a little crazy for the matter :) ) but it really works. The Beaufort scale just didn't work here, as the trees don't break at all unless the winds are greater than 120mph, and hand held anemometers really aren't that fun to use in winds that strong.

Just my 2 yen
 
On the hurricane side, my impression is that many hurricane chasers overestimate winds-- sometimes very generously.

For example, on the leading, weaker side of Hurricane Wilma, one of my companions described the winds as "over 100 mph". But almost all of the trees in the nearby parking lot were still standing, so the estimate seemed extravagant. I think the winds were perhaps gusting to 60 or 70 kt. (Note: Winds were much more severe later, after the eye.)

In another example, I saw video footage from an experienced chaser who estimated the winds at 110 mph. But the footage showed his friend walking (with difficulty) in those winds, which would not be possible at 110 mph. Furthermore, cheap-looking strip-mall signs in the shot were not getting blown out. To me it looked more like 50 or 60 kt-- and when I compared the chaser's location with the HRD wind swath, my estimate was pretty close.

Generally, I'm pretty conservative in my estimates. I find it very difficult to estimate winds while they are happening-- I don't have enough experience and the Beaufort scale seems very subjective, very difficult to apply.

To get a very rough, ballpark idea of wind speeds after the storm has passed, I base my estimates on observed damage according to the Saffir Simpson scale-- in the same way that one uses the Fujita scale to class a tornado based on damage. For example, if there are lots of trees blown down and signs blown out, some broken windows, and plentiful examples of roof surfaces and/or small portions of roof removed (but no complete unroofings), I would correlate that with high-end Cat 1/low-end Cat 2 and estimate max winds around 80-85 kt. The Saffir-Simpson scale wasn't meant to be used this way, but since I haven't had any formal training for estimating winds, this is the best I can do. :)
 
On the hurricane side, my impression is that many hurricane chasers overestimate winds-- sometimes very generously.

In another example, I saw video footage from an experienced chaser who estimated the winds at 110 mph. But the footage showed his friend walking (with difficulty) in those winds, which would not be possible at 110 mph. Furthermore, cheap-looking strip-mall signs in the shot were not getting blown out. To me it looked more like 50 or 60 kt-- and when I compared the chaser's location with the HRD wind swath, my estimate was pretty close.

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This is a big problem visually estimating winds. Somebody at the walking/biking/jogging level is experiencing a dramatically different wind that at standard anemometer level (10m). So you're outside experiencing the wind on your body trying to estimate what the wind is at 10m and there could be a 50% difference. At the same time you're looking at the wind impacts on trees in order to estimate the wind and the trees are most likely exposed to the wind much differently than a standard anemometer setting. Unfortunately we're all trying to relate winds to more official anemometer readings. Where's the official reading taken but at an airport like setting with nothing around except grass. We're typically a long ways away from that site.

A great place to feel a wide variety of winds as close as possible to an official anemometer is Mt. Washington, or the nearest wind tunnel.
 
This is a big problem visually estimating winds. Somebody at the walking/biking/jogging level is experiencing a dramatically different wind that at standard anemometer level (10m). So you're outside experiencing the wind on your body trying to estimate what the wind is at 10m and there could be a 50% difference. At the same time you're looking at the wind impacts on trees in order to estimate the wind and the trees are most likely exposed to the wind much differently than a standard anemometer setting. Unfortunately we're all trying to relate winds to more official anemometer readings. Where's the official reading taken but at an airport like setting with nothing around except grass. We're typically a long ways away from that site.

A great place to feel a wide variety of winds as close as possible to an official anemometer is Mt. Washington, or the nearest wind tunnel.
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Yeah, that's a good point Re: the standard for a truly representative sustained wind reading (1-min average at 10-m elevation in an exposed location). And it makes you realize how few readings and estimates actually conform to this standard. I know the HRD has a variety of formulas for converting readings taken at non-standard elevations/averaging periods to the 10-m/1-min standard-- but even then, I imagine the conversions can only be so accurate, as every cyclone has a unique wind profile.
 
Of all the information that forecast offices receive from spotters, wind speed estimates may be the most prone to error. Some reports are based on damage while others are based on spotter-derived estimates. These estimates are very subjective! While spotters do their best, they tend to overestimate win speeds (LaDue, 2003).

This issue can be a particular problem at marginally severe or sub-severe wind speeds since more attention has been paid to observing these events over the last several decades (Weiss et al., 2002).

In the cases where damage is reported, there is at least some objective result to the wind event. The problem is that wind damage is often not well reported (or not well documented before it gets to the warning forecaster).

From a small sample of events, we found that reports in phone logs generally had some flavor of wind damage listed in only 1 in 5 reports. The climatological record also lacks detailed records of damage
for ¾ of reports (Weiss and Vescio, 1996).

Even if damage is reported, much of the wind damage reports are characterized by tree damage. It’s doubtful that many spotters know all the factors that may impact how strong winds must be to damage a tree. In some areas of the country, significant tree damage can occur at wind speed below the severe criteria.

The point here is that it is very easy for spotters to misjudge the intensity of thunderstorm winds. How are warning forecasters supposed to know if spotters are getting it right?

While wind gust estimates may not always be accurate, they do have value. Much like hail reports, forecasters should be aware of people seeming to repeat back forecast wind speed values from your products.

In our review of some previous events, it was found that about 2/3 of wind reports included some kind of wind estimate.

Instead of focusing on the numerical value of the wind estimate, it might be better to look at where the estimate fits into a range of values relative to the severe threshold. Say something like 0-20 (light), 20-45 (strong, but definitely sub-severe), 45-65 (marginally sub-severe to marginally severe), 65-80 (definitely severe), and 80+ (take cover now).

The numbers will, and should, vary depending on your CWA. One key to such a system is to have a good idea at what wind speed tree and other wind damage occurs in your CWA. Why you ask? So you can use reports of wind damage to QC the wind estimates. Of course, you can’t use wind damage to quality control estimates if you don’t receive reports of damage.

When a report comes in, especially if you’re receiving a first hand report, ask if there was any damage. Make sure you document the answer! You’re likely to forget which damage occurred where in a few minutes if you don’t! Another good way to QC wind estimates, if possible, is to use measured wind speeds from METARs, mesonet sites, or spotters (via portable or hand-held anemometers) located near by.

It is helpful if peak gust values from these sites can be recorded on spotter log sheets as storms move through. Even if the data comes in minutes, or an hour later, it helps to get the information in your logs.

From: http://www.wdtb.noaa.gov/courses/awoc/docu...sson3_print.pdf[/b]

Mike
http://www.chaseseason.blogspot.com/
 
My favorite ones are examples given instead of speeds. One I heard one night when asked by the NWS over the radio was "Well, I'm in a Tahoe and have made a couple of unintentional lane changes". I think citing damage can be more informational than guestimating speeds (or in addition to guestimation).
 
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