Radar Meteorology: VIL (Vertically Integrated Liquid) and How To/Not To Use It

What is VIL?

Vertically Integrated Liquid (VIL) is the total amount of rain that would fall if all the liquid water in a column inside a rain cloud (usually a thunderstorm) would be brought  to the surface. Basically what you do is sum up (integrate) all the water in a column.

VIL is not observed, it is calculated based on radar reflectivity. Because of that anything that affects reflectivity affects VIL.

VIL is not the same as precipitable water (PW). PW is a measure of the total water vapor in a column that could be condensed into rain.

The units for VIL  are kg m^-2. It may see, strange that when discussing a 3D cloud volume VIL is measured in kilograms per square meter but it makes a great deal of sense if you consider this:

• A cube of water, siting on the ground 1 meter on a side (a cubic meter) weighs 1000 kg (2,200 pounds or a metric ton).
• The depth of the water over the square meter of land covered is 1 meter or 39.37".
• So a VIL of 1000  kg m^-2 is the same as 1 meter of rain or in English units 39.37".
• VIL values do not reach 1000  kg m^-2 , this is just a reference value I use to explain the concept.

Now we can convert VIL values to inches of rain using this formula:

[VIL/1000] *39.37 = Inches of rain 

Units Check:
[[kg m^-2/kg m^-3] *[in m^-1]] = inches

or the simplified version

VIL * 0.03937 = Inches of Rain

Example: VIL = 79.5 kg m^-2

79.5 kg m^-2 * 0.03937 = 3.13" of rain

We will re-visit this value shortly.

Liquid Water Does Not Float in the Atmosphere!

In fact neither do clouds. Sorry to burst your romantic bubble poetry fans, William Wordsworth was dead wrong when he penned the following:

"I wandered lonely as a cloud 

That floats on high o'er vales and hills, 

When all at once I saw a crowd, 

A host, of golden daffodils; 

Beside the lake, beneath the trees, 

Fluttering and dancing in the breeze." 
I Wandered Lonely As A Cloud
-William Wordsworth (1770 - 1850)

As a side note I do not think William Wordsworth would mind that I called him out, he also said:

OK! Enough English Romanticism, let's get back to radar meteorology.

Because raindrops, cloud drops, hailstones, and dust - all off which are found in a cloud - do not float in the atmosphere something must hold them up.

That something is the force of the updraft. Even in non-thunderstorm clouds - cloud materials are held aloft by updrafts which can be very weak in stratiform clouds. 

The stronger the updraft the more liquid water than can remain aloft and the higher the VIL. 

Strong thunderstorm updrafts also support large hail. But ... Does a large VIL value indicate large hail?

VIL - What Is It Good For?

For years VIL was touted as having great potential for forecasting hail size. Large VIL values meant a strong updraft and that's where large hail is found.

In the 90s NWS even used something called VIL-of-the-Day (VOTD) to forecast hail size. It was not very successful because, VIL it turns out, is subject to many complicating factors.

The truth is, when used alone, VIL is a poor indicator of hail size for a number of reasons:

Complication #1
VIL is calculated using reflectivity and anything that has an effect on reflectivity will modify VIL. 

For example, VIL was intended to measure liquid water only. To remove the contributions of  ice to VIL reflectivity is capped at 56.5dBz. Any return greater than that is reduced back to 56.5dBz resulting in error when no ice is present but reflectivity from water content of an updraft is higher.

When hail is present VIL will be higher than if the column contained only liquid water.

Complication #2
VIL calculations show a raindrop-size bias. In the example below both cubes have the same reflectivity (Z). The left cube has 381.7 mm³ of water while the right cube has 14.1 mm³ of water. But because the two volumes yield the same reflectivity, VIL calculated for the left cube is the same as VIL for the right cube.

Complication #3
A thunderstorm too close to the radar can be partially obscured by the "cone of silence". Because part of the updraft is not sampled, VIL may be underestimated.

Complication #4
The VIL of a thunderstorm far from the radar can be exaggerated or VIL can be underestimated.  

Because the altitude of the radar beam increases as it travels away from the antenna, the beam may overshoot the storm and underestimate VIL or  pass right through a mid level hail core and overestimate VIL. If the storm is far enough away lower storm elevations are not sampled at all.

Complication #5
The upper reaches of the updraft core in tilted thunderstorms may extend out of the sampling  volume into a neighboring grid box resulting in an underestimate of VIL.

Complication #6
A fast moving storm may move so much during the time it takes for an entire volume scan to be completed by a NEXRAD Doppler Radar the upper reaches of the updraft may move out of the sampled volume resulting in an underestimate of VIL.

Complication #7
The VIL equation assumes all reflectivity is from liquid water in the thunderstorm. 

Even small hail is bigger than large rain drops. Hail is also solid and when water coated it backscatters much more energy than raindrops which increases reflectivity and therefore VIL.

When hail is present the calculated value of VIL is too high because of the high reflectivity of hail, not because of high liquid water content. 

Complication #8
VIL is higher for wet hail than dry hail and both backscatter much more energy than even the largest raindrops. 

If radar to storm distance is an issue - See Complication #4 above - the radar beam may pass through the top of the hail shaft where hail is usually drier giving a lower VIL estimate than if the beam passes through lower portions of the hail shaft or through the melting layer where water coated hail produces greater reflectivity.

Complication #9
VIL has air mass and seasonal dependencies primarily based on temperature structure and moisture availability.

The wet bulb temperature (T_w) is the temperature TO WHICH air can be cooled by evaporating water into a column of air.  

The value of  T_w  is always greater than the dew point temperature (T_d) temperature and less than the ambient air temperature EXCEPT at equilibrium (RH = 100%) when 
T_d = T_w = T.

 The web bulb zero level is the lowest altitude where the air can be cooled to 0°C by evaporation.

As hail falls and melts and liquid water drops evaporate in air warmer than freezing the air column can be cooled enough to significantly lower the freezing level.

At elevations lower than the wet bulb zero level evaporation cannot cool the air to freezing so hail always melts as it falls.


When the wet bulb zero height is low (7000' for example)  the radar beam samples hail or other frozen targets through a large vertical distance and VIL is likely to be overestimated and so is hail size.

When the wet bulb zero height, and by implication the freezing level, is high (14,000' for example) melting can take place rapidly and the radar sees a zone of enhanced reflectivity centered on the freezing level. Liquid drops through the large vertical distance beneath the wet bulb zero level return less energy than the hail above, meaning a lower estimate of VIL. 

However if the storm is tall enough and the updraft strong enough the volume of hail above the freezing level can severely skew VIL calculations to higher values.  See the case study below for more.

If the web bulb zero level is high enough even large hail may not make it to the ground.

How VIL and the wet bulb zero level interact is complicated by how warm the air is within a thunderstorm and how quickly it changes vertically (i.e. the environmental lapse rate).

Every storm is an individual with its own quirks.


SO ....

VIL is only good as a crude, first estimate of hail or hail size.  When used with dualpol products and other observations like hail spikes (three-body scatter spikes) and melting layer altitude VIL is more effective.

HOWEVER ....

VIL is a good indicator of updraft strength, but beware of extreme values caused by hail.

AND

A rapid decrease of VIL may indicate a collapsing thunderstorm and the onset of a wet microburst.

FINALLY 

VIL calculations are most accurate: 

• When a storm is a moderate distance from the radar
• The storm is moving slowly
• The updraft is vertical (not tilted) and 
• The freezing level is high.

It just so happens that during the evening of Friday 21 JUL 2017, centered on 8:10PM EDT (00:10z 22 JUL 2017) just such a storm formed south of Cincinnati near Walton, KY.

Case Study: 

High VIL Thunderstorm 21-22 July 2017

The cell we are talking about formed just to the northwest of Walton, KY along a non-frontal surface convergence line. The thunderstorm was moving towards the southeast at 5 mph, according to NWSILN's severe thunderstorm warning.

Digital Atmosphere/Front Paint Surface Divergence Maps

Animated gif with pauses

Quasi-stationary frontal positions are based on surface convergence only. Diffuse summertime fronts located in this manner may suffer from lack of continuity in position, i.e. show a great deal of motion in a short period of time. Plotted with Digital Atmosphere. Fronts drawn with Front Painter avaliable from weathergraphics.com

The updraft core underwent explosive development growing 21,000 feet in 10 minutes. During the same period VIL increased rapidly from 55.5 to 79.5  kg m^-2. 

At 8:10 PM EDT 21 JUL 2017 VIL was measured at 79.5 kg m^-2 equal to 3.13" of rain by KILN NEXRAD Doppler Radar. 

RadarScope Loops - Data time - lower right corner.

With the very high VIL NWSILN was concerned about the development of a wet microburst and issued the following severe thunderstorm warning:

Courtesy: VTEC Browser, Iowa State University

Courtesy: VTEC Browser, Iowa State University

RAOB Plot
From  the KILN sounding 00Z 22 JUL 2017 
Freezing Level 16,192' msl
Wet Bulb Zero Level 14,427' - 15,320' msl
Low Wind Shear Environment

Note: The Wet Bulb Zero level is at most 1765' lower than the freezing level. If maximum evaporative/hail melt cooling took place the lowered freezing level was still very high. In the warm air below the lowered freezing level hail melt would be rapid and it is not likely that much, if any, hail would make it to the surface.

Maximum Reflectivity Profile from GR2Analyst
Maximum Reflectivity in the main updraft at  00:10z

54462' agl (10.1°)  37.5 dbz

44165' agl (8.0°)    52.5 dbz

35836' agl (6.4°)    56.0 dbz

28645' agl (5.1°)    57.0 dbz

23167' agl (4.0°)    61.0 dbz

18653' agl (3.2°)    61.5 dbz

14761' agl (2.4°)    65.5 dbz

8822' agl (1.3°)      60.0 dbz

6335' agl (0.9°)      61.5 dbz

4217' agl (0.5°)      56.0 dbz

Note that the maximum reflectivity (65.5 dbz) is just below the the freezing level on the KILN sounding. The high reflectivity is likely due to melting hail because water coated ice backscatters more radiation than ice or liquid water alone.

GR2Analyst Slice

RadarScope Individual Frames 8:05 PM - 8:10 PM EDT (00:05z - 00:10z)

Tilt 1 0.5° Beam Center Altitude at Walton 4054' Temperature 21.9°C

Tilt 2 0.8° Beam Center Altitude at Walton 6144' Temperature 17.8°C

Tilt 3 1.2° Beam Center Altitude at Walton 8480' Temperature 13.9°

Tilt 4 1.7° Beam Center Altitude at Walton 10792' Temperature 7.6°C

VIL, Reflectivity and hail-size contour (yellow).

Evolution of the Thunderstorm

Time Line of the Thunderstorm's Evolution

23:54 Updraft core reaches the freezing level.
00:05 Updraft core extends up to 48,000', Max VIL reached
00:10 Max VIL maintained, updraft core begins to weaken
00:16 Top of the updraft core down to 33k ft. VIL down to 51.4.
00:21 00:32  Top of updraft core - >+50 dBz - pulsing between 20 - 30k ft.
00:37 Top of 50 dBz core down to 17,000' agl.
00:48 All  >=50 dBz of core gone.

GR2Analyst 3D Volumetric Animation
Animated gif with pauses

3D time lapse of the thunderstorm using GR2Analyst. Red is reflectivity >=50.5 dBz.

Summary

SURFACE CONVERGENCE LINE - The thunderstorm developed in a high surface dew point environment along a non-frontal surface convergence line. 

The convergence was likely due to a quasi-stationary front to the north, southwesterly winds on the back side of a surface high flowing towards the front and the interaction of terrain with the winds.

Despite the moist surface environment, total CAPE from the surface through  750  mb (hPa) was negative based on the nearest sounding at KILN. 

Above the LFC through 100 mb (hPa) 16396 m/53792 ft. agl the total CAPE was 1545.4 J/kg explaining the explosive development.

LOW WIND SHEAR ENVIRONMENT - The vertical wind shear was small leading to a vertical (i.e. not tilted) updraft core.

EXPLOSIVE DEVELOPMENT - The updraft core underwent explosive development after 7:49 PM EDT resulting in a VIL of 79.5 kg m ^-2 that persisted for 5 - 10 minutes. Small to moderate hail developed enhancing  reflectivity and therefore VIL.

Just as the 50 dBz reflectivity core began to decay (about 8:10 PM) a mix of hail and rain was observed on radar at KILN as low as 8565' agl. The sounding temperature at KILN at that level was approximately 13°C (55.4°F) leading to rapid melting.

It is not surprising given the warm atmosphere, rural location and time of day no hail was reported to NWSILN.

Animated gif

RAPID DECAY - The updraft core underwent rapid decay after 8:10 PM EDT and VIL decreased from 79.5 kg m^-2 to 51.4 kg m^-2 in 6 minutes. 

A rapid decrease of VIL can mean a collapsing thunderstorm and that a wet microburst may be developing. 

It can also indicate rapid melting of small hail and the decreasing influence of the enhanced reflectivity of water coated hail. In this case it looks like both were occurring. 

The gradual decline of the storm's echo top on the KILN radar indicates the storm was weakening and not undergoing complete collapse even though the updraft core was rapidly weakening. 

Check out my blog post on the Hilliard, OH microburst for an example of total thunderstorm collapse. Compare the 3D timelapses. You can find it here:

Hilliard, OH Microburst, July 10, 2013

 By 8:13 PM EDT NWSILN became concerned about a wet microburst and issued a severe thunderstorm warning for winds gusts to 60 mph.

"POURING WATER DOWN THE CHIMNEY" - Because the updraft core was not tilted heavy  rain and hail were falling through the updraft core. This is likely the mechanism for the short life of the strong core and its rapid demise.

The mechanical force of falling rain drops and hailstones combined with the thermodynamic effects of melting hail and evaporating rain worked against long-term maintenance of the updraft core.
A more detailed study may show  terrain influences and competition for resources (moisture) with neighboring cells as additional causes of the quick decline.

THE LARGE VIL - was likely caused by a large volume of small to moderate hail and enhanced backscattering as the hail melted in the warm environment. As this hail melted a great deal of thermal energy was removed from the updraft core - another factor shortening the life of the updraft. 

The hail was likely only small to moderate in size because the short life of the strong updraft did not provide enough time for large hail to grow.  Small hail size was also a factor in the rapid the rate of melting.

SEVERE THUNDERSTORM WARNING/WET MICROBURST 

In my opinion this warning was a "good" warning - justified by the information available at the time even though it is an un-verified warning. 

Post-event analysis is different than real-time observation giving more time to dig deep into the available data unlike operational meteorologists at NWSILN who must make decisions quickly.  

Post-event analysis indicates a wet microburst was unlikely because the large VIL observed was likely due to radar reflectivity enhanced by a large volume of small hail and a thunderstorm in decline not rapid collapse. 

However, the KILN 00z sounding does indicate the potential for sufficient evaporative cooling to enhance downdraft outflow by observing  the spread between T_w and T through a deep layer of the atmosphere (see the sounding plot).

FORECASTING MICROBURSTS

Take a look - this is cool!

https://www.weather.gov/media/lmk/soo/pulse_svr_flowchart.pdf

Meteorolgical Software used in this post:

RadarScope Pro Tier 2

GR2Analyst

RAOB

Digital Atmosphere 2015/Front Paint

Other Software used:

Adobe Photoshop CC

Camtasia Studio

Microsoft Excel

GIF Maker (iphone)

Services Used:

VTEC Browser, Iowa State University

Level II Archive, Allison House

College of DuPage, METAR Archive

Tornado Warning 2017.07.07 by @NWSILN - No Tornado but a Good Warning Part III

PART III - 3D Views

3d view of the supercell from the southeast at 21:17:26z. All reflectivity values >+ 52.5 dBz in solid red represent the core of the storm and the heavy rain. Lower reflectivity values are translucent to show general storm structure and higher values are not visible. KILN Radar using GR2Analyst.

 The Bounded Weak Echo Region (BWER) is clearly visible. This is where there is little or no rain due to the warm, moist inflow and the intense, rapid updraft. The rain drops cannot fall through the updraft because it exceeds their terminal velocity. The BWER was formerly called the vault or echo free vault.

The inflow and updraft. The inflow not only transports warm, humid air into the storm but it imports rotation gained from the environment caused by wind shear. The mechanism is partly explained in Part II and more fully explained here:  http://stevehorstmeyer.blogspot.com/2013/03/thunderstorm-primer-part-6-supercell.html

I have now added NROT (normalized rotation we call it N-ROT) to the image. Normalized Rotation was originally developed at SPC and operationalized by Gibson Ridge Software in GR2Analyst. I have found it a remarkably accurate and useful tool in pinpointing tornadoes, even small leading edge spin-ups. This confirms the updraft is rotating.

The final overlay is Spectrum Width which can be roughly understood by calling it turbulence. Imagine a wind blowing in a constant direction and at a constant velocity - that is no gustiness - that ideal wind has a spectrum width value of ZERO. In other words it is not gusty. Now imagine a turbulent tornado or severe thunderstorm updraft environment. Winds are changing direction and gusting violently. In other words the environment is turbulent and the spectrum width is high.  Spectrum Width measures the spread or variation of wind speeds and directions. Above, red is very turbulent and notice how it is in the same location as the updraft and rotation.  Spectrum width is a useful tool when trying to locate tornadoes and severe thunderstorm winds and identifying strong updrafts.

The 3D volumetric time lapse shows the evolution of the supercell and how spectrum width and NROT coincide with the rotating updraft.

Tornado Warning 2017.07.07 by @NWSILN - No Tornado but a Good Warning Part II

PART II:
An Outflow Boundary, An Inflow Jet, and Spin Up

In Part I of this multi-part post I showed you what radar and @NWSILN saw Friday evening 2017.07.07 that lead up to the tornado warning they issued at 5:18 PM EDT (21:18 UTC).

Now we want to look how the spin-up occurred.

The Past as a Key to the Future
 At 3:36 PM EDT (17:36 UTC) KILN Doppler Radar showed an outflow boundary north of the Ohio River stretching from southeast Ohio, westward into southeast Indiana south of Connersville. In the second image the boundary is just north of the line I drew. Notice how you can see it taper off south of Connersville.

The video shows the movement of the outflow. Over southern Ohio it is pushing south while to the west from Finneytown to south of Connersville it is stationary.

An outflow boundary (aka gust front) is a mini front. We mostly think of them as mini cold fronts, the leading edge of air, cooled by evaporation in the downdraft moving away from the thunderstorm.  It is that cool air blast you have often felt before the thunderstorm downpour arrives.

In my experience doing point nowcasting, outflow boundaries can become stationary or stop and turn around. Thunderstorms born from the interaction of inflow jets and outflow boundaries can be tough to deal with when rain threatens an outdoor event.

Outflow boundaries often cause thunderstorms system to strengthen by acting as a source of lift. Warm moist air flowing towards the thunderstorm glide up and over the cold air advancing away from the storm. 

Thunderstorms can be boosted from routine to severe as they encounter outflow boundaries.

Outflow boundaries can also help create rotation in the environment surrounding a thunderstorm. When air is transported into the thunderstorm  and tilted to nearly vertical in the updraft, the rotation gained when inflow interacts with an outflow boundary can add enough spin to the total and help create a tornado.

The images below should give you a basic idea of how it works.

The animation below shows the specifics for the tornado warning of 7July2017.

Finally the last two animations: Watch the shower develop south of Connersville, develop explosively as the inflow jet pushes it into the outflow, merge with the main cell and the velocity couplet (right  panel) form north of Oxford.

 Below: Following the couplet

So it looks like all the elements were there and radar indicated spinup, eventhough there was no tornado in my book this is a good warning.

NEXT: PART III - 3D Views of the storm.

Tornado Warning 2017.07.07 by @NWSILN - No Tornado but a Good Warning Part I

PART I:
What @NWSILN Saw on Radar that Lead to the Warning

The Grey Zone
In the grey zone of meteorological knowledge is that shadowy region between rotation in a thunderstorm and damage on the ground thousands of feet below when a tornado touches down.

Thanks to doppler radar we can clearly see rotation in thunderstorms. Thanks to intense research efforts we now know that the rotation for a tornado is mostly imported to the storm, drawn in with the inflow and tilted to nearly vertical by the updraft. As the inflow is stretched by upwards acceleration in the updraft the rotation rate increases. Spin-up is taking place.

Think of the ice skater.

Voilà! We can now forecast and warn for tornadoes.

Not so fast.  Between cloud base and the ground, in the grey zone, something happens. What it is and how it works is masked by a fog created by an environment too dangerous to make observations, by the small scale of the funnel and by the capricious nature of tornado occurrence.

A Weak Link
We have a weak link in our cascade of knowledge between rotation in the storm and rotation in the environment leading to a tornado on the ground.

That weak link is one reason there are so many false alarms -  tornado warnings without a tornado.

Friday evening, 2017.07.07 was one of those false alarms. But not all false alarms are equal.

A number of tornado warnings have been issued over the years by @NWSILN that have made me cringe. The polite version of my initial comment would be, "Just what are they thinking?" You can probably guess what the gritty version contains.

The tornado warning of 2017.07.07 was not one of those. I was a good but an un-verified warning. Good, because all the elements were there for a tornado touchdown.

Radar Views from Friday Evening 2017.07.07
Take a look at KILN Super-Res Velocity at 5:25PM EDT (21:25 UTC) 2017.07.07. below.

Doppler radar can only measure the component of the wind directly towards or away from the radar which is along a radial like the long arrow.  It does not measure the true wind only the "radial" part of the wind.

At 5:25 PM EDT KILN saw a tight velocity couplet between Oxford and Germantown. Red indicates wind blowing away from the radar or positive velocity. Green indicates winds blowing towards the radar - negative velocity.

Here are some closeup screen grabs.

On the left is reflectivity - precipitation  rate, on the right radial velocity. Remember the true velocity is higher because radar is looking only at the wind component along the radar pulse radial path.

Velocity values peaked a bit higher about 10 minutes before these images.

This is a tight velocity couplet and could indicate enough spin-up for a tornado to touch down. In addition the couplet weakened and strengthened several times, indicating here was plenty of energy and rotation and the couplet was not yet dying. In this case I feel the warning was a good one.

Watch the video to see the velocity couplet form, move and dissipate.

Coming Soon:

Part II - The Meteorology of the Spin-up

Part III - 3D Radar Views

Why I Critisize @NWSILN

Over the years I have not hesitated to be very critical of the National Weather Service Forecast Office in Wilmington, OH.  I will continue to speak out when there is something the public needs to know. After all NWS works, indirectly, for you and you have the right to know how your tax dollars are being spent.

Most recently I discussed what seems to me to be an over-the-top approach to Areal Flood Advisories (AFA). The number issued by @NWSILN is way more, in fact 261% more through July 7, 2017 at 10:10 AM than any other NWSFO in the region. That is the subject of my previous blog post dated July 6, 2017.

A local Cincinnati TV meteorologist suggested that I just ignore the huge number of AFAs because they are not "life threatening". He scolded me for calling attention to @NWSILN and questioning the unusually large number of AFAs.

There is no benefit from his head-in-the sand approach to dealing with real issues that impact public safety. Frankly I was surprised at the naive suggestion by the meteorologist and his reluctance to use his authority to better inform the public.

He is correct that Areal Flood Advisories do not represent immediate life threatening situations. They are meant to call attention to potentially life-threatening situations and are therefore a "heads up".

However, this well meaning meteorologist seems to have forgotten about the "cry wolf effect".

Image Courtesy of: http://www.insurancejournal.com

The public is now barraged with a confusing assemblage  of advisories, watches and warnings leading to information overload.  False Alarm Rates are high  because of the very nature of weather events, the limited availability of real-time data and the fact that all of us involved in informing the public are human and we do not always get it right.

Include in the mix the "social media/app effect" and an individual may get a single warning multiple times.

After a while it all becomes blah-blah-blah.

My point is that modern communications technology may very well multiply the "cry wolf effect".

Two recent studies find that the "cry wolf effect" (links below) is real and false alarms reduce the number of people who take action during threatening weather. Both studies also find that the issue is complex and a small reduction in the FALSE ALARM RATE has little effect.

Reading between the lines: my thought is that large reductions in the FALSE ALARM RATE may reduce inaction by weather information users. But for the reasons above that may not be possible.

What the authors did find is a clarification statement like, "there is a 90% chance of flash flooding ..." decreases the number of people who ignore potentially life-saving weather information.

Before you go apoplectic, I know there are problems with probability statements and some other form of qualifier may work better.

Here's is another thought.

Instead of blasting the public, every time it looks like a funnel may touch down due to rotation seen by radar, with "tornado warning .... take cover immediately"; Why not qualify the warning.  with something like, "Tornado warning ... radar indicates a small funnel may touch down with winds possible to 90 mph... take cover immediately".

Meteorologists know the difference between the leading edge spin-ups and the monster funnels born from a strong mesocyclone. Isn't the public deserving of the whole truth?

Luckily, most tornadoes are F/EF0s and F/EF1s.  That's is important because in the county warning area under the responsibility of @NWSILN, since 1950 there have been no deaths - ZERO -  from F/EF0 and F/EF1 tornadoes. (Some sources report a single death in Grant Co. from an F1 but it is unconfirmed).

Current initial NWS tornado warnings treat a weak EF0 funnel as being equal to devastating, deadly, much stronger, longer-lived mesocyclone tornadoes. (Note this is not an @NWSILN policy but a policy set up for the entire NWS).

Here is an example of a "tornado"  that was 10 yards wide and on the ground for 20 yards (10 yards/20 yards - you read it correctly) on May 1, 2012 west of Lebanon, OH. Here is the link:

https://www.weather.gov/iln/20120501_WLebanon/


We all remember the EF4 tornado that struck Piner, KY and the EF3 that struck Moscow, OH on March 2, 2012.

The initial warnings for these killers treated them no differently than the 10/20 whirlwind linked to above.

I am really just trying to help viewers make an informed decision by calling @NWSILN out when I see something that is not in the public interest.

I hold nothing against any @NWSILN meteorologist. I am sure they arrive at work each day ready and willing to do the best they can.

 If I am willing to openly criticize @NWSILN, however, I have an obligation to point out events when they perform well.

Friday July 7, 2017 @NWSILN issued a tornado warning but there was no tornado. Nevertheless they performed well.  I explain that in my next blog post later this week.

____
____

Here are links to the two academic articles concerning the cry wolf effect. They are full of research jargon.

https://www.stat.berkeley.edu/~aldous/157/Papers/leclerk.pdf

https://www.utdallas.edu/~emk120030/crywolf_post.pdf



Here is where you can read a summary article meant for the general public:

http://www.insurancejournal.com/news/national/2015/01/28/355667.htm

Why Does the NWS Forecast Office in Wilmington, OH Issue So Many Areal Flood Advisories?

Below is the number of Areal Flood Advisories issued by NWS Wilmington, OH per year since 2008. Notice the high False Alarm Rate and the great increase through the end of June 2017.  Why the increase? I do not know.

It seems the False Alarm Rate is independent of the number of Areal Flood Advisories issued. My interpretation of this is too high a reliance on automatic algorithms and too low a level of critical human thinking.

I received justified criticism because how do we know  NWS ILN is over issuing Areal Flood Advisories if we do not know how other NWS offices compare. Take a look below.

Then I received one more criticism of my claim - again justified AND a good example of how honest, professional discourse can move the understanding of an issue along.

The individual asked if all NWS County Warning and Forecast Areas (CWFA) were the same size.  They are not.

So the graph below normalizes the number of Areal Flood Advisories by area.

[(Advisories issued) / (CWFA area sq. mi.)]  x 10000 = Number Issued per 10,000 sq. mi

NWS ILN is so far out in front here that it makes me wonder if there is a problem with the data source.

But the other 19 offices are consistent with each other in the number of Areal Flood Advisories issued and with terrain considerations.

For example, Jackson, KY and Morristown, (Knoxville area), TN have a great deal of steep terrain which increases runoff and the chance of flooding.  Northern Indiana is flat and not so prone to flooding so you would expect the first two NWS offices to issue more Areal Flood Advisories per 10k sq. mi.than Northern Indiana.

 Notes:
An Areal Flood Advisory verifies if there is at least one Local Storm Report of flooding, no matter how minor, within or on the border of the defining polygon. If there is a Local Storm Report of flooding outside the polygon, no matter how close it does not count for verification.

Advisory Data: Iowa State University

Iowa Environmental Mesonet, VTEC Browser

NWS Office  CWFA Areal Coverage:

in  SQ MI from NWS Service Manual 10-507

NOV 10, 2009