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Using Water Vapor Images to Quantify Atmospheric Water Vapor Is Bad Science

By: Lee Grenci , 6:27 PM GMT on January 07, 2017

Last evening, while watching a national weather show on cable TV, a meteorologist began his presentation about the threat of heavy precipitation in California with an enhanced water vapor image (see below; Larger image). As I have preached and preached for years, using water vapor images to quantify atmospheric water vapor is just plain old bad science. And, yet, that's exactly what the meteorologist did.


The enhanced water-vapor image from GOES-15 at 02 UTC on January 7, 2017. The two areas circled in white indicate high, cold cloud tops, not water vapor. Larger image. Courtesy of Penn State.

I'll begin today's sermon with the simple observation that a water-vapor image is really nothing more than a glorified infrared satellite image (the wavelengths for water-vapor imagery cluster near 7 micrometers, which falls squarely in the infrared portion of the electromagnetic spectrum). For more tangible proof, focus your attention of the standard infrared satellite image (below) at 02 UTC on January 7, 2017 (Larger image). Note that I circled two areas that encompass high, cold cloud tops. Now compare the two areas on this IR image with the two areas I annotated on the water-vapor image. They're identical!!!! I...dentical! Would anyone here argue that they're looking at two areas of water vapor (instead of cold cloud tops) on this standard infrared satellite image? Man, I hope not.

I think we all agree that we're looking at high, cold cloud tops inside the two black circles on the standard IR image. On the enhanced water-vapor image, the patterns of reds and yellows you see inside the corresponding two circles are obviously identical to the two patterns of bright white on the standard infrared image.


The standard infrared image from GOES-15 at 02 UTC on January 7, 2017. The two areas circled in black clearly indicate the presence high, cold cloud tops. Larger image. Courtesy of Penn State.

Inescapable Conclusion: The patterns of reds and yellows within the two white circles on the enhanced infrared satellite image are high, cold clouds tops and NOT water vapor.

By the way, the temperature of the highest cloud tops (dark red on the color-enhanced water-vapor image) was roughly 205 Kelvins, which converts to approximately minus 68 degrees Celsius. Dew points equal to minus 68 degrees Celsius indicate that very, very, very little of water vapor was present at the rarefied altitudes where the high cloud tops were observed. So pointing to color-enhanced cloud tops on water vapor imagery and pontificating that these features represent a lot of water vapor is completely absurd. And yet, the practice continues by some TV broadcasters.

On Friday evening, the broadcast meteorologist on the national cable show claimed that the plume of reds and yellows arcing northeastward from low latitudes (Area #1) was water vapor. He further stated that these reds and yellows indicated a LOT of water vapor. On the second count, the meteorologist was right but for the wrong reason. Take a look at the reds and yellows inside Area #1 (again these are high, cold cloud tops). Now look at the corresponding precipitable water over southern British Columbia. Good grief!!!! Looks like bad science to me.


The GFS model analysis of precipitable water (PWAT) at 00 UTC on January 7, 2017. Courtesy of Penn State.

In my view, the only way to assess the amount of water vapor in the troposphere is to look at precipitable water. The 00 UTC model analysis of PWAT (above) shows that the plume of reds and yellows did indeed correspond to a lot of water vapor.

Lessons Learned: 1) A water-vapor image is a special kind of infrared satellite image; 2) High, cold cloud tops contaminate water-vapor images; and 3) High, cold cloud tops on water-vapor images do NOT guarantee that there is a lot of water vapor present in the troposphere.

Here endeth the lesson.

Lee


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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16. dyqik
9:13 PM GMT on February 27, 2017
You can measure precipitable water vapor (PWV) in a few ways I know of from doing mm and sub-mm wave astronomy. You can use water vapor radiometry around the 22 GHz or 183 GHz water molecule spectroscopic lines to measure water vapor directly, and you can measure mm-wave (e.g. 150 GHz, 225 GHz) atmospheric transparency with a radiometric tipper, which correlates well with PWV. An interesting newer method is to use GPS ground stations to measure the time delay from GPS satellites to fixed points, which is affected by water vapor in the line of sight from satellites to the ground stations. That provides fairly global coverage (with varying spatial resolution, as the density of GPS ground stations isn't uniform) without having to put instruments in the field.

I'm sure there are other methods as well.
Member Since: December 31, 1969 Posts: Comments:
15. MikeinNewMexico
6:34 PM GMT on February 27, 2017
Lee, your blog has been very helpful. I know that satellite IR can readily measure clouds, but how is preciptable water measured, other than by radiosonde? Thanks.
Member Since: December 31, 1969 Posts: Comments:
14. LivinginthePass
1:49 PM GMT on February 18, 2017
Interesting, but after all what are clouds anyway if not water vapor?
Member Since: December 31, 1969 Posts: Comments:
13. retiredweathercop
1:10 AM GMT on January 29, 2017
The problem with knowledge,
is we don't know much and those that say they do, don't!
As with Donald Trump, someone who knows more about everything then everyone
What we interpret as truth or facts can change based on how much information we reliably collect
I offer some of the prose from
An Essay on Criticism
by Alexander Pope

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.
Member Since: December 31, 1969 Posts: Comments:
12. DrFahmy
9:17 AM GMT on January 27, 2017
Very interesting piece of info, indeed. Yes, there is a big gap between the two types of photos as one indicates very low temperature (with no moisture present) and the other is showing lot of moisture probably at modest low temperatures that approach the dew point. Raining-out is a rather complicated phenomenon yes but the most important is the presence of moisture not the very low temperatures with no moisture. If I've fully understood your post ("preached sermon", as you my call it), I fully agree with it.
Member Since: December 31, 1969 Posts: Comments:
11. Some1Has2BtheRookie
8:46 PM GMT on January 19, 2017
Lee,

I have learned much by reading your blogs. I wish that I had been a student of yours. I know that I would have walked away a much more informed person. My areas of interests during my school years had less to do with academics and more to do with what will the weather be like this weekend. Well, you know what they say about hindsight. sigh I try to instill in my grandchildren how important it is to learn all they can while they are in school, even when the material being studied does not currently hold their interest. Thanks, and keep up the excellent work that you do.
Member Since: December 31, 1969 Posts: Comments:
10. Lee Grenci , Retired Senior Lecturer and Forecaster
11:10 PM GMT on January 14, 2017
Quoting 9. Astrometeor:

You should see Dr. Masters' blog during hurricane season. People will do the opposite. They're looking for dry air. They'll point at a spot where there aren't any clouds and be like "no water vapor here, won't get any thunderstorms". A look a buoy will show high dewpoints and relative humidities for the area. But a lot of folks hold satellites in high regard, but interpret the data incorrectly.

I just don't get how you can infer low level moisture from high altitude cloud tops.

I still love your blogs, Lee. Thanks for coming back.

-Nathan

P.S. Is the national weather show's acronym TWC? Just wondering. :P


Completely agree, Nathan. Thanks. Yes to your last question. I don't believe many of them truly understand water vapor imagery.
Member Since: December 31, 1969 Posts: Comments:
9. Astrometeor
5:11 AM GMT on January 13, 2017
You should see Dr. Masters' blog during hurricane season. People will do the opposite. They're looking for dry air. They'll point at a spot where there aren't any clouds and be like "no water vapor here, won't get any thunderstorms". A look a buoy will show high dewpoints and relative humidities for the area. But a lot of folks hold satellites in high regard, but interpret the data incorrectly.

I just don't get how you can infer low level moisture from high altitude cloud tops.

I still love your blogs, Lee. Thanks for coming back.

-Nathan

P.S. Is the national weather show's acronym TWC? Just wondering. :P
Member Since: December 31, 1969 Posts: Comments:
Quoting 7. philnyc:

Great lesson there, Lee. A LOT of other TV mets make that mistake, so you can never state this enough. PWAT is the way to go.


Thanks Phil. That such misinterpretation and bad science could be prevalent among the media, especially national enterprises that hold themselves up as a gold standard, speaks volumes about the worth of real truth in this country.
Member Since: December 31, 1969 Posts: Comments:
7. philnyc
9:39 PM GMT on January 09, 2017
Great lesson there, Lee. A LOT of other TV mets make that mistake, so you can never state this enough. PWAT is the way to go.
Member Since: December 31, 1969 Posts: Comments:
Quoting 5. Barefootontherocks:

"What's up with the WU glitches?"
I don't know where to begin, Lee.
Behind the scenes programming going on is the culprit, supposedly. One explanation I've seen posted by Jeff Masters: The wu is in process of switching to new servers (? I guess you'd call it servers.) at the amazon cloud. Pretty sure the site's been on Google cloud since IBM took over a year or so ago. Also, dropping the old format and shifting the blogs to software called "drupal" is planned.

One glitch takes a click on the bloggers current blog title way back to the first blog, like what happened to me the first time I tried to access your new blog. Right now the bounce-back happens as often as not. If you try to access a current blog from someone who removed his/her first entry, as I did with StormDrain (my first handle) and Barefootontherocks, half the time you get a "this entry has been removed" message when clicking on the current blog title.

According to Jeff Masters, the retro bounce-back is supposed to be fixed by mid-month. He did not say what month. LOL

Another glitch (been happening for a while, off and on) signs you in and greets you as the first part of your email address instead of greeting your handle, and you can see a comment box but cannot comment or use other blog features.

Sometimes when you try to access a blog, you get error messages over and over, sometimes "This user does not appear to have a wunderblog."

Any change you make in your profile takes a while, or even a sign out and sign back in (if you can lol) before the change takes effect. That has also been happening for a while.

Sometimes the site is so slow to do anything, you just give up. Many comments do not post or take several minutes before the page acts like it's posting the comment. Blogging and commenting can be a frustration, to say the least.

I've also seen comments here and there about the weather data and forecasts being screwed up.

I don't know what, if any, glitches are happening on the photo part of the site.

Thing is, it seems improved on and off, and with patience you can get where you want to go and do what you want to do, as long as you've got all day to do it.
:)


Many thanks...I have experienced some of the things you told me about. I'm sure they'll get things fixed.

Thanks again.

lee
Member Since: December 31, 1969 Posts: Comments:
5. Barefootontherocks
9:44 PM GMT on January 07, 2017
"What's up with the WU glitches?"
I don't know where to begin, Lee.
Behind the scenes programming going on is the culprit, supposedly. One explanation I've seen posted by Jeff Masters: The wu is in process of switching to new servers (? I guess you'd call it servers.) at the amazon cloud. Pretty sure the site's been on Google cloud since IBM took over a year or so ago. Also, dropping the old format and shifting the blogs to software called "drupal" is planned.

One glitch takes a click on the bloggers current blog title way back to the first blog, like what happened to me the first time I tried to access your new blog. Right now the bounce-back happens as often as not. If you try to access a current blog from someone who removed his/her first entry, as I did with StormDrain (my first handle) and Barefootontherocks, half the time you get a "this entry has been removed" message when clicking on the current blog title.

According to Jeff Masters, the retro bounce-back is supposed to be fixed by mid-month. He did not say what month. LOL

Another glitch (been happening for a while, off and on) signs you in and greets you as the first part of your email address instead of greeting your handle, and you can see a comment box but cannot comment or use other blog features.

Sometimes when you try to access a blog, you get error messages over and over, sometimes "This user does not appear to have a wunderblog."

Any change you make in your profile takes a while, or even a sign out and sign back in (if you can lol) before the change takes effect. That has also been happening for a while.

Sometimes the site is so slow to do anything, you just give up. Many comments do not post or take several minutes before the page acts like it's posting the comment. Blogging and commenting can be a frustration, to say the least.

I've also seen comments here and there about the weather data and forecasts being screwed up.

I don't know what, if any, glitches are happening on the photo part of the site.

Thing is, it seems improved on and off, and with patience you can get where you want to go and do what you want to do, as long as you've got all day to do it.
:)
Member Since: December 31, 1969 Posts: Comments:
Quoting 3. Barefootontherocks:

Thank you, Lee. Good to see a new, right-on "sermon" from you.
Happy New Year.

Oh. As you may or may not be realize, the wu blogs right now are amess with glitches. I got directed to your first blog when I clicked on the title to this one - but that was fun and apropos, as that Dec 12, 2012 blog is entitled "Arctic Air Masses."


It is good to hear from you, my friend. I miss my old WU blogging job and interacting with great people like you. What's up with the WU glitches?

Happy New Year!

Lee
Member Since: December 31, 1969 Posts: Comments:
3. Barefootontherocks
8:47 PM GMT on January 07, 2017
Thank you, Lee. Good to see a new, right-on "sermon" from you.
Happy New Year.

Oh. As you may or may not be realize, the wu blogs right now are amess with glitches. I got directed to your first blog when I clicked on the title to this one - but that was fun and apropos, as that Dec 12, 2012 blog is entitled "Arctic Air Masses."
Member Since: December 31, 1969 Posts: Comments:
Quoting 1. ggwx:

Good points and I agree. I think that some of the misunderstanding may come from (mis)using color palettes that are similar to those used for radar, where yellows, oranges and red do equate to higher precip.


You made a good point, too. Thanks.
Member Since: December 31, 1969 Posts: Comments:
1. ggwx
7:08 PM GMT on January 07, 2017
Good points and I agree. I think that some of the misunderstanding may come from (mis)using color palettes that are similar to those used for radar, where yellows, oranges and red do equate to higher precip.
Member Since: December 31, 1969 Posts: Comments:

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About 24hourprof

Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.