February 22, 2019, 08:17:09 AM

Author Topic: Ask The Weather Expert!  (Read 16971 times)

phw115wvwx

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Re: Ask The Weather Expert!
« Reply #120 on: January 17, 2013, 10:14:04 PM »
So after the snowfall in Dallas the other day, and looking at the NWS daily weather summary for the day, does the precipitation report include snowfall?  I would think snowfall is considered precipitation, so it should be included, but I know they have a separate section for snowfall and precip.  I ask this because the snowfall report for DFW Airport was .3 inches, but the precip report was only 0.05 inches.  I read somewhere online where you need to divide by 10 to convert a snowfall total to a rainfall total, but it appears there was also rain from that day too.
When you have snow, you must melt what was collected in the gauge to get the liquid equivalent, which is reported as the precipitation.  However, you can never assume a 10:1 snow-liquid ratio!  It has been proven over and over that this ratio can vary widely with time and space.  Snow is generally drier as it gets colder, so the snow-liquid ratio increases.  Furthermore, you have to account for the microphysics involved in snow growth along with your moisture source.  Wet snow right near the freezing point can be down at 3:1.  At the other extreme, dry snow in the Rocky Mountains and lake-effect snow in the Northeast have reached up to 100:1.  The 10:1 ratio is just a common average that was thought to be a rule of thumb, but we have learned better thanks to modern research.  The liquid equivalent of 0.05" looks good to me as it gives a 6:1 ratio, and your area was just below freezing when it snowed at DFW. :yes:

Offline TWCCraig

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Re: Ask The Weather Expert!
« Reply #121 on: February 26, 2013, 05:17:05 PM »
Quote
While that is true, we are in March now where our wavelengths are shorter than they are in December. Thus, you can more easily get away with having a ridge east of its ideal position.

-Dsnowx53 http://www.americanwx.com/bb/index.php/topic/39435-late-february-medium-and-long-range-discussion-thread/page-18?

Hey Patrick, can you explain what this meteorologist means when he refers to "wavelengths". I don't think he's referring to wavelengths like with solar radiation, something different. After a Google search, this is the best definition I could find:

Quote
The least distance between particles moving in the same phase of oscillation of a wave.

http://meteorology.geography-dictionary.org/Meteorology-and-Weather-Dictionary/WAVE_LENGTH

To be honest, I don't clearly understand what that means. What does he mean when he refers to wavelengths being shorter in March than December? I wonder if he is referring to solar radiation. IDK   :wacko:
« Last Edit: February 26, 2013, 05:19:23 PM by TWCCraig »
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phw115wvwx

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Re: Ask The Weather Expert!
« Reply #122 on: February 26, 2013, 05:28:56 PM »
Craig, look at the pattern of upper-level ridges and troughs either in the forecast models or in the weather analysis maps.  Those are atmospheric waves.  A wavelength is the distance of a full wave (trough to trough, or ridge to ridge).  So, a shorter wavelength means the distance between an upper-level trough and an upper-level ridge is smaller.  These varying wavelengths result in completely different weather patterns.  You have to spend a whole chapter just on waves when you take Physics, and now you see why.  Nature, including weather, is full of them. :yes:

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Re: Ask The Weather Expert!
« Reply #123 on: February 26, 2013, 05:51:44 PM »
Ooooooooh! Now I get it. I was thinking it was something more complicated than that. Thanks Patrick  :thumbsup:
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