Error when calculating Parcel Path for sounding

[Stormfreak10]

Hi everyone,

I made an account just to ask a question about an error that has recently arose and I can't seem to find a way around. I am pretty new to coding and am following the MetPy Monday tutorial videos on Youtube (and using more updated code in the MetPy example gallery to keep it compatible with v1.1). I am currently on video 19, creating the parcel path line, and when I run the code in Jupyter Notebook, I get an error stating:

---

InvalidSoundingError Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_1852/2258894206.py in
1 # Calculate full parcel profile and add to plot as black line
2
----> 3 prof = mpcalc.parcel_profile(p, t[0], td[0]).to('degC')
4 skew.plot(p, prof, 'k', linewidth=2)

~\anaconda3\envs\weather\lib\site-packages\metpy\xarray.py in wrapper(*args, **kwargs)
1214
1215 # Evaluate inner calculation
-> 1216 result = func(*bound_args.args, **bound_args.kwargs)
1217
1218 # Wrap output based on match and match_unit

~\anaconda3\envs\weather\lib\site-packages\metpy\units.py in wrapper(*args, **kwargs)
244 'that the function is being called properly.\n') + msg
245 raise ValueError(msg)
--> 246 return func(*args, **kwargs)
247
248 return wrapper

~\anaconda3\envs\weather\lib\site-packages\metpy\calc\thermo.py in parcel_profile(pressure, temperature, dewpoint)
742
743 """
--> 744 _, _, _, t_l, _, t_u = _parcel_profile_helper(pressure, temperature, dewpoint)
745 return concatenate((t_l, t_u))
746

~\anaconda3\envs\weather\lib\site-packages\metpy\calc\thermo.py in _parcel_profile_helper(pressure, temperature, dewpoint)
899 Pressure does not decrease monotonically in your sounding.
900 Using scipy.signal.medfilt may fix this."""
--> 901 raise InvalidSoundingError(msg)
902
903 # Find the LCL

InvalidSoundingError:
Pressure does not decrease monotonically in your sounding.
Using scipy.signal.medfilt may fix this.

I have looked up this error and cannot seem to find anyone else who has experienced a similar problem. Do any of you know why this error would arise, and if so, how to fix it? Many thanks in advance. I apologize if this was a rather silly question to ask, but I am just stuck on this error.

[dopplershift]

The error you're seeing is InvalidSoundingError: Pressure does not decrease monotonically in your sounding.. What that means is that the pressure values in your sounding are not consistently decreasing. That means for one or more indices n+1 in the pressure array of your data, the value is equal or less than the pressure at index n. Most of MetPy's sounding calculations assume that pressure is decreasing as you go along in the array.

The error message suggests using scipy.signal.medfilt as a way to try to filter your pressure values to make them decrease if the problem is just due to noise in measurements. Something like:

import scipy.signal
pressure = scipy.signal.medfilt(pressure, 5)

What does your p array look like?

Also, is there some way we can improve the error message to make this more clear?

[Stormfreak10]

My P array looks like this:

p [933.0 925.0 912.0 910.2 879.4 850.0 820.2 791.9 782.0 764.4 758.0 742.0 737.6 700.0 686.2 661.6 648.0 626.0 617.0 614.6 586.0 580.0 570.1 567.0 562.0 549.0 548.9 526.0 520.0 516.0 511.0 508.0 502.0 500.0 488.9 485.0 480.0 466.0 451.9 447.0 442.0 437.0 434.5 427.0 420.0 415.0 405.0 401.1 400.0 399.0 385.1 384.0 373.0 369.7 364.0 357.0 354.8 354.0 348.0 345.0 341.0 335.0 328.0 326.4 300.0 299.8 293.0 276.0 275.2 263.0 257.0 250.0 245.0 241.0 233.0 227.0 216.0 203.0 200.0 186.0 169.0 150.0 144.0 138.0 134.0 131.0 128.1 124.0 118.0 109.0 105.0 100.0 92.5 86.6 84.1 83.2 80.0 77.5 77.2 70.0 66.5 62.4 50.0 49.7 47.2 45.7 38.2 36.0 31.8 30.0 29.3 27.9 26.5 25.6 24.7 24.2 22.1 20.9 20.1 20.0 19.8 19.2 19.1 18.3 17.5 16.7 15.9 15.2 14.5 14.5 13.3 12.7 12.2 12.1 11.6 11.5 11.1 10.1 10.0 9.9 9.2 8.8 8.2 8.1 7.7 7.5]
This is an image of the error I recieved:

I will try the scipy.signal code and see if that helps.

Edit: It seems the Scipy.Signal code doesn't work (or I am applying it wrong, which is entirely possible) as I am still getting the same error when attempting to calculate the parcel path.

[dopplershift]

The problem is caused by the duplicate point with a pressure of 14.5 hPa (indices 128 and 129). The easiest work around (unless levels above 25mb are important to you) is to just cut off the data:

mask = p > (25 * units.hPa)
t = t[mask]
td = td[mask]
p = p[mask]

You really only need the last line to make parcel_profile work, but good to keep them synchronized if you're planning on adding other calculations.

[Stormfreak10]

Thanks! I added this code and it worked successfully!