metar_parse.py

"""A script for processing METAR data.

This uses the metar library available at:
https://github.com/python-metar/python-metar
"""

from datetime import datetime
from metar import Metar
import pytz


class metobs:
    """A class to store METAR observations.

    temp = temperature in C
    dewp = dewpoint in C
    w_s = wind speed in kts
    w_d = wind direction in deg
    w_g = wind gusts in kts
    cb = boolean specifying CBs near airport
    vis = visibility in km
    pres = pressure in hPa
    cld = cloud base in ft
    """

    def __init__(self, temp, dewp, w_s, w_d, w_g, cb, vis, pres, cld):
        """Setup the class."""
        self.temp = temp
        self.dewp = dewp
        self.w_s = w_s
        self.w_d = w_d
        self.w_g = w_g
        self.cb = cb
        self.vis = vis
        self.pres = pres
        self.cld = cld


def get_metars(inf, verbose):
    """A function to parse metars from a file and convert into a dict of metobs objects.
    Input:
        -   inf: The input file (as a string filename)
    Output:
        -   a dict of metobs read from the file
    """

    fid = open(inf, 'r')

    met_dict = {}

    for line in fid:
        data = line.rstrip('\n').split(',')
        metdate = datetime.strptime(data[1], '%Y-%m-%d %H:%M')
        metdate = metdate.replace(tzinfo=pytz.UTC)
        mettxt = data[2]
        obs = Metar.Metar(mettxt, strict=False)
        obs.time = metdate
        try:
            temp = obs.temp.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad temperature data", e)
            temp = 15
        try:
            dewp = obs.dewpt.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad dewpoint data", e)
            dewp = 10
        try:
            w_s = obs.wind_speed.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad wind speed data", e)
            w_s = 0
        try:
            w_g = obs.wind_gust.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad wind gust data", e)
            w_g = 0
        try:
            w_d = obs.wind_dir.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad wind direction data", e)
            w_d = 0
        try:
            press = obs.press.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad pressure data", e)
            press = 1013.25
        try:
            vis = obs.vis.value()
        except Exception as e:
            if verbose:
                print("ERROR: Bad visibility data", e)
            vis = 10000

        cb = False
        try:
            for wx in obs.sky:
                if (wx[2] == "CB"):
                    cb = True
        except Exception as e:
            if verbose:
                print("ERROR: Bad CB data", e)

        cld = 10000
        if (len(obs.sky) > 0):
            if obs.sky[0][1] is not None:
                cld = obs.sky[0][1].value()

        cur_obs = metobs(temp, dewp, w_s, w_d, w_g, cb, vis, press, cld)
        met_dict[metdate] = cur_obs

    return met_dict