Update Upper Air Obs (DIFAX) example

This was failing due to a redirect in its custom station data
information retrieval. Update to use the station data information
available directly from MetPy.

notebooks/synoptic/Upperair_Obs.ipynb

@@ -38,6 +38,7 @@
     "import numpy as np\n",
     "import xarray as xr\n",
     "\n",
+    "from metpy.io import add_station_lat_lon\n",
     "from metpy.plots import StationPlot\n",
     "from metpy.units import units\n",
     "from siphon.simplewebservice.iastate import IAStateUpperAir"
@@ -123,119 +124,6 @@
     "                marker='x', color='black', transform=transform)"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {
-    "cell_marker": "######################################################################"
-   },
-   "source": [
-    "Station Information\n",
-    "-------------------\n",
-    "\n",
-    "A helper function for obtaining radiosonde station information (e.g.,\n",
-    "latitude/longitude) requried to plot data obtained from each station.\n",
-    "Original code by github user sgdecker."
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "lines_to_next_cell": 1
-   },
-   "outputs": [],
-   "source": [
-    "def station_info(stid):\n",
-    "    r\"\"\"Provide information about weather stations.\n",
-    "\n",
-    "    Parameters\n",
-    "    ----------\n",
-    "    stid: str or iterable object containing strs\n",
-    "         The ICAO or IATA code(s) for which station information is requested.\n",
-    "    with_units: bool\n",
-    "         Whether to include units for values that have them. Default True.\n",
-    "\n",
-    "    Returns\n",
-    "    -------\n",
-    "    info: dict\n",
-    "         Information about the station(s) within a dictionary with these keys:\n",
-    "             'state': Two-character ID of the state/province where the station is located,\n",
-    "                       if applicable\n",
-    "             'name': The name of the station\n",
-    "             'lat': The latitude of the station [deg]\n",
-    "             'lon': The longitude of the station [deg]\n",
-    "             'elevation': The elevation of the station [m]\n",
-    "             'country': Two-character ID of the country where the station is located\n",
-    "\n",
-    "    Modified code from Steven Decker, Rutgers University\n",
-    "\n",
-    "    \"\"\"\n",
-    "    # Provide a helper function for later usage\n",
-    "    def str2latlon(s):\n",
-    "        deg = float(s[:3])\n",
-    "        mn = float(s[-3:-1])\n",
-    "        if s[-1] == 'S' or s[-1] == 'W':\n",
-    "            deg = -deg\n",
-    "            mn = -mn\n",
-    "        return deg + mn / 60.\n",
-    "\n",
-    "    # Various constants describing the underlying data\n",
-    "    url = 'https://www.aviationweather.gov/docs/metar/stations.txt'\n",
-    "    # file = 'stations.txt'\n",
-    "    state_bnds = slice(0, 2)\n",
-    "    name_bnds = slice(3, 19)\n",
-    "    icao_bnds = slice(20, 24)\n",
-    "    iata_bnds = slice(26, 29)\n",
-    "    lat_bnds = slice(39, 45)\n",
-    "    lon_bnds = slice(47, 54)\n",
-    "    z_bnds = slice(55, 59)\n",
-    "    cntry_bnds = slice(81, 83)\n",
-    "\n",
-    "    # Generalize to any number of IDs\n",
-    "    if isinstance(stid, str):\n",
-    "        stid = [stid]\n",
-    "\n",
-    "    # Get the station dataset\n",
-    "    infile = urllib.request.urlopen(url)\n",
-    "    data = infile.readlines()\n",
-    "\n",
-    "    state = []\n",
-    "    name = []\n",
-    "    lat = []\n",
-    "    lon = []\n",
-    "    z = []\n",
-    "    cntry = []\n",
-    "\n",
-    "    for s in stid:\n",
-    "        s = s.upper()\n",
-    "        for line_bytes in data:\n",
-    "            line = line_bytes.decode('UTF-8')\n",
-    "            icao = line[icao_bnds]\n",
-    "            iata = line[iata_bnds]\n",
-    "            if len(s) == 3 and s in iata or len(s) == 4 and s in icao:\n",
-    "                state.append(line[state_bnds].strip())\n",
-    "                name.append(line[name_bnds].strip())\n",
-    "                lat.append(str2latlon(line[lat_bnds]))\n",
-    "                lon.append(str2latlon(line[lon_bnds]))\n",
-    "                z.append(float(line[z_bnds]))\n",
-    "                cntry.append(line[cntry_bnds])\n",
-    "\n",
-    "                break\n",
-    "        else:\n",
-    "            state.append('NA')\n",
-    "            name.append('NA')\n",
-    "            lat.append(np.nan)\n",
-    "            lon.append(np.nan)\n",
-    "            z.append(np.nan)\n",
-    "            cntry.append('NA')\n",
-    "\n",
-    "    infile.close()\n",
-    "\n",
-    "    return {'state': np.array(state), 'name': np.array(name), 'lat': np.array(lat),\n",
-    "            'lon': np.array(lon), 'elevation': np.array(z), 'country': np.array(cntry),\n",
-    "            'units': {'lat': 'deg', 'lon': 'deg', 'z': 'm'}}"
-   ]
-  },
   {
    "cell_type": "markdown",
    "metadata": {
@@ -312,9 +200,7 @@
     "df = data[data_subset]\n",
     "\n",
     "# Get station lat/lon from look-up file; add to Dataframe\n",
-    "stn_info = station_info(list(df.station.values))\n",
-    "df.insert(10, 'latitude', stn_info['lat'])\n",
-    "df.insert(11, 'longitude', stn_info['lon'])"
+    "df = add_station_lat_lon(df)"
    ]
   },
   {