import pandas as pd
from pandas import Series

import matplotlib.pyplot as plt

temperature = pd.read_csv(
    "https://milliams.com/courses/data_analysis_python/cetml1659on.txt",  # file name
    skiprows=6,  # skip header
    delim_whitespace=True,  # whitespace separated
    na_values=['-99.9', '-99.99'],  # NaNs
)

fig, ax = plt.subplots()

temperature['JAN'].plot(color="steelblue", ax=ax)
temperature['JUN'].plot(color="firebrick", ax=ax)
temperature['YEAR'].plot(color="green", linestyle="--", ax=ax)

ax.set_xlabel(r'Year')
ax.set_ylabel(r'Temperature ($^\circ$C)')
ax.legend(loc='upper left')

warm_winter_year = temperature['JAN'].idxmax()
warm_winter_temp = temperature['JAN'].max()

ax.annotate('Warmest winter',
            xy=(warm_winter_year, warm_winter_temp), xycoords='data',
            xytext=(-100, +30), textcoords='offset points', fontsize=12,
            arrowprops=dict(arrowstyle="->", connectionstyle="arc3,rad=-.2"))

plt.show()

Introduction to Data Analysis in Python