Has the end of April 2016 been unusually cold?

import os
import numpy as np
import matplotlib.pyplot as plt

import matplotlib
matplotlib.rcParams['font.family'] = 'sans-serif'
matplotlib.rcParams['font.sans-serif'] = 'Lato'
csfont = {'fontname':'Lato Regular'}

# Constraints on the data analysis; location of the data files
YEAR_MIN, YEAR_MAX = 1996, 2016
DAY_MIN, DAY_MAX = 17, 30
DATA_DIR = os.path.join(os.getenv('HOME'), 'Downloads/daily-text')

LIGHT_GREY = '#dddddd'

nyears = YEAR_MAX-YEAR_MIN + 1
ndays = DAY_MAX - DAY_MIN + 1

# Find the average maximum temperature for the last ndays of April
av_maxT = np.zeros(nyears)
for i in range(nyears):
    year = YEAR_MIN + i
    nmissing = 0
    for day in range(DAY_MIN, DAY_MAX+1):
        filename = os.path.join(DATA_DIR,
                        '{year:4d}_04_{day:2d}'.format(year=year, day=day))
        try:
            temperatures = np.loadtxt(filename, usecols=(1,), skiprows=8)
        except FileNotFoundError:
            nmissing += 1
        av_maxT[i] += max(temperatures)
    av_maxT[i] /= (ndays - nmissing)
    print(av_maxT[i])

# Find the average maximum temperature for the last ndays in April across all
# years.
av_T = np.mean(av_maxT)

# The deviations from the average for each year.
dT = av_maxT - av_T

# Plot our chart
fig, ax = plt.subplots(facecolor='w')
years = YEAR_MIN + np.linspace(0,nyears-1,nyears)
bars = ax.bar(years, dT, align='center', alpha=0.3, ec='none')  
# Colour all years with temperatures above the mean in red
for bar in bars:
    if bar.get_y() >= 0:
        bar.set_color('r')
# Highlight the last year by setting its opacity to 1
bar.set_alpha(1)

# Tidy up the plot with some nice styles.
ax.set_xticks(years)
ax.set_xlim(YEAR_MIN-0.5, YEAR_MAX+0.5)
ax.set_ylim(np.floor(min(dT)), np.ceil(max(dT)))
ax.set_ylabel(r'$T_\mathrm{max} - \bar{T}_\mathrm{max} / ^\circ\mathrm{C}$')
for tick in ax.get_xticklabels():
    tick.set_rotation(90)
for spine_pos in ('top', 'right', 'bottom', 'left'):
    ax.spines[spine_pos].set_visible(False)
ax.xaxis.set_ticks_position('none') 
ax.yaxis.set_ticks_position('none') 
ax.yaxis.set_tick_params(pad=10)
ax.axhline(lw=2, color='k')
ax.yaxis.grid(which='major', c=LIGHT_GREY, lw=2, ls='-')
ax.set_axisbelow(True)

plt.savefig('cold_april.png')
plt.show()