Generates NWS Heat Index Reference Chart

metpy_heatindex_chart.py

"""Create a pretty table."""

import numpy as np
from pyiem.plot.use_agg import plt
import matplotlib.colors as mpcolors
from matplotlib.font_manager import FontProperties
from matplotlib import patches
from metpy.calc.basic import heat_index
from metpy.units import units
from metpy.plots import add_metpy_logo

COLORS = ['#ffff02', '#ffcc00', '#fe6500', '#cc0001']
LEVELS = [0, 91, 103, 126, 200]
LABELS = ['Caution', 'Extreme Caution', 'Danger', 'Extreme Danger']
# Hard coded non-dimensional x-coordinate on the plot
LEGENDLOCS = [0.15, 0.3, 0.6, 0.75]


def main():
    """Go Main Go."""
    titlefont = FontProperties()
    titlefont.set_weight('bold')
    titlefont.set_size(22)

    lblfont = titlefont.copy()
    lblfont.set_size(13)

    rh1d = np.arange(5, 101, 5)
    tmpf1d = np.arange(80, 131, 2)
    tmpf, rh = np.meshgrid(tmpf1d, rh1d)
    hi = heat_index(tmpf * units.degF, rh * units.percent)
    hi[hi > 137.5 * units.degF] = np.nan
    fig = plt.Figure(figsize=(12.48, 7.44))

    faux = fig.add_axes([0, 0, 1, 1])
    faux.xaxis.set_visible(False)
    faux.yaxis.set_visible(False)
    ax = fig.add_axes([0.11, 0.15, 0.86, 0.7])
    plt.setp(ax.spines.values(), linewidth=3)

    # Large outline around the entire plot
    rect = patches.Rectangle(
        (0.02, 0.02), 0.96, 0.96, linewidth=2, edgecolor='k',
        facecolor='none')
    faux.add_patch(rect)
    # line around chart and labels
    rect = patches.Rectangle(
        (0.06, 0.15), 0.91, 0.76, linewidth=3, edgecolor='k', facecolor='none')
    faux.add_patch(rect)

    for color, label, loc in zip(COLORS, LABELS, LEGENDLOCS):
        rect = patches.Rectangle(
            (loc, 0.055), 0.02, 0.02, linewidth=1, edgecolor='k',
            facecolor=color)
        faux.add_patch(rect)
        fig.text(
            loc + 0.03, 0.06, label, va='center', ha='left',
            fontproperties=lblfont)

    fig.text(
        0.06, 0.93, "NWS Heat Index", color='blue', ha='left',
        fontproperties=titlefont)
    fig.text(
        0.5, 0.1,
        ("Likelihood of Heat Disorders with Prolonged Exposure or "
         "Strenuous Activity"), ha='center', fontproperties=lblfont
    )
    cmap = mpcolors.ListedColormap(COLORS, "")
    cmap.set_bad(COLORS[-1])
    norm = mpcolors.BoundaryNorm(LEVELS, cmap.N)
    ax.imshow(
        hi, cmap=cmap, norm=norm,
        interpolation='nearest', origin='upper', aspect='auto',
        extent=[tmpf1d.min() - 1, tmpf1d.max() + 1,
                rh1d.max() + 2.5, rh1d.min() - 2.5])

    for col, _ in enumerate(tmpf1d):
        for row, _ in enumerate(rh1d):
            if np.isnan(hi[row, col].m):
                continue
            ax.text(
                tmpf1d[col], rh1d[row], "%.0f" % (hi[row, col].m, ),
                ha='center', va='center', fontsize=14)
    # add some guide lines
    for y in range(25, 100, 25):
        ax.axhline(y + 2.5, lw=0.5, color='k')
    ax.set_xticks(tmpf1d)
    ax.set_yticks(rh1d[::-1])
    ax.set_yticklabels([str(x) for x in rh1d[::-1]])
    ax.set_xticklabels([str(x) for x in tmpf1d])
    ax.set_ylim(rh1d.max() + 2.5, rh1d.min() - 2.5)
    ax.set_xlim(tmpf1d.min() - 1, tmpf1d.max() + 1)
    ax.xaxis.tick_top()
    ax.xaxis.set_label_position('top')
    ax.tick_params(axis='both', which='both', length=0)
    ax.set_ylabel(
        "Relative Humidity (%)", fontproperties=lblfont, labelpad=15 * 1.2)
    ax.set_xlabel(
        r"Temperature ($^\circ$F)", fontproperties=lblfont, labelpad=20 * 1.2)
    plt.setp(
        ax.yaxis.get_majorticklabels(), rotation=0, fontproperties=lblfont)
    plt.setp(
        ax.xaxis.get_majorticklabels(), rotation=0, fontproperties=lblfont)
    add_metpy_logo(fig, 1030, 110, size='large')

    fig.savefig('test.png')  # , orientation='landscape')


if __name__ == '__main__':
    main()

Resulting plot

Requires currently un-released MetPy 0.11

Plot updated to include more RH range and remove seaborn requirement.