Forecast Bands (Fan Chart)#

A fan chart (or forecast bands plot) shows a central forecast line with uncertainty ranges. This example uses standard deviation to simulate a confidence interval around a time-series trend.

import pandas as pd
import numpy as np
import hvplot.pandas  # noqa

np.random.seed(1)
dates = pd.date_range("2024-01-01", periods=50, freq="D")
mean = np.cumsum(np.random.normal(0, 1, 50))
std = np.linspace(1.0, 2.5, 50)
df = pd.DataFrame({
    'date': dates,
    'mean': mean,
    'upper': mean + std,
    'lower': mean - std
})

band = df.hvplot.area(
    x='date', y='lower', y2='upper', alpha=0.3,
    color='gray', label='Uncertainty'
)
line = df.hvplot.line(x='date', y='mean', color='blue', label='Forecast')

band * line

import pandas as pd
import numpy as np
import hvplot.pandas  # noqa
hvplot.extension('matplotlib')

np.random.seed(1)
dates = pd.date_range("2024-01-01", periods=50, freq="D")
mean = np.cumsum(np.random.normal(0, 1, 50))
std = np.linspace(1.0, 2.5, 50)
df = pd.DataFrame({
    'date': dates,
    'mean': mean,
    'upper': mean + std,
    'lower': mean - std
})

band = df.hvplot.area(
    x='date', y='lower', y2='upper', alpha=0.3,
    color='gray', label='Uncertainty'
)
line = df.hvplot.line(x='date', y='mean', color='blue', label='Forecast')

band * line