Plotting Use Case: Spread–Skill Relationship

This use case demonstrates how to use VCasT’s plotting module to visualize the spread–skill relationship using pre-aggregated ensemble statistics computed from MET .stat files.

It uses a sample configuration file (plot.yaml) to generate a line plot showing the evolution of metrics such as spread, RMSE, and their ratio across lead times.

Prerequisites

Before running the example, you need an input file agg.data created in the previous use case MET Stat Use Case: Spread–Skill Relationship.

Run the Example

Clone the test repository:

git clone https://github.com/NOAA-GSL/VCasT-tests
cd VCasT-tests/examples/MET/spread-skill

Run VCasT with the plotting YAML file:
```
vcast plot.yaml
```
This will generate a plot illustrating the spread–skill relationship across lead times.

YAML Configuration Explained

Below is the content of plot.yaml, which configures VCasT to:

Load a pre-aggregated CSV file with ensemble verification statistics
Plot fcst_lead on the x-axis and spread/skill metrics on the y-axis
Focus on metrics like spread, rmse, and optionally the ratio (spread-plus-oerr / rmse)

Sample plot.yaml configuration

start_date: "2024-04-29_12:00:00"
end_date: "2024-05-31_12:00:00"
interval_hours: "1"              

average: false
scale: 1

plot_type: line

fcst_var: TMP

vars:
  - spread_plus_oerr: "./agg.data"
  - rmse: "./agg.data"
  - ratio: "./agg.data"

unique:  

plot_title: "Temperature at 2m"
legend_title: "Stat"
labels:
  - "RRFS_GDAS_GF.SPP.SPPT ECNT_SPREAD_PLUS_OERR"
  - "RRFS_GDAS_GF.SPP.SPPT ECNT_RMSE"
  - "RRFS_GDAS_GF.SPP.SPPT RATIO"
    
line_color:
  - "red"
  - "purple"
  - "green"

line_marker:
  - "o"
  - "x"
  - "^"

line_type:
  - "-"
  - "-."
  - "--"

line_width:
  - 0.5
  - 0.5
  - 0.5

output_filename: spread_skill.png

x_label: "Lead Time"
y_label: "Statistic value"
ylim: [0.6, 2.4]
xlim: [0,36]
grid: true
yticks:   
xticks: [0, 3, 6, 9 ,12 ,15 ,18, 21, 24, 27, 30, 33, 36] 

Output

The generated plot will be saved to the location specified by output_filename, such as spread_skill.png.