Parser and plotter for NEXRAD VAD retrievals.

The script downloads the VAD data from the NEXRAD Radar Product Dissemination page, parses the binary file, and plots the VAD retrieval as a hodograph. It also computes and displays some parameters of interest.

NumPy and Matplotlib are the only requirements to run this script.

python vad.py RADAR_ID [ -m STORM_MOTION ] [ -s SFC_WIND ] [ -t TIME ] [ -f IMG_NAME ] 
                       [ -p LOCAL_PATH ] [ -c CACHE_PATH ]

• RADAR_ID is a 4-character radar identifier (e.g. KTLX, KFWS)
• STORM_MOTION is the storm motion vector. It can take one of two form. The first is either BRM for the Bunkers right-mover vector or BLM for the Bunkers left-mover vector. The second form is DDD/SS, where DDD is the direction the storm is coming from in degrees, and SS is the storm speed in knots. An example might be 240/35 (from the WSW at 35 kts). If the argument is not specified, the default is to use the Bunkers right-mover vector.
• SFC_WIND is the surface wind vector. Its form is the same as the DDD/SS form of the storm motion vector. A dashed red line will be drawn on the hodograph from the lowest point in the VWP to the surface wind to indicate the approximate wind profile in that layer.
• TIME is the plot time. It takes the form [YYYY-mm-]dd/HHMM, where YYYY is the 4-digit year, mm is the month, dd is the day, HH is the hour, and MM is the minute. The year and month are optional. The script will plot the most recent VAD as of this time.
• IMG_NAME is the name of the image the script produces. If not given, it defaults to <RADAR_ID>_vad.png.
• LOCAL_PATH is the path to a local file from which to load the VWP data (assumed to have been downloaded from NCDC's NEXRAD archive). The name of the file should not be given; the script will construct the file name using the other information.
• CACHE_PATH is the path to a local directory in which to cache downloaded files. The downloaded files can be read in directly using the -p option.

An example of the output is given below. See the interpretation section for more information.

A "hodograph" is a graph of wind as a function of height. The u component of the wind is on the x axis and the v component of wind is on the y axis. Area on the hodograph is proportional to helicity, an important parameter in severe convective storm forecasting.

The colors denote different height layers, and follow the Storm Prediction Center's convention for their hodographs: red denotes the 0-3 km layer, light green denotes the 3-6 km layer, dark green denotes the 6-9 km layer, purple denotes the 9-12 km layer, and cyan denotes the layer from 12 km on up. The colored circles are proportional in radius to the RMS error in the VAD retrieval at each level.

When computing the parameters, in the absence of a specified surface wind, the "surface" is taken to be the lowest data point in the VWP, which is often ~100 m AGL.