diff --git a/README.rst b/README.rst
index c240d0d..236e3be 100644
--- a/README.rst
+++ b/README.rst
@@ -97,6 +97,25 @@ This will download new datasets as necessary and load the new data into the ``da
 Example
 -------
 
+Plot data from the command line
+```````````````````````````````
+
+Running the following from the command line will plot the variable *significant wave height*
+from the WAVEWATCH III *at_4m* grid. Note that the time of day (in this case, 15:00) is
+separated from the date with a ``T`` (i.e. times can be given as ``YYYY-MM-DDTHH``)
+
+.. code:: bash
+
+  $ ww3 plot --grid=at_4m --data-var=swh "2010-09-15T15"
+
+.. image:: https://raw.githubusercontent.com/csdms/bmi-wavewatch3/main/docs/source/_static/hurrican_julia.png
+  :width: 100%
+  :alt: Hurricane Julia
+
+Plot data from Python
+`````````````````````
+
+This example is similar to the previous but uses the *bmi_wavewatch3* Python interface.
 
 .. code:: python
 
diff --git a/bmi_wavewatch3/cli.py b/bmi_wavewatch3/cli.py
index 2b45c16..2412f59 100644
--- a/bmi_wavewatch3/cli.py
+++ b/bmi_wavewatch3/cli.py
@@ -10,10 +10,12 @@
 from multiprocessing import Pool, RLock
 
 import click
+import matplotlib.pyplot as plt
 from tqdm.auto import tqdm
 from .downloader import WaveWatch3Downloader
 from .errors import ChoiceError, DateValueError
 from .source import SOURCES
+from .wavewatch3 import WaveWatch3
 
 
 out = partial(click.secho, bold=True, file=sys.stderr)
@@ -26,7 +28,7 @@
 def validate_date(ctx, param, value):
     source = SOURCES[ctx.parent.params["source"]]
 
-    for date_str in value:
+    for date_str in [value] if isinstance(value, str) else value:
         try:
             source.validate_date(date_str)
         except DateValueError as error:
@@ -39,7 +41,7 @@ def validate_quantity(ctx, param, value):
     if not value:
         return sorted(source.QUANTITIES)
 
-    for quantity in value:
+    for quantity in [value] if isinstance(value, str) else value:
         try:
             source.validate_quantity(quantity)
         except ChoiceError as error:
@@ -47,6 +49,30 @@ def validate_quantity(ctx, param, value):
     return value
 
 
+def validate_data_var(ctx, param, value):
+    data_var_to_quantity = {
+        "dirpw": "dp",
+        "swh": "hs",
+        "perpw": "tp",
+        "u": "wind",
+        "v": "wind",
+        "swdir": "pdir",
+        "swell": "phs",
+        "swper": "ptp",
+    }
+    source = SOURCES[ctx.parent.params["source"]]
+    try:
+        quantity = data_var_to_quantity[value]
+    except KeyError:
+        raise click.BadParameter(ChoiceError(value, list(data_var_to_quantity)))
+
+    try:
+        source.validate_quantity(quantity)
+    except ChoiceError as error:
+        raise click.BadParameter(error)
+    return value
+
+
 def validate_grid(ctx, param, value):
     source = SOURCES[ctx.parent.params["source"]]
     if not value:
@@ -244,6 +270,53 @@ def clean(ctx, dry_run, cache_dir, yes):
         out(f"Removed {len(cache_files)} files ({total_bytes} bytes)")
 
 
+@ww3.command()
+@click.argument("date", callback=validate_date)
+@click.option("--grid", default=None, help="Grid to download", callback=validate_grid)
+@click.option(
+    "--data-var",
+    help="Data variable to plot",
+    default="swh",
+    callback=validate_data_var,
+)
+@click.pass_context
+def plot(ctx, date, grid, data_var):
+    """Plot WAVEWATCH III data by date."""
+    verbose = ctx.parent.params["verbose"]
+    silent = ctx.parent.params["silent"]
+    source = ctx.parent.params["source"]
+
+    data_var_to_quantity = {
+        "dirpw": "dp",
+        "swh": "hs",
+        "perpw": "tp",
+        "u": "wind",
+        "v": "wind",
+        "swdir": "pdir",
+        "swell": "phs",
+        "swper": "ptp",
+    }
+    quantity = data_var_to_quantity[data_var]
+
+    if not silent:
+        out(f"source: {source}")
+        out(f"grid: {grid}")
+        out(f"date: {date}")
+        out(f"data_var: {data_var} ({quantity})")
+
+    ww3 = WaveWatch3(date, source=source, grid=grid)
+    if not silent and verbose:
+        [out(f"source file: {url}") for url in ww3._urls]
+
+    ww3.data
+    if not silent and verbose:
+        [out(f"cache file: {ww3._cache / url.filename}") for url in ww3._urls]
+
+    ww3.data[data_var][ww3.step, :, :].plot()
+    plt.gca().set_aspect(1)
+    plt.show()
+
+
 def _retreive_urls(urls, disable=False, force=False):
     tqdm.set_lock(RLock())
     p = Pool(initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
diff --git a/bmi_wavewatch3/source.py b/bmi_wavewatch3/source.py
index 9063509..4da3ac6 100644
--- a/bmi_wavewatch3/source.py
+++ b/bmi_wavewatch3/source.py
@@ -121,7 +121,7 @@ def validate_date(cls, date):
         try:
             datetime.datetime.fromisoformat(date)
         except ValueError as error:
-            raise DateValueError(error)
+            raise DateValueError(str(error))
         date_in_range_or_raise(date, lower=cls.MIN_DATE, upper=cls.MAX_DATE)
 
         return date
diff --git a/docs/source/_static/hurricane_julia.png b/docs/source/_static/hurricane_julia.png
new file mode 100644
index 0000000..a439378
Binary files /dev/null and b/docs/source/_static/hurricane_julia.png differ
diff --git a/news/13.bugfix b/news/13.bugfix
new file mode 100644
index 0000000..a045302
--- /dev/null
+++ b/news/13.bugfix
@@ -0,0 +1,3 @@
+Fixed a bug in the reporting of an error caused by an invalide datatime
+string.
+
diff --git a/news/13.feature b/news/13.feature
new file mode 100644
index 0000000..b66b45d
--- /dev/null
+++ b/news/13.feature
@@ -0,0 +1,5 @@
+Added a new subcommand, *plot*, to the *ww3* command-line program.
+``ww3 plot`` with download (if the data files are not already cached) and
+create a plot of the requested data.
+
+
diff --git a/pyproject.toml b/pyproject.toml
index 63ffab8..55369f0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -38,6 +38,7 @@ dependencies = [
   "bmipy",
   "cfgrib",
   "click",
+  "matplotlib",
   "tomli",
   "tqdm",
   "xarray",