By: Kevin Goebbert
This example uses the declarative syntax available through the MetPy package to allow a more convenient method for creating simple maps of atmospheric data. To plot aboslute vorticity, the data is scaled and reassigned to the xarray object for use in the declarative plotting interface.
from datetime import datetime
import xarray as xr
from metpy.plots import declarative
from metpy.units import units# Set date for desired dataset
dt = datetime(2012, 10, 31, 12)
# Open dataset from NCEI
ds = xr.open_dataset('https://www.ncei.noaa.gov/thredds/dodsC/'
f'model-gfs-g4-anl-files-old/{dt:%Y%m}/{dt:%Y%m%d}/'
f'gfsanl_4_{dt:%Y%m%d}_{dt:%H}00_000.grb2'
).metpy.parse_cf()
# Subset Data to be just over CONUS
ds_us = ds.sel(lon=slice(360-160, 360-40), lat=slice(65, 10))syntax error, unexpected WORD_WORD, expecting SCAN_ATTR or SCAN_DATASET or SCAN_ERROR
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KeyError Traceback (most recent call last)
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/file_manager.py:219, in CachingFileManager._acquire_with_cache_info(self, needs_lock)
218 try:
--> 219 file = self._cache[self._key]
220 except KeyError:
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/lru_cache.py:56, in LRUCache.__getitem__(self, key)
55 with self._lock:
---> 56 value = self._cache[key]
57 self._cache.move_to_end(key)
KeyError: [<class 'netCDF4._netCDF4.Dataset'>, ('https://www.ncei.noaa.gov/thredds/dodsC/model-gfs-g4-anl-files-old/201210/20121031/gfsanl_4_20121031_1200_000.grb2',), 'r', (('clobber', True), ('diskless', False), ('format', 'NETCDF4'), ('persist', False)), 'fd42aa58-053d-4b34-b5d5-bff14f238b1f']
During handling of the above exception, another exception occurred:
OSError Traceback (most recent call last)
Cell In[2], line 5
1 # Set date for desired dataset
2 dt = datetime(2012, 10, 31, 12)
3
4 # Open dataset from NCEI
----> 5 ds = xr.open_dataset('https://www.ncei.noaa.gov/thredds/dodsC/'
6 f'model-gfs-g4-anl-files-old/{dt:%Y%m}/{dt:%Y%m%d}/'
7 f'gfsanl_4_{dt:%Y%m%d}_{dt:%H}00_000.grb2'
8 ).metpy.parse_cf()
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/api.py:613, in open_dataset(filename_or_obj, engine, chunks, cache, decode_cf, mask_and_scale, decode_times, decode_timedelta, use_cftime, concat_characters, decode_coords, drop_variables, create_default_indexes, inline_array, chunked_array_type, from_array_kwargs, backend_kwargs, **kwargs)
601 decoders = _resolve_decoders_kwargs(
602 decode_cf,
603 open_backend_dataset_parameters=backend.open_dataset_parameters,
(...) 609 decode_coords=decode_coords,
610 )
612 overwrite_encoded_chunks = kwargs.pop("overwrite_encoded_chunks", None)
--> 613 backend_ds = backend.open_dataset(
614 filename_or_obj,
615 drop_variables=drop_variables,
616 **decoders,
617 **kwargs,
618 )
619 ds = _dataset_from_backend_dataset(
620 backend_ds,
621 filename_or_obj,
(...) 632 **kwargs,
633 )
634 return ds
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/netCDF4_.py:771, in NetCDF4BackendEntrypoint.open_dataset(self, filename_or_obj, mask_and_scale, decode_times, concat_characters, decode_coords, drop_variables, use_cftime, decode_timedelta, group, mode, format, clobber, diskless, persist, auto_complex, lock, autoclose)
749 def open_dataset(
750 self,
751 filename_or_obj: T_PathFileOrDataStore,
(...) 768 autoclose=False,
769 ) -> Dataset:
770 filename_or_obj = _normalize_path(filename_or_obj)
--> 771 store = NetCDF4DataStore.open(
772 filename_or_obj,
773 mode=mode,
774 format=format,
775 group=group,
776 clobber=clobber,
777 diskless=diskless,
778 persist=persist,
779 auto_complex=auto_complex,
780 lock=lock,
781 autoclose=autoclose,
782 )
784 store_entrypoint = StoreBackendEntrypoint()
785 with close_on_error(store):
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/netCDF4_.py:529, in NetCDF4DataStore.open(cls, filename, mode, format, group, clobber, diskless, persist, auto_complex, lock, lock_maker, autoclose)
525 else:
526 manager = CachingFileManager(
527 netCDF4.Dataset, filename, mode=mode, kwargs=kwargs, lock=lock
528 )
--> 529 return cls(manager, group=group, mode=mode, lock=lock, autoclose=autoclose)
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/netCDF4_.py:429, in NetCDF4DataStore.__init__(self, manager, group, mode, lock, autoclose)
427 self._group = group
428 self._mode = mode
--> 429 self.format = self.ds.data_model
430 self._filename = self.ds.filepath()
431 self.is_remote = is_remote_uri(self._filename)
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/netCDF4_.py:538, in NetCDF4DataStore.ds(self)
536 @property
537 def ds(self):
--> 538 return self._acquire()
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/netCDF4_.py:532, in NetCDF4DataStore._acquire(self, needs_lock)
531 def _acquire(self, needs_lock=True):
--> 532 with self._manager.acquire_context(needs_lock) as root:
533 ds = _nc4_require_group(root, self._group, self._mode)
534 return ds
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/contextlib.py:141, in _GeneratorContextManager.__enter__(self)
139 del self.args, self.kwds, self.func
140 try:
--> 141 return next(self.gen)
142 except StopIteration:
143 raise RuntimeError("generator didn't yield") from None
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/file_manager.py:207, in CachingFileManager.acquire_context(self, needs_lock)
204 @contextmanager
205 def acquire_context(self, needs_lock: bool = True) -> Iterator[T_File]:
206 """Context manager for acquiring a file."""
--> 207 file, cached = self._acquire_with_cache_info(needs_lock)
208 try:
209 yield file
File ~/micromamba/envs/metpy-cookbook/lib/python3.14/site-packages/xarray/backends/file_manager.py:225, in CachingFileManager._acquire_with_cache_info(self, needs_lock)
223 kwargs = kwargs.copy()
224 kwargs["mode"] = self._mode
--> 225 file = self._opener(*self._args, **kwargs)
226 if self._mode == "w":
227 # ensure file doesn't get overridden when opened again
228 self._mode = "a"
File src/netCDF4/_netCDF4.pyx:2522
-> 2522 'Could not get source, probably due dynamically evaluated source code.'
File src/netCDF4/_netCDF4.pyx:2159
-> 2159 'Could not get source, probably due dynamically evaluated source code.'
OSError: [Errno -70] NetCDF: DAP server error: 'https://www.ncei.noaa.gov/thredds/dodsC/model-gfs-g4-anl-files-old/201210/20121031/gfsanl_4_20121031_1200_000.grb2'Contour Intervals¶
Since absolute vorticity rarely goes below zero in the Northern Hemisphere, we can set up a list of contour levels that doesn’t include values near but greater than zero. The following code yields a list containing: [-8, -7, -6, -5, -4, -3, -2, -1, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45]
# Absolute Vorticity colors
# Use two different colormaps from matplotlib and combine into one color set
clevs_500_avor = list(range(-8, 1, 1))+list(range(8, 46, 1))The Plot¶
Using the declarative interface in MetPy to plot the 500-hPa Geopotential Heights and Absolute Vorticity.
# Set Contour Plot Parameters
contour = declarative.ContourPlot()
contour.data = ds_us
contour.time = dt
contour.field = 'Geopotential_height_isobaric'
contour.level = 500 * units.hPa
contour.linecolor = 'black'
contour.linestyle = '-'
contour.linewidth = 2
contour.clabels = True
contour.contours = list(range(0, 20000, 60))
# Set Color-filled Contour Parameters
cfill = declarative.FilledContourPlot()
cfill.data = ds_us
cfill.time = dt
cfill.field = 'Absolute_vorticity_isobaric'
cfill.level = 500 * units.hPa
cfill.contours = clevs_500_avor
cfill.colormap = 'PuOr_r'
cfill.image_range = (-45, 45)
cfill.colorbar = 'horizontal'
cfill.scale = 1e5
# Panel for plot with Map features
panel = declarative.MapPanel()
panel.layout = (1, 1, 1)
panel.area = 'uslcc'
panel.projection = 'area'
panel.layers = ['coastline', 'states', 'borders']
panel.layers_edgecolor = ['black', 'grey', 'black']
panel.layers_linewidth = [1.25, .75, 1]
panel.title = (f'{cfill.level} GFS Geopotential Heights'
f'and Absolute Vorticity at {dt}')
panel.plots = [cfill, contour]
# Bringing it all together
pc = declarative.PanelContainer()
pc.size = (15, 14)
pc.panels = [panel]
pc.show()