Grib2Reader

Importer for NSSL's Multi-Radar/Multi-Sensor System (MRMS) rainrate product (grib format).

The rainrate values are expressed in mm/h, and the dimensions of the data array are [latitude, longitude]. The first grid point (0,0) corresponds to the upper left corner of the domain, while (last i, last j) denote the lower right corner.

Due to the large size of the dataset (3500 x 7000), a float32 type is used by default to reduce the memory footprint. However, be aware that when this array is passed to a pystep function, it may be converted to double precision, doubling the memory footprint. To change the precision of the data, use the dtype keyword.

Also, by default, the original data is not downscaled but can be done by setting window_size=4 (resulting in a ~4 km grid spacing). In case that the original grid spacing is needed, use window_size=1. But be aware that a single composite in double precipitation will require 186 Mb of memory.

Finally, if desired, the precipitation data can be extracted over a sub region of the full domain using the extent keyword. By default, the entire domain is returned.

Notes

In the MRMS grib files, "-3" is used to represent "No Coverage" or "Missing data". However, in this reader replace those values by the value specified in the fillna argument (NaN by default).

Note that "missing values" are not the same as "no precipitation" values. Missing values indicates regions with no valid measures. While zero precipitation indicates regions with valid measurements, but with no precipitation detected.

Parameters

filename: str
    Name of the file to import.
extent: None or array-like
    Longitude and latitude range (in degrees) of the data to be retrieved.
    (min_lon, max_lon, min_lat, max_lat).
    By default (None), the entire domain is retrieved.
    The extent can be in any form that can be converted to a flat array
    of 4 elements array (e.g., lists or tuples).
window_size: array_like or int
    Array containing down-sampling integer factor along each axis.
    If an integer value is given, the same block shape is used for all the
    image dimensions.
    Default: window_size=4.

{extra_kwargs_doc}

Returns

precipitation: 2D array, float32
    Precipitation field in mm/h. The dimensions are [latitude, longitude].
    The first grid point (0,0) corresponds to the upper left corner of the
    domain, while (last i, last j) denote the lower right corner.
quality: None
    Not implement.
metadata: dict
    Associated metadata (pixel sizes, map projections, etc.).