Finnish Meteorological Institute Probabilistic Precipitation Nowcasting system (FMI-PPN)

FMI-PPN is a modular weather-radar-based nowcasting system built for research and operational usage.

Subsystems

Precipitation motion

Current implementation of FMI-PPN uses Lucas-Kanade optical flow method to estimate precipitation movement from radar measurements.

Nowcasting

Currently FMI-PPN uses pysteps to generate ensemble nowcasts.

Known issues and limitations

• Parameter SEED must be None or an integer between 0 and 2**32 - 1. This is a limitation in numpy.random.
• OpenMPI conflicts with dask when both are installed, leading to significant decrease FMI-PPN performance. Workaround is to set OpenMPI use only one thread. In Linux you can set environment variable OMP_NUM_THREADS=1.

Usage

Installation

1. Install conda (Miniconda is recommended)
2. Clone this repository
3. Change directory to FMI-PPN folder
4. Setup conda environment: $ conda env create -f environment.yml
5. Modify pystepsrc file: Add your data source configuration under data_sources (see pysteps documentation for details)
6. Replace the value for DOMAIN parameter under defaults with your data source configuration's name
7. Activate conda environment: $ conda activate fmippn
8. Run FMI-PPN with default settings: $ python run_ppn.py

Running FMI-PPN

Before running FMI-PPN, you should configure pysteps (via pystepsrc file) and PPN by adding your parametrisations to ppn_config.py.

How to run:

1. Activate your conda environment
2. Run FMI-PPN with your settings: $ python run_ppn.py -c your_config_parametrisation

Configuration

Adding new parametrisations

Create a json file with parameters you want to change from defaults and put it in config folder. The file's name (without file type extension) will be used to select the settings.

The ppn_config.py module has a utility function dump_defaults() for creating a configuration file based on default settings.

Parametrisations

Parameter	Explanation	Default value
DOMAIN	Data source used from pystepsrc	fmi
ENSEMBLE_SIZE	Number of ensemble members	24
FFT_METHOD	FFT method used in pysteps calculations	pyfftw
FIELD_VALUES	Select the units to store the nowcast (before scaling). Valid units are dbz for dBZ and rrate for mm/h.	dbz
GENERATE_DETERMINISTIC	Calculate extrapolation-only nowcast	True
GENERATE_ENSEMBLE	If True, then calculate ensemble members	True
GENERATE_UNPERTURBED	Calculate nowcast using pysteps, but without noise	False
KMPERPIXEL	Pixel size in kilometers	1.0
LOG_FOLDER	Path where log files should be stored	../logs
LOG_LEVEL	Logging level used by Python Logging Module	20
MAX_LEADTIME	How long your nowcast will be (in minutes)	120
NORAIN_VALUE	Value assigned to dry pixels during thresholding. Units depend on VALUE_DOMAIN parameter (dBZ or mm/h). Must be less than RAIN_THRESHOLD value!	1.5
NOWCAST_TIMESTEP	Timestep between consecutive nowcast images	5
NUM_CASCADES	How many cascade levels are used in cascade decomposition by pysteps	8
NUM_PREV_OBSERVATIONS	Number of previous observations used in optical flow calculation	3
NUM_TIMESTEPS	How many timesteps will be calculated in nowcasts (If this setting is None, this value is automatically calculated based on MAX_LEADTIME and NOWCAST_TIMESTEP parameters)	None
NUM_WORKERS	Number of worker threads used in parallel computing	6
OPTFLOW_METHOD	Optical flow method (see pysteps docs)	lucaskanade
OUTPUT_PATH	If not None, then use this path to store output instead of setting in pysteprc	None
OUTPUT_TIME_FORMAT	Python datetime format for showing timestamps	%Y-%m-%d %H:%M:%S
RAIN_THRESHOLD	Thresholding value for rain. Pixels with values under this parameter are regarded as dry pixels. Units depend on VALUE_DOMAIN parameter (dBZ or mm/h).	6.5
REGENERATE_PERTURBED_MOTION	Re-calculate motion for each ensemble member (requires SEED != None)	False
SCALER	Scaling coefficient for output	100
SCALE_ZERO	Value for "0" after scaling the output. Setting to "auto" or None uses the minimum value found in data before scaling.	auto
SEED	Seed parameter for random number generation. Use None for unseeded nowcasts.	None
STORE_DETERMINISTIC	Write "deterministic" nowcast in output file	True
STORE_ENSEMBLE	Write all ensemble members in output file	True
STORE_MOTION	Write optical flow motion field in output file	True
STORE_PERTURBED_MOTION	Write optical flow motion for each ensemble member in output file	True
STORE_UNPERTURBED	Write "unperturbed" nowcast in output file	True
VALUE_DOMAIN	Choose if nowcasting is performed for data in dBZ or mm/h units. Valid parameters are dbz for dBZ and rrate for mm/h.	dbz
VEL_PERT_KWARGS	Parameters for velocity perturbation (see pysteps docs). Set this parameter to None to use default pysteps values.	{'p_par': [2.20837526, 0.33887032, -2.48995355], 'p_perp': [2.21722634, 0.32359621, -2.57402761]}
VEL_PERT_METHOD	Velocity perturbation method used in pysteps	bps
WRITE_LOG	If True, then generate a log file	False
ZR_A	Value for coefficient a in R(Z) relation	223.0
ZR_B	Value for coefficient b in R(Z) relation	1.53