NCAR Hydrometeorology Prediction System

National Center for Atmospheric Research
NCAR Hydrometeorology Prediction System
The NCAR Hydrometeorology Prediction System is a realtime system designed to advance the prediction of heavy
rainfall, flash floods and streamflow prediction through
the integration of state-of-the-art rainfall estimation,
precipitation forecasting, and hydrology modeling techniques
into one seamless system. This system provides 0-12 hour
forecasts and 0-1 hour nowcasts of rainfall accumulations
on very high resolution spatial grids (from 100 m to 3 km in
resolution) and identifies location-specific regions of heavy
rainfall and potential flash floods. The Hydrometeorology
Prediction System was run in real time from 7 July - 31
August 2014 to test its predictive skill along the Colorado
Front Range and to advance short term prediction of highimpact weather.
The fully-integrated components of this prediction system are
described below.
Quantitative Precipitation Estimation
Timely and accurate Quantitative Precipitation Estimates
(QPE) are essential for forecasting streamflow, flash
floods and localized urban flooding. Radar and rain gauge
based QPE are being used in this prediction system for
determining: "How hard it is raining? How much rain has
fallen in the intermediate past?" Quality-controlled QPE
fields, produced from dual-polarization radar data, are
being used in this prediction system as input for precipitation
nowcasts (QPN), as input into the hydrology model (WRFHydro), for evaluation of radar-based QPE compared to rain
gauge measurements of precipitation, and for verification of
precipitation forecasts (QPF).
1.15 in
(28 mm)
QPE - 1 hour Precipitation Accumulation
The impact of the Colorado flood of 2013 is one of the
motivations for developing this integrated prediction system.
Quantitative Precipitation Forecast
Quantitative Precipitation Forecast (QPF) is a critical
input for hydrological models in order to produce accurate
streamflow prediction. Current operational NWP weather
models are useful in providing guidance for precipitation
forecast, but not adequate in providing QPF with timing
and location precision that is required by the hydrological
models. One of the key aspects in improving the accuracy of
short-term QPF is to initialize the NWP models with high
density and high frequency data. At NCAR, data assimilation
systems have been developed that have the capability to
assimilate conventional data as well as radar observations.
The WRFDA 3DVar, a 3-dimensional, variational data
assimilation system assimilating conventional observations
and radar radial velocity and reflectivity with 1-3 hourly
rapid update cycles, is being run this summer in the NCAR
Hydrometeorology Prediction System. Additional state-ofthe art NWP models are also being run and tested in real-time.
Quantitative Precipitation Nowcast
The skill of Quantitative Precipitation Nowcasting (QPN)
decreases very rapidly in the first hour using basic storm
extrapolation techniques. In addition, NWP techniques
have insufficient skill to provide suitable, accurate warnings
of heavy precipitation on the scale needed for flash flood
forecasting. Thus, a heuristic nowcast system called
Autonowcaster/Trident (ANC), that blends observations with
numerical model analyses, is used to improve upon simple
precipitation extrapolation techniques. This is a unique
state-of-the-art real-time system that provides explicit
prediction of precipitation and warnings of heavy rainfall.
The ANC system automatically assesses the instability of the
atmospheric using numerical model analyses and combines
this information with observational data sets (radar,
satellite, surface stations, soundings, and high-resolution
4-D boundary layer winds from FINECAST) to predict the
location and timing of new storm initiation, storm growth
and dissipation. This system provides 0-1 hour precipitation
accumulation nowcasts and warning products, updated every
minute, with a spatial resolution of 1 km.
Rapidly updated, high resolution meteorological analysis is
one of the key requirements for improvement of forecasting
various hazardous weather events. The Fine-Scale Analysis
and Nowcast System (FINECAST) assimilates high density
and frequency observations from the NEXRAD radars into
a convection-permitting model to produce high resolution
wind fields and buoyancy fields. By optimally fitting model
trajectories to observations using the 4DVar technique,
dynamically consistent meteorological fields are retrieved
that include convergence, vertical velocity, buoyancy, vertical
wind shear, CAPE and relative humidity.
WRF-Hydro Flood Forecasts
Flood forecasts depend on knowledge of the state of
atmospheric features that trigger heavy rain as well as the
state of surface and subsurface water, including the heights
of rivers and reservoirs and the amount of soil saturation.
Although both meteorological and hydrological models have
improved in detail and accuracy over recent years, they
can be difficult to operate in a simultaneous and integrated
fashion. The hydrological extension of the Weather Research
and Forecasting model (WRF-Hydro) is a community-based
framework designed to link models of the atmosphere and
terrestrial hydrology. The configuration of WRF-Hydro
running in the Hydromet Prediction System ingests WRF3DVar atmospheric model output and ANC nowcasts
with selected WRF-Hydro hydrology physics options to
produce analyses and forecasts of water cycle processes and
WRF 3DVAR Precipitation Forecast With Radar Data Assimilation.
Counties are overlaid. Boulder is at the black dot.
Recent Changes in Streamflow Quantified as
Current Minus the 10-Day Average Streamflow
streamflow prediction over a range of spatial and temporal
scales. A spatially-continuous 100m resolution grid is being
used for streamflow prediction along the Colorado Front Range.
Performance Evaluation
Timely verification of the Hydromet Prediction System
components can pinpoint strengths of the system, areas for
improvement, and aid in interpretation of the forecasts.
Verification statistics are being computed in near-realtime
to evaluate the precipitation forecasts from the WRF-3DVar
with radar data assimilation, the WRF-3DVar without radar
data assimilation, and performance of the radar-based QPE
compared to rain gauge precipitation measurements. The
NCAR Model Evaluation Tools (MET) software package is
being used to produce statistics based on the comparison
of an input forecast (QPF, QPN, Streamflow) and an input
verification data set (QPE, rain gauges, NSSL MultiRadar/Multi-Sensor QPE product, stream gauges). For
evaluation of the QPE, the QPE field is treated as a forecast
and evaluated using rain gauge observations. Streamflow
forecast evaluation will also be included in the system at a
later time.
For More Information, Contact:
Rita Roberts
National Center for Atmospheric Research
Research Applications Laboratory
PO Box 3000 Boulder CO 80307-3000
[email protected]