Geoscience Reference
In-Depth Information
4
Nowcasting
Clive Pierce 1 , Alan Seed 2 , Sue Ballard 3 , David Simonin 3 and Zhihong Li 3
1 Hydro-Meteorological Research, Met Office, FitzRoy Road, Exeter,
2 Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne,
3 Joint Centre for Mesoscale Meteorology, Met Office, Meteorology Building,
University of Reading, Earley Gate, Reading,
1,3 UK
2 Australia
1. Introduction
The somewhat inelegant term, nowcasting , was devised in the mid-1970s (Browning, 1980). It
encapsulates a broad spectrum of observation intensive techniques developed for predicting
the weather up to a few hours ahead. These techniques are reliant on the rapid processing
of high resolution data sets collected by weather radars and satellites. As such, the evolution
of nowcasting as a branch of operational meteorology has been closely bound up with post-
second world war advances in remote sensing, telecommunications and digital computing.
A comprehensive treatment of the subject matter is beyond the scope of this Chapter. In a
topic about Doppler radar the authors make no apology for focusing on radar based
nowcasts of precipitation.
We begin with a brief justification for the use of nowcasts in operational meteorology.
This is followed by an overview of nowcasting techniques. A description of some of the
key, historical developments in nowcasting is followed by sections on deterministic
extrapolation-based nowcasting techniques, errors in precipitation nowcasts and their
treatment within nowcasting system frameworks. The remaining sections consider
advances in high resolution Numerical Weather Prediction (NWP) model-based
nowcasting and review some of the issues and developments surrounding the
application of quantitative precipitation nowcasts (QPN) to hydrological forecasting and
warning. The Chapter closes with a brief consideration of future prospects for
nowcasting.
2. An overview of nowcasting techniques
Operational weather forecasts are produced by primitive equation models known
collectively, as Numerical Weather Prediction models. The predictive skill of these models is
limited by a number of factors including the accuracy and coverage of routinely available
weather observations, the extent to which their model formulations and grid lengths allow
the relevant physical and dynamical processes to be modelled accurately, and the non-linear
response of the atmospheric system to small perturbations in its state.
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