  Skilful Machine Learned weather forecasts have challenged our approach to
numerical weather prediction, demonstrating competitive performance compared to
traditional physics-based approaches. Data-driven systems have been trained to
forecast future weather by learning from long historical records of past
weather such as the ECMWF ERA5. These datasets have been made freely available
to the wider research community, including the commercial sector, which has
been a major factor in the rapid rise of ML forecast systems and the levels of
accuracy they have achieved. However, historical reanalyses used for training
and real-time analyses used for initial conditions are produced by data
assimilation, an optimal blending of observations with a physics-based forecast
model. As such, many ML forecast systems have an implicit and unquantified
dependence on the physics-based models they seek to challenge. Here we propose
a new approach, training a neural network to predict future weather purely from
historical observations with no dependence on reanalyses. We use raw
observations to initialise a model of the atmosphere (in observation space)
learned directly from the observations themselves. Forecasts of crucial weather
parameters (such as surface temperature and wind) are obtained by predicting
weather parameter observations (e.g. SYNOP surface data) at future times and
arbitrary locations. We present preliminary results on forecasting observations
12-hours into the future. These already demonstrate successful learning of time
evolutions of the physical processes captured in real observations. We argue
that this new approach, by staying purely in observation space, avoids many of
the challenges of traditional data assimilation, can exploit a wider range of
observations and is readily expanded to simultaneous forecasting of the full
Earth system (atmosphere, land, ocean and composition).
