  Active regions are the source of the majority of magnetic flux rope ejections
that become Coronal Mass Ejections (CMEs). To identify in advance which active
regions will produce an ejection is key for both space weather prediction tools
and future science missions such as Solar Orbiter. The aim of this study is to
develop a new technique to identify which active regions are more likely to
generate magnetic flux rope ejections. The new technique will aim to: (i)
produce timely space weather warnings and (ii) open the way to a qualified
selection of observational targets for space-borne instruments. We use a
data-driven Non-linear Force-Free Field (NLFFF) model to describe the 3D
evolution of the magnetic field of a set of active regions. We determine a
metric to distinguish eruptive from non-eruptive active regions based on the
Lorentz force. Furthermore, using a subset of the observed magnetograms, we run
a series of simulations to test whether the time evolution of the metric can be
predicted. The identified metric successfully differentiates active regions
observed to produce eruptions from the non-eruptive ones in our data sample. A
meaningful prediction of the metric can be made between 6 to 16 hours in
advance. This initial study presents an interesting first step in the
prediction of CME onset using only LOS magnetogram observations combined with
NLFFF modelling. Future studies will address how to generalise the model such
that it can be used in a more operational sense and for a variety of simulation
approaches.
