Two overview papers have been prepared by the SNAP (Stratospheric Network for the Assessment of Predictability) community, and have recently been published int he Journal of Geophysical Research: Atmospheres. The publications are now available online:

The role of the stratosphere in subseasonal to seasonal prediction Part I: Predictability of the stratosphere. By D. I. V. Domeisen, A. H. Butler,  A. J. Charlton‐Perez, B. Ayarzagüena, M. P. Baldwin, E. Dunn‐Sigouin et al. in the Journal of Geophysical Research: Atmospheres.

The role of the stratosphere in subseasonal to seasonal prediction Part II: Predictability arising from stratosphere ‐ troposphere coupling. By By D. I. V. Domeisen, A. H. Butler,  A. J. Charlton‐Perez, B. Ayarzagüena, M. P. Baldwin, E. Dunn‐Sigouin et al. in the Journal of Geophysical Research: Atmospheres.