The predictability of the downward vs. non-downward propagation of
sudden stratospheric warmings in S2S hindcasts
Abstract
Roughly one-third of sudden stratospheric warming (SSW) events lack a
strong canonical surface impact, and this can lead to a forecast bust if
a strong impact had been predicted. Hence, it is important to predict
before the SSW onset if an event will propagate downward. The
predictability of the downward impact of SSWs is considered in 7
subseasonal-to-seasonal forecast models for 16 major SSWs between 1998
and 2022, a larger sample size than considered by previous works. The
models successfully predict which SSWs have a stronger downward impact
to 100hPa, however they struggle to predict which have a stronger
tropospheric impact. The downward impact is stronger if the deceleration
of the 10hPa winds is better predicted. Downward impact is stronger for
split and for absorbing SSWs, and is better predicted in high-top
models. In contrast, there is little relationship between SSWs with
above-average predictability and the subsequent downward impact.