Study of the effects of the tropical initial state on extratropical forecasts

14 November 2025

Photo: FS

A recently published study by PhD student Chen Wang and colleagues provides a scale perspective on the effects of the tropical initial state in global numerical weather prediction. Tropical circulation affects extratropical processes on timescales ranging from days to weeks and beyond, but the importance of various tropical scales for the accuracy of extratropical forecasts has not been well understood.
Employing a novel modelling framework, Wang et al. show that the initialization of synoptic scales in the deep tropics is key to improving the accuracy of medium-range extratropical forecasts. In contrast, the effects of sub-synoptic scales remain trapped on the equatorward side of the subtropical jet.

Read the full study in AMS Monthly Weather Review: Wang, C., N. Žagar, and S. Vasylkevych, 2025: On the Effects of the Tropical Initial State on Extratropical Forecasts: A Scale Perspective. Mon. Wea. Rev., 153, 2069–2083, https://doi.org/10.1175/MWR-D-25-0009.1