Synoptic-scale conditions and convection-resolving hindcast experiments of a cold-season derecho on 3 January 2014 in western Europe
In: Natural hazards and earth system sciences: NHESS, Band 19, Heft 5, S. 1023-1040
ISSN: 1684-9981
Abstract. A major linear mesoscale convective system caused severe weather over
northern France, Belgium, the Netherlands and northwestern Germany on
3 January 2014. The storm was classified as a cold-season derecho with
widespread wind gusts exceeding 25 m s−1. While such derechos
occasionally develop along cold fronts of extratropical cyclones, this
system formed in a postfrontal air mass along a baroclinic surface pressure
trough and was favoured by a strong large-scale air ascent induced by an
intense mid-level jet. The lower-tropospheric environment was characterised
by weak latent instability and strong vertical wind shear. Given the poor
operational forecast of the storm, we analyse the role of initial and lateral
boundary conditions to the storm's development by performing
convection-resolving limited-area simulations with operational analysis and
reanalysis datasets. The storm is best represented in simulations with high
temporally and spatially resolved initial and lateral boundary conditions
derived from ERA5, which provide the most realistic development of the
essential surface pressure trough. Moreover, simulations at
convection-resolving resolution enable a better representation of the
observed derecho intensity. This case study is testimony to the usefulness of
ensembles of convection-resolving simulations in overcoming the current
shortcomings of forecasting cold-season convective storms, particularly for
cases not associated with a cold front.