Synoptic-scale conditions and convection-resolving hindcast experiments of a cold-season derecho on 3 January 2014 in western Europe

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 midlevel 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 convectionresolving 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 coldseason convective storms, particularly for cases not associated with a cold front.

Severe Convective Storms across Europe and the United States. Part II: ERA5 Environments Associated with Lightning, Large Hail, Severe Wind, and Tornadoes

“…However, while wind shear in cold-season cases is large, CAPE at the same time is marginal (Figure 2a). This is consistent with prior studies on HSLC environments (Sherburn and Parker 2014;Anderson-Frey et al 2019) that have been shown to have an enhanced potential for producing severe winds (Mathias et al 2019;Gatzen et al 2020;Celiński-Mysław et al 2020). Patterns for severe weather categories in 0-1 km stormrelative helicity (not shown) and low-level jet (as 1-3 km mean wind) are very similar to those of 0-3 km and 0-1 km wind shear (Figure 4).…”

“…Over Europe highest STP is found over the central Mediterranean and northwestern Russia, consistent with increased occurrence of significant tornadoes over these areas (Miglietta and Matsangouras 2018;Chernokulsky et al 2019Chernokulsky et al , 2020Ingrosso et al 2020). Enhanced values of SCP, SHIP and STP found in a corridor from central France to western Germany also correspond with the location of major severe weather outbreaks (Hamid 2012;Mathias et al 2017;Antonescu et al 2018), which can be linked to 'Spanish Plume' synoptic patterns (Carlson and Ludlam 1968). However, these values are notably lower compared to the Great Plains, again indicating a considerably lower potential for significant severe thunderstorms over Europe.…”

“…Higher lapse rates over Europe may be linked to synoptic patterns that support wintertime windstorm events (Gatzen et al 2020;Celiński-Mysław et al 2020). Typically in those situations, eastwardly traveling deep troughs with a polar or arctic air masses allow for the development of steep lapse rates and marginal CAPE over western and central Europe (Kolendowicz 2012;Wapler and James 2015;Piper et al 2019;Mathias et al 2019).…”

“…A consistent result between all studies has been the clear dependence of the severity of thunderstorms on the covariate relationship of CAPE and vertical wind shear (Rasmussen and Blanchard 1998;Craven and Brooks 2004;Brooks 2009Brooks , 2013Allen and Karoly 2014;Púčik et al 2015;Anderson-Frey et al 2016;Taszarek et al 2017Taszarek et al , 2019Ingrosso et al 2020). A notable focus in recent years has been also on high shear low CAPE (HSLC) environments with an enhanced potential of producing severe weather, typically during cold-season as evidenced for western and central Europe and the southeastern U.S. (Sherburn and Parker 2014;Sherburn et al 2016;Gatzen et al 2020;Anderson-Frey et al 2019;Mathias et al 2019;Celiński-Mysław et al 2020).…”

“…Over Europe, EML development is confined to Iberian Peninsula, Alps, Turkey and northwestern Africa (Carlson and Ludlam 1968) and is comparatively rare without favorable southerly wind component. However, 'Spanish Plume' events displacing EML from the Iberian Peninsula are typically linked to severe weather outbreaks over western Europe(Hamid 2012;Mathias et al 2017;Antonescu et al 2018).…”