Synoptic Composites of Tornadic and Nontornadic Outbreaks

Abstract

Tornadic and nontornadic outbreaks occur within the United States and elsewhere around the world each year with devastating effect. However, few studies have considered the physical differences between these two outbreak types. To address this issue, synoptic-scale pattern composites of tornadic and nontornadic outbreaks are formulated over North America using a rotated principal component analysis (RPCA). A cluster analysis of the RPC loadings group similar outbreak events, and the resulting map types represent an idealized composite of the constituent cases in each cluster. These composites are used to initialize a Weather Research and Forecasting Model (WRF) simulation of each hypothetical composite outbreak type in an effort to determine the WRF's capability to distinguish the outbreak type each composite represents.Synoptic-scale pattern analyses of the composites reveal strikingly different characteristics within each outbreak type, particularly in the wind fields. The tornado outbreak composites reveal a strong low-and midlevel cyclone over the eastern Rockies, which is likely responsible for the observed surface low pressure system in the plains. Composite soundings from the hypothetical outbreak centroids reveal significantly greater bulk shear and storm-relative environmental helicity values in the tornado outbreak environment, whereas instability fields are similar between the two outbreak types. The WRF simulations of the map types confirm results observed in the composite soundings.

Synoptic-Scale Precursors to Tropical Cyclone Rapid Intensification in the Atlantic Basin

“…(iii) an eigenanalysis of the correlation matrix, which included reducing the dimensions of the eigenvector matrix: this reduction was done using the congruence test [37]; after data reduction, 4 RPCs remained for RI storms and 3 RPCs for non-RI storms (Table 1 provides the variance explained of each RPC for each intensification type);…”

The forecasting of tornado events: the synoptic background of two different tornado’s case study

“…Some main synoptic flow patterns favourable for the occurrence of a tornado have been distinguished: upper-level trough the west of the location of the tornado that contributes to deepening of a surface low; sufficient instability commonly associated with the presence of low level moisture in a warm sector; upper level jet streak collocated with a centre of rapid decrease in surface pressure contributing to intensification of the synoptic cyclone; and increasing vertical wind shear (Rotunno, Klemp 1982;Schafer, Doswell 1984;Houze 1993;Corfidi et al 2010;Mercer et al 2012). Although the conditions in the larger synoptic scale create a favourable thermodynamic environment, the formation of deep convective phenomena is determined by mesoscale conditions.…”

Strong Along-Channel Winds on the Coast of British Columbia: Synoptic Climatology and Case Studies.

“…However, synoptic studies are also conducted for wind phenomena other than gap flows (e.g. Chenoli et al, 2012;Mercer et al, 2012;Moore and Renfrew, 2005;Harden et al, 2011;Goyette, 2010). For example, a synoptic composite was built for severe wind events at McMurdo station, Antarctica (Chenoli et al, 2012), following procedures similar to Sharp and Mass (2004).…”

“…For example, a synoptic composite was built for severe wind events at McMurdo station, Antarctica (Chenoli et al, 2012), following procedures similar to Sharp and Mass (2004). As another example, synoptic composites have been made for tomadic and nontomadic outbreaks within the United States (Mercer et al, 2012). In another case, satellite data were used instead o f the surface-based observations to determine barrier wind events around Greenland (Moore and Renfrew, 2005) and then synoptic averages were created depending on six years of available satellite data.…”

“…Synoptic analyses based on composites of a number of events have been performed for many other wind studies (Chenoli et al, 2012;Harden et al, 2011;Mercer et al, 2012), as well as in the present study. Two general approaches have been used in synoptic climatology studies (Yamal, 1993), environment-to-circulation (e.g.…”