Geoscience Reference
In-Depth Information
(2006) discuss the tools to help bridge the convective initiation phase to the severe phase of
thunderstorm nowcasting. The science or theory of thunderstorm is still evolving (Brooks et
al, 1994; Brunner et al, 2007; Markowski, 2002; Rasmussen et al, 1994; Weisman and
Rotunno, 2004).
Fig. 4. A time-height diagram through the core of a long lived thunderstorm with a
mesocyclone. The “nose” on the left side of the shading indicates the precipitation and the
mesocyclone originate at mid-levels of the atmosphere and develop vertically up and down.
In the collapse phase of the storm or mesocyclone top, the severe weather reaches the
ground (adapted from Burgess et al, 1993; Lemon and Doswell, 1979).
3.2 Other data sets
This contribution focuses on radar and its use in the preparation of warnings. In fact, all
sources of observations and information are used to validate and enforce the conceptual
models used to produce the warnings. Satellite imagery, such as provided by MSG and the
future GOES-R, will be able to provide 5 minute updates over limited areas. Lightning
networks are now prevalent and often used as surrogates for radar data where none is
available. They also directly observe the lightning hazard (Branick et al, 1992; Gatlin et al,
2010; Goodman et al, 1988; Knupp et al, 2003; Lang et al, 2004; Schultz et al, 2011;). Even
though a single lightning flash can cause serious harm or death, table 2 indicates that, in
Canada, a propensity of lightning strikes is needed before a lightning warning will be
issued. Surface wind reports can be also used. However, a tornado or a microburst is
relatively small and most operational networks are too sparse to effectively sample the
atmosphere for such a small feature. At some airports, a dense network of anemometers is
established for this specific problem (Wilson et al, 1998). An important data set are eye
witness reports (Doswell et al, 1999; Moller 1978; Smith, 1999). In the past, eye witness
reports were required before a tornado warning would be issued. This made all tornado
warnings "late" with negative lead times. This was done in order not to "cry wolf" and
"alarm the public". An emerging source of information is the use of high resolution NWP
(Hoekstra et al 2011; Li, 2010; Stensrud et al 2009). While phase errors exist (time and
location of the thunderstorm), the models appear to be able to capture the morphology of
the storm (see Fig. 2). While radar is the core observation system for severe weather
warnings at the convective scale, these are not available everywhere. A warning service that
does not include radar has yet to be effectively demonstrated.
