Tornadoes - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 327

perature is maximized at and just east of the dryline and CAPE is greatest there
also, if the conditions aloft are uniform. Storms are also initiated along fronts and
outflow boundaries where there is upward motion driven by mesoscale vertical
circulations at their leading edges.
Other regions that have supercell tornadoes are associated with synoptic
patterns consistent with the necessary environmental shear and CAPE for super-
cells, but are different from those responsible for supercells in the Great Plains of
the U. S. in the spring. For example, over eastern Colorado and Wyoming ( Figure
6.21 ) it is common for the air to the rear of (north of ) cold fronts to be moister
than air ahead of (south of ) cold fronts. In addition, the upslope flow of surface
easterly winds enhances the vertical wind shear underneath westerly (or south-
westerly or westerly or northwesterly) flow aloft. Furthermore, as air that has had
contact with the elevated mountainous region has heated up, it flows downstream,
producing a cap that inhibits storm formation. But near the western edge of the
low-level upslope regime, convective temperature may be attained and storms may
form there first, before moving eastward onto lower terrain.
Figure 6.21. Composite High Plains severe convective storm parameter chart. Fronts indicated
by conventional symbols; surface isodrosotherms ( F) denoted by fine lines; dryline at the
surface indicated by scalloped line; surface flow indicated by large arrows; 700 hPa thermal
ridge indicated by dash-dot line; wind barbs show winds at 500 hPa (half barb represents
2.5m s 1 ; full barb represents 5m s 1 ; flag represents 25m s 1 ); heavy dashed lines indicate
locations of shortwave troughs at 500 hPa; chain of arrows marks the core of strong winds at
high altitudes, above 500 hPa; stippling denotes region of severe convective storm threat (from
Doswell, 1980).