Ordinary-cell convective storms - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 127

Figure 3.27. Meteogram from a surface station in the Oklahoma Mesonet of a heat burst at
about 23:30 cdt on June 9, 2011 (courtesy of Chris Fiebrich). During the heat burst, the
temperature rose rapidly from the low 80s to the low 90s while the dew point dropped around
25 F in a few tens of minutes and was coincident with winds gusting as high as 50mph and a
pressure drop of over 4 hPa. No precipitation was occurring during the event.
Heat bursts are therefore triggered when negatively buoyant air, which has
evaporated/sublimated all its water substance and become unsaturated, overshoots
its equilibrium level on the way down and penetrates a low-level stable layer,
where potentially warm air is forced to the surface ( Figure 3.28 ). There is also
evidence that the downdrafts that initiate heat bursts can also occur not only
when they are forced on the convective scale by negative buoyancy in unsaturated
air, but also when they are forced by mesoscale descent at the rear of convective
systems. The nature of mesoscale vertical circulations in convective systems will be
discussed in Chapter 5.