Hail Size Forcasting
Once the forecaster has determined that the
probability of hail exists, as previously outlined, the next
logical question will relate to the size of the hail that may
be anticipated. The following text discusses the method
that uses the Skew T Log P diagram.
The first step in forecasting hail is to determine the
convective condensation level (CCL). This parameter
is evaluated on the adiabatic chart by finding the mean
and following this saturation, mixing ratio line to its
intersection with the sounding dry-bulb temperature
curve. Next, the moist adiabat through the CCL is traced
up to the pressure level where the dry-bulb temperature
is -5°C. This pressure level, the dry-bulb temperature
curve, and the moist adiabat through the CCL form a
triangle, outlining a positive area. Figure 5-9 illustrates
this procedure. The horizontal coordinate in figure 5-9
is the length of the horizontal side of the triangle in
The length is measured from the
mixing ratio in the moist layer of the lowest 150 hPa.
pressure at the base of the triangle.
Figure 5-9.-Example of hail size forecast sounding.