The Analysis of Convective
Storms
Thermodynamic Diagrams
There are three desirable characteristics of
atmospheric thermodynamic diagrams:
• The area enclosed by any cyclic process
should be proportional to energy or work.
• The more straight lines the better.
• The angle between isotherms and dry
adiabats should be as large as possible.
• Emagram—Abscissa is T, ordinate is
proportional to ln p. (From energy/mass).
• Tephigram—Abscissa is T, ordinate is
logarithm of potential temperature,
sometimes diagram is rotated (From T-phi)
R/c
• Stuve—Abscissa is T, ordinate is p
Area is not proportional to energy.
• Skew T-ln p—Similar to emagram, but
temperature lines are skewed to increase the
angle with dry adiabats.
p
Convection Parameters
• Lifted Condensation Level (LCL) – level at
which a parcel lifted from the surface will
saturate
• Convective Condensation Level (CCL) –
level at which a parcel from the surface
heating to its convective temperature will
saturate
• Convective Temperature – the temperature
that the surface layer would need to be
heated to to convect
Convection Parameters (cont.)
• Level of Free Convection (LFC) – level at
which a lifted parcel becomes warmer than
its surroundings, and hence buoyant.
• Equilibrium Level (EL) – level at which a
previously buoyant parcel’s temperature
again equals the environmental temperature.
This is an approximate height for
thunderstorm anvils.
Convection Parameter (cont.)
• Convective Inhibition (CIN) – the
“negative” energy area below a parcel’s
level of free convection.
• Convective Available Potential Energy
(CAPE) – The “positive” energy area where
a parcel is accelerating upward.
• Downdraft Convective Available Potential
Energy (DCAPE) – The negative energy
area where a parcel can be accelerated
downward evaporative cooling.
pf
CAPE  Rd
(
T

T
)
d
(ln(
p
))
 p e
pi
Vmax  2CAPE
3
DMaxHail  3  10 CAPE
Vdown   2 DCAPE
Stability Parameters
All indices are useful diagnostics but should
not be used blindly
• Lifted index (LI)
• Showalter index (SI)
• Total totals (TT)
• Severe Weather Threat Index (SWEAT)
• Bulk Richardson Number
• Storm Relative Helicity
Miller Type I “loaded gun sounding”
Firing gun sounding?
Miller Type IV “Inverted V sounding
Miller Type II (tropical sounding)
Miller Type III Sounding
Thunderstorm Types
• Single cell (pulse)—can be strong, but no
severe
• Multicell—can be severe, but don’t
generate strong tornadoes
• Supercell—rotating updraft, most severe
storms
Single Cell Thunderstorm
Multicell Thunderstorm
Supercell Thunderstorm
Conversion of Horizontal
Vorticity to Vertical Vorticity
Storm Splitting
Tornado probability from Storm
Prediction Center
Early afternoon satellite photo
Late afternoon satellite photo