Richard (Rick)Jones Regional Training Workshop on Severe Weather
Forecasting Macau, April 8 -13, 2013 Slide 2 Overview Overview of
the key ingredients of deep convection Key stability indices and
precipitable water (PW) or total column water TCW PW is the prime
driver of convection Forecast deep convection and limits of
predictability Slide 3 Basic Ingredients Source of moisture best
described by precipitable water (PW) Sustained PW plumes are often
associated with prolonged and record/near record events related to
convectively available potential energy Method to lift the air
Topography upslope Density boundaries fronts; sea-breeze fronts
Instability -> maximize lift & sustain development Slide 4
Classic Stability forecast Indices & Methods The K-index The
Totals Totals Index The Lifted Index Showalter Stability index
(more mid-latitude) CAPE & CIN Slide 5 Based on 850 to 500 hPa
lapse rate to identify convective and heavy-rain producing
environments as it accounts for moisture. With contribution of 850
hPa dew point and 700 hPa dewpoint depression KI =
(T850-T500)+Td850-(T700-Td700) KI = (T850-T500)+Td850-(DD700) Slide
6 KI normally above ~28-38 KI good for potential areas of
convection Related to heavier rainfall when have lift and moisture
Limitations when terrain above 850 hPa Good in models and in
soundings Slide 7 KI JMA Slide 8 PW - JMA Slide 9 KI KMA Slide 10
PW - KMA Slide 11 Using the K-index Heavy rainfall combination of
instability and deep moisture Favors values of K-index upper 20s to
mid 30s. Still need deep moisture and lift to get convective
response Sample values tropical heavy (Laing 2004) Slide 12 Totals
Totals Index (TTI) Stability relative to 850 hPa and 500 hPa 2
components: Cross Totals: CT = Td 850 T 500 Vertical Totals: VT = T
850 - T 500 TTI = (T 850 + T 850 ) 2T 500 Focus on instability
between 850 and 500 hPa with a component of moisture at 850 hPa
Slide 13 TTI - KMA Slide 14 Lifted Index (LI) Lifted index is based
on a parcel reaching the Lifting condensation level (LCL) then
adiabatically lifting it to 500 hPa. It is often surface or moist
boundary layer based Accounts instability based on difference LI =
T lift - T 500 Slide 15 LI Areas Low LI often have convection LI
< 0 is a good starting point LI often related to CAPE and as we
will see CAPE often relates to Precipitable water Slide 16 LI KMA
Slide 17 Showalter Stability Index (SSI) SSI similar to Lifted
index but based an 850 hPa parcel reaching the Lifting condensation
level (LCL) then adiabatically lifting it to 500 hPa. It is often
surface or moist boundary layer based Accounts instability based on
difference SI = T 500 -T lift Slide 18 The Power of Convective
Available Potential Energy (CAPE) On energy diagram Tephi or Skew-T
area proportional to energy Integrated value and like SSI & LI
a theoretical parcel is lifted adiabatically from the LCL until the
equilibrium level is reached. CAPE: convective available potential
energy Release of energy produces deep updrafts Greater the area
stronger the updraft Can have fat or skinny CAPE Slide 19 CIN:
convective inhibition Another equal area value based on Tephi- or
Skew-T diagram CIN is negative and represents stability and the
lift must be able to over to overcome it unless it is diminished
Slide 20 CCl and LCL Slide 21 LFC and LCL See LFC2 Slide 22 CAPE
Slide 23 CAPE ValueStability 0Stable 0-1000Marginally Unstable
1000-2500Moderately Unstable 2500-3500Very Unstable 3500 or greater
Extremely Unstable Slide 24 CAPE and updrafts CAPE may also be
related to updraft velocity via the relation Wmax = sqrt(2*CAPE)
For example a CAPE of 2500 J/kg, the maximum updraft velocity would
be about 71 m/s!! In reality, water loading, entrainment, and other
factors can reduce Wmax by as much as a factor of 2. Slide 25 CAPE
Slide 26 Direct Link CAPE & LI NE US based study CAPE
~1200JKg-1 with LI
