Forecast Parameters

CAPE•Convective Available Potential Energy – obviously, positive buoyancy is helpful for producing convection

–100 mb mixed layer CAPE, MU CAPE, SB CAPE (which do you use?)•Recall, parcel theory is assumed in the calculation•Then, Wmax = (2xCAPE)1/2

DCAPE•Downdraft Convective Available Potential Energy – a measure of downdraft potential strength

From Gilmore and Wicker, 1998, MWR

CIN, LCL, and LFC•Convective Inhibition – is bad…..•CIN is the negative area in the sounding below the LFC•Represents the amount of energy that must be given to the parcel to reach the LFC•LCL and LFC heights are also looked at:

–Supercells with lower LCLs are more likely to be tornadic–LFC – LCL difference is often related to amount of CIN and therefore, CI

Lifted Index (LI)•Is the difference in temperature at 500 mb between a parcel of air lifted according to parcel theory and the environment

–LI < 0 – potential for convection–LI < -4 or so – increasing potential for severe convection–LI < -10 – watch out!

Storm-relative environmental helicity•h, the inflow depth is typical taken to be 3 km, but also 1 km•What are the units of SREH?

Storm-relative environmental helicity•The green dot on the diagram below is estimated storm motion•The SREH is 2 x area swept out from 0 – 3 km by relative storm motion vector (the green area)•Note, storm motion must be estimated to calculate SREH

Storm-relative environmental helicity

Bulk Richardson Number

Bulk Richardson Number•Can be used to roughly distinguish between supercells and multicell storms•The cut off appears to be about 50

Energy Helicity Index

CAPE/Shear Phase Space•The CAPE-shear diagram below nicely summarizes the convective mode one might expect on a given day•But, notice the overlap….•The diagram below is based on idealized modeling work•There are many more recent studies that have examined the different environmental characteristics that produce different convective modes.

From Brooks et al. 2003 – Atm. Research

Best indicators for tornadoes:• Low LCLs• Large 0-1 km

shear

Forecast Parameters used at the SPChttp://www.spc.noaa.gov/exper/sref/index.phphttp://www.spc.noaa.gov/exper/mesoanalysis/

SREF:

Go to the meso analysis page for a description of these and other parameters