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Forecast Parameters

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, W max = (2xCAPE) 1/2. DCAPE.

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Forecast Parameters

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  1. Forecast Parameters

  2. 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

  3. DCAPE Downdraft Convective Available Potential Energy – a measure of downdraft potential strength From Gilmore and Wicker, 1998, MWR

  4. 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

  5. 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!

  6. 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?

  7. 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

  8. Storm-relative environmental helicity

  9. Bulk Richardson Number

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

  11. Energy Helicity Index

  12. 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.

  13. From Brooks et al. 2003 – Atm. Research

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

  15. Forecast Parameters used at the SPC Go to the meso analysis page for a description of these and other parameters http://www.spc.noaa.gov/exper/sref/index.php http://www.spc.noaa.gov/exper/mesoanalysis/ SREF:

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