theweatherprediction.com
[--MAIN HOME--] [--ALL HABYHINTS--] [--FACEBOOK PAGE--]

SEVERE WEATHER INDICES PAGE

METEOROLOGIST JEFF HABY

TOTAL TOTALS
<44 Convection not likely
44-50 Likely thunderstorms
51-52 Isolated severe storms
53-56 Widely scattered severe
>56 Scattered severe storms
SPEED SHEAR
0-3 Weak
4-5 Moderate
6-8 Large
8+ Severe


K INDEX
15-25 Small convective potential
26-39 Moderate convective potential
40+ High convective potential
CAPE
1 - 1,500 Positive
1,500 - 2,500 Large
2,500+ Extreme


SWEAT
150-300 Slight severe
300-400 Severe possible
400+ Tornadic possible
SR HELICITY
150-300 Possible supercell
300-400 Supercells favorable
400+ Tornadic possible


LIFTED INDEX / SWI
-1 to -4 Marginal instability
-4 to -7 Large instability
-8 or less Extreme instability
BRN
<45 Supercells favorable
<10 Too sheared
teens Optimum


EHI
EHI >1 Supercells likely
1 to 5 F2, F3 tornadoes possible
5+ F4, F5 tornadoes possible




NOTES:

*Max uvv = square root of 2 CAPE
*BRN (Bulk Richardson Number) = CAPE / (0-6 km) Shear
*Showalter (SWI) = used when elevated convection is most likely (cool season)
*EHI = (SR HEL CAPE) /160,000
*SWEAT = 12(850Td) +20(TT-49) +2(V850) + (V500) +125(sin(dd500-dd850) + 0.2)
*Total Totals = (T850- T500) + (Td850 - T500)= vertical totals plus cross totals
*K index = (T850 -T500) + (Td850 - Tdd700)
*SR Helicity : determines amount of horizontal streamwise vorticity available for storm ingestion
*streamwise = parallel to storm inflow
*Important to look for thermal and dewpoint ridges (THETA-E)
*For tornado, inflow must be greater than 20 knots
*20 to 30% of mesocyclones produce tornadoes
*Tornado types: rope, needle, tube, wedge
*Look for differential advection; warm/ moist at surface, dry air in mid levels
*Severe weather hodograph: veering, strong sfc to 850 directional shear
* >100 J/kg negative buoyancy is significant
*Good match: BRN < 20 and CAPE >2,000 J/kg
*Strong cap when > 2 degrees Celsius
*Study depth of moisture, TT unreasonable when low level moisture is lacking
*KI used for heavy convective rain, values vary with location/season
*Instability enhanced by ... daytime heating, outflow boundaries
*Models generally have weak handle on return flow from Gulf, low level jet, convective rainfall, orography, mesoscale boundaries, and boundary conditions
*Large hail when freezing level >675 mb, high CAPE, supercell
*Synoptic scale uplift from either surface WAA or upper level divergence
*Fair weather cumulus: cumulus humulus, cumulus mediocrus
*T-storm warning when Hail > 3/4", wind > 58 mph, gate to gate shear > 90 knots
*Sounding types: Inverted V, goal post, Type C, wet microburst