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Bulk Richardson Number Calculator

 

 

Enter ML50 CAPE*

J/kg

Enter average 0 - 0.5 km wind direction

deg

Enter average 0 - 0.5 km wind speed

kts

Enter average 0 - 6 km wind direction

deg

Enter average 0 - 6 km wind speed

 kts

The Bulk Richardson Number is



 

 

* ML50 CAPE = conservative estimate of CAPE, lifting an average parcel in the bottom 50 hPa of a sounding. This value can be found via soundings of Wyoming.

Maps of forecasted CAPE on the internet = surface-based CAPE (or SBCAPE) which starts in lowest 2 meter.

Convert SBCAPE to ML50 CAPE with estimation table:

SBCAPE ML50 CAPE Factor
10 0.6 0.06
20 1.6 0.08
50 5.5 0.11
100 14 0.14
200 36 0.18
500 130 0.26
1000 330 0.33
1500 585 0.39
2000 880 0.44
2500 1175 0.47
3000 1500 0.50
4000 2240 0.56
5000 3100 0.62

 

BRN < 10: low risk severe thunderstorms.
BRN between 15 to 50: risk for supercells (upper teens are optimal) 
BRN >  35: low risk for supercells, but risk for single cells or multicells.

 

The BRN is a better indictor of storm type than of storm severity or storm rotation.
-Works best with CAPE between 1500-.3500 J/Kg
- CAPE < 1000 J/Kg and accompanied by moderate wind shear, the BRN number may indicate supercells, but lack of buoyancy is likely to inhibit severe weather occurrence.
-CAPE >3500 J/Kg with moderate wind shear, BRN values may suggest multicells, but buoyancy energy will be sufficient to produce tornadoes and large hail

 

Formula used: BRN = ML50 CAPE / (0,5 * UČ) 

(U = vector difference between 0-6km mean wind and 0-0,5km mean wind)  

 

 

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