List of Meteorological Formulas

The Wind Index (WINDEX) is defined as a parameter, developed by McCann (1994), that indicates the maximum possible convective wind gusts that could occur in thunderstorms. The WINDEX is represented by the following equation:

WI = 5[HM*RQ(G^2 - 30 + QL - 2QM)]^0.5

where HM is the height of the melting level in km above the ground; G is the temperature lapse rate in degrees C km-1 from the surface to the melting level; QL is the mixing ratio in the lowest 1 km above the surface; QM is the mixing ratio at the melting level; and RQ = QL/12 but not > 1

Cap Strength (Lid Strength Index)= Saturated wet bulb potential temperature (Theta-E) between the surface and 500 mb MINUS the maximum saturated wet bulb potential temperature (Theta-E) in the lowest 100 mb of the atmosphere. Note in the formulas below M = Mixing Ratio & WBc = Wet Bulb Temperature in °C.

MB = Surface Level Pressure Do until MB <= 500 Q = (WBc + 273.15) * ( 1000 / Mb ) ^ 0.286 + (3 * M) If Q > Qsw then Qsw = Q End If MB = MB - 25 Loop SFC100 = Surface Level Pressure - 100 MB = Surface Level Pressure Do until MB <= SFC100 Q = (WBc + 273.15) * ( 1000 / Mb ) ^ 0.286 + (3 * M) If Q > Qwmax then Qwmax = Q End If MB = MB - 25 Loop LSI = Qsw - Qwmax

A cap of 2 degrees Celsius or greater is a good inhibitor of convection. A strong cap is can hold energy down too much and thus cause thunderstorms not to break. A weak cap can cause development to occur before enough energy builds up for the cells to become severe. A median of a strong cap and a weak cap (a cap strength from 1-2°C) is generally ideal to allow enough time for energy to build and then break the cap, allowing storms to go severe and possibly tornadic.

SWEAT = 12 [Td(850 mb)] + 20 (TT - 49) + 2 (850mb wind speed) + 500mb wind speed + 125 (sin(500mb wind dir - 850mb wind dir) + 0.2) where D = Td850 (°C); if D < 0, change it to D = 0 TT = total totals index; if TT < 49 then drop term v8 = 850 mb wind speed (kts) v5 = 500 mb wind speed (kts) S = sin [wind direction at 500 mb (degrees) - wind direction at 850 mb] the term 125(S + 0.2) should be dropped in any of the following cases: when the wind direction at 850 mb is between 130° and 250° when the wind direction at 500 mb is between 210° and 310° when (wind direction at 500 mb - wind direction at 850 mb) > 0 when v8 < 15 kts and v5 < 15 kts

SWEAT is only used to predict severe thunderstorms. Values over 300 are considered a severe producing atmosphere.

Meaux Saturation Pressure Curve Formula dryr = (dry bulb temperature deg.F) + 459.67 <--conversion to Rankine Psat = 29.9213 / (EXP((671.67 - dryr) * 35.913 * (dryr ^ -1.152437))) Note on this formula from the author: 14 years ago I purchased a SF901 computer automotive engine dynometer. The dyno came with a psychrometric lookup chart to lookup vapor pressure. Part of engine dyno testing , is the "ability" to have repeatable "standardized" testing...this means that along with trying to control / isolate every componet variable...weather influences / conditions have to accounted for! (Note=> the racing industry uses 60 deg F instead of 59 degF as part of STP ) The raw, uncorrected Horsepower and Torque output is corrected (standardized) to 29.92 inches Hg. / 60 deg. F / 0.00 % Relative Humidity through a "correction factor" in part computed by = Barometric press. Hg - Vapor press Hg. The more accurate the weather data ..the more accurate / repeatable testing. The included dyno vapor pressure chart was hard to read and hard to determine vapor pressure accuracy to better than a 1/10th inch Hg., so I began research 14 years ago at local college libraries on various weather formulas ..... I came across Smithsonian Meteorological Tables from -60 F to +212F with saturation data to .00001 accuracy, just what I was looking for, but the formulas listed in Smithsonian Tables did not always match their data especially being able to use only 1 formula to cover -60F to +212F range, so I researched through all the saturation - vapor pressure formulas I could find ......couldn't find one single formula that would "mirror" the Smithsonian data,..so I began to develop my own formula....in 1995 I finally finished my formula that does "mirror" Smithsonian data from -60F to 212 F with as much accuracy as their published data! (c)1995 by Larry Meaux/MaxRace Software, All Rights Reserved. Larry Meaux ( MaxRace Software & Meaux Racing Heads/Engines) 9827 LA Hwy. 343 Abbeville, LA 70510 337-893-1541 This formula "mirrors" Smithsonian Meteorlogical Tables from -65 F to 212 F deg Wet Bulb Temperature Here is a process requiring only Tc, RH and P (mb) as input: ** Note that if you want to estimate Wet Bulb and not have to enter Pressure, replace all 'P' variables ** with a realistic average pressure for the level you are calculating. Example: Surface might be best ** represented with an average P of about 985. Error should be no more than 0.2° by using this constant. Variables: Tc = Temperature in Degrees C RH = Relative Humidity in form 88 not 0.88 Optional Variable (for more accuracy): P = Pressure or Constant (with up to 0.2° inaccuracy): P = 985 Tdc = ((Tc - (14.55 + 0.114 * Tc) * (1 - (0.01 * RH)) - ((2.5 + 0.007 * Tc) * (1 - (0.01 * RH))) ^ 3 - (15.9 + 0.117 * Tc) * (1 - (0.01 * RH)) ^ 14)) E = (6.11 * 10 ^ (7.5 * Tdc / (237.7 + Tdc))) WBc = (((0.00066 * P) * Tc) + ((4098 * E) / ((Tdc + 237.7) ^ 2) * Tdc)) / ((0.00066 * P) + (4098 * E) / ((Tdc + 237.7) ^ 2))