| Tf= | Temperature degrees Farenheit |
| RH= | Relative Humidity (I.E. 76...not 0.76 or 76%) |
| Tc= | Temperature degrees Celsius |
| WC= | Wind Chill |
| Tk= | Temperature degrees Kelvin |
| Es= | Saturation Vapor Pressure |
| UTf= | 850mb Temperature in degrees F |
| E= | Vapor Pressure |
| Tdc= | Temperature Dew Point Celsius |
| Mb= | Millibars |
| Tdf= | Temperature Dew Point Farenheit |
| Pa= | Pascals |
| Ms= | Saturation Mixing Ratio |
| M= | Mixing Ratio |
| SI= | Showalter Index |
| EI= | Engergy Index |
| LI= | Lifted Index |
| KI= | K Index |
| TT= | Total Totals Index |
| THE= | Theata-E Index (50 mile radius Max minus Min) |
| DPR= | 50 mile radius Max minus Min Dewpoint (Tf) |
| WS= | Wind Speed (MPH) |
| LL= | 850Mb wind angle to surface wind plus surface WS |
| UL= | 250Mb wind angle to surface wind plus surface WS |
| JS= | 250Mb jet stream winds distance away in miles (Traditional Jet stream) |
| MLJS= | 850Mb jet stream winds distance away in miles (mid-level winds) |
| ABS= | Absolute Value (I.E. -1 = 1) all numbers are positive |
| SQRT= | Square Root |
| IN= | Inches of Mercury |
| Tp= | Temp Celsius of an air parcel |
| Temp(F)= | Tf= (1.8*Tc)+32 |
| Temp(C)= | Tc= (Tf-32)/1.8 |
| Kelvin(Tk)= | Tk= 273+Tc |
| Knots= | Knots= Wind Speed MPH/1.15 |
| MPH= | MPH= Knots*1.15 |
| Pascals(Pa)= | Pa= (Mb*100) |
| Millibars(Mb)= | Mb= (In*33.86388158) |
| Inches of Mercury(In)= | In= (Mb/33.86388158) |
| Meters= | M= Feet*0.3048 |
| Feet= | Ft= Meters*3.2808 |
| Dew Point(F) Knowing Tc= | X= 1-(0.01*RH) K= Tc-(14.55+0.114*Tc)*X-((2.5+0.007*Tc)*X)^3- (15.9+0.117*Tc)*X^14 Tdf= (K*1.8)+32 |
| Dew Point(F) Knowing Tf= | Tdf= ((((Tf-32)/1.8)-(14.55+0.114*((Tf-32)/1.8))* (1-(0.01*RH))-((2.5+0.007*((Tf-32)/1.8))*(1-(0.01*RH))) ^3-(15.9+0.117*((Tf-32)/1.8))*(1-(0.01*RH))^14)*1.8)+32 |
| Wind Chill(F)= | Wc= 0.0817*(3.71*SQRT(WIND SPEED MPH)+ 5.81-0.25*WIND SPEED MPH)*(Tf-91.4)+91.4 |
| Heat Index(HI)= | HI= -42.379 + 2.04901523(Tf) + 10.14333127 (RH) - 0.22475541(Tf)(RH) - 6.83783x10^(-3)*(Tf^(2)) - 5.481717x10**(-2)*(RH^(2)) + 1.22874x10^(-3)* (Tf^(2))*(RH) + 8.5282x10^(-4)*(Tf)*(RH^(2)) - 1.99x10^(-6)*(Tf^(2))*(RH^(2)) |
| Summer Simmer Index(SSI)= | SSI= 1.98(Tf - (0.55 - 0.0055(RH))(Tf-58)) - 56.83
|
| Saturation Vapor Pressure(Mb)= | Es= (6.11*10^(7.5*Tc/(237.7+Tc))
|
| Vapor Pressure(Mb)= | E= (6.11*10^(7.5*Tdc/(237.7+Tdc))
|
| Specific Humidity(g/kg)= | SH= (0.622*E)/(Mb-(0.378*E))
|
| Relative Humidity(%)= | RH= (E/Es)*100
|
| Relative Humidity(%) Knowing Tdf and Tf= | RH = (((6.11*10^(7.5*((Tdf-32)/1.8)/(237.7+((Tdf-32)/1.8))))/((6.11*10^(7.5*((Tf-32)/1.8)/ (237.7+((Tf-32)/1.8)))))*100)) |
| Height of Cumulus Clouds(FT)= | H= 222(Tf-Tdf)
|
| Rankine Temperature(R)= | R= Tf+460
|
| Saturation Mixing Ratio(g/kg)= | Ms= 3.884266*10^[(7.5*Tc)/(237.7+Tc)]
|
| Mixing Ratio(g/kg)= | M= RH*Ms/100 & M= ((0.622*E)/(Mb-E))*1000 |
| Virtual Temperature(C)= | Tv= [(1+1.609*M)/(1+M)]*Tc
|
| Lifted Index= | LI= Tc(500mb) - Tp(500mb)
|
| Showalter Index= | SI= 1) From the 850mb temp, raise a parcel dry
adiabatically to the mixing ratio line
that passes through the Tdc(850mb) 2) From that point, raise the parcel moist adiabatically to 500mb. 3) SI= Tc(500mb) - Tp(500mb) |
| Total Totals= | TT= Tc(850mb) + Tdc(850mb) - 2*Tc(500mb)
|
| K Index= | KI= Tc(850mb) - Tc(500mb) + Tdc(850mb) - 2* Tdc(750mb) - Tc(750mb) |
SWEAT Index= This one has its own set of rules.... its a bit strange. Keep the
following in mind when calculating SWEAT:
D= Tdc(850mb), if this term is negative, set it to zero.
TT= Total Totals Index
F8= Wind speed in Knots at 850mb
F5= Wind speed in Knots at 500mb
Z= Veering number. Figured in the following way:
Find veering direction, (difference between the 850mb and
500mb wind directions in degrees) Then Z is found from
the following table:
Veering # Z
0 0
10 .05
20 .10
30 .25
40 .45
50 .70
60 .95
70 1.00
80 .95
90 .70
100 .55
110 .45
130 .40
150 .35
170 .30
Set the Z term to Zero under the following conditions:
1) 850mb wind is not from between 130 and 250 degrees
2) 500mb wind is not from between 210 and 310 degrees
3) (500mb wind dir) - (850mb wind dir) = negative #
4) if 850mb and 500mb winds are both UNDER 15 knots.
SWEAT= 12D+20(TT-49)+2(F8)+F5+125(Z)
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
Input Variables
T Temperature (�C)
Hr Relative Humidity (use numbers between 0 [for 0%] and 1 [for 100%])
P Barometric Pressure (millibars)
Temporary Variables (those generated during the procedure)
Es Saturation vapor pressure (millibars)
E Actual vapor pressure (millibars)
Tdp Dewpoint temperature (�C)
gamma something to help calculate Twb
delta something to help calculate Twb
Output Variable
Twb Wet-bulb temperature (�C)
Procedure
1. Calculate Saturation Vapor Pressure
Es = 6.112 * 10 ^ ((7.5 * T) / (237.7 + T))
2. Calculate Actual Vapor Pressure
E = Hr * Es
3. Calculate Dewpoint Temperature
Tdp = (237.7 * log10 (E / 6.112)) / (7.5 � log10 (E / 6.112))
4. Calculate these equations to help figure Twb
gamma = 6.6e�4 * P
delta = (4098 * E) / ((Tdp + 237.7) ^ 2) * Note: 6.6e�4 = 6.6 � 10�4 = 0.00066
5. Calculate Wet-Bulb Temperature
Twb = ((gamma * T) + (delta * Tdp)) / (gamma + delta)
* Note that log10 (x) is in base 10, not base e.
If you have the dewpoint, you may start at step 4.
For questions or comments about these formulas, or if you would like a formula that you
don't see listed here, email us: Convective Development