Temperature has an effect on brine density so it is very critical to compensate loss of density due to temperature. Higher wellbore temperature will reduce the brine density more. The calculation below demonstrates how to determine brine weight to mix on surface in order to get required brine density at a wellbore condition.
Brine weight with temperature correction equation is listed below;
Brine Density to Mix = Brine Density at Average Wellbore Temp + (Average Wellbore Temp – Surface Temp) x Weight Loss Factor
Where;
Brine Density to Mix = ppg
Brine Density at Average Wellbore Temp = ppg
Average Wellbore Temp = F
Surface Temp = F
Weight Loss Factor = ppg/F
Weight Loss Factor can be found in the table below;
Determine the weight of brine that you need to mix on surface based on the following information.
Surface temperature = 90 F
Wellbore temperature at TD = 300 F
Density of brine required for this well = 10.0 ppg
Solution
Average Wellbore Temp = (Surface Temperature + Wellbore Temperature) ÷ 2
Average Wellbore Temp = (90 + 300) ÷ 2= 195 F
According to the table, the weight loss factor for this case is 0.0025 ppg/F. This figure is selected because the desired weight is 10.0 ppg.
Brine Density to Mix = Brine Density at Average Wellbore Temp + (Average Wellbore Temp – Surface Temp) x Weight Loss Factor
Brine Density to Mix = 10 + (195 – 90) x 0.0025
Brine Density to Mix = 10.26 ppg
The brine density on surface must be 10.3 ppg (round up figure) to suit with this condition.
Reference books: 
Well Control Books