Precipitable Water

[Michael Riedl]

Can you use forecasted precipitable water amounts to forecast what mode (HP, LP, or Classic) of supercell a storm will be? I know that the lower precipitable water amount there is, the less water loading there will be on a hail stone as it falls therefore the hailstone will be bigger. Obviously there are more variables in forecasting hail size then just PW. I would assume that the higher the PW the better chance a supercell will have of being HP and vice versa with lower PW. Please correct me if I am wrong.

Basically what I am asking is, how useful is PW in forecasting convection?

 

[Wes Carter]

I'm going to attempt to throw an answer at this that might need some tweaking or correction.

PW can be used as an indication of the type of supercell that is most likely. The more water that is contained in the troposphere the more is available for convection. PW values of 2 inches or more can be a good indicator of HP storms while values less than 1 inch tend to favor LP supercells while classic mode falls somewhere between the two.

Another place to look is at the 9-11 km storm relative winds. Classic supercells tend to favor 9-11km winds of 40-60 knots. Below 40 knots HP supercells are more likely. Above 60 knots LP supercells become more likely.

I've been trying to learn this myself recently so take this not as a definitive answer from an experienced chaser but as a newb who just happened to recently had the same question.