Additional modifiers for extreme cold?

[Bathawk]

Was adapting a unique character concept for Gurps

In a WWII campaign a Superhuman German Soldier....in gurps terms...has the ability to create, say, 2000 gallons of water at a range of 500 yards (40 levels of create with ranged and increased range
Instead of deploying him, say, in the desert. They put him in the mountains. The idea being he can drench allies soldiers soaking wet to increase the chances of hypothermia
Now according to the rules, barring any mitigators like temperature tolerance, someone in below 35 degree weather has to make a HT roll once every 30 minutes, 15 minutes in light wind, with a -5 for wet clothes
But there is no modifier for extreme temperatures. 30 degrees is no more or less an issue than -30 degrees unless I’m looking at the wrong page

Plus would being drenched by a few hundred gallons of water count as “sudden shock”? In say 20 degree weather? I can’t imagine allied soldiers being able to fight normally for another 15 minutes before having to make a single HT roll