Hold on a sec.
What is "-4 at altitude" (I'm spanish)
That means it was -4ºC at 13.000 ft?
Last saturday, in Huesca (Spain) we jumped at -25ºC (13.000ft).
That was too hard. First jump, when we landed, my fingers were freeze and I had to shake them before picking parachute up.
The video cam guy couldn't take her helmet off for continuing recording the tandem.
We jumped three times. :-)
Regards
Mariano. www.velocidadvertical.com