Yes there is. You add all units in that area to a unit group and instead use damage target with a condition.
Trigger:
blizzard
Events
Unit - A unit Starts the effect of an ability
Conditions
(Ability being cast) Equal to Blizzard
Actions
Set temp_point = (Target point of ability being cast) Set temp_group = (units within 200.00 of temp_point)
Unit Group - Pick every unit in (temp_group) matching (((Matching unit) belongs to an enemy of (Owner of (Triggering unit)) Equal to True)) and do (Actions)
Loop - Actions
Unit - Cause (Triggering unit) to damage (Picked unit), dealing 500.00 damage of attack type Spells and damage type Normal