You shouldn't be spamming howling blast for several reasons...
1. Howling blast should mainly be used when it procs for a free use off of obliterate
2. Obliterate generates more runic power per use than Howling blast, meaning you will have more frost strikes available, which is your main damage attack
3. Howling blast is mainly an aoe attack, as such its better used on multiple targets if you really want to spam it, for single target however it does less damage and generates less runic power than obliterate, so for aoe damage yes, single target no
So ideally you should keep dis