In describing the Alien threat that they (Ripley and the tactical team) are facing as the evening wears on, the young female protagonist, Newt,  states:

“They mostly come out at night. Mostly.”

When Ripley tries to assuage her by sharing that there are armed soldiers to protect her, Newt states:

“It won’t make any difference”

Newt and Ripley

Analysis: 

Let’s define this particular Risk Register item “Alien attack at night”

We have it from a first-hand observer of multiple instances of Alien attack, Newt, that they mostly come out at night. (Mostly).  If we’re using Low, Medium, & High to represent probabilities  0 < p < 33%, 33% < p < 67%, 67% < p < 100%, respectively, then I think we can safely convert these observations to High likelihood of Alien attack at night.

We have direct observations of destruction and further interviewing of a first hand observer who shares that having several well-armed soldiers in place “won’t make any difference”.  Given this information and defining Impact as Low = no fatalities/minor injuries, Medium = 1 to 3 fatalities (or capture with subsequent implantation & cocooning) & severe injuries , and High = greater than 3 fatalities (or capture w/subsequent implantation & cocooning) & very severe injuries (that includes Alien acid-blood burns), I believe that we can call this a High Impact.

If Hudson were keeping his Risk Register current, I think he could reasonably update with:

• Risk Description: Alien attack @ night
• Probability: High
• Impact: High

How would you assess this situation?