It can help control traffic when there's a storm warning (4)
I believe the answer is:
cone
'it can help control traffic when' is the definition.
The definition suggests a singular noun which matches the answer.
'a storm warning' is the wordplay.
I cannot really understand how this works, but
'a' could be 'one' and 'one' is located in the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'there's' is the link.
Can you help me to learn more?
(Other definitions for cone that I've seen before include "Volcano peak" , "Figure (for traffic control?)" , "may obstruct lane" , "Tapered object" , "Edible ice cream container" .)