Gusty westerly winds will continue to usher in a seasonably cool air m

The clause "I'm not sure" appears in the line just before your question!

Dealing with the discomfort of uncertainty is part of the game when it comes to SC. Rather than attempting to understand any confusing aspect of a sentence with 100% certainty, you want to ask yourself if there's a reasonable interpretation available. If there is, don't treat whatever you're evaluating as a definitive error. Take another example:

Tim's map of America, which is dotted with frowny faces and tiny sketches of crying children, depresses him.

If you wanted to evaluate "which" here, the first thing you'd ask yourself is whether there's a noun or noun phrase it could be logically describing. Does it make sense to say that America is dotted with frowny faces and sketches of crying children? Probably not. Seems far more logical to say that it's the map that's covered in the aforementioned doodles. (And the question of whether "which" is describing the "map" or the "map of America" is an irrelevant one. "Of America" is simply describing the map in question, so the two interpretations are identical.)

Do I know that for sure that my interpretation is right? Nope. I suppose America could be covered in sad faces. But my understanding seems reasonable, so if I saw this is as an option on the test, I'm not getting rid of it on this basis.

In this case, if you read (E) and thought it might make sense for the "pressure" to bring the fair and dry weather, rather than the "broad area of pressure" you'd still hold on to the answer choice and search for other, more concrete errors.

The takeaway: you don't have to have certainty to get to the right answer! The point of the post is that if you're unsure about an issue, you'd prefer not to use it as a decision point! So don't agonize over the uncertainty. Rely on the issues you know are wrong first; revisit the confusing element only if you have to.

I hope that helps!