。
The forecast said there would be even more snowfall.
Literal
Forecast [topic-は] further snowfall [subject-が] exist [quotative-と] convey-[past-progressive-ていた].
Reported speech using the quotative と: 「降雪がある」と伝えていた = 'was conveying that there would be snowfall.' The ~ていた past-progressive on 伝える here means the forecast was in the state of reporting this — a continuous background state, not a one-time utterance. さらに ('further, additionally') adds to an already-stated quantity, distinct from もっと which is more colloquial.