This is the 5713th most frequent Japanese word.
だとすれば
"If that's the case" or "If we assume so."
The phrase 'だとすれば' in this sentence is used to introduce a logical condition or assumption, conveying 'if it is the case that'.
もし彼が病気だとすれば、病院へ行くべきです。
If he is sick, he should go to the hospital.
Here, 'だとすれば' introduces a hypothesis based on a rumor or report, considering its truth for the explanation.
その噂が本当だとすれば、彼はとても秘密主義ですね。
If that rumor is true, he is very secretive, isn't he?
In this case, 'だとすれば' connects the assumption about the weather forecast's accuracy to a prediction about today's weather.