下文中的should be doing明显是现在时,但竟然可以用来描写过去式?

题目

下文中的should be doing明显是现在时,但竟然可以用来描写过去式?
I looked at the map and then at the milometer.I had come ten miles since leaving the town,and at this point ,according to my father,i should be looking at farms and cottages in a valley...
should be doing明显是现在时,而这里上下文是过去式,不合逻辑.难道should be doing可以用在过去式?
在牛津字典上有相似的句子,和我想的一样是用现在时：It should be snowing now,according to the weather forecast.

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