How to interpret the weather forecast??

Question

If it says the weather in SF will be high 70, low 56.. does that mean that it WILL 100% reach 70 at some point? Or does it mean it can go as high as 70 and as low as 56. Or does the 56 mean only at night?

Answer 1

They predict a high daytime temp of 70 and a low night time temp of 56. Of course they may not necessarily be correct.

Answer 2

The forcast is saying that the highest temperature of the day will be 70 and the lowest temerature will be 56.  The 56 may occurr just after midnight on the morning of the day in question.  The 70 may not be reached until late in the day or if there is a cold front passage due, the high may occur early in the day and the low temperature may occur later in the day.  

It is simply the highest and lowest temperatures expected to occur on a particular day.  You need more detail to determine what part of the day will see which temperature.  A day is normally a 24 hour period, 12 midnight to 12 midnight.  Many forcasts specify a day and evening temperatue.  

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Answer 3

If these forecast temperatures are associated with a city, town, or some other point location, then the high usually represents the warmest daytime temperature at that point.

For example, using the forecast high and low given on your question, for the city of San Francisco, the highest daytime temperature will be 70 degrees.  It may be lower, but is not forecast to be higher during the day period.  

However, if the high and low represents an area, then the temperature forecast high represents the average highs of the forecast area.  

For example, if it says the for the San Francisco Bay Area will be 70 degrees.  Then the 70 degrees in the average high for the area.  So that area, I would expect the highs to range from about 68 to about 72 degrees in the daytime.

The same idea for the forecast overnight low temperature.