rainfall data entry for hourly observations

[scottylad501]

As discussed in our last meeting (Aug 29,2024), the data key entered for Synop purpose has a section for rainfall since last observation. Typically with a synop message this was set to 6 hours, i.e. rainfall over the last 6 hours because we send rainfall data every 6 hours. However with the recommended move to sending hourly observations we need to make provision for instances when no rainfall is read for 1 or 2 hours(or whatever period) when the rainfall is read next there is a check done to record how many hours have past.