I don't understand how the temperature with the humidity is predicted for later days in the week..?

Question

Like how can you predict humidity?

some care to explain..

Answer 1

Humidity travels with air masses (those are seperated with fronts. Cold fronts = cool, dry air moving in. Warm fronts = warm, moist air.) So the humidity hovers around the same area unless a different air mass moves in.

Also, cool air can't hold as much moisture as warm air, so that's how you decide the cool, dry and warm, moist thing.

Answer 2

Forecasting today relies on very large computer programs called numerical weather prediction models.  They can be global, covering the entire world or mesoscale, just covering a local region.  Various things come out of these programs, but temperature, humidity, and pressure are probably the most important.  These forecast on a horizontal scale ranging from one mile to tens of miles and also at various levels vertically.  The forecasts are typically for every three or six hours for as long as the forecast is run (up to two weeks).

Those "gridpoint" values for temperature, humidity, etc. are then combined with local knowledge for a particular area to come up with those forecasts you're asking about.  They're usually reasonably accurate for a few days, but they get pretty shaky when you're looking out a week or more.