How The National Weather Service Forecasts Weather

 There are several different methods used in determining a forecast.  These
 methods change from one area to another, and sometimes a forecast is a
 combination of methods.

 The 'Statistical' method uses mathematical formulas based on the past
 occurrences in the vicinity.  EXAMPLE : The temperature a year ago was 74,
 the average over the last 15 years on this day is 70, yesterday's temperature
 was 66, so the temperature today will be 70.

 There is the 'Numeric' method, complete with all its variations.  Basically,
 it uses the Earth's physical laws in relation to how the atmosphere reacts
 with fluid dynamics.  This idea considers bodies of water, land surfaces,
 moisture bearing land surfaces, and laws of heat and moisture transfer to
 create a forecast.  The immediate problem with this method is that scientists
 lack basic natural laws, and long term experience.  Both those are necessary
 for this method to work.  With the assistance of today's computers, this
 may become more and more popular.

 Possibly the most widely used method is termed 'Syntopic'.  It uses a synopsis
 (summary) of the entire weather picture to obtain its forecast.  The movement
 of large weather systems are shown on series of maps, these maps are called
 syntopic charts.  Observations from thousands of worldwide weather stations,
 taking samples several times daily, formulate the forecast.  This is
 currently considered the most accurate, overall.

 As I stated earlier, some independent meteorologists choose to combine these
 methods.  Why would they do this?  Possibly because of specialized local
 conditions such as a mountainous area.  Remember, the temperature drops as
 the elevation rises.  Another reason could be an agricultural area full of
 quick growing, green alfalfa.  A large area of green plants 'breath' and they
 evaporate quite a bit of moisture which creates humidity.  Being that humidity
 slows temperature change, this is a real concern.  Is there a lake nearby?
 There are many localized conditions which cause meteorologists to custom
 make a forecast for a certain area.  Some professional computer programs
 consider these items into a forecast, but many times it is the individual
 meteorologist's choice as to which conditions are to be used.