Why don't weather forecast models normally take solar eclipses into account? Since there is a total solar eclipse somewhere almost every year, I would have thought it would be included as a standard option in weather forecast models.  However, I've learned that is not really the case.  

The moon does not normally affect weather, but during a solar eclipse, there is reduced solar radiation reaching the surface of the Earth.  This causes cooler temperatures and changes in wind speed/direction than would not otherwise be predicted.   The NOAA ESRL HRRR took the solar eclipse of August 21, 2017 into account when doing the weather forecast and found cooling of up to 6 degrees Celsius in some places.  Do any other weather forecast models take solar eclipses into account?  Or, is this the first time?  Why don't weather forecast models normally take solar eclipses into account?
Total solar eclipses are rare.  Globally, they only happen every 18 months.  In any given spot, they are much, much rarer, with a recurrence period of many hundreds of years.

Solar eclipses are localised in time and space.  Although model resolution may be just about small enough (in time) to resolve the totality, it only has a limited impact.

One could implement solar eclipses in weather forecast models, but there's plenty of more important things to worry about improving.  Operational weather forecast models are complex beasts, so you really want to change things only if it may yield a significant improvement.  The potential improvement of implementing a consideration of solar eclipses is minimal, so it's simply not worth the effort or the risk.

Experimental models are a different category and as you have seen, eclipses have been implemented in those.  But the risks involved are much smaller; nobody really cares if experimental models go totally wrong, but you really don't want to be responsible for breaking the operational weather forecast model.



You might be interested in this article on The weather’s response 
to a solar eclipse that  my colleagues wrote.