The NOAA Magnetic Field Calculator

July 1, 2015 | Amateur Science | By: Mark VandeWettering

Just bookmarking this for now:

The NOAA Magnetic Field Calculator

This website can accept a latitude longitude (or, conveniently, a Zip code) and will give the you predictions of what the inclination and declination of the magnetic field is. John used this apparently to make predictions about the field near my location.