JF Enhancement

The JF curve is a hybrid enhancement scheme used to highlight both sea surface temperatures,
and cold cloud tops associated with thunderstorms and other weather systems.  It is somewhat
simpler to interpret than the later JJ curve.  The coldest portion of the curve (less than -33C) is
nearly identical to the general-use MB curve.  Maximum enhancement is provided at the warm
end (25 to 10C) to depict sea surface temperatures and warm low clouds in tropical and sub-tropical areas.