I don't have and don't know is there is meteorological evidence to back this up, but I would have to say March is the toughest month to forecast for the medium-to-long range (I suppose you can throw one of the fall months into this). But with March you are fighting the seasonal transition, probably starting to see wavelengths shorten, you're introducing the potential for a greater degree of convection, and obviously big changes are occurring within the higher latitudes relating to increased sunlight, jet stream winds, and changes to both the TPV and SPV.