The Best Months for the Lowbands

I have been collecting QSO data on 80 and 160m bands over the past few years and here is what I arrived at.  These are mostly unique DXCC's captured over a period of 4 years and based on my operating habits.   138/150 QSO's are unique for the 80m QSOs. 97/112 of the 160m QSOs were unique DXCC.  The plots below show that 160m is open less months than 80m.   With daylight hours being longer, the area coverage of darkness is much shorter for 160m long range QSOs during the warmer months.  This is data collected from the southeast US and there are likely regional variations with the west coast seeing less DX in the warmer month.  January and February in both cases are the best months, being the coldest  months of the year in SC.  For whatever reason there had been downturns in December, and I don't know why.