Year,Jan.,Feb.,Mar.,Apr.,May.,Jun.,Jul.,Aug.,Sep.,Oct.,Nov.,Dec.,24-Hour Annual Avg., 1998,15643,17603,19535,20959,20492,20146,20483,,20470,21102,19658,18052,, 1999,17069,18208,21223,21794,22465,23854,25000,25380,25100,22537,22009,18777,21951, 2000,16752,20065,,21715,22556,,,21279,19360,,,16612,, 2001,16615,,,,,,,,,,,,, 2002,,,,,,,,,,,,,, 2003,,20461,22993,22246,25123,26485,23800,27335,26754,,,,, 2004,,,,25083,24303,27252,26754,26201,25809,25134,21646,20316,, 2005,,,,,,,,,,,,,, 2006,,,,,,,,,,,,,, 2007,,,,,,,,,,,,,, 2008,,,,,,,,,,,,,, 2009,,,,,,,,,,,,,, 2010,,,,,,,,,,,,,, 2011,15617,16417,18456,,,,,,,,,16587,, 2012,15422,,,,,,,,,,,,, 2013,14541,16239,18118,,,,,,,,18381,16829,, 2014,15731,15769,19188,,20313,,,21926,20936,20426,18007,17508,, 2015,17247,18992,21105,21718, , , , , , , , , , 2016, , , , , , , , , , , , , , 2017,17415, ,22644, , , , , , , , , , , 2018, , , , , , , , , , , , , , 2019,17635,17113,22160,23549,24563,26391,26222,26267,24573,22981,20566,16912,22445, 2020, , , , , , , , , , , , , , 2021, , , , , , , , , , , , , , 2022, , , , , , , , , , , , , , 2023, , , , , , , , , , , , , , 2024, , , , , , , , , , , , , ,