Even with the weather today a bit chillier than it has been of late, the days are still getting longer, and by larger increments. Today is 10 hours, 54 minutes and 36 seconds long, which is three minutes and 17 seconds longer than yesterday. By the time of the equinox on March 19, the daily increase grows to three minutes and 22 seconds.
If you do the math, that adds up to around 23 minutes of additional daylight added each week; a noticeable difference. The longer day length, combined with the higher position of the sun in the sky during the day, all lead to a daily increase of solar radiation.
This, in a nutshell, is why spring happens. Weather, of course, with its random fronts and wind changes, tries its best to conceal the inevitable. Late-season snows and cold snaps are certainly going to happen. But the increasing light and heat from the sun will not be persuaded. Spring will come relatively soon.