SPRINGFIELD, Mass (WWLP) – It wouldn’t be autumn in the Pioneer Valley without the bright reds, oranges and yellows of the fall foliage.

Western Massachusetts still has a long way to go, with most of the area only seeing some changing colors. Hampshire County is a little behind Berkshire, Franklin and Hampden counties.

The first trees to change are the maples and sugar maples, which give us the oranges and yellows. Red maples are changing too. Later in the season, we’ll have to wait for the oaks and hickories.

But why do we see the change?

“Whenever the days start to get shorter, the organelles in the plant start to shut down, and we’re most familiar with chloroplast, chloroplast manufactures the green pigment chlorophyll, and they start to shut down around this time of year,” Rick Harper, an extension associate professor of urban forestry at UMass, told 22News.

The shutdown of chlorophyll leads to the green color dissipating, revealing the light orange and yellow colors that are hidden beneath the green year-round. The bright red and purple colors are instead manufactured by the leaves in the autumn.

The shorter daylight hours are the primary driver behind the changing colors, but the weather plays a part as well.

The ample rain western Massachusetts saw in the spring will help with the vibrancy of colors. But during autumn, the best conditions for vibrant colors are lots of sunshine, limited amounts of rain and cool overnight temperatures — just not too cold; an early frost could result in dull colors.

The peak this year in Springfield will happen around October 12-16.