How frost this weekend could kickstart the emergence of fall foliage

If you have been waiting for vibrant red and purple leaves to take over Mid-Missouri, this weekend is the ultimate make-or-break moment. We are officially entering our prime window for autumn color, but the drastic temperature plunge heading our way tonight will dictate exactly what kind of show we get.

Currently, we are seeing mostly patchy color across Central Missouri. Our local sugar maples are in their earliest stages, but the near-frost temperatures expected this weekend should force them to blossom in the coming week.

Historically, the color progression starts earliest in Northern Missouri and gradually moves southward. The Central and St. Louis regions typically peak in late October and into the first week of November. To hit that peak with brilliant colors, however, the trees need a very specific weather recipe.

Shorter daylight gets the color-changing process started by breaking down the green chlorophyll in the leaves. But producing those fiery reds and deep purples requires a delicate balance of temperature and sunlight.

Clear sky conditions and warm days allow the tree leaves to produce an abundance of excess sugar. As the sun sets and temperatures plunge into the 30s and 40s, the veins inside the leaves actually constrict. This physically traps all of that excess sugar inside the leaf. That trapped sugar triggers the production of anthocyanins, which are the exact chemical pigments responsible for our brightest red and purple colors.

Here is where the weekend's forecast becomes critical. A light chill in the mid-30s acts as a catalyst that kicks the anthocyanin process into high gear. If your neighborhood sees a light frost, it will actually accelerate the fall color.

However, if temperatures crash into a hard freeze, dropping below 28 degrees, it is game over for the leaves. The extreme cold causes the plant cells to rupture, which effectively kills the foliage. The leaves will turn brown and fall off the branches before they ever get the chance to peak.

The National Weather Service has already issued frost advisories for areas north of I-70 through 9 A.M. tomorrow, but this is just the first round of the chill.

By Sunday morning, another wave of cold, dense air is expected in Mid-Missouri. Because this cold air sinks, there could be noticeable differences in microclimates. The Columbia and Jefferson City areas are set to stay safely in the mid-30s, meaning urban areas will likely see a fantastic, accelerated burst of color next week. However, if you live in the lower river valleys or rural pockets away from the city heat, temperatures could near that hard freeze mark. For those low-lying spots, this weekend's frost and potential freeze could end the fall foliage season before it truly begins.