Forecasting fall foliage; what to expect this season
Fall officially arrived earlier this week with the autumnal equinox on Sep. 22, and mother nature is acting accordingly in terms of local temperatures. Like clock-work, consistently cooler weather has graced the Mid-Missouri River Valley this week, with highs running closer to 70 degrees, rather than 80 or 90 degrees. The average high in St. Joseph for mid to late September is between 75 and 78 degrees. By that standard, it’s even been a touch cooler than ‘normal’ in recent days.
It may be feeling like fall, but for most native hardwood trees across Northwest Missouri and Northeast Kansas, it doesn’t yet look like it. Colors of the season will inevitably start to emerge in area foliage over the next month or two. With that being said, any experienced 'leaf peeper' knows the quantity and quality of fall foliage can vary from year to year, largely depending on the weather.
The primary trigger of the annual color change in deciduous trees is not weather related. Instead, it’s based on changes in duration and intensity of sunlight. As the sun angle lowers going into the colder season, a net decrease in solar radiation makes deciduous leaves start to go dormant. In this process, cells from each leaf stem stop the regular flow of fluids. Sugars are then trapped within the leaf, causing a change in pigment before they fall to the ground.
Trends in temperature and precipitation through late summer and fall often impact the general health of most trees, thus influencing their ability to successfully change color for any appreciable length of time, or in some cases at all.
This year, heat waves and dry stretches lingered across the Central Plains and Midwest in late August and the first half of September. The harsh conditions placed some trees under stress, harming foliage and leading to premature leaf drops for certain species. Less established trees and those with pre-existing poor health also suffered most.
Luckily, a much wetter pattern developed locally in mid-September, dropping inches of needed rain over several days. The moisture may have arrived just in time to preserve the health of many native hardwoods despite the unforgiving heat in weeks prior. According to the Climate Prediction Center’s extended outlook, above average precipitation is likely to persist regionally over the next 6 to 14 days. That’s good news for this year’s colors.
Fall foliage is known to peak in this part of the country from late October to early November. Unseasonably warm conditions can sometimes mute the vibrancy of hues, or delay their arrival by days or weeks. Seasonably cool nights and mild sunny days are best for promoting the brightest and deepest hues of yellow, orange, and red.
Assuming precipitation will remain sufficient, October temperatures will likely play a key role in the timing and intensity of local fall hues this season.
