Autumn Foliage Forecast

Pius Lee

Autumn is pleasant. It has many public holidays for the most populous countries in the northern hemisphere. In the U.S. we have Labor Day, Columbus Day and the Veterans Day. In China there are Mid-Autumn Festival and Double-Yang Festival. Likewise, just to name a few, there is Oktoberfest in Germany, Diwali Festival in India, Chuseok in Korea, and Dia De Los Muertos in Mexico. In short, autumn is the time to relax and play.

The weather in the northern hemisphere is usually cooperating. In autumn, large scale pressure systems are associated with subsidence flows. Subsidence flows result with cloudless skies and a lot of sunshine. However, one should not rule out hurricanes. Whenever the sea surface temperature of the oceans surpasses the hurricane genesis threshold of 26-degree centigrade, the oceans are capable of brewing hurricanes. As a matter of fact, the entire fall season lies within the official hurricane season of the U.S. from June 1 to November 30. Therefore despite the more than frequent gorgeous crispy days in the fall, do not romanticize autumn to the degree of letting down guards against inclement and destructive weather.

Time to Play and Hike

The playful mood of autumn is veritably earned by its pleasant temperatures, the air’s low humidity and plenty of sunshine. The Chinese saying of “秋高氣爽 (qiu gao qi shuang)” meaning “autumn high air crisp” speaks volumes about the breeze of freshness and freedom in the air. Due to the subsiding air flow that dominates the autumn weather, clear sky also dominates. With no clouds and a lot of sunshine, visibility is the farthest compared to other seasons. No wonder autumn is the prime season for sightseeing and hiking excursions.

Autumn is an ideal season for hiking and traveling for many who take advantage of the gorgeous sunshines and waning heat of the summer. The naked eye feasts on the beautiful autumn foliage and mountains for hundreds of miles on a clear autumn day. Indeed the autumn season has the highest likelihood the human eye can achieve its within-atmosphere visibility limit of 275 miles in the northern hemisphere. As a meteorologist, I have to chime in with a little disappointment for those tourists who start hiking early in the morning in the low lying areas with lakes or large water bodies in their proximity. Radiative fog is a common phenomenon in the dawn hours in those landscapes. Moistened air experiences rapid cooling there. Without clouds and with low air humidity, air cools quickly after sunset due to emission of long wave radiation from the earth. Fogs will form and linger in those low lying areas until daybreak when the short wave radiation from the sun reheats the land/water surfaces and consequently dissipates the fog.

People enjoy Recreation

          As a young man I studied environmental meteorology in Japan. I was rather serious and a lopsided extremist to “clean the world for our offsprings and children and grandchildren”. I knew the Japanese people worked long hours and with few holidays. Nonetheless, I was so eager to learn how the Japanese achieved so much in cleaning up their Minamata disease (新潟水俣病) and Yokkaichi Asthma (四日市哮喘). I decided to stay in Japan to work after a long five years of postgraduate studies. The former environmental crisis referred to years of negligent and unconscientious discharge of mercury waste to waterways and streams by factories in the 1960’s. The latter referred to huge air pollution problems in the Osaka areas due to clustering of oil refineries and chemical plants in the 1970’s. The country did a fabulous job to tackle both at a lightning speed relative to the ecological timescales. Japan reclaimed much of the damaged environmental sustainability and biodiversity. I worked in a non-profit governmental liaison meteorological research institution called “The Japanese Meteorological Association”. To my amazement, the company had not just long hours and few holidays, but was actually very fun to work in. It forecasted the laundry index for house-makers and keepers. It also forecasted autumn foliage for sightseers. In Japanese, autumn foliage “紅葉” written in Chinese characters have two ways of japanese-native pronunciations, called 訓讀み: (1) “koyo” meaning autumn foliage, and (2) “momiji” meaning the Crimson Red Japanese Maple Tree (椛). I was thrilled to see and share the playful sides of the Japanese people when our team analyzed the autumn foliage forecasts. How wholesome is the leadership of the government institutions to promote recreation, vacation, sightseeing and outdoor enjoyment for a nation whose people are usually overwork and overstrained. I was thrilled the same way as I saw Americans doing similar forecasts 20 years later.

Risky but Ludicrous Business

          Recreation is a great industry. Tourism is a ludicrous money-maker. Therefore, the autumn season is an exciting time for tourist hot spots and travel points-of-interest. However, as a forensic detective says it well: “Follow the money”. Indeed, money drives. With a lot of tourism money in stake, autumn foliage forecast must be applicable: “temporally and spatially”. It also should have enough lead time so the excursion packages can promote their attractions.

Autumn foliage forecast is a complex and multi-disciplinary science. The leading disciplines that govern the colors of the foliage in their descending orders are: plant phenology, meteorology, hydrology, lithology, alkalinity of the soil, and geological topology and formations. If you are an arboriculturalist, you can experiment with these factors in your bonsai pots in your front yard, or in a climate-controlled garage. The type of the trees and their characteristics are obviously the most decisive factor, then followed by water, sunshine, and temperature.

With satellite-observation-aided initialization to assist forecast models, short term forecasts in terms of foliage front advances in several days are rather accurate. This is often not acceptable for planners. One cannot give a probabilistic forecast either, as tourists cannot be half-committing. Only a few tourists have plan B and indulge himself/herself with refund insurance. I am glad that I do not have plan B when I embark on an excursion I always bring a hat and a wind-breaker to minimize unpleasant surprises. As a tourist, he/she should be a lenient shopper that takes things easily and not penny-pinching to get every buck returned. Had the advertised red hue faded a little or had the projected leave-density lessened, there should be no grumble or lament. With this tourist’s latitude of forgiveness there is no need for plan B. In essence, the coloring of the leaves are the waning dominance of green in the chlorophyll and the annexation of it by two other classes of pigments: yellowish-brownish-orangish and reddish. Their dominance depends on the array of factors I mentioned above.

The Natural Tapestry

The excitement of seeing the mountain-ridges upon mountain-ridges of autumn foliage is of course not the variety in a tree or in a wood, but forests upon forests of mixes and matches. The interlace of maples, oaks, tulip poplars — the deciduous species; and the pines, spruces, hemlocks and junipers — the conifers. The entire visible spectrum seems in full display on the natural tapestry of infernos within oases of endless ridge lines.

          A tourist heart is often captivated and rhymed with the autumn foliage across the palette colors of yellow, brown and red. From the Appalachian mountains to the Rockies, from the Alps to the rugged terrains of the Norwegian fjords, from Hokkaido plains to Kagoshima (鹿児島), my eyes marveled at the creativity of our intelligent, playful and limitless imaginative Creator. “Let the heavens rejoice, let the earth be glad; let the sea resound, and all that is in it. Let the fields be jubilant, and everything in them; let all the trees of the forest sing for joy” (Psalm 96:11-12).

Author: Pastor Dr. Pius Lee is the Director of the Development Division of NYSTM. Pastor Lee previously worked in the National Oceanic and Atmospheric Administration. (NOAA) where he was selected the winner of the Administrator’s Award for NOAA’s Air Pollution Forecasting Group in 2020.

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