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The fall foliage may be sooner this year

by RANDY MANN
| September 18, 2023 1:05 AM

We’re into the early stages of the fall season and the beauty of the Inland Northwest is being enhanced by the annual “fall foliage.” Some of the best displays of color should be from now through the middle of October.

During this time of year, a mixture of reds, purples, oranges and especially yellows will dot the landscape. Some of the trees that are common in the Pacific Northwest include the vine maples, which provide hues of yellow, orange and red and are often found along many of the hiking trails. The larch and aspen trees will provide yellow and gold colors, which also helps to make for spectacular displays.

Here in North Idaho, peak color this year is expected in late September and early October. This is a bit earlier than usual due to summer drought, as the trees will likely lose their leaves sooner than average.

In southern Idaho, the peak season is expected around early to mid-October. Boise is often referred to as “The City of Trees,” and will often showcase very colorful displays, especially at the Idaho Botanical Garden.

There is a website, www.smokymountains.com, that has a good fall foliage map for the entire country. At this time of year, it’s continuously updated to provide the best times to view the fall foliage. If you’re looking to see the fall colors near their current peak, some recommend the Idaho Section of the International Selkirk Loop, which goes through Priest River, Sandpoint and Bonners Ferry. The Pend Oreille National Scenic Byway is another good place to see fall colors.

In spring and summer months, green leaves serve as food factories for trees' growth. This food-making process takes place in the leaf, which contains a chemical called chlorophyll. This amazing chemical absorbs energy from sunlight that is used to transform carbon dioxide and water into carbohydrates, like sugars and starch. Chlorophyll also gives the leaf its green color.

As we move through the early fall season, changes in daylight hours and cooler temperatures result in the leaves stopping their food-making process. The chlorophyll breaks down and the leaf’s green color disappears. The other colors of red, orange and yellow pigments in the leaf now become visible making for spectacular displays before the leaves eventually fall off the trees. Sugar maples and birch trees often show the most array of colors at this time of year.

For the best fall foliage, the trees usually need moisture during the summer season. Extended periods of abnormal dryness, such as the recent summer, will often lead to leaves prematurely falling off trees and changing colors sooner than normal, which is expected this year. The foliage is the most spectacular when there are also sunny days and cool nights in the late summer and early fall. The best colors are from trees that are less stressed. The lack of water in the summer will often lead to more stress for trees, so the fall colors may not be quite as brilliant.

As I mentioned last week, sea-surface temperatures across much of the Earth are warmer than normal. Despite a moderate El Niño event, the number of named tropical storms in the Atlantic and Caribbean waters is now above normal. We currently have 15 named storms, compared to the normal of 14. Six of those storms were hurricanes with three of them listed in the “major” Category 3 or higher. The latest one, Hurricane Lee, did hit the northeastern coastline and southeastern Canada as a strong tropical storm resulting in widespread flooding along the coast of Maine and Nova Scotia.

In terms of our local weather, the first half of September has been very dry across the Inland Northwest. Only 0.15 inches of rain has fallen at Cliff’s station this month. At the Spokane International Airport, a puny 0.03 inches has fallen since the beginning of the month. However, the second half of the month does look wetter across the Inland Northwest. There is the possibility of some shower activity later this week, but the best chance for rain is expected around the end of the month. The long-range forecast models are showing this change around the full moon cycle that begins Sept. 29. This is also another supermoon, which will often increase the chances of moisture in our part of the country.

Temperatures this week are going to be much cooler. On Saturday, many locations flirted with the 90-degree mark. In Coeur d’Alene, the high temperature topped out at 88 degrees, with 88 degrees also reported in Spokane. Some outlying locations, such as Post Falls and Rathdrum, did hit the 90-degree mark.

According to Cliff’s records, the hottest day in mid- to late September was 98 degrees Sept. 19, 1938. The latest 90-degree day happened during the torrid summer of 1963, when a high of 90 degrees landed Sept. 26.

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Contact Randy Mann at randy@longrangeweather.com.