The transition from summer to fall is arguably the most beautiful time of the year in the high country. The high peaks receive their first dusting of snow and the trees glow with gold, scarlet, and orange leaves. 

The timing of peak color varies by location and elevation across the U.S. Generally speaking, leaves turn earlier across higher elevation areas and more northerly locations, and later across lower elevation areas and more southerly locations.

Climatological Peak Color by Region:

Rockies:

Mid-September to Early October, depending on elevation and latitude with higher elevations in Northern/Central Colorado usually turning earliest.

California:

Late September to Early October in the Sierra, and Mid to Late October in the foothills and lower elevations.

Southwest:

Mid-October to Early November, depending on elevation.

Pacific Northwest:

Mid to late October.

Great Lakes:

Mid-September to Mid-October

New England:

Late September to Mid-October

Mid-Atlantic and Southern Appalachians:

Early October to Early November depending on elevation.

Weather Factors that Influence the Timing and Intensity of Peak Color

The effects of weather and soil conditions on fall colors can be tricky to nail down and there are always uncertainties with regard to timing and vibrancy, but there are at least a few factors we can look at.

The following conditions typically result in the most vibrant fall colors:

• Wet (or non-drought) conditions during the spring.
  
  
• Near-normal mid to late summer rainfall.
  
  
• Warm, sunny days and cool nights during the fall.
  
  
• A lack of "extreme" weather events in the fall (such as heat waves, cold snaps, or heavy precipitation and wind events).

Temperatures and Fall Colors

Temperatures relative to normal during September and October can influence the progression of fall foliage. Late-season heat waves or extended (multi-week) stretches of well-above-normal temperatures can result in peak color occurring later than normal.

On the other hand, significant early-season cold snaps (well below normal temperatures) that involve hard freezes can have a negative impact on fall colors, causing leaves to quickly reach "past peak" status and fall off the trees sooner.

Let's take a look at the temperature forecast...

Over the next week, above-average temperatures are expected across the West and below average temperatures are expected across the East.

During the week of September 10th-17th, above-average warmth spreads into the Eastern Rockies and Central U.S. with cooling near the West Coast. The East will also see a warming trend to more seasonal levels for mid-September. 

Confidence in the temperature outlook is inherently lower as we get further out in time, but we can still take a look at long-range models to see if they offer any clues.

During the month of October, the European Model's monthly outlook has a return to above-average warmth across the Western U.S. and near-average temperatures across the East, the latter of which highlights the potential for periodic cool snaps. 

Moisture and Fall Colors

Wet spring and early summer conditions (from rainfall and snowmelt) are favorable for fall foliage, whereas drought conditions that persist through the summer months can result in peak color happening earlier than usual depending on early fall temperatures.

On the other hand, if rainfall is heavier and more consistent than normal late in the summer and early in the fall, this can result in a delay in peak color – though often the fall color display is outstanding once the leaves do turn.

Looking back, soil moisture was close to average across most of the West heading into early summer, except for Northern Idaho and Montana where it was below average. Soil moisture was well above average across the Upper Midwest and near average for most of the East.

During mid to late summer, rainfall was variable across the Western U.S. with above-average rainfall for portions of Utah and Colorado, and below-average rainfall for parts of the Southwest and Interior Northwest.

In the East, rainfall was well below average in West Virginia and to a lesser extent the Southern Appalachians, but well above average across New England and the Northern Mid-Atlantic. 

Drought conditions are currently present over the Interior Northwest and Northern Rockies, as well as portions of the Mid-Atlantic (most notably West Virginia).

Bottom line, barring any weather extremes during September and October, this should be a great fall foliage season in most areas, with some areas in the Mid-Atlantic possibly turning earlier than normal due to the combination of drought conditions and the potential for early fall cool snaps. 

Some areas in the West may turn a little bit later than usual with above-average temperatures projected in September and October, though the temperature influence could also be negated in areas that are experiencing drought conditions. 

Keep in mind that, similar to winter season forecasts, fall foliage forecasts contain an inherent degree of uncertainty, and peak color typically does not vary that much from year to year.

Also, as is the case with powder days during ski season, there will always be at least a few days (if not weeks) when the colors are really popping, so get out there and enjoy this fall!

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Alan Smith