Thursday is the first day of fall, and in New England, that means hopes for some excellent leaf-peeping.

And the forecast so far?

Richard Primack is a professor of biology and a plant ecologist at Boston University. He says fall foliage is mostly determined by the weather in August, September, and even into October.

"If we keep cooling down without a frost right now," Primack says, "we've mostly been having days in the 70s, sometimes in the low 80s, with temperatures at night in the 50s; these are really kind of ideal conditions — combined with the shortening day length and the longer nights — for what should be a really spectacular year for fall foliage."

Primack says the one twist is that in the greater Boston area, it will be a bit duller than usual — almost all the Norway Maples got hit with a leaf-killing fungus, although other trees in the area are set to put on a lovely show.

Extreme events could yet interfere with that forecast, says Primack. If temperatures drop precipitously before the autumn show is set to take the stage, we could lose out with frost causing a premature dropping of leaves before they blaze with brilliance. But right now, we're on track, Primack says, with gradually cooling days and warm enough nights.

Besides the right temperatures, transitioning in just the right way, Primack says the other thing we want is "a moderate but below average amount of rainfall."

But not too below average — it's Goldilocks conditions we're looking for.

"Years in which there is extreme drought — for example, last year we actually had extreme dry weather," Primack says, "and that caused many leaves to start drying out and changing color and falling off prematurely, particularly birches."

But this season's low amount of rainfall is just right — not too wet, not too dry.

"The ground is fairly dry but not bone dry," Primack says. "And that's actually surprisingly good for the trees. So the trees are reacting to this by keeping their leaves, but gradually drying out."

Combine that with just the right temperatures, Primack says — not too cold, not too warm — and an eye-popping display is on the way.