Meteorological Fall: Why September 1 Marks the Start of Autumn
According to our calendars, we still have a few weeks of summer left to enjoy. But in meteorological circles, fall begins September 1st. Why are there two dates? We explain.
Quick Reference: Meteorological Fall
- Start date: September 1 every year, no exceptions.
- End date: November 30 every year.
- Months included: September, October, November.
- Astronomical fall: Starts on the autumnal equinox, around September 22 or 23 in the Northern Hemisphere.
- Why the split: Meteorologists group by temperature cycle. Astronomers group by Earth’s 23.5 degree axial tilt.
- Who uses it: NOAA, the National Weather Service, and climatologists worldwide, for cleaner month-based recordkeeping.
September is here, and by the calendar and the Farmers’ Almanac, a few weeks of summer are still on the books. Fall does not officially start until mid-September with the arrival of the autumnal equinox. But in meteorological circles, September 1 marks the first day of fall. Two dates, two frameworks, and both are correct. Here is why.
What Is the Difference Between Meteorological Fall and Astronomical Fall?
Meteorologists divide the year into seasons a bit differently than our calendars do. The meteorological calendar groups the twelve months into four three-month blocks tied to the annual temperature cycle. That gives climatologists tidy, comparable data windows that always start on the first of a month.
Meteorological Seasons:
- Fall: Begins September 1 (September, October, November); ends November 30.
- Winter: Begins December 1 (December, January, February); ends the last day of February.
- Spring: Begins March 1 (March, April, May); ends May 31.
- Summer: Begins June 1 (June, July, August); ends August 31.
The reason is simple. Meteorological seasons are based on the annual temperature cycle. Summer would run June through August, which makes intuitive sense. Those are the months most people associate with summer temperatures. Astronomers, on the other hand, determine the seasons by the Earth’s tilt. While it may seem that seasons are caused by the planet’s changing distance from the Sun, they are actually driven by that 23-degree axial slant. The tilt lets the Sun stay above the horizon for different lengths of time and determines whether its rays hit at a low glancing angle or more directly.
Astronomical Seasons:
- Fall begins with the autumnal equinox. At this point, the Earth’s tilt is moving away from its maximum lean toward the Sun; the rays are aiming directly at the equator.
- Winter begins with the winter solstice. The Earth tilts away from the Sun, and the Sun’s rays are aiming directly at southern latitudes.
- Spring begins with the vernal equinox. The Earth moves from its maximum lean away from the Sun to a point that is equal distance from the Sun; the rays are aiming directly at the equator again.
- Summer begins with the summer solstice. The Earth is tilting its farthest toward the Sun, and its rays are aiming directly at northern latitudes.
In short, the fall you are familiar with, the one that starts on the date of the autumnal equinox as listed on your calendar, is astronomical. But for some, fall starts September 1.
Why NOAA Uses Meteorological Seasons
The NOAA National Centers for Environmental Information switched to meteorological seasons for climate monitoring for a plain reason: the equinox and solstice dates shift by a day or two every year, which makes month-based averages a headache. Sticking to whole months (September, October, November) gives climatologists 92-day, 92-day, 90-day, and 91-day blocks they can compare cleanly across decades.
The National Weather Service follows the same convention. So when you read “the meteorological fall of 2025 was the warmest on record for the contiguous United States,” that data window ran September 1 through November 30, 2025. The astronomical fall of 2025 (September 22 to December 21) would have produced slightly different totals.
Regional Fall Timing Across the US and Canada
Neither calendar changes what leaves actually do. First frost varies wildly by region. Here is a rough guide to when peak fall shows up across North America, drawn from Almanac and USDA sources:
| Region | Typical First Frost | Peak Foliage Window |
|---|---|---|
| Alaska + Northern Canada | Late August to mid-September | Early to mid-September |
| Upper Midwest, New England, Ontario, Quebec | Late September to mid-October | Late September to mid-October |
| Mid-Atlantic, Great Lakes, Southern Prairies | Mid to late October | Mid to late October |
| Ozarks, Appalachian foothills, PNW valleys | Late October to early November | Late October to early November |
| Deep South, Gulf Coast, coastal California | Rare or never | Mostly evergreen, muted color |
Related Almanac Reading
Ready for autumn? Check out our peak Fall Foliage Dates here.
Which Fall Do You Follow?
What do you think: would you rather follow the meteorological seasons, with fall starting September 1, or wait for the equinox? Share your take in the comments below.
Frequently Asked Questions
When does meteorological fall start?
Meteorological fall starts on September 1 every year and runs through November 30. The dates never shift because they are tied to calendar months, not to the Earth’s axial tilt.
Why is meteorological fall different from astronomical fall?
Meteorologists group seasons by the annual temperature cycle, so the coldest three months become winter and so on. Astronomers group them by Earth’s 23-degree axial tilt, which puts the equinox and solstice at the seasonal boundaries. Both are valid; they just answer different questions.
Who decided that fall starts on September 1?
The convention comes from climatology. NOAA, the National Weather Service, and international meteorological agencies use whole-month seasons so that historical data can be compared cleanly year to year without the equinox drifting by a day or two.
Does meteorological fall feel like fall?
In the Upper Midwest, New England, Ontario, and Quebec, most years it already does by September 1. Farther south, it depends on the year. The label is about data windows, not what the thermometer reads on your porch.
Do farmers use meteorological or astronomical seasons?
Neither, strictly. Most farmers plan around frost dates, growing-degree days, and the moon phases (the Farmers’ Almanac Best Days calendar covers that). The equinox is a nice marker; frost dates are the real deadline.
What are the meteorological dates for all four seasons?
Meteorological spring: March 1 to May 31. Meteorological summer: June 1 to August 31. Meteorological fall: September 1 to November 30. Meteorological winter: December 1 to the last day of February. Every season is exactly three whole months.
Caleb Weatherbee
Caleb Weatherbee is the official forecaster for the Farmers' Almanac. His name is actually a pseudonym that has been passed down through generations of Almanac prognosticators and has been used to conceal the true identity of the men and women behind our predictions.
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Some cultures believed the equinoxes and solstices were the middle of their respective seasons instead of the beginning. In Celtic circles, summer began on May 1, Beltaine, where winter began on November 1, Samhuinn. This is why summer solstice is also called and celebrated as midsummer in Scandinavia and other places.
And by the way m, the spices we use to make peach cobbler are the same ones we use to make pumpkin pie. I’ll enjoy my spices no matter what time of year it is. 😜
This is great information! Thank you for sharing.
The fall I like is the astronomicsl
fall…when the
fall begins in the middle of Sept. Right now it is too hot to think of pumpkin spice latte,creamer . etc.it just seems logical this way….
I used to go with the astrological seasons, but that never left enough time to enjoy fall things and the spooky season before the festive Christmas/ holiday season kicked in 11/1. I still recognize the equinox, Thanksgiving, and the solstice, but now I go off the meteorological calendar enjoying autumn things 9/1-10/31 and Yuletide things 11/1-12/31. Two full months for both! Cheers fall is almost here! ? ? ☃️ ?
It used to be that meteorologists stuck to the True/astronomically based seasons. But, for the purposes of data consistency they moved to fixed dates. This actually has nothing to do with the temperature cycle. In point of fact, it would be necessary to extend past the astronomical based dates due to the lag in the temperature cycle. So, for example, a true meteorologically based fall would occur nearer the end of September. And, of course, most of us know that this tends to be true.
In northern Idaho Fall lasts for a month or two and generally starts in late September. Winter lasts for 5-6 months and generally starts in mid-October. But, most of us stick to the astronomical designations because those are the closest guide to planting/harvesting.
Going by meteorological seasons may seem easier, but I prefer to go by astronomical seasons. I live in Virginia, and since the beginning of meteorological fall this year, it has still been hot enough to go swimming outdoors. The temperature is supposed to go up to the 90s this week, and I can’t associate heat with fall. I associate fall with the leaves changing colors and a cool breeze.
I would rather follow the meteorological seasons, with fall starting September 1. I can see the temperature gradually drops from 100 degrees to 90 degrees during the third week of August and begin to feel fall like weather in the first week of September instead of third week of astronomical autumn.
It would be much easier, wouldn’t it?
Meterological seasons align with the Essenes calendar, and with this calendar, they were able to predict when the ages over 6,000 years would occur, when Jesus would be born, when He would die, when we would see Him again (2032 AD, exactly 2,000 years after He was crucified in 32 AD, which is the Church, or Age of Grace, where we can enter into God Most High’s presence, through His Only Begotten Son, Jesus Christ), when the Great Tribulation Age would begin (2025 AD). They have been able to predict everything, and had 100% accuracy, some 200 years before Jesus appeared.
The astronomical seasons are the ones that the Talmud rabbic calendar is established on, and this is why there is much confusion as to when the Lord’s Feast Days occur. With the Essenes calendar, there is no confusion.
Saving this. Wonder if it will pan out?
Well,meteorological seasons are a man-made event where as astronomical seasons are based in fact. Since September will arrive in the 90’s, I will stick with astronomical. I only wish fall would start soon, with cooler temps! Summer is just sweat and bug bites.
My Open Windows Devotional uses Metereological Seasons. So I stick with that.
I’ve only heard of the astronomical times. What is the reason for the meteorological times?
Hi b, it’s because the astronomical seasons are based on the position of Earth in relation to the Sun, whereas the meteorological seasons are based on the annual temperature cycle, which meteorologists closely follow.