Phenology Daybook: September 1, 2020

September 1st

The 244th Day of the Year


First September touching


(like moons)

and fondling yellowed sassafras.




Sunrise/set: 6:02/7:07

Day’s Length: 13 hours 5 minutes

Average High/Low: 81/60

Average Temperature: 70

Record High: 97 – 1953

Record Low: 44 – 1967


The Daily Weather

Temperatures today are usually in the 80s (a 55 percent chance) or 70s (a 40 percent chance), with only a five percent chance of a hot day in the 90s. There is a 30 percent chance of a thundershower, 25 percent chance of completely overcast conditions, 50 percent chance of a pleasantly cool night below 60 degrees.


The Weather in the Week Ahead

The likelihood of rain remains at 35 percent though September 3rd, then diminishes to 25 percent on the 4th and 5th, finally dropping to ten percent on the 6th – the lowest of the entire month. The effects of the first September cold wave usually appear by the 2nd, which is the first day since June 4th that 90s become unlikely. Then on the 3rd, there is a 55 percent chance of highs only in the 70s, and the chances of frost suddenly become one in a hundred.

The long period during which there is at least a ten percent chance of highs below 70 degrees begins on September 4th. Warmer conditions typically return on the 5th and 6th, but the second high-pressure system of the month, which arrives between the 5th and 11th, pushes lows into the 30s one year in 20.

September 6th is the first day of the season on which there is about a five percent chance of light frost on the gardens of the Lower Midwest. Chances increase at the rate of about one percent per day through the 15th of the month. Between the 15th and the 20th, chances grow at the rate of two percent per day. Between the 20th and 30th, they grow at the rate of five percent per day.

The day’s length shortens by 14 minutes this week, dropping below 13 hours for the first time since the first week of April, and down 120 minutes since solstice.


The Outlook for September

Throughout the month, normal highs drop eight degrees, falling to the lower 70s across the Lower Midwest. Average lows decline from the upper 50s to the upper 40s.

September’s average precipitation usually drops below three inches (2.70 is the Dayton area average) for the first time since February. The days most likely to be dry are the 6th, 10th, 11th, 13th, 15th, 19th, 25th, 26th, and 28th, each having a 20 percent chance or less for rain (the 6th and the 28th have less than a ten percent chance).

The wettest September days, those with a 40 percent or better chance of precipitation: the 9th, 18th, 21st, 22nd. September’s cloudiest days, those with better than a 40 percent chance of completely overcast conditions throughout the day are: the 12th, 18th, 21st, and 22nd.

The sunniest days, those with at least a 75 percent chance of sun, are the 5th, 6th, 7th, 8th, 9th, 10th, 11th, 19th, 20th, 24th, 25th, 26th, 27th, 28th and 29th, with the 6th, 7th, 8th, 10th, and 28th having a 90 percent chance of clear skies.

The warmest September days, those with a 50 percent chance of highs above 80 degrees, usually occur during the first 11 days of the month, the warmest days of all being September 1st, 2nd, 6th, 7th, 9th, 10th, 11th, and 30th.

The chilliest days of the month, those with better than a 30 percent chance of highs only in the 60s, are September 19th, 22nd, 23rd, 24th, 25th, and 26th.

Lows in the 30s occur as early as September 6th, but there is usually little danger of light frost until the end of the month’s third week. The September mornings most likely to bring a light freeze are 24th and the 27th (20 percent chance). Each day after the 19th carries about a ten percent chance of lows in the low 30s.


Summercount and Autumncount

Between the last week of May and the first week of September, the 15 major cool fronts of summer cross the United States. The last of these weather systems arrives as September begins. Subsequent fronts belong to the 18 major weather systems of early, middle and late autumn.


September 2: This weather system is typically a gentle one, and Late Summer continues throughout the central and southern states for the next few days. Chances of precipitation are low both before and after this first September high. In spite of the mild nature of this front, it does reflect the gradual transition to fall, and brings one chance in a hundred for a light frost as far south as the Border States.


September 8: The likelihood of precipitation increases at this front’s arrival, and once the system goes through, it almost always brings in Early Fall, a month-long period of Judas maples, late goldenrod, and the encroachment of chillier nights. Temperatures, which began to cool at the pivot time of August 10th, decline more noticeably.


September 12: A slightly stronger system often follows the September 8th high, making the 12th one of the two cloudiest and wettest days in September. The 12th also marks the beginning of a decline in percentage of daily sunshine, a downward shift that continues through December (the year’s darkest month). Chances of a light freeze increase on the 13th and 14th as this third high-pressure system of the month shows its full power.


September 15: The fourth high of September is followed by one the greatest shifts so far in the season. As the sun moves to within a few degrees of equinox, Late Summer’s grip grows measurably weaker. As this weather system moves along the 40th parallel, brisk afternoons in the 50s or 60s are four times as likely as during the first week of the month. The mornings are chilly, and the possibility of a light freeze grows steadily.


September 20: Although the day before the September 20th front is one of autumn’s warmest, when the front actually arrives, the likelihood of days in the 90s disappears all across the northern half of the nation. Even 80s will be gone there in only three weeks. The odds for an afternoon in the 50s or 60s this week doubles over those odds last week. And the season of light frosts deepens all across the northern half of the country. The chances of a light freeze become a minimum of ten percent per night until the first week of October—when odds quickly increase. On the positive side, pollen season declines quickly after the passage of this weather system.


September 24: Chances of precipitation increase as this front approaches from the west, and after the September 24th high moves east, light frost occurs more often than at any other time up to this point in September.


September 29: Although the day before the September 29th front’s arrival is usually dry and mild, this final high of September is the first to bring real danger of a hard frost to the North and slight risk of tomato damage across the mid-Atlantic region and the East. Average temperatures now start to fall at the rate of four degrees per week.


Key to the Nation’s Weather

The typical September temperature at average elevations along the 40th Parallel, the average of the high of 77 and the low of 57, is 67 degrees. Using the following chart based on weather statistics from around the country, one can calculate approximate temperatures in other locations close to the cities listed.

For example, with the base of 67 you can estimate normal temperatures in Minneapolis by subtracting five degrees from the base average. Or add 7 degrees to find out the likely conditions in Atlanta during the month.



Fairbanks AK             -23

Cheyenne WY             -10

Seattle, WA                             -7

Portland, ME                          -7

Minneapolis MN                    -5

Des Moines IA                       -2


St. Louis MO              +4

New York NY             +2

Washington D.C.                    +2

Atlanta            GA                              +6

New Orleans   LA             +12

Miami FL                     +14



The following chart shows the chances that frost will have occurred at average elevations along the 40th Parallel by the date indicated. The data can be adjusted by adding five percent for each 100 miles north or south of the 40th parallel.


Date                Chance of Light Frost   Chance of Killing Frost

September 1:               5%                                                   0%

September 10 :            10 %                                                  1%

September 15:       15%                                                          2%

September 20: 30%                                                  3%

September 25     55%                                                  5%

September 30:  80%                                                  8%



A Floating Sequence

For the Blooming of Wildflowers and Perennials

August 1:                    Mad-Dog Skullcap (Scutellaria lateriflora)

Giant Yellow Hyssop (Agastache nepetoides)

August 2:                    Prickly Mallow (Sida spinosa)

Great Ragweed (Ambrosia trifida)

August 3:                    Milk Purslane (Euphorbia maculate)

August 4:                    Willow Herb (Epilobium angustifolium)

August 5:                    Japanese Knotweed (Fallopian japonica)

August 7:                    Love Vine (Cassytha filiformis)

August 8:                    False Boneset (Brickellia eupatoriodes)

August 9:                    Bur Cucumber (Cucumis anguria)

August 10:                  Three-Seeded Mercury (Acalypha rhomboidea)

August 11:                  Water Horehound (Lycopus americanus)

August 12:                  Tall Goldenrod (Solidago altissima)

August 13:                  Climbing False Buckwheat (Fallopia scandens)

August 14:                  Great Blue Lobelia (Lobelia siphilitica)

August 15:                  Shaggy Soldier (Galinsoga quadriradiata)

August 16:                  Rose Pink (Glandularia canadensis)

August 18:                  Carpetweed (Mollugo verticillata)

August 19:                  Heart-leaved umbrellawort (Mirabilis nyctaginea)

August 23:                  Hog Peanut (Amphicarpaea bracteata)

August 24:                  Jerusalem Artichoke (Helianthus tuberosus)

August 29:                  Beggarticks (Bidens frondosa)

August 30:                  Bur Marigold (Bidens tripartite)

August 31:                  Heath Aster (Symphyotrichum           ericoides)

September 1:               New England Aster (Symphyotrichum                                                                                                novae-angliae)

September 3:               Small White Aster (Symphyotrichum ericoides) September 4                        Heart-Leafed Aster (Symphyotrichu cordifolium)

September 6:               Nodding Bur Marigold (Bidens cernua)

September 8:               Zigzag Goldenrod (Solidago flexicaulis)

September 10 :            Panicled Aster (Symphyotrichum lanceolatum)


Estimated Pollen Count

(On a scale of 0 – 700 grains per cubic meter)

September 1:  300

September 5: 240

September 10 : 160

September 15:  60

September 20: 10

September 30: 10


Estimated Mold Count

(On a scale of 0 – 7,000 grains per cubic meter)

September 1:  5500

September 5:  4800

September 10 : 4300

September 15: 2600

September 20: 3600

September 25: 1500

September 30: 1300


When-Then Phenology

When asters bloom in the waysides and bur marigolds flower in the swamps, then farmers start cutting corn for silage.

When zigzag goldenrod blossoms in the woods, then the rose of Sharon shrub drops most of its flowers and the great decline of summer wildflowers begins in the fields.

When fallen leaves start to accumulate in the backwaters and farm ponds, then the grapes should be getting ripe, and over half of the tomatoes and potatoes should be ready for harvest.

When the first black walnut trees are almost bare, then the third cut of alfalfa is typically complete and farmers are preparing the soil for planting canola, grasses and small grains.

When bright patches of scarlet sumac and Virginia creeper mark the fencerows and streaks of gold have appeared on the silver olive bushes, then kingbirds, finches, ruddy ducks, cedar waxwings, herring gulls and yellow-bellied sapsuckers move south. Bobolinks and woodcocks follow. The last young grackles and hummingbirds leave their nests.

When katydids refuse to chant and crickets songs are slow, then frost could threaten near dawn.

When squirrels scatter buckeye hulls along the trails and locust pods fall beside them, then the first soybeans will be ready to harvest.

When farmers plant wheat in northern fields, then throughout the South, cotton growers defoliate their cotton plants, a process that increases fiber quality.

When doves stop calling in the mornings, then Fletcher scale attacks the arborvitae. Locust borers assault the locusts. Pine root collar weevils move to the pine trees.

When cobwebs are all over in the woods and butterflies multiply in the garden, that’s the time to plant the last lettuce and radishes of the year, complete the harvest of summer apples and start to pick fall apples.

When red berries appear on the silver olives, orange berries on the American mountain ash and purple berries on the pokeweed, then violet autumn crocuses blossom in town, and sandhill cranes have started their migration to the Gulf Coast.

When the autumn leafturn has begun along the 40th Parallel, the deciduous trees are bare in northern Canada. In New England and in the Rocky Mountains, foliage colors are approaching their best.

When the huge pink mallows of the wetlands have died back, then the juniper tip midge appears on junipers, and gall adelgids attack the spruce threes.

When milkweed pods open, then late hosta bloom comes to a close in town. In the woods, Middle Spring’s sedum is growing stronger. Henbit, mint and catchweed revive as the canopy thins. Waterleaf has fresh shoots. Snow-on-the-mountain has recovered from its mid-summer slump and can be as thick and as beautiful as in Early Spring.

When most of the black walnuts have fallen and wood nettle seeds are black and brittle, then gardeners begin autumn bulb planting and the transplanting of perennials in the garden.

When the ash trees turn red and gold, then the season of killing frosts has arrived.

When the day’s length falls below 12 hours, then the sugar beet, pear, cabbage and cauliflower harvests commence in the Great Lakes region. In Wisconsin, Massachusetts, New Jersey, Oregon and Washington State, the cranberry harvest begins as berries darken in the cooler weather.

When goldenrod flowers are tufted and gray, then daddy longlegs disappear from the undergrowth and bird migrations reach their peak.


Natural Calendar

In the last week of Late Summer, the final tier of wildflowers starts to open. White and violet asters, orange beggarticks, burr marigolds, tall goldenrod, zigzag goldenrod and Japanese knotweed bloom, blending with the brightest of the purple ironweed, yellow sundrops, blue chicory, golden touch-me-nots, showy coneflowers and great blue lobelia. In gardens, September hostas, virgin’s bower and late heliopsis keep their color.

On the farm, pickle season is usually over, and peaches can be done for the year. Grapes are about to come in, and elderberries are deep purple and sweet for picking. Nearly half of the tobacco has been cut, half the commercial tomatoes have been picked, about a fourth of the potatoes dug.

Hickory nutting season opens as sweet-corn time winds down. Burrs from tick trefoil stick to pants legs and stockings. Lizard’s tail drops its leaves into the creeks and sloughs. Beside the deer paths of the forests, the undergrowth is tattered and cluttered with the remnants of the year.

Firefly larvae flicker in the grass, the adult fireflies gone. Red-headed woodpeckers, red-winged blackbirds, house wrens, scarlet tanagers, indigo buntings, Eastern bluebirds and black ducks migrate. Sometimes great swarms of dragonflies migrate through the Lower Midwest.



1983: Geese fly over to Ellis Pond, 6:30 p.m.


1985: Jacoby East: First small white asters are blooming. July’s avens is yellowing. Cobwebs everywhere. Watercress growing back. Joe Pye still strong. Squirrels have been opening the buckeyes. Flurries of leaves falling through the trees. Some jumpseeds completely done jumping. Waterleaf growing back. Two huge puffball mushrooms found. Brown acorns on the path. Two smaller puffballs seen growing in the shade across the creek, like moons in the dark grass. Some wingstem bowing to set its seeds. Some ironweed done. Agrimony gone. Cicadas loud, insistent. Touch-me-nots still full. One rose pink found in full bloom at Upper Prairie.


1986: Cardinal heard twice today.


1987: Cardinal songs, intermittent.


1988: Stopped between the Covered Bridge and Corry Street: Waterleaf has grown a whole new layer of foliage. Most agrimony gone to seed, burs on their stems. Cardinal sings 5:30 a.m., heard off and on before 7:00, then again late afternoon. Yellow elm leaves falling.


1991: Purple loosestrife gone now.


1992: Our cherry tree has lost almost all its foliage. Maple leaves falling in front of the house. Mornings heavy with dew, cool in the 50s, smell of autumn, of vegetation past its prime, settling into the earth, bearing fruit. Raspberries continue to come in. I pick them remembering Marshfield, when I filled pans with raspberries, exulting in my picking skills and my mother’s admiration.


1993: All the purple loosestrife in the yard has finished blooming, but in the countryside, some plants are still open. What appears to be the final balloon flower opened today. Doves still called before sunrise. More patches of yellow on the poplars and black walnut trees. On the way to Wilberforce, dozens of monarchs seen, most of them flying across the road south. I ran into two or three, many more killed on the highway. All the Japanese beetles have disappeared in the rose garden.


1997: Japanese beetles still present in the yard. Tonight just one firefly, and he was blinking in the grass. Deterioration of the showy coneflowers is underway today.


1998: Sparrows in the pear trees on Xenia Avenue: 5:50 a.m., crows: 5:37, cardinal 5:40. A few dozen yellow coneflowers left in the garden, five golden mums open. The pond is clear in the cool morning. Two water lilies blooming. Hops still flowering along the north hedge. Pokeweed growing back and in bloom.


1999: Doves were calling this morning at 7:00. At 8:30, the sun was well up into the southeast, and cirrus clouds north of it glittered with a rainbow sundog, sign of fall. The last arrowhead wilted by sundown.


2000: With Buttercup at the Cascades: Robins clucking, asters budding, jumpseeds jumping (had been loose in front of the house three days ago), red Virginia creeper leaves on the path, touch-me-nots popping, zigzag goldenrod just opening, white snakeroot early. Sprouts of garlic mustard up in a runoff area of one hillside, responding to the increase in moisture there. Along the highway, more and more Judas maples. Soybeans have started to turn. Catalpas and cottonwoods aging to ocher. In town, stonecrop sedum approaching full bloom.


2001: Cardinal at 6:45 a.m., doves, crows and a jay a minute or so later. A brief flurry of song, then quiet again. Fishing all day with John at Caesar Creek. Not even a nibble in eight hours on the water. Many cormorants or darters in the water and roosting in dead trees at sundown. Great blue herons common. Arrowhead: last day of blooming season, the same as in the pond at home. No other flowers seen except some patches of goldenrod along the highway.


2003: Virgin’s bower is in full bloom in the back yard and everywhere in town.


2004: New England aster buds are turning purple by the north trellis. Virgin’s bower is only maybe a fifth in bloom there. Goldenrod has emerged fully here, and a great ragweed plant in the garden is still bright with pollen. One yellow swallowtail in the zinnias this afternoon, no monarchs. Showers of black walnut leaves off and on through the day.


2005: Casey called this morning from the golf course at the edge of town. “Blackbirds are movin’,” he said. “Can you hear them?” And I heard a faint clucking over the phone. He added that a friend had seen a female turkey with seven chicks in a tree near G. Stanley Hall at the edge of town. Some virgin’s bower is in full bloom around town, but ours is still not flowering. The very first goldenrod, however, is coming in along the north garden. Most of the peaches fell from their branches yesterday, only a handful left.


2007: The tall coneflowers in the alley have ended their season now. A few yards away, the thin-leafed coneflowers are still in full bloom. One giant swallowtail visited the zinnias and butterfly bush this morning. A large flock of geese flew over the center of town about 6:00 this morning.


2008: The skunk was in the back yard when I got up this morning around 6:00, and it stayed until broad daylight at 6:35. One painted lady (Cynthia) in the butterfly bush this noon. Jeanie found a three-inch praying mantis in the hosta and fern bed. A starling came to the suet feeder this morning, the first time I’ve seen one here through Late Summer. Large yellow garden spider (black-and-yellow argiope) in the front garden.


2010: Only a few intermittent crow and cardinal calls off and on after 5:30 this morning, no robins heard. Dry, hot weather continues. A few monarchs, tiger swallowtails, spicebush butterflies today, skippers numerous. In the alley, Mateo’s black walnut is almost bare, and the tall yellow coneflowers are more than half gone. Scattered tall goldenrod seen in full bloom around the village. A few New England asters are open at the store. A great flock of blackbirds filled the back trees at noon, then moved on. No robin vespers heard this evening.


2011: Rain near sunrise quieted the tree crickets. Crows at 5:45, cardinal chipping call at 6:00, and hummingbirds, too. Squirrels started exactly at 7:00. One spicebush swallowtail seen this morning before I left for work at the center. Mateo’s black walnut still has most of its leaves. High in the middle 90s today, and the most oppressive evening of the year when I walked Bella at 7:00. One firefly seen at the triangle park. So hot, the tree crickets were silent until we went to bed at 7:00. Marianne called tonight to say that a giant swarm of dragonflies was circling above her house. Cynthia McDonald also saw swarms in Cedarville.


2012: Soft rain, the remnants of Hurricane Isaac, this morning. Humid and hot throughout the afternoon. Many skippers, whites, admirals, fritillaries and checkerspots today. All the peaches fell by evening, almost all the phlox were gone, and the heliopsis were tattered. Wingstem and ironweed still in full bloom throughout the area. More webworms in our redbuds. A catbird seen in the quince, a young pair of cardinals at the feeder.


2014: A smaller, more colorful orb-weaver has set up its web in the back yard between branches of Jeanie’s redbud.


2015: In the middle of a heat wave, monarchs and swallowtails continue to come to the zinnias and tithonias. The first beggarticks have opened by the back porch, and the first New England asters in the north garden are showing purple.


2016: A long flock of blackbirds passed over the highway as I drove south to Xenia. Soybean fields still solid green. Hurricane Hermine, the first hurricane to strike the United States this year, comes ashore on the Gulf Coast of Florida. In the east apple tree garden, the autumn hostas are in bloom: the large white-flowered ones and the narrow-leafed violet-flowered ones.


2017: Hurricane Harvey approaches from the south, brings two days of rain and cold temperatures in the 60s. One painted lady (Cynthia) came to the garden in the cold and drizzle.


2019: Hurricane Dorian, the strongest storm ever recorded in the Caribbean, devastates the Bahamas, stalls and spins just east of Miami. Here at Keuka Lake, acorns continue to accumulate, crunch as we walk.


2020: It seems the butterflies are fewer the past few days, this afternoon only one tiger swallowtail and a monarch, along with a silver-spotted skipper and a cabbage white. Tropical Storm Nana drives west into Honduras. No fireflies along Union Street tonight, the first time.


Early September was a luxurious time. The air was warm and moist but not hot and sticky quiet but not stifling. The tangles of poison ivy and wild grape had thinned somewhat, and few biting insects were active. Early-turning leaves echoed the brilliance of late-blooming flowers, and the air was rich with pleasant smells – ripe apples, aromatic herbs, fallen leaves.

David Rains Wallace



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