Sumac William O'Brien State Park

Month by month

Marine on St. Croix in September

Golden prairie, mushroom season and some of the most comfortable days of the year.

Photo: Lorie Shaull / CC BY 2.0, via Wikimedia Commons

72°Faverage high
56°Faverage low
3.35 inprecipitation8 wet days
2hot daysreaching 85°F or more
12.5 hdaylightsunrise 6:48 AM · sunset 7:24 PM

What September is like

September is the quiet sweet spot: the crowds of summer are gone, humidity fades and the sumac on the savanna turns scarlet. After rain it is prime mushroom season, and hawks begin migrating south along the river valley. Water is still warm enough for paddling early in the month.

In September, Marine on St. Croix averages a high of 72°F and a low of 56°F. Expect about 3.4 in of rain spread over roughly 8 wet days. On average 2 days reach 85°F or warmer. Days last about 12.5 hours, with roughly 9.7 hours of sunshine.

The river in September

Long-term average flow at St. Croix Falls in September is 3,432 cfs — 24% below the yearly average, so sandbars appear and the current is gentle.

Best things to do in September

Based on climate normals and when wildlife is most often recorded, September is a good month for: paddling the st. croix, hiking, wildflowers, mushrooms.

  • Hike the prairie and savanna loops as grasses turn gold.
  • Look (don’t pick without expert help) for chicken-of-the-woods and other fall fungi.
  • Take a late-season paddle on a calm afternoon.

What to pack

  • light layers for cool mornings
  • rain jacket
  • insect repellent (ticks and mosquitoes are common in woods and wetlands)

Wildlife to look for in September

Species with a large share of their local iNaturalist records in September. The strip shows each species' records across the year.

Birds

Green Heron

Green Heron

Butorides virescens

48 local records · peak September

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(c) Tom Kennedy, some rights reserved (CC BY), uploaded by Tom Kennedy

Philadelphia Vireo

Philadelphia Vireo

Vireo philadelphicus

2 local records · peak September

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(c) vtjohn, some rights reserved (CC BY-NC)

Bay-breasted Warbler

Bay-breasted Warbler

Setophaga castanea

4 local records · peak September

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(c) Jorge Emmanuel Escobar, some rights reserved (CC BY-NC), uploaded by Jorge Emmanuel Escobar

Chestnut-sided Warbler

Chestnut-sided Warbler

Setophaga pensylvanica

20 local records · peak May

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(c) Weston Barker, some rights reserved (CC BY-NC), uploaded by Weston Barker

Plants & wildflowers

closed bottle gentian

Closed bottle gentian

Gentiana andrewsii

38 local records · peak September

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(c) Bonnie Kinder, some rights reserved (CC BY-NC), uploaded by Bonnie Kinder

New England aster

New England aster

Symphyotrichum novae-angliae

30 local records · peak September

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(c) musicmanz, some rights reserved (CC BY-NC), uploaded by musicmanz

broad-leaved goldenrod

Broad-leaved goldenrod

Solidago flexicaulis

23 local records · peak September

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(c) Dan Mullen, some rights reserved (CC BY-NC-ND)

winterberry holly

Winterberry holly

Ilex verticillata

18 local records · peak September

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(c) Paul Donahue, some rights reserved (CC BY-NC), uploaded by Paul Donahue

Mushrooms & fungi

Aborted entoloma

Aborted entoloma

Entoloma abortivum

15 local records · peak September

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(c) Fluff Berger, some rights reserved (CC BY-SA), uploaded by Fluff Berger

hen of the woods

Hen of the woods

Grifola frondosa

23 local records · peak September

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(c) Davide Puddu, some rights reserved (CC BY), uploaded by Davide Puddu

Resinous Polypore

Resinous Polypore

Ischnoderma resinosum

22 local records · peak September

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(c) sdifalco, some rights reserved (CC BY-NC), uploaded by sdifalco

chicken of the woods

Chicken of the woods

Laetiporus sulphureus

35 local records · peak September

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(c) jonathantellerelsberg, some rights reserved (CC BY-NC-SA)

Insects & butterflies

Narrow-headed Marsh Fly

Narrow-headed Marsh Fly

Helophilus fasciatus

7 local records · peak September

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(c) Thomas Shahan, some rights reserved (CC BY-NC), uploaded by Thomas Shahan

Banded Tussock Moth

Banded Tussock Moth

Halysidota tessellaris

25 local records · peak September

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(c) Trey Wardlaw, some rights reserved (CC BY-NC), uploaded by Trey Wardlaw

American Dagger

American Dagger

Acronicta americana

8 local records · peak September

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(c) Ilona L, some rights reserved (CC BY-NC-SA)

Brown-hooded Owlet

Brown-hooded Owlet

Cucullia convexipennis

5 local records · peak September

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(c) Chelsea Gottfried, some rights reserved (CC BY-NC), uploaded by Chelsea Gottfried

Mammals

Domestic Cat

Domestic Cat

Felis catus

32 local records · peak September

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(c) Von.grzanka, some rights reserved (CC BY-SA)

White-tailed Deer

White-tailed Deer

Odocoileus virginianus

256 local records · peak July

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(c) jefferykarafa, some rights reserved (CC BY-NC), uploaded by jefferykarafa

Coyote

Coyote

Canis latrans

12 local records · peak December

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(c) ryan_krantz, some rights reserved (CC BY-NC)

Northern Short-tailed Shrew

Northern Short-tailed Shrew

Blarina brevicauda

12 local records · peak June

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(c) laraoutside, some rights reserved (CC BY-NC)

Reptiles & amphibians

Spring Peeper

Spring Peeper

Pseudacris crucifer

26 local records · peak September

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(c) Bruce J. Mohn, some rights reserved (CC BY-NC), uploaded by Bruce J. Mohn

False Map Turtle

False Map Turtle

Graptemys pseudogeographica

9 local records · peak September

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(c) Charlotte Kirchner, some rights reserved (CC BY), uploaded by Charlotte Kirchner

Common Five-lined Skink

Common Five-lined Skink

Plestiodon fasciatus

3 local records · peak September

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(c) Andrew Hoffman, some rights reserved (CC BY-NC-ND)

Eastern Milksnake

Eastern Milksnake

Lampropeltis triangulum

13 local records · peak September

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(c) Carrie Seltzer, some rights reserved (CC BY), uploaded by Carrie Seltzer