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Detroit Mosquito Forecast

Today's mosquito activity in Detroit, the week ahead, and what to do about it. Updated hourly.

Bite Index · Sunday, November 8

Low

Mosquito activity in Detroit is low today.

Few mosquitoes. You may see one or two at dusk near water.

About normal for November in Wayne County (typically around 0).

  • Off-season: even with rain and warmth, populations are a fraction of summer's.
  • At a two-week average of 54°F, larvae develop slowly and the population stays small whatever the rain.
  • Tonight: a cool 47°F evening, light wind — poor flying weather, so fewer bites than the population alone would suggest.

The week ahead

Each day's Bite Index, from this week's weather and the rain that is still hatching. Forecast days get less certain as the week goes on.

  1. Today
    1Low57°/35°dry
  2. Mon
    0Low53°/37°dry
  3. Tue
    0Low62°/41°dry
  4. Wed
    0Low56°/47°0.2 in
  5. Thu
    0Low48°/40°0.4 in
  6. Fri
    0Low42°/37°dry
  7. Sat
    0Low45°/34°dry

Protect tonight

You can probably skip repellent tonight.

  1. If you're near a creek, pond or heavy shade at dusk, a light application on ankles and arms is plenty.
  2. Good night to tip out any containers holding water; what you empty now won't hatch next week.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Detroit's mosquitoes do what they do

Detroit's summers are warm and humid enough for a full Culex season between the Detroit River and the Rouge, and Wayne County records West Nile-positive mosquitoes, birds and human cases most years. The season is short — June through September — but August is reliably the worst month for both bites and virus.

  • Rouge River and the Detroit River: floodplain and shoreline habitat through the city.
  • Catch basins: urban Culex pipiens breed in storm drains; the Asian tiger mosquito has arrived in Wayne County.
  • Humid Great Lakes summers: July and August dusk conditions are ideal for flight.
  • Short season: June through September; the index is zero from October to May.

A typical year in Wayne County

What the Bite Index typically reads here each month, from Wayne County's 30-year climate normals run through the same model as today's number. The month you're in is marked; the season map shows the same long-run picture for every county.

  1. JJanuary: 0
  2. FFebruary: 0
  3. MMarch: 0
  4. AApril: 0
  5. MMay: 8
  6. JJune: 45
  7. JJuly: 64
  8. AAugust: 63
  9. SSeptember: 45
  10. OOctober: 5
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Wayne County's health department traps and tests mosquitoes through the season and publishes positive West Nile pools by ZIP code. When your ZIP has an active advisory, follow it regardless of today's number.

How the Bite Index is scored

The index is a model of conditions, not a mosquito count. Warmth and water set the size of the population, tonight's weather sets how much of it flies, and the season and local reports adjust the result. Every factor and today's value for it is listed here so you can check the number yourself. Warmth and Water are exactly the climate core of our county-level mosquito season map; the map shows that core on 30-year normals for every county, and “typical for this month” is the same model run on this county's normals, so the comparison is like for like.

WWater

Rain over the egg-to-adult window (0.5 in. between Oct 8 and Oct 23), expressed as a monthly rate on the same wetness curve the season map uses. At summer temperatures eggs become biting adults in about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it. Irrigation, creeks and pools keep a 35% floor even in a drought.

Role scales
Today 23%

TWarmth

The trailing two-week average temperature on the season map's curve: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat. Multiplied with Water, so a cool fortnight caps the index however wet it has been.

Role gates
Today 15%

ATonight

Whether the population that exists will actually fly and bite this evening: dusk temperature (65–85°F is ideal), wind (they stop flying around 10 mph), humidity, and rain around sunset. Scales the index between half and full.

Role 0.5–1×
Today 0%

GGround truth

A nudge from local trap counts and reports when we have them. For Detroit this is neutral today; the health department's surveillance is linked above and will feed this factor as we wire it in.

Role ±15%
Today neutral

SSeason gate

A multiplier from the calendar: fully open in the city's season months, half-open in the shoulder months, nearly closed in deep winter unless the week is warm. Below a 50°F weekly average the index is simply 0.

Role ×
Today 15%

index = 100 × S × [T × (0.35 + 0.65·W)] × (0.5 + 0.5·A) × (1 + 0.15·G)

Bands: Low 0–20 · Moderate 21–40 · High 41–60 · Very High 61–80 · Severe 81–100. Weather is from Open-Meteo (observations and the 7-day forecast), refreshed hourly. The lag and temperature thresholds follow published work on Culex and Aedes development (Rueda et al. 1990; Cornell NRCC degree-day emergence; JAMCA 2024 on rainfall two to four weeks before trap peaks).

Questions people ask about mosquitoes in Detroit

When is mosquito season in Detroit?
June through September, peaking in July and August. The first frost, usually October, ends it.
Why is August the worst month in Detroit?
Heat and the summer's accumulated rain peak together, and Culex pipiens numbers build through the season in catch basins. West Nile detections also peak in August.
Is West Nile virus a risk in Detroit?
Yes. Wayne County confirms positive mosquito samples and human cases most summers. The Health Department's announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Detroit, scored by our documented model with the northern breeding lag, and compared with Wayne County's season-map climatology. Not a trap count.

Also covers Dearborn, Warren, Livonia, Southfield, Royal Oak, Windsor, Belle Isle, the Riverwalk: the forecast point is central Detroit, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 5:28 PM local time.

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