Skip to content

Salt Lake City Mosquito Forecast

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

Bite Index · Sunday, November 8

Low

Mosquito activity in Salt Lake City is low today.

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

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

  • The week has averaged 46°F, below the 50°F where mosquitoes stop flying and breeding. Nothing to forecast until it warms up.

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
    0Low65°/36°dry
  2. Mon
    0Low66°/35°dry
  3. Tue
    0Low62°/36°dry
  4. Wed
    0Low61°/50°dry
  5. Thu
    0Low63°/50°dry
  6. Fri
    0Low64°/51°dry
  7. Sat
    0Low63°/50°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 Salt Lake City's mosquitoes do what they do

Salt Lake City sits between the Wasatch and the Great Salt Lake's vast freshwater and brackish marshes, which produce floodwater mosquitoes by the billion in a wet spring. The Salt Lake City Mosquito Abatement District, one of the oldest in the country, treats those marshes and traps across the city; its season is short but the marsh broods can be the worst in the West.

  • Great Salt Lake wetlands: Farmington Bay and the Jordan River delta are among the largest mosquito-producing marshes in North America.
  • Snowmelt: a big snow year means a big spring flood and a big June brood.
  • Irrigation: the valley's canals and watered lawns breed Culex tarsalis, the West Nile vector, through the dry summer.
  • Very short season: June through September; the index is zero from October to May.

A typical year in Salt Lake County

What the Bite Index typically reads here each month, from Salt Lake 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: 2
  6. JJune: 23
  7. JJuly: 32
  8. AAugust: 33
  9. SSeptember: 21
  10. OOctober: 1
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Salt Lake 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 (1.2 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 83%

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 0%

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 Salt Lake City 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 Salt Lake City

When is mosquito season in Salt Lake City?
June through September, peaking in late June and July after the marsh brood emerges, with West Nile risk in August. Frost ends it by October.
Why is Antelope Island so bad for mosquitoes?
The Great Salt Lake's marshes and the island's shoreline are vast floodwater-mosquito habitat, and in a wet year the brood is immense. The district treats the marshes nearest the city; the island itself is left wild.
Is West Nile virus a risk in Salt Lake City?
Yes, in late summer. Utah records cases most years and the district finds positive pools in most Augusts. Its announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Salt Lake City, scored by our documented model with the northern breeding lag, and compared with the county's climate normals run through the same model. Snowmelt flooding isn't in the weather data.

Also covers West Valley City, Sandy, Murray, Bountiful, Park City, Draper, the Jordan River Parkway, Antelope Island: the forecast point is central Salt Lake City, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 3:28 PM local time.

Related guides