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Phoenix Mosquito Forecast

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

Bite Index · Sunday, November 8

Moderate

Moderate mosquito activity in Phoenix today and climbing toward very high by Nov 13: expect some bites at dusk.

Some bites at dusk and dawn, mostly near creeks, gardens and shade.

Worse than a typical November in Maricopa County (usually around 21).

  • 1.2 in. of rain Oct 22–Oct 30 is now producing adults (cool weather slowed the hatch, so the window is longer than usual).
  • It's the edge of the season; warm weeks like this one keep it going past the calendar.
  • A two-week average of 69°F keeps populations growing, just more slowly than midsummer.

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
    40Mod.83°/60°dry
  2. Mon
    45High83°/56°dry
  3. Tue
    45High81°/61°dry
  4. Wed
    45High81°/70°dry
  5. Thu
    45High82°/69°dry
  6. Fri
    64V·High82°/70°dry
  7. Sat
    64V·High78°/70°dry

Protect tonight

Worth repellent if you'll be outside at dusk or dawn.

  1. A botanical or 10% picaridin lotion covers a patio evening; reapply after about two hours.
  2. A fan on the patio does real work: mosquitoes are weak fliers and avoid moving air.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Phoenix's mosquitoes do what they do

Phoenix is a desert with a mosquito problem, and the problem is water people bring: irrigated lawns and citrus, flood-irrigated fields, canals, and green pools. The monsoon from July to September adds real rain and the Valley's mosquito counts climb with it. Maricopa County runs one of the biggest trap networks in the country and Arizona led the nation in West Nile cases in 2026.

  • Monsoon: July–September storms are the only natural breeding water; the index climbs about ten days after each one.
  • Flood irrigation: Culex tarsalis, the West Nile vector, breeds in irrigated fields and lawns around the Valley's edges.
  • Green pools: neglected pools in a city of backyard pools are the single biggest urban breeding source; the county tracks and treats them.
  • Heat: 110°F afternoons suppress mosquitoes, and dry 20% humidity grounds them; the index weights both, so Phoenix scores lower than its rain alone would suggest.

A typical year in Maricopa County

The long-run mosquito index by month from our season map (NOAA climate normals plus effort-corrected sightings). Today's Bite Index is the live version of this; the month you're in is marked.

  1. JJanuary: 8
  2. FFebruary: 13
  3. MMarch: 18
  4. AApril: 23
  5. MMay: 30
  6. JJune: 35
  7. JJuly: 41
  8. AAugust: 60
  9. SSeptember: 57
  10. OOctober: 39
  11. NNovember: 21
  12. DDecember: 10

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Maricopa 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. Four weather factors are combined on a 0–100 scale, then scaled by the season. Every factor and today's value for it is listed here so you can check the number yourself. It uses the same temperature curve and rain logic as our county-level mosquito season map, which has been validated against effort-corrected sighting data across 41 states.

BBreeding pressure

Rain 7–14 days ago (1.2 in. between Oct 22 and Oct 30). Eggs need water to hatch, and at summer temperatures the egg-to-biting-adult cycle takes about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it as shallow water evaporates.

Weight 40%
Today 77%

DDevelopment

The trailing two-week average temperature, on the same curve as our national season map: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat.

Weight 25%
Today 67%

ATonight's activity

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.

Weight 25%
Today 50%

GGround truth

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

Weight 10%
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.

Weight ×
Today 60%

index = 100 × S × (0.40 × (0.2 + 0.8·B) + 0.25 × D + 0.25 × A + 0.10 × (0.5 + 0.5·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 Phoenix

When is mosquito season in Phoenix?
Monsoon season, roughly July through September, with activity lingering into October and a smaller spring bump in irrigated areas. Winter is quiet; summer before the monsoon is too hot and dry for much flight.
Why does Phoenix have mosquitoes at all?
Irrigation. Flood-irrigated fields, lawns and citrus, canals and green pools create standing water in a place that has none naturally. Add monsoon rain and humidity and the Culex tarsalis population that carries West Nile explodes.
Is West Nile virus a risk in Phoenix?
Very much so. Maricopa County regularly has the most West Nile cases of any county in the country, and Arizona led the nation in 2026. The county's positive-trap map and fogging notices are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for central Phoenix, scored by our documented model with desert-specific humidity and heat terms, and compared with Maricopa County's season-map climatology. Irrigation isn't in the weather data, so the index may run low in irrigated neighborhoods.

Also covers Scottsdale, Mesa, Tempe, Chandler, Gilbert, Glendale, Peoria, the Salt River bottoms: the forecast point is central Phoenix, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 11:38 AM local time.

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