Today's Mosquito Risk in Washington: Real-Time Forecast & Activity Map
Check your ZIP code for local mosquito activity, West Nile risk, and prevention insights.
Built from CDC and NOAA data
Mosquito Surveillance Insights
- Annual WNV Cases
- about 5 to 15 confirmed cases annually
- Based on CDC ArboNET surveillance data
- Risk Tier
- Tier 4: Low
- Yakima Valley irrigated agriculture is the WNV focus area; coastal Washington stays mostly mosquito-free thanks to dry summers.
- Per mosquito-risk-model regional tier
- Highest-Risk Areas
- Yakima, Benton, Franklin, Grant (Columbia Basin and Yakima Valley)
Current Situation in Washington
Washington carries a low WNV burden of roughly 5 to 15 confirmed human cases annually, with risk concentrated almost entirely east of the Cascade Mountains across the Yakima Valley and Columbia Basin irrigated farmland. The Cascades split the state into two mosquito climates: the wet marine western side from the Olympic Peninsula through Puget Sound and the Skagit Valley stays mostly mosquito-free thanks to dry July and August weather, and the arid east runs hot and irrigated, with the Yakima Valley apple, hop, and alfalfa belt sustaining dense Cx. tarsalis populations through summer. Cx. pipiens fills in the urban storm drain load west of the Cascades. Aedes aegypti and Aedes albopictus are not established. EEE is rare. Biting season runs June through September.
Snapshot of the current mosquito situation in Washington, drawn from CDC ArboNET surveillance and the regional risk model.
- Risk Level
- Low
- Peak Activity
- May through October
- Dominant Vector
- Western Encephalitis Mosquito (Culex tarsalis) east of the Cascades and dominant WNV vector
Where Mosquitoes Breed in Washington
Washington mosquito habitat is built on the Columbia Basin irrigation grid east of the Cascades. The Yakima Valley through the Tri-Cities at the Columbia and Snake confluence holds the densest Cx. tarsalis populations in the state, with center pivot fields, flood-irrigated pastures, and tail-water ponds across Yakima, Benton, and Franklin counties producing sustained summer biting. The Columbia Basin around Moses Lake carries the same pattern off the Grand Coulee project. The Wenatchee River corridor holds seasonal Cx. tarsalis off orchard irrigation. The Skagit Valley produces snowmelt Aedes hatches. Storm drains in Seattle, Tacoma, Spokane, and Vancouver carry the urban Cx. pipiens load.
Hotspot Counties & Areas
- Yakima County (Yakima Valley irrigated agriculture, WNV focus)
- Benton and Franklin counties (Tri-Cities, Hanford Reach)
- Grant County (Moses Lake, Columbia Basin)
- King County (Seattle metro)
- Spokane County (Spokane)
- Pierce County (Tacoma)
- Clark County (Vancouver, lower Columbia)
- Skagit Valley (Skagit County floodwater Aedes)
Seasonal Activity Pattern
Biting starts in mid June across the Columbia Basin as irrigation cycles open up, peaks late July through August, and tapers through September. WNV cases concentrate in August across Yakima, Benton, Franklin, and Grant counties, with the Yakima Valley typically leading per-capita rates. The wet west side runs cool and dry through July and August, with biting limited to dawn and dusk in shaded riparian corridors. Snowmelt off the Cascades produces floodwater Aedes pulses through June on lowland river bottoms.
Monthly Biting Intensity (West Coast)
Washington Mosquito Risk Profile
- WNV burden level
- Low
- about 5 to 15 confirmed cases annually
- EEE risk
- Rare
- Peak biting season
- June through September
- Top urban risk areas
- Seattle (King)
- Spokane (Spokane)
- Tacoma (Pierce)
- Vancouver (Clark)
Signature habitat: Yakima Valley irrigated farmland, Columbia Basin, Puget Sound stormwater, Cascade foothill wetlands.
Climate driver: Yakima Valley irrigated agriculture is the WNV focus area; coastal Washington stays mostly mosquito-free thanks to dry summers.
Check Your Local Mosquito Risk
Ready to see current mosquito activity in your area? Get today's forecast and personalized risk assessment for your ZIP code.
Common Mosquitoes in Washington
Understanding which mosquitoes are active in Washington helps you identify threats and take appropriate precautions. Click any card for details.
Southern House Mosquito
Culex quinquefasciatus
Risk: West Nile virus, St. Louis encephalitis, dog heartworm.
Key feature: Medium brown body with banded abdominal segments and no leg stripes.
Active: Year-round in the deep South; summer peak elsewhere. Most active from dusk through the first few hours after sunset.
Yellow Fever Mosquito
Aedes aegypti
Risk: Zika, dengue, yellow fever, chikungunya.
Key feature: Black body with white lyre-shaped markings on the thorax.
Active: Year-round in southern Florida and the Gulf; summer-only further north.
Asian Tiger Mosquito
Aedes albopictus
Risk: Eastern Equine Encephalitis, dengue, chikungunya, Zika, dog heartworm.
Key feature: A single bright white stripe down the center of the back.
Active: Spring through first hard frost. Eggs overwinter in cold climates and hatch when flooded by spring rain.
West Nile Virus
Vector: Southern House Mosquito
West Nile Virus
The most common mosquito-borne illness in the US. About 80% of infections cause no symptoms; less than 1% develop neuroinvasive disease.
What to watch for
- Onset typically 2 to 15 days after a bite
- Most cases mild or asymptomatic, small fraction severe
- Neurological signs (severe headache, neck stiffness, confusion) need ER care
Breaking the Cycle in Washington
The mosquito lifecycle takes about a week. These habits cut local biting pressure faster than anything else, building multiple layers of protection.
Drain the Yard Weekly
Empty buckets, planter saucers, kiddie pools, tarps, and clogged gutters. A week of standing water is one full mosquito generation.
Repel Before Going Out
EPA-registered DEET (20-30%), picaridin (20%), IR3535, or oil of lemon eucalyptus. Apply before going outside, especially at dusk and dawn.
Seal the House
Window and door screens with no tears. AC and porch fans both work. Mosquitoes struggle to fly upwind even at 1-2 mph air speed.
Treat Outdoor Clothing
Permethrin-treated long sleeves and pants for evening yard work, hiking, or fishing. Remains effective through 70+ wash cycles.
If You Develop Symptoms
Most mosquito bites are harmless. A small fraction can transmit illness, and knowing the timeline matters more than panicking at every itch.Five things to know.
Watch for fever
Fever, body aches, headache, or fatigue 2 to 15 days after a bite. West Nile often feels like flu, and most infections never get diagnosed.
Note where and when
A rough record of where and when you got bitten helps your doctor decide what to test for. Date, location, mosquito-heavy areas you visited.
Get help fast for neuro signs
Severe headache, neck stiffness, confusion, vision changes, or sudden muscle weakness can mean neuroinvasive WNV or EEE. Both are medical emergencies.
Pregnant exposure?
If pregnant and bitten in an area with documented Zika or local dengue transmission, mention to your OB. Same goes for travel exposure.
Children and seniors
Higher risk of severe disease from WNV, EEE, and dengue in adults over 60 and children under 5. Early call to the pediatrician or PCP if symptoms appear.
When does mosquito season end in Washington?
Mosquito activity winds down after the first hard freeze, which in Washington typically arrives around Oct 28. See the local first-frost window and city-by-city freeze dates.
Washington first frost datesAlso worried about ticks in Washington?
Lyme disease risk and tick activity track different seasonal patterns than mosquitoes. See your Washington tick forecast.
View Washington tick forecastStay Safe in Washington
Get personalized mosquito forecasts and prevention tips for your area