Rainy Seasons Across the United States: Regional Breakdown

There's no single "US rainy season"—the continent's vast geography creates dramatically different precipitation calendars. Understanding regional patterns is essential for agriculture, travel, construction, and flood preparedness.

1. Pacific Northwest (WA, OR, ID panhandle)

Wet Season: October - May (peaks Nov-Jan)
Pattern: Relentless frontal systems; 60-150+ inches annually west of Cascades. Summer dry but not rainless.

2. California (Mediterranean Climate)

Wet Season: November - March (80-90% of annual rain)
Gradient: North (60+") to South (10-15"). Summer virtually rain-free. Atmospheric rivers drive extreme events.

3. Southwest Monsoon (AZ, NM, NV, UT, CO)

Monsoon Season: July - September
Mechanism: Thermal low draws Gulf of California/Gulf of Mexico moisture. Intense afternoon thunderstorms, flash floods, haboobs. Rest of year: arid.

4. Gulf Coast / Southeast (TX, LA, MS, AL, FL, GA, SC)

Year-Round Rainfall with dual peaks:
• Spring severe weather (Mar-May): Tornadoes, squall lines
• Summer tropical (Jun-Nov): Hurricanes, tropical storms
• Winter fronts: Steady rain

5. Midwest & Great Plains

Peak: April - June (spring convective season)
Mechanism: Gulf moisture + jet stream + frontal boundaries = supercells, MCSs, flooding. Winter: snow. Summer: sporadic storms.

6. Northeast / Mid-Atlantic

No Distinct Dry Season. Year-round precipitation:
• Winter: Nor'easters (snow/rain mix)
• Spring: Frequent frontal rain
• Summer: Humid, thunderstorms
• Fall: Tropical remnants + fronts

Key Climate Drivers

• ENSO (El Niño/La Niña) shifts storm tracks
• Climate change: intensifying extremes, shifting seasons
• Topography: orographic lift (mountains), rain shadows

For precision: consult NOAA Climate Normals (1991-2020) for your specific county, not state-level generalizations.