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Castro Valley, California

Community in Alameda County, California

Air quality

The air at Castro Valley

Index 45, good, led by ozone. Read at 8 PM from its reporting area, Fremont (CA), 11 miles off.

45Good
  • Fine particles (PM2.5)-13.6 mi
  • Ozone45Good19 ppb13.6 mi
  • Nitrogen dioxide18Good19.1 ppb13.6 mi
  • Sulfur dioxide0Good0.4 ppb13.6 mi
  • Carbon monoxide-0.5 ppm13.6 mi

The days ahead

Good each day through Tue Oct 20, led by ozone. Yesterday measured 33, good.

Smoke, the next 45 hours

Little smoke near the ground through Sat 5 PM: the index from smoke stays at 17 or under.

FriSat

Precipitation

What has fallen at Castro Valley

None in the last 3 days, to Thu 8 PM. Measured by radar and rain gauges, as water.

Last 24 hours
0.00in
Last 3 days
0.00in

Visibility

How far you can see at Castro Valley, the next 45 hours

Visibility stays 10 miles or more through Sat 5 PM.

FriSat

On the radar over Castro Valley, CaliforniaReflectivityStorm topsRain rateRain, last 24 hoursForecast temperatureForecast rain totalEvery picture

What is measuring near here

The 6 instruments nearest Castro Valley, how far away each one is, how high it stands, and what kind of measurement it makes. The nearest is 1.2 miles away.

measured now4 instruments

HaywardHWD

At an airfield/3.9 mi away/29 ft/182 ft below here

temp, wind, gust, visibility, precip, pressure

Rank7of 4,465

measured daily2 instruments

Oakland - Upper San LeanfroUSLC1

At a cooperative observer's station/6.9 mi away/316 ft/105 ft above here

snowfall, snow depth, precip, high, low

Rank-

Station report

The weather at Hayward, drawn

The nearest airport reporting now, 3.9 mi from Castro Valley, California. From its report of Oct 15, 2026, 8:54 PM local time: 3 of its 6 sheets.

The sky

No cloud below 12,000 ft; visibility 10 mi or more.

Section of the sky over Hayward, height above the station to scale: no cloud detected below 12,000 feet, the reach of its ceilometer, and visibility of 10 mi or more.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT HWDFIG. A THE SKY OVER HAYWARDSECTION, HEIGHT ABOVE THE STATION TO SCALE, EACH LAYER AT THE HEIGHT OF ITS BASE AS REPORTED; COVER IN EIGHTHS OF THE SKY; TOPS NOT MEASUREDFT ABOVE THE STATION05001,0001,5002,0002,5003,000ETAGESLOWTHE STATIONTHE CEILOMETER READS TO 12,000 FT, ABOVE THIS SHEETNO CLOUD DETECTED BELOW 12,000 FTVISIBILITY, MILES: 10 MI OR MORE0510TITLEHayward, the skySTATION REPORT · ASOS HWDTYPESECTIONSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 1 of 6DATE2026-10-16IDSR-HWD-1DRAWN AS linework on paperSOURCES FB-SKY-001

The air

68.0 F with a dew point of 55.0 F, 63 per cent relative humidity. Air lifted from the station would cool to its dew point, where cloud forms, about 3,000 ft up.

Chart of the air at Hayward: temperature 68.0 degrees Fahrenheit and dew point 55.0, 63 per cent relative humidity; air lifted from the station cools along the dry rate and meets its dew point about 3,000 feet above the station; height to scale.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT HWDFIG. B THE AIR AT HAYWARDTHE REPORTED TEMPERATURE AND DEW POINT, AND AIR LIFTED FROM THE STATION WITHOUT MIXING UNTIL IT SATURATES; HEIGHT ABOVE THE STATION TO SCALEFT ABOVE THE STATION01,0002,0003,0004,00040 F50 F60 F70 F80 FSATURATES 3,000 FT ABOVE THE STATION, AT 52.1 FTEMPERATURE 68.0 FDEW POINT 55.0 FSPREAD 13.0 FRELATIVE HUMIDITY 63 PER CENTTHE AIR COOLS ABOUT 5.4 F EACH 1,000 FT IT RISES, AND ITS DEW POINT ABOUT 1 FSOLID: THE LIFTED AIR'S TEMPERATURE; DASHED: ITS DEW POINTTITLEHayward, the airSTATION REPORT · ASOS HWDTYPECHARTSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 2 of 6DATE2026-10-16IDSR-HWD-2DRAWN AS linework on paperSOURCES FB-WAT-002, FB-ENG-011, FB-ENG-005

The wind

From the south southwest (210 degrees) at 9 mph: force 3, a gentle breeze on the Beaufort scale.

Plan of the wind at Hayward, north up: blowing from 210 degrees, the south southwest, at 9 miles an hour; beside it the Beaufort scale from calm to hurricane force, force 3, gentle breeze, marked.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT HWDFIG. C THE WIND AT HAYWARDPLAN, NORTH UP: THE WIND AS REPORTED, AND WHERE IT SITS ON THE BEAUFORT SCALENESWTHE STATIONFROM 210°BEAUFORT FORCELEAST WIND, MPH0CALM01LIGHT AIR12LIGHT BREEZE43GENTLE BREEZE8NOW, 9 MPH4MODERATE BREEZE135FRESH BREEZE196STRONG BREEZE257NEAR GALE328GALE399STRONG GALE4710STORM5511VIOLENT STORM6412HURRICANE FORCE73TITLEHayward, the windSTATION REPORT · ASOS HWDTYPEPLAN north upSCALENOT TO SCALEREVAS REPORTED SHEET 3 of 6DATE2026-10-16IDSR-HWD-3DRAWN AS linework on paperSOURCES FB-EVT-150, FB-ENG-008, FB-INS-002

The full report of Hayward, in 6 sheets, each beside the Field Book plates that explain it

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Snow on the ground

Elsewhere in California

33 places, each with its own forecast and its own instruments.

Near Castro Valley

The nearest places, each with its own forecast and the instruments nearest it.

Near Castro Valley

River and lake gauges