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Alum Rock, California

Community in Santa Clara County, California

Air quality

The air at Alum Rock

Index 51, moderate, led by ozone. Read at 7 PM from its reporting area, San Jose (CA), 5 miles off.

51Moderate
  • Fine particles (PM2.5)49Good2.7 mi
  • Ozone51Moderate40 ppb13.2 mi
  • Nitrogen dioxide18Good19.9 ppb2.7 mi
  • Carbon monoxide-0.6 ppm2.7 mi

The days ahead

Highest moderate, Sat Oct 17, led by fine particles. Yesterday measured 49, good.

Smoke, the next 41 hours

Little smoke near the ground through Sat 11 AM: the index from smoke stays at 17 or under.

ThuFriSat

Precipitation

What has fallen at Alum Rock

None in the last 3 days, to Thu 6 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 Alum Rock, the next 41 hours

Visibility stays 10 miles or more through Sat 11 AM.

ThuFriSat

On the radar over Alum Rock, CaliforniaReflectivityStorm topsRain rateRain, last 24 hoursForecast temperatureForecast rain totalEvery picture

What is measuring near here

The 6 instruments nearest Alum Rock, how far away each one is, how high it stands, and what kind of measurement it makes. The nearest is 1.1 miles away.

measured now4 instruments

measured daily2 instruments

San Jose 6.0 NCA-SC-78

In a volunteer observer's own ground/1.6 mi away/237 ft/79 ft above here

precip, snowfall, snow depth

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Station report

The weather at San Jose/Reid/Hillv, drawn

The nearest airport reporting now, 2.6 mi from Alum Rock, California. From its report of Oct 15, 2026, 6:47 PM local time: 3 of its 6 sheets.

The sky

Clear; visibility 10 mi or more.

Section of the sky over San Jose/Reid/Hillv, height above the station to scale: a clear sky, and visibility of 10 mi or more.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT RHVFIG. A THE SKY OVER SAN JOSE/REID/HILLVSECTION, 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 STATIONCLEARVISIBILITY, MILES: 10 MI OR MORE0510TITLESan Jose/Reid/Hillv, the skySTATION REPORT · ASOS RHVTYPESECTIONSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 1 of 6DATE2026-10-16IDSR-RHV-1DRAWN AS linework on paperSOURCES FB-SKY-001

The air

78.8 F with a dew point of 42.8 F, 28 per cent relative humidity. Air lifted from the station would cool to its dew point, where cloud forms, about 8,200 ft up.

Chart of the air at San Jose/Reid/Hillv: temperature 78.8 degrees Fahrenheit and dew point 42.8, 28 per cent relative humidity; air lifted from the station cools along the dry rate and meets its dew point about 8,200 feet above the station; height to scale.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT RHVFIG. B THE AIR AT SAN JOSE/REID/HILLVTHE REPORTED TEMPERATURE AND DEW POINT, AND AIR LIFTED FROM THE STATION WITHOUT MIXING UNTIL IT SATURATES; HEIGHT ABOVE THE STATION TO SCALEFT ABOVE THE STATION02,0004,0006,0008,00010,00020 F40 F60 F80 FSATURATES 8,200 FT ABOVE THE STATION, AT 35.2 FTEMPERATURE 78.8 FDEW POINT 42.8 FSPREAD 36.0 FRELATIVE HUMIDITY 28 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 POINTTITLESan Jose/Reid/Hillv, the airSTATION REPORT · ASOS RHVTYPECHARTSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 2 of 6DATE2026-10-16IDSR-RHV-2DRAWN AS linework on paperSOURCES FB-WAT-002, FB-ENG-011, FB-ENG-005

The wind

Calm.

Plan of the wind at San Jose/Reid/Hillv, north up: calm; beside it the Beaufort scale from calm to hurricane force, force 0, calm, marked.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT RHVFIG. C THE WIND AT SAN JOSE/REID/HILLVPLAN, NORTH UP: THE WIND AS REPORTED, AND WHERE IT SITS ON THE BEAUFORT SCALENESWTHE STATIONCALMBEAUFORT FORCELEAST WIND, MPH0CALM0NOW, 0 MPH1LIGHT AIR12LIGHT BREEZE43GENTLE BREEZE84MODERATE BREEZE135FRESH BREEZE196STRONG BREEZE257NEAR GALE328GALE399STRONG GALE4710STORM5511VIOLENT STORM6412HURRICANE FORCE73TITLESan Jose/Reid/Hillv, the windSTATION REPORT · ASOS RHVTYPEPLAN north upSCALENOT TO SCALEREVAS REPORTED SHEET 3 of 6DATE2026-10-16IDSR-RHV-3DRAWN AS linework on paperSOURCES FB-EVT-150, FB-ENG-008, FB-INS-002

The full report of San Jose/Reid/Hillv, 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 Alum Rock

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

Near Alum Rock

River and lake gauges