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Half Moon Bay, California

City in San Mateo County, California

Air quality

The air at Half Moon Bay

Index 42, good, led by fine particles. Read at 1 AM from its reporting area, Redwood City (CA), 12 miles off.

42Good
  • Fine particles (PM2.5)42Good13.1 mi
  • Ozone16Good15 ppb13.1 mi
  • Nitrogen dioxide12Good13.3 ppb13.1 mi
  • Carbon monoxide-0.3 ppm13.1 mi

The days ahead

Good each day through Tue Oct 20, led by ozone. Yesterday measured 46, good.

Smoke, the next 41 hours

Little smoke near the ground through Sat 5 PM: the index from smoke stays at 11 or under.

FriSat

Precipitation

What has fallen at Half Moon Bay

None in the last 3 days, to Fri 12 AM. 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 Half Moon Bay, the next 41 hours

Visibility stays 10 miles or more through Sat 5 PM.

FriSat

On the radar over Half Moon Bay, CaliforniaReflectivityStorm topsRain rateRain, last 24 hoursForecast temperatureForecast rain totalEvery picture

What is measuring near here

The 5 instruments nearest Half Moon Bay, how far away each one is, how high it stands, and what kind of measurement it makes. The nearest is 0.2 miles away.

measured now3 instruments

measured daily2 instruments

Half Moon Bay 0.8 SCA-SM-12

In a volunteer observer's own ground/0.2 mi away/70 ft/5 ft above here

precip, snowfall, snow depth

Rank-

Half Moon BayHMBC1

At a cooperative observer's station/0.9 mi away/23 ft/42 ft below here

snowfall, snow depth, precip, high, low

Rank122of 4,465

Station report

The weather at Half Moon Bay, drawn

The nearest airport reporting now, 5.0 mi from Half Moon Bay, California. From its report of Oct 16, 2026, 1:55 AM local time: 3 of its 6 sheets.

The sky

No cloud below 12,000 ft; visibility 9 mi.

Section of the sky over Half Moon Bay, height above the station to scale: no cloud detected below 12,000 feet, the reach of its ceilometer, and visibility of 9 mi.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT HAFFIG. A THE SKY OVER HALF MOON BAYSECTION, 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: 9 MI0510TITLEHalf Moon Bay, the skySTATION REPORT · ASOS HAFTYPESECTIONSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 1 of 6DATE2026-10-16IDSR-HAF-1DRAWN AS linework on paperSOURCES FB-SKY-001

The air

50.0 F with a dew point of 44.6 F, 82 per cent relative humidity. Air lifted from the station would cool to its dew point, where cloud forms, about 1,200 ft up.

Chart of the air at Half Moon Bay: temperature 50.0 degrees Fahrenheit and dew point 44.6, 82 per cent relative humidity; air lifted from the station cools along the dry rate and meets its dew point about 1,200 feet above the station; height to scale.1122334455667788AABBCCDDEE© 2026 STORM STATION 247THE FIELD BOOKSTATION REPORT HAFFIG. B THE AIR AT HALF MOON BAYTHE REPORTED TEMPERATURE AND DEW POINT, AND AIR LIFTED FROM THE STATION WITHOUT MIXING UNTIL IT SATURATES; HEIGHT ABOVE THE STATION TO SCALEFT ABOVE THE STATION01,0002,0003,00030 F40 F50 F60 FSATURATES 1,200 FT ABOVE THE STATION, AT 43.4 FTEMPERATURE 50.0 FDEW POINT 44.6 FSPREAD 5.4 FRELATIVE HUMIDITY 82 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 POINTTITLEHalf Moon Bay, the airSTATION REPORT · ASOS HAFTYPECHARTSCALEHEIGHT TO SCALEREVAS REPORTED SHEET 2 of 6DATE2026-10-16IDSR-HAF-2DRAWN AS linework on paperSOURCES FB-WAT-002, FB-ENG-011, FB-ENG-005

The wind

Calm.

Plan of the wind at Half Moon Bay, 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 HAFFIG. C THE WIND AT HALF MOON BAYPLAN, 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 FORCE73TITLEHalf Moon Bay, the windSTATION REPORT · ASOS HAFTYPEPLAN north upSCALENOT TO SCALEREVAS REPORTED SHEET 3 of 6DATE2026-10-16IDSR-HAF-3DRAWN AS linework on paperSOURCES FB-EVT-150, FB-ENG-008, FB-INS-002

The full report of Half Moon Bay, 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 Half Moon Bay

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

Near Half Moon Bay

River and lake gauges