PaloAltoWeather.com
Weather, Air Quality & Seismic Activity
Reading the wind gauge
The red needle points to where the wind is coming from, the way a weather vane turns into it: pointing at NNE, the wind is blowing from the north-northeast. It is hidden when the air is calm.
The lighter, shorter needle is the strongest gust of the last ten minutes, pointing to where that gust came from. There is none when nothing has gusted, and a gust from the wind’s own direction lies under the red needle.
The short arc inside the rim is today’s prevailing direction: where the wind has blown from since midnight, with the stronger winds counting for more.
| Measure | Reading | Reads as | Scale |
|---|---|---|---|
| Dew point | 50.1°F | ||
| Barometer | 30.150 inHg | ||
| AQI | 18 | PM2.5 3 µg/m³ | |
| UV Index | 0.0 | ||
| Radiation | 47 W/m² | ||
| CO2 | 464 ppm |
The week ahead
The chart is the past seven days this station recorded, then the week the National Weather Service forecasts, on one temperature scale, with the nights shaded. Above it, each day’s forecast: its sky, its high and its low (a dash where the forecast no longer carries that half of the day, as today’s high after dark), and the droplet, the chance of measurable precipitation, the likelier of the day’s and the night’s. Under 15% it is left blank, as weather.gov does, so no droplet means no meaningful chance.
The 7 Day page has the whole forecast, with wind and each day’s daylight.
Patchy fog before 10am. Partly sunny. High near 72, with temperatures falling to around 68 in the afternoon. Northwest wind 1 to 5 mph.
7-Day and Hourly Forecast pages →Solar radiation and UV
Solar radiation is the sunlight arriving on a level surface, in watts per square meter (W/m²). A clear summer noon here brings about 1,000; a low winter sun, clouds, early morning and evening bring far less, and night is zero.
UV index is the strength of the sunburning part of that light: 3 and up calls for protection, 8 and up for avoiding the midday sun.
Evapotranspiration
Evapotranspiration (ET) is the water the ground gives back to the air: evaporation from soil and surfaces, plus what plants draw up and breathe out through their leaves.
The station estimates it from sunshine, temperature, humidity and wind, as the water a well-watered lawn would lose. Set beside rain, it tells you whether the ground is gaining water or drying out, and about how much irrigation would replace it.
Wind RMS and vector average
Wind RMS is the root-mean-square of the wind speeds: square each reading, average the squares, take the square root. It weighs the stronger winds more than a plain average does, so it always reads at or above the average, and the wider the gap between the two, the gustier the wind. The wind’s push on a wall or a sail grows with the square of its speed, so RMS is the steady wind that would have pushed as hard.
Vector average adds the readings as arrows: a wind that holds its direction keeps its speed, and one that swings around cancels itself out. Its direction is where the wind blew from on balance.
Patchy fog before 10am. Partly sunny. High near 72, with temperatures falling to around 68 in the afternoon. Northwest wind 1 to 5 mph.
7-Day and Hourly Forecast pages →Sun and moon
The strip across the top is today, midnight to midnight, as on the Celestial page: the night, the three twilights and the day as bands, a tick where the sun and the moon each rise and set, and a line that moves with the time now.
Under it are today’s sunrise and sunset with tomorrow’s, the moon’s phase and its rise and set, the next new or full moon, the next equinox or solstice, and an eclipse when one is coming. Twilight & daylight, below, has its own (i).
Nearby
The official monitor is the Bay Area Air District’s nearest to this station, with the EPA’s NowCast AQI for PM 2.5 through the last hour it has reported, beside this station’s own reading now. The two differ by design: a regulatory instrument some miles away against a low-cost sensor here, and the monitor’s hour arrives some time after it ends. Its readings are preliminary, not yet verified, and may change.
The fires are NASA FIRMS’s detections of the last 24 hours within the reach shown, each one heat seen from orbit by the VIIRS instruments on two satellites that pass over a few times a day, grouped into fires and placed by the nearest detection; steady hot spots such as refinery flares are left out. Not every detection is a wildfire, and none says where the smoke goes.
The Air quality gauge’s card on the Gauges page has the detail: the monitor beside this station hour by hour, the district’s forecast, and every fire.