Why Are Forecasters Always Talking About The Barometer During A Storm?
KPIX 5 Morning Weather Anchor Roberta Gonzales answers the questions you never get to ask on-air.
Q: What exactly does a barometer measure?
A: I'm sure you hear the word "barometer" tossed around when referring to the Weather. Last Thursday in a 24 hour frame, the Bay Area experienced up to 10 inches of rain and a tremendous drop in barometric pressure.
KPIX Viewer Bill Sherman, from Hayward, contacted me and shared just how low the barometer dropped during the storm's arrival on Thursday. Before you take a peek at his very cool time lapse video, let me explain the function of the barometer.
Surface air pressure is measured by a barometer. A barometer indicates pressure in units known as millibars (mbs) or inches of mercury. Barometers are the standard for measuring surface air pressure for weather purposes.
If you live at sea level near the equator, standard 'normal' sea level air pressure would be about 1000 mbs. If a relatively strong high-pressure system were to move over your home, the barometer might indicate the pressure at around 1020 mbs.
Conversely, if a strong low-pressure system were to move in, the barometer might register about 970 mbs. (Surface air pressure tends to be less as you travel north or go up in elevation). Of note, both high and low pressure systems typically cover at least many hundreds of miles in area, and move rather slowly. So you typically won't see a change in pressure from one extreme to the other in a matter of hours, but more over a time periods of days or weeks. It's doubtful you feel change in air pressure, but you'll certainly see the weather changes associated with pressure change. Under high pressure, weather is typically fair, cloudless skies.
But under low pressure, rain, wind and stormy conditions prevail.
Please feel free to send me your questions, pictures or observations at: Gonzales@kpix.cbs.com