California · 91 m elevation

Barometric Pressure in Los Angeles, CA

• 29.97Average pressure (inHg, sea level)
• 45.6Swing days a year · 47th of 50
• 7.5Big-swing days a year (≥10 hPa)
• 19.9Significant 24h drop days a year

Overview

Los Angeles averages 45.6 significant pressure swing days a year vs a 180.7 national median, with mean pressure near 29.97 inHg (1014.9 hPa).

Los Angeles has one of the quietest barometers of any major U.S. city. Mean sea-level pressure over 2015-2024 was 29.97 inHg (1014.9 hPa), and the median hour sat at 29.96 inHg (1014.4 hPa). The 5th-to-95th percentile spread runs from 29.80 inHg (1009.2 hPa) to 30.17 inHg (1021.8 hPa) — a working range of well under half an inch of mercury. Standard deviation is 0.12 inHg (3.91 hPa), about 57% of the national median of 6.87 hPa.

The more telling number is how little pressure changes from one day to the next. The median 24-hour change is 0.05 inHg (1.6 hPa), essentially nothing. Even at the 95th percentile, a day's move is only 0.17 inHg (5.9 hPa) — below the 6 hPa threshold that defines a significant swing. Over six hours, the typical range is -0.09 to +0.07 inHg (-2.9 to +2.5 hPa). For most of the year the needle simply sits still.

Nationally, Los Angeles ranks #47 of 50 for significant swing days, #48 for big-swing days, and #48 for day-to-day variability. Only Tampa, San Diego, and Miami log fewer swing days, and Tampa still runs a higher standard deviation and more big swings than LA does. One practical note: at 91 m elevation, average station pressure is 29.65 inHg (1004.1 hPa), about 0.32 inHg (10.8 hPa) below the sea-level values airports and forecasts report. In a city with this little natural variation, an uncalibrated home barometer's offset is larger than most of the real weather signal, so set the instrument against a nearby official reading before reading anything into small moves.

Migraine & pressure-sensitivity outlook

• Low — under 6 hPa (0.18 inHg)
• Elevated — 6 to 10 hPa
• High — 10 hPa (0.30 inHg) or more
• Dashed outline = forecast (after today)

Association only. This calendar shows days when pressure changed — or is forecast to change — sharply over 24 hours, conditions associated with pressure sensitivity in some people. It is not a prediction of symptoms, not a diagnosis, and not medical advice. The 30 days of history are there so you can compare the days you actually felt something against what the barometer did. Talk to a clinician about headache or migraine management.

For people who track barometric pressure as a possible trigger, Los Angeles offers an unusually stable baseline. The city averages 45.6 significant swing days and 19.9 drop days per year — days with a significant 24-hour fall — plus just 7.5 big-swing days at or above 0.30 inHg (10 hPa). The national medians are 180.7 swing days and 86.1 big-swing days, so LA sees roughly a quarter of the median city's swing days, and the median big-swing count is about 11.5 times LA's. Against Denver, the most volatile city in the set, the ratios are roughly 6.2x for swing days and 22.6x for big swings.

Within California, Los Angeles sits between its coastal neighbors: San Francisco logs about 1.8 times as many swing days, while San Diego is quieter still, with LA at roughly 1.3 times San Diego's count. Miami is the national floor at 19.8 swing days; Los Angeles runs about 2.3 times that. Quiet, but not featureless.

The seasonal split matters more here than the annual totals. December is the busiest month at 8.8 swing days and 4.3 drop days, followed by January, February, and March at 3.6 drop days each. From May through October the counts are near zero, with June showing no significant swings at all. That leaves a defined November-through-March window rather than a year-round pattern. It also means that when a Pacific storm drives a 0.18 inHg (6 hPa) move through Los Angeles, it stands out sharply against a baseline this flat — the kind of abrupt change many pressure-sensitive people report as a trigger, even though such days are far rarer here than in most of the country.

Seasonal patterns

Nearly all of the year's pressure activity is compressed into the cool season. Los Angeles averages 45.6 significant swing days — a 24-hour change of at least 0.18 inHg (6 hPa) — and about 81% of them fall between November and March: December 8.8, January 8.2, February 7.9, March 7.3, November 4.8. Monthly variability peaks at 4.26 hPa in February and 4.16 hPa in January. These are the months when Pacific frontal systems and cutoff lows actually reach Southern California.

Summer is the opposite extreme. June averaged 0.0 significant swing days per year across the ten-year record; July managed 0.2 and August 0.5. Monthly standard deviation bottoms out at 1.91 hPa in July. With the East Pacific high anchored offshore and the marine-layer regime in charge, the barometer drifts rather than moves. The seasonal cycle in mean pressure is shallow too — from 30.08 inHg (1018.7 hPa) in January down to 29.88 inHg (1011.8 hPa) in September, a spread of only 0.20 inHg (6.9 hPa) across the whole calendar.

The extremes cluster in a few winter storms. The record low of 29.35 inHg (994 hPa) came at 2:00 p.m. on January 20, 2017 — the same timestamp as the largest 24-hour fall in the record, -0.55 inHg (-18.7 hPa). Seven days later, on January 27, 2017, pressure hit the record high of 30.40 inHg (1032.9 hPa). The entire ten-year range of 1.15 inHg (38.9 hPa) was bracketed inside a single week. The next largest 24-hour drops were -0.46 inHg (-15.7 hPa) on February 17, 2017, -0.44 inHg (-14.9 hPa) on February 21, 2019, -0.43 inHg (-14.6 hPa) on December 16, 2017, and -0.38 inHg (-12.8 hPa) on December 22, 2015 — every one of them in December, January, or February, and two within a month of each other in early 2017.

Month by month

Swing days: 24-hour change of at least 6 hPa (0.18 inHg). Drop days: 24-hour fall of at least 6 hPa. Averages per year, 2015–2024.

Records and extremes

Sharpest 24-hour drops, 2015–2024

Nearby cities

• San Diego, CA
• Fresno, CA
• Las Vegas, NV
• San Jose, CA
• San Francisco, CA
• Phoenix, AZ

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