California · 33 m elevation

Barometric Pressure in San Jose, CA

• 30.02Average pressure (inHg, sea level)
• 77.4Swing days a year · 43rd of 50
• 18.1Big-swing days a year (≥10 hPa)
• 37.7Significant 24h drop days a year

Overview

San Jose averages 77.4 significant pressure-swing days a year vs a 180.7 national median — and 62% of them fall in December through March.

San Jose sits at 33 meters (108 feet) above sea level, and its sea-level-adjusted pressure averages 30.02 inHg (1016.5 hPa) across the 2015-2024 record. Half of all hours land within a hair of 30.00 inHg (1016 hPa), and the middle 90% of readings fall between 29.81 inHg (1009.4 hPa) and 30.27 inHg (1025 hPa) — a span of just 0.46 inHg (15.6 hPa). The standard deviation is 0.14 inHg (4.83 hPa), which ranks #45 of the 50 cities analyzed and sits well below the national median of 0.20 inHg (6.87 hPa).

The elevation correction here is small but real. Mean station pressure — what an uncorrected barometer on a San Jose shelf actually reads — is 29.90 inHg (1012.5 hPa), about 0.12 inHg (4.0 hPa) below the sea-level figure quoted in forecasts. A home unit that reads consistently about a tenth of an inch low is showing altitude, not a defect.

By national standards San Jose is quiet. It logs 77.4 significant swing days per year (24-hour change of 0.18 inHg / 6 hPa or more), against a national median of 180.7 — the median US city in this set sees 2.3 times as many. Big-swing days of 0.30 inHg (10 hPa) or more come 18.1 times a year versus a median of 86.1, a 4.8x gap. Denver, the most volatile city in the set, runs 3.6 times San Jose's swing days and 9.4 times its big-swing days. San Jose ranks #43 of 50 on both swing counts. It is not, however, California's calmest: Los Angeles sees 45.6 swing days and San Diego 35.4, so San Jose runs 1.7x and 2.2x those cities respectively. Its closest statistical twin is San Francisco at 80.6 swing days and 20.2 big-swing days — essentially the same pressure climate.

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 symptom trigger, San Jose ranks among the least active cities in this set — with a well-defined exception. A typical 24-hour change here is just 0.06 inHg (2 hPa), and the 95th-percentile change is 0.21 inHg (7.2 hPa). Significant swings come 77.4 days a year and drops — falls of 0.18 inHg (6 hPa) or more — come 37.7 days a year. The median US city in the set sees 180.7 swing days.

What matters more than the annual count is when those days occur. Drop days cluster hard: 7.0 in January, 6.3 in March, 6.1 in December, versus 0.3 in July and 0.6 in August. That works out to a falling-pressure day roughly every four or five days in January, and close to none across the summer. The clustering itself is worth knowing — Denver and Boston post 281.6 and 257.6 swing days a year, totals large enough that no comparable quiet stretch exists.

Low frequency does not mean low magnitude. San Jose ranks #36 of 50 on its single largest 24-hour drop, higher than its #43 rankings for swing frequency, meaning the storms that do arrive can produce falls comparable to those in far more volatile cities — 0.78 inHg (26.3 hPa) in a day, as on February 17, 2017. These are the conditions many pressure-sensitive people report as triggers, and in San Jose they arrive a handful of times a winter rather than steadily year-round. Within the region, San Francisco at 80.6 swing days is statistically indistinguishable, Sacramento at 85.3 is marginally more active, and Fresno at 72.3 marginally less.

Seasonal patterns

The annual average badly undersells the seasonal split. San Jose's barometer is close to motionless from June through September and does nearly all of its work between December and March. January alone carries 13.0 swing days, March 12.6, December 12.0, and February 10.7 — 48.3 of the year's 77.4 swing days, or 62%, in four months. Monthly variability follows the same curve: standard deviation runs 0.18 inHg (5.97 hPa) in January and collapses to 0.07 inHg (2.36 hPa) in July, when the city averages 0.7 swing days. August adds 0.9 and June 1.4.

The mechanism is straightforward. In summer the North Pacific High parks offshore and pressure has little to react to. From late fall through early spring, Pacific frontal systems and atmospheric-river storms track across the coast, and each passage drags the barometer down and back up. Mean pressure tracks the same rhythm, peaking at 30.12 inHg (1020 hPa) in January and bottoming at 29.92 inHg (1013.3 hPa) in September.

The extremes are all cold-season. The record low of 29.15 inHg (987.1 hPa) came at 6 p.m. on February 17, 2017 — the same storm that produced the largest 24-hour fall in the record, 0.78 inHg (26.3 hPa) ending at noon that day. The next four largest drops: 0.73 inHg (24.6 hPa) on March 21, 2023; 0.56 inHg (18.8 hPa) on February 4, 2024; and two of 0.53 inHg (17.8 hPa) on January 20, 2017 and November 27, 2019. Every one falls between November and March. The record high, 30.60 inHg (1036.2 hPa), was set January 5, 2020. The sharpest six-hour fall on record is 0.40 inHg (13.7 hPa), and the largest 24-hour rise is 0.68 inHg (23 hPa).

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 Francisco, CA
• Sacramento, CA
• Fresno, CA
• Los Angeles, CA
• Las Vegas, NV
• San Diego, CA

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