California · 98 m elevation

Barometric Pressure in Fresno, CA

• 29.98Average pressure (inHg, sea level)
• 72.3Swing days a year · 45th of 50
• 15.1Big-swing days a year (≥10 hPa)
• 34.5Significant 24h drop days a year

Overview

Fresno averages 29.98 inHg (1015.1 hPa) and just 72.3 significant pressure-swing days a year — 45th of 50 US cities. Winter carries almost all of them.

Fresno's barometer is one of the quietest in the country, and its typical day is genuinely uneventful. Mean sea-level pressure over 2015–2024 was 29.98 inHg (1015.1 hPa), with the middle of the distribution running from 29.75 inHg (1007.3 hPa) at the 5th percentile to 30.26 inHg (1024.8 hPa) at the 95th. The median 24-hour change is 0.06 inHg (1.9 hPa) — small enough that most people would never notice it without an instrument.

Nationally, Fresno ranks #45 of 50 for significant swing days (72.3 per year, against a national median of 180.7) and #45 for big-swing days (15.1 per year, against a median of 86.1). The median US city sees about 2.5 times Fresno's swing days and 5.7 times its big-swing days. Denver, the most volatile city in the set, records 3.9 times Fresno's swing days and 11.2 times its big-swing days. Among California cities Fresno lands in the middle: Sacramento logs about 18% more swing days (85.3), while Fresno records about 1.6 times as many as Los Angeles (45.6).

One wrinkle worth noting: Fresno's standard deviation of 0.16 inHg (5.51 hPa) ranks #39, better than its #45 swing rank. That gap exists because much of Fresno's variance is seasonal drift rather than day-to-day motion — the January mean sits at 30.13 inHg (1020.5 hPa) while June runs 29.84 inHg (1010.5 hPa). At 98 m elevation, station pressure averages 29.63 inHg (1003.5 hPa), about 0.34 inHg (11.6 hPa) below the sea-level figures quoted in forecasts. An uncalibrated home barometer in Fresno will read near 29.63 inHg on an ordinary day, not 29.98.

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, Fresno is a low-frequency city with a concentrated risk window. It records 72.3 days a year with a 24-hour change of at least 0.18 inHg (6 hPa), and 34.5 of those are falls rather than rises. Only 15.1 days a year reach the 0.30 inHg (10 hPa) big-swing threshold. The 95th-percentile 24-hour move is 0.21 inHg (7.1 hPa), and the sharpest 6-hour fall on record is 0.32 inHg (11.0 hPa) — the kind of rapid change many pressure-sensitive people report as a trigger, but one that shows up here rarely.

The seasonal split matters more than the annual total. December and January each deliver about 6.5 and 6.4 drop days, and March adds 5.8; July delivers none at all, and June and August produce 0.2 each. Practically, the conditions some people associate with symptoms are packed into roughly four months, from December through March, and largely absent from June through September. Tracking a barometer in Fresno is likely to be most informative in winter and close to pointless in midsummer.

Against other cities, the contrast is stark. The median US city sees 180.7 swing days and 86.1 big-swing days a year; Fresno sees 72.3 and 15.1. Denver residents encounter 11.2 times as many big-swing days. Within California, Fresno sits between Sacramento (85.3 swing days, 23.0 big) and Los Angeles (45.6 and 7.5), and runs close to Phoenix (75.8 and 17.7). If pressure changes are among the things you notice, Fresno offers long stretches of stability broken by a handful of Pacific systems — a different pattern from the year-round churn of the Midwest and Northeast.

Seasonal patterns

Fresno's pressure year is close to binary. December and January are the active months, with 12.2 and 11.9 significant swing days respectively, followed by March (10.8) and February (10.2). Roughly 45 of the year's 72.3 swing days fall in the December-through-March window, and January carries the highest month-to-month variability at 0.16 inHg (5.58 hPa). This is the Pacific storm track season, when frontal systems and atmospheric-river landfalls push far enough inland to register in the San Joaquin Valley.

Summer is a flatline. July averages 0.3 swing days and 0.0 drop days per year; August adds 0.5 swing days and 0.2 drop days. July's standard deviation of 0.07 inHg (2.46 hPa) is less than half January's. The Pacific subtropical high and the persistent valley thermal low keep the barometer parked near 29.85 inHg (1010.7 hPa) for weeks at a time, and 24-hour changes of any consequence essentially stop.

The extremes cluster in exactly the months you'd expect. The record low of 29.29 inHg (992.0 hPa) came on 17 February 2017 at 18:00, two hours after the sharpest 24-hour fall on record — a 0.64 inHg (21.7 hPa) drop ending at 16:00 that same day. The record high of 30.60 inHg (1036.3 hPa) followed on 28 January 2017. Other steep falls: 0.51 inHg (17.2 hPa) ending 20 January 2017, 0.48 inHg (16.2 hPa) on 21 March 2023, 0.46 inHg (15.5 hPa) on 21 February 2023, and 0.45 inHg (15.4 hPa) on 3 October 2015. Even Fresno's worst drop is modest by national standards — Boston's maximum is 2.4 times larger — and Fresno ranks #39 of 50 on that measure.

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

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