Oregon · 13 m elevation

Barometric Pressure in Portland, OR

• 30.05Average pressure (inHg, sea level)
• 188.5Swing days a year · 24th of 50
• 86.1Big-swing days a year (≥10 hPa)
• 105.1Significant 24h drop days a year

Overview

Portland, OR averages 30.05 inHg (1017.6 hPa) with 188.5 significant pressure swing days a year — 23.7 in December but just 3.4 in July.

Portland sits at 30.05 inHg (1017.6 hPa) on average, measured at sea level, with a standard deviation of 0.20 inHg (6.7 hPa). Ninety percent of hours fall between roughly 29.72 inHg (1006.4 hPa) and 30.37 inHg (1028.6 hPa) — the 5th and 95th percentiles. The city sits at 13 meters, so there is almost nothing separating station pressure from sea-level pressure: mean surface pressure is 30.00 inHg (1016.0 hPa), about 0.05 inHg (1.6 hPa) below the sea-level figure. A home barometer reading raw station pressure will track the airport numbers closely.

Nationally, Portland is remarkably average. It ranks #24 of 50 cities for significant swing days — days with a 24-hour change of at least 0.18 inHg (6 hPa) — at 188.5 per year against a national median of 180.7. It ranks #25 for big-swing days at 86.1 per year, which is precisely the national median. It ranks #27 for standard deviation and #27 for sharpest single 24-hour drop. Four independent measures, four ranks between 24 and 27.

That averageness is an illusion produced by adding two very different halves of the year together. From November through March Portland behaves like a storm-track city; from June through September it is quieter than most of California. The annual totals split the difference and describe neither season accurately.

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.

On a typical Portland day, pressure moves 0.10 inHg (3.3 hPa) over 24 hours — the median absolute change. The 95th percentile is 0.37 inHg (12.5 hPa). Across the year the city logs 188.5 significant swing days of at least 0.18 inHg (6 hPa), 86.1 big-swing days of at least 0.30 inHg (10 hPa), and 105.1 drop days, where the significant 24-hour move is a fall. Falling pressure is the pattern many pressure-sensitive people report as a trigger, and Portland's falls are heavily seasonal: 13.9 drop days in January and 13.6 in December, against 1.6 in July.

Comparatively, Portland lands mid-pack. Seattle, the nearest peer on the same storm track, runs 203.8 swing days and 99.1 big-swing days — about 8 percent and 15 percent more than Portland. Denver, ranked #1 for swing days nationally, has 169.8 big-swing days, close to double Portland's 86.1. In the other direction, San Francisco records 80.6 swing days and 20.2 big-swing days, so Portland has roughly 2.3 times the swing days and 4.3 times the big-swing days of a city on the same coast. Miami, at 19.8 swing days, sees about a tenth of Portland's total.

For anyone tracking symptoms against a barometer, the practical read is that Portland is two cities. November through March delivers frequent and sometimes large pressure falls, and every one of the five sharpest 24-hour drops on record except the April 2022 event falls inside that window. July and August are the opposite: 3.4 and 6.2 swing days respectively, with August's spread of 0.10 inHg (3.32 hPa) the narrowest of any month. May at 12.5 swing days marks the transition down, and October at 17.4 marks it back up.

Seasonal patterns

Monthly mean pressure barely moves: February is the highest month at 30.10 inHg (1019.3 hPa), August the lowest at 29.99 inHg (1015.7 hPa), a spread of about 0.11 inHg (3.6 hPa) across the entire calendar. What changes dramatically is volatility. February's monthly standard deviation is 0.28 inHg (9.53 hPa); August's is 0.10 inHg (3.32 hPa) — nearly a threefold difference in how far pressure wanders from its baseline.

Swing counts tell the same story more bluntly. December averages 23.7 significant swing days, January 23.0, March 22.2, and February and April 19.7 each. July averages 3.4. December runs about seven times July's count. December, January and February together supply 66.4 swing days, roughly 35 percent of the annual total in a quarter of the year, while July and August combined contribute 9.6 days, about 5 percent. The driver is the Pacific storm track, which drops south over Oregon in the cool season and lifts north of the region under the summer East Pacific ridge.

The extremes cluster in the same window. The record low of 29.01 inHg (982.4 hPa) came at 07:00 on December 27, 2022, two hours after the largest 24-hour fall in the record — a 0.90 inHg (30.5 hPa) drop ending at 05:00 that morning. The record high, 30.71 inHg (1040.1 hPa), was set under a winter ridge on January 25, 2023. The next-largest 24-hour falls were 0.81 inHg (27.3 hPa) on November 26, 2019, 0.77 inHg (26.0 hPa) on February 17, 2016, another 0.77 inHg (26.0 hPa) on April 11, 2022, and 0.76 inHg (25.6 hPa) on December 26, 2024. The single sharpest six-hour fall was 0.50 inHg (17.1 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

• Seattle, WA
• Sacramento, CA
• San Francisco, CA
• San Jose, CA
• Fresno, CA
• Salt Lake City, UT

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