Washington · 59 m elevation

Barometric Pressure in Seattle, WA

• 30.03Average pressure (inHg, sea level)
• 203.8Swing days a year · 18th of 50
• 99.1Big-swing days a year (≥10 hPa)
• 117.4Significant 24h drop days a year

Overview

Seattle averages 203.8 significant pressure-swing days a year, but the barometer splits sharply by season: 25.7 in December versus just 3.0 in July.

Seattle's mean sea-level pressure over 2015–2024 was 30.03 inHg (1017.1 hPa), with a median of 30.04 inHg (1017.3 hPa). Most hours fall in a fairly tight band: the 5th percentile is 29.67 inHg (1004.8 hPa) and the 95th is 30.37 inHg (1028.3 hPa). The standard deviation is 0.21 inHg (7.02 hPa), just above the national median of 6.87 hPa and good for a rank of #22 of 50.

The city sits at 59 meters, so the elevation correction is small but visible on a home instrument. The average station (uncorrected) pressure is 29.82 inHg (1009.9 hPa) against the 30.03 inHg (1017.1 hPa) sea-level average — a gap of about 0.21 inHg (7.2 hPa). If your barometer reads consistently low against the airport or forecast value, that offset is the reason. It does not affect trends, only the absolute number.

Nationally, Seattle ranks #18 of 50 for significant swing days at 203.8 per year (national median 180.7) and #23 for big-swing days at 99.1 (median 86.1). Those middle-of-the-pack ranks are the least useful numbers on this page. Seattle does not run one pressure climate — it runs two, and averaging them together hides both.

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 the barometer, Seattle is best understood as two cities. The typical 24-hour change is 0.11 inHg (3.6 hPa), which is unremarkable, and the 95th-percentile change is 0.40 inHg (13.4 hPa). Across the year there are 203.8 days with a change of at least 0.18 inHg (6 hPa), 99.1 days at or above 0.30 inHg (10 hPa), and 117.4 drop days — significant 24-hour falls, the direction many pressure-sensitive people report as the more troublesome one.

Those days are heavily concentrated. December brings 15.6 drop days and January 15.0; July brings 1.4 and August 2.1. July is the floor at 3.0 swing days, with August at 6.3 and September at 10.0 — a stretch when Seattle's barometer is about as quiet as anywhere in the country. From November through March, by contrast, the city delivers conditions many pressure-sensitive people report as triggers on the majority of days in the month.

Comparatively, Seattle runs 1.08 times Portland's swing days (203.8 vs 188.5) and 1.15 times its big-swing days (99.1 vs 86.1) — the two cities share the same storm track and behave similarly. Against San Francisco, Seattle has 2.5 times the swing days and 4.9 times the big-swing days, despite both being West Coast marine climates. Against Denver, the most volatile city in the set at 281.6 swing days, Seattle runs about 72 percent as many. If you are weighing a move, the relevant question is not Seattle's annual average but whether a very quiet summer offsets a five-month winter that behaves like a top-tier volatility city.

Seasonal patterns

The split is stark. December produces 25.7 significant swing days, January 25.0, March 23.7, November 22.9 and February 22.0. July produces 3.0. That is a factor of roughly 8.6 between the busiest and quietest months. Monthly variability tells the same story: the standard deviation is 0.29 inHg (9.72 hPa) in January and 0.10 inHg (3.33 hPa) in July. For scale, Seattle's January variability exceeds the year-round standard deviation of Salt Lake City (8.64 hPa), the most variable city in this 50-city set, while Seattle's July variability is below Miami's annual figure of 3.57 hPa — Miami being the calmest city on the list.

The driver is the North Pacific storm track. From roughly October through March, maturing lows cross the Gulf of Alaska and drive into Puget Sound in sequence, each one dropping and then rebuilding the barometer. In summer the East Pacific High parks offshore and deflects that track north, leaving a shallow marine-layer regime with almost nothing for the barometer to do. Notably, the monthly mean pressure barely moves all year — from 30.01 inHg (1016.1 hPa) in August to 30.06 inHg (1018.1 hPa) in February. Seattle's seasonality is entirely in the variance, not the level.

All five of the sharpest 24-hour drops on record fell between October and February. The largest was a 0.91 inHg (30.7 hPa) fall ending at midday on December 27, 2022 — the same storm that produced the all-time low of 28.87 inHg (977.7 hPa) at 07:00 that morning. Next are 0.87 inHg (29.3 hPa) ending November 13, 2020; 0.86 inHg (29.1 hPa) ending December 26, 2024; 0.71 inHg (24.2 hPa) ending February 17, 2016; and 0.71 inHg (23.9 hPa) ending October 13, 2016. The record high, 30.73 inHg (1040.7 hPa), came on January 25, 2023 — one month after the record low, which is a fair summary of a Seattle winter. The steepest six-hour move on record was a 0.53 inHg (18 hPa) fall, and the largest 24-hour rise was 1.08 inHg (36.5 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

• Portland, OR
• Sacramento, CA
• San Francisco, CA
• Salt Lake City, UT
• San Jose, CA
• Fresno, CA

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