Airport weather · KSEA

SEA Airport Weather by Month

Weather at Seattle-Tacoma International Airport, 2000 to 2025: flight categories, fog, storms and runway crosswinds from the airport's own hourly reports.

Compiled by PilotPassionReviewed by Keith M.
Updated October 20, 2026Cited 3 sources
The Seattle-Tacoma International Airport control tower rising above airport buildings under a blue sky with broken cloud
The control tower at Seattle-Tacoma International Airport

VFR hours

73.4%

18.9% marginal VFR; 7.8% IFR or worse

Highest IFR-or-worse share

January

14.9% of hours

Lowest IFR-or-worse share

April

3.5% of hours

Fog, average year

141 hours

1.62% of hourly reports

Thunderstorms, average year

3 hours

Storms reported at the airport

Crosswind coverage at 13 kt

97.9%

At least one runway axis at or below this component

Precipitation, average year

38.8 in

156 wet days

On this page
  1. 01SEA weather, month by month
  2. 02Flight categories at SEA
  3. 03Weather by time of day
  4. 04Fog
  5. 05Thunderstorms, precipitation and snow
  6. 06Wind and runway crosswinds
  7. 07Temperature, humidity and daylight
  8. 08Check a date
  9. 09Year to year
  10. 10SEA, RNT, BFI compared
  11. 11Best and worst months by hazard
  12. 12Records and extremes
  13. 13Planning with SEA climate records
  14. 14Questions about SEA weather
  15. 15Sources and method

SEA reports VFR in 73.4% of hours and IFR or worse in 7.8%. The IFR-or-worse category means a ceiling below 1,000 feet or visibility below 3 statute miles.

January has the highest share of IFR-or-worse hours, at 14.9%. April has the lowest, at 3.5%.

This page uses 226,690 hourly reports from 2000 to 2025, covering 99.46% of hours in the period. Daily temperature and precipitation come from GHCN-Daily station USW00024233.

01

SEA weather, month by month

Pick a month to see the data.

January

14.9% of hours at IFR or worse.

January ranks 1 of 12 for the share of hours at IFR or worse, from highest to lowest: 14.9%. VFR accounts for 60.0%.

The highest IFR-or-worse share is 4 am to 5 am (19.9%); the lowest is 6 pm to 7 pm (8.9%). Times are local.

Average daily highs are 47°F and lows 37°F. Precipitation averages 5.7 in across 18.6 wet days.

Fog appears in 4.72% of hours; thunderstorms at the airport in 0.01%; wind or gusts of 25 kt or more in 2.6%.

Snowfall averages 0.8 in in this month.

VFR hours
60.0%
IFR or worse
14.9%
High / low
47°F / 37°F
Daylight
8.8 h
Precipitation
5.7 in
Snowfall
0.8 in
Fog hours
4.72%
25 kt+ wind
2.6%

February

9.4% of hours at IFR or worse.

February ranks 5 of 12 for the share of hours at IFR or worse, from highest to lowest: 9.4%. VFR accounts for 66.6%.

The highest IFR-or-worse share is 7 am to 8 am (16.6%); the lowest is 3 pm to 4 pm (3.7%). Times are local.

Average daily highs are 49°F and lows 37°F. Precipitation averages 3.6 in across 16.1 wet days.

Fog appears in 1.97% of hours; thunderstorms at the airport in 0.02%; wind or gusts of 25 kt or more in 3.1%.

Snowfall averages 2.0 in in this month.

VFR hours
66.6%
IFR or worse
9.4%
High / low
49°F / 37°F
Daylight
10.2 h
Precipitation
3.6 in
Snowfall
2.0 in
Fog hours
1.97%
25 kt+ wind
3.1%

March

5.1% of hours at IFR or worse.

March ranks 7 of 12 for the share of hours at IFR or worse, from highest to lowest: 5.1%. VFR accounts for 73.0%.

The highest IFR-or-worse share is 7 am to 8 am (10.3%); the lowest is 3 pm to 4 pm (1.9%). Times are local.

Average daily highs are 53°F and lows 39°F. Precipitation averages 4.0 in across 17.5 wet days.

Fog appears in 0.50% of hours; thunderstorms at the airport in 0.01%; wind or gusts of 25 kt or more in 2.3%.

Snowfall averages 0.2 in in this month.

VFR hours
73.0%
IFR or worse
5.1%
High / low
53°F / 39°F
Daylight
11.8 h
Precipitation
4.0 in
Snowfall
0.2 in
Fog hours
0.50%
25 kt+ wind
2.3%

April

3.5% of hours at IFR or worse.

April ranks 12 of 12 for the share of hours at IFR or worse, from highest to lowest: 3.5%. VFR accounts for 77.9%.

The highest IFR-or-worse share is 8 am to 9 am (8.9%); the lowest is 8 pm to 9 pm (0.9%). Times are local.

Average daily highs are 58°F and lows 43°F. Precipitation averages 2.9 in across 14.7 wet days.

Fog appears in 0.12% of hours; thunderstorms at the airport in 0.01%; wind or gusts of 25 kt or more in 1.4%.

Snowfall averages 0.0 in in this month.

VFR hours
77.9%
IFR or worse
3.5%
High / low
58°F / 43°F
Daylight
13.6 h
Precipitation
2.9 in
Snowfall
None to trace
Fog hours
0.12%
25 kt+ wind
1.4%

May

4.1% of hours at IFR or worse.

May ranks 10 of 12 for the share of hours at IFR or worse, from highest to lowest: 4.1%. VFR accounts for 79.6%.

The highest IFR-or-worse share is 7 am to 8 am (11.2%); the lowest is 2 pm to 3 pm (0.4%). Times are local.

Average daily highs are 65°F and lows 48°F. Precipitation averages 1.9 in across 11.2 wet days.

Fog appears in 0.21% of hours; thunderstorms at the airport in 0.05%; wind or gusts of 25 kt or more in 0.6%.

Snowfall averages 0.0 in in this month.

VFR hours
79.6%
IFR or worse
4.1%
High / low
65°F / 48°F
Daylight
15.1 h
Precipitation
1.9 in
Snowfall
None to trace
Fog hours
0.21%
25 kt+ wind
0.6%

June

3.9% of hours at IFR or worse.

June ranks 11 of 12 for the share of hours at IFR or worse, from highest to lowest: 3.9%. VFR accounts for 80.0%.

The highest IFR-or-worse share is 7 am to 8 am (12.1%); the lowest is 9 pm to 10 pm (0.3%). Times are local.

Average daily highs are 71°F and lows 53°F. Precipitation averages 1.5 in across 9.3 wet days.

Fog appears in 0.09% of hours; thunderstorms at the airport in 0.06%; wind or gusts of 25 kt or more in 0.4%.

Snowfall averages 0.0 in in this month.

VFR hours
80.0%
IFR or worse
3.9%
High / low
71°F / 53°F
Daylight
15.9 h
Precipitation
1.5 in
Snowfall
None to trace
Fog hours
0.09%
25 kt+ wind
0.4%

July

4.7% of hours at IFR or worse.

July ranks 9 of 12 for the share of hours at IFR or worse, from highest to lowest: 4.7%. VFR accounts for 84.1%.

The highest IFR-or-worse share is 7 am to 8 am (16.2%); the lowest is 5 pm to 6 pm (0.0%). Times are local.

Average daily highs are 78°F and lows 57°F. Precipitation averages 0.4 in across 3.5 wet days.

Fog appears in 0.48% of hours; thunderstorms at the airport in 0.07%; wind or gusts of 25 kt or more in 0.1%.

Snowfall averages 0.0 in in this month.

VFR hours
84.1%
IFR or worse
4.7%
High / low
78°F / 57°F
Daylight
15.6 h
Precipitation
0.4 in
Snowfall
None to trace
Fog hours
0.48%
25 kt+ wind
0.1%

August

5.0% of hours at IFR or worse.

August ranks 8 of 12 for the share of hours at IFR or worse, from highest to lowest: 5.0%. VFR accounts for 81.9%.

The highest IFR-or-worse share is 7 am to 8 am (17.8%); the lowest is 1 pm to 2 pm (0.4%). Times are local.

Average daily highs are 77°F and lows 57°F. Precipitation averages 0.9 in across 4.8 wet days.

Fog appears in 0.44% of hours; thunderstorms at the airport in 0.08%; wind or gusts of 25 kt or more in 0.1%.

Snowfall averages 0.0 in in this month.

VFR hours
81.9%
IFR or worse
5.0%
High / low
77°F / 57°F
Daylight
14.3 h
Precipitation
0.9 in
Snowfall
None to trace
Fog hours
0.44%
25 kt+ wind
0.1%

September

7.3% of hours at IFR or worse.

September ranks 6 of 12 for the share of hours at IFR or worse, from highest to lowest: 7.3%. VFR accounts for 78.6%.

The highest IFR-or-worse share is 7 am to 8 am (20.3%); the lowest is 3 pm to 4 pm (1.7%). Times are local.

Average daily highs are 71°F and lows 54°F. Precipitation averages 1.8 in across 9.0 wet days.

Fog appears in 1.14% of hours; thunderstorms at the airport in 0.06%; wind or gusts of 25 kt or more in 0.2%.

Snowfall averages 0.0 in in this month.

VFR hours
78.6%
IFR or worse
7.3%
High / low
71°F / 54°F
Daylight
12.7 h
Precipitation
1.8 in
Snowfall
None to trace
Fog hours
1.14%
25 kt+ wind
0.2%

October

11.4% of hours at IFR or worse.

October ranks 3 of 12 for the share of hours at IFR or worse, from highest to lowest: 11.4%. VFR accounts for 69.9%.

The highest IFR-or-worse share is 7 am to 8 am (23.9%); the lowest is 8 pm to 9 pm (3.9%). Times are local.

Average daily highs are 60°F and lows 47°F. Precipitation averages 4.1 in across 14.7 wet days.

Fog appears in 2.97% of hours; thunderstorms at the airport in 0.04%; wind or gusts of 25 kt or more in 1.5%.

Snowfall averages 0.0 in in this month.

VFR hours
69.9%
IFR or worse
11.4%
High / low
60°F / 47°F
Daylight
11.0 h
Precipitation
4.1 in
Snowfall
None to trace
Fog hours
2.97%
25 kt+ wind
1.5%

November

11.0% of hours at IFR or worse.

November ranks 4 of 12 for the share of hours at IFR or worse, from highest to lowest: 11.0%. VFR accounts for 66.6%.

The highest IFR-or-worse share is 5 am to 6 am (18.6%); the lowest is 5 pm to 6 pm (5.0%). Times are local.

Average daily highs are 51°F and lows 40°F. Precipitation averages 6.2 in across 17.9 wet days.

Fog appears in 3.36% of hours; thunderstorms at the airport in 0.03%; wind or gusts of 25 kt or more in 2.8%.

Snowfall averages 0.2 in in this month.

VFR hours
66.6%
IFR or worse
11.0%
High / low
51°F / 40°F
Daylight
9.4 h
Precipitation
6.2 in
Snowfall
0.2 in
Fog hours
3.36%
25 kt+ wind
2.8%

December

13.1% of hours at IFR or worse.

December ranks 2 of 12 for the share of hours at IFR or worse, from highest to lowest: 13.1%. VFR accounts for 61.6%.

The highest IFR-or-worse share is 8 am to 9 am (18.6%); the lowest is 4 pm to 5 pm (7.2%). Times are local.

Average daily highs are 46°F and lows 37°F. Precipitation averages 5.8 in across 18.9 wet days.

Fog appears in 3.40% of hours; thunderstorms at the airport in 0.01%; wind or gusts of 25 kt or more in 3.6%.

Snowfall averages 1.3 in in this month.

VFR hours
61.6%
IFR or worse
13.1%
High / low
46°F / 37°F
Daylight
8.5 h
Precipitation
5.8 in
Snowfall
1.3 in
Fog hours
3.40%
25 kt+ wind
3.6%

02

Flight categories at SEA

Pilots sort every weather report into four flight categories using the lowest cloud ceiling and the visibility. The chart shows how many hours each month fall short of VFR, split by how far short.

January has the highest share of IFR-or-worse hours. For LIFR alone, the highest share is in January; for MVFR it is in December.

Share of hours below VFR, by month

Percent of all hourly reports in each month that fell short of VFR.

0204060%40.0Jan33.4Feb26.9Mar22.1Apr20.4May20.0Jun16.0Jul18.1Aug21.4Sep30.1Oct33.4Nov38.5Dec
0204060%Jan40.0Feb33.4Mar26.9Apr22.1May20.4Jun20.0Jul16.0Aug18.1Sep21.4Oct30.1Nov33.4Dec38.5
  • LIFR
  • IFR
  • MVFR
View the numbers
Share of hours by flight category and month, SEA
MonthVFRMVFRIFRLIFRIFR or worse
January60.0%25.1%6.7%8.2%14.9%
February66.6%24.0%5.4%4.0%9.4%
March73.0%21.8%3.3%1.8%5.1%
April77.9%18.6%2.6%0.9%3.5%
May79.6%16.3%3.0%1.1%4.1%
June80.0%16.1%2.8%1.1%3.9%
July84.1%11.3%3.0%1.7%4.7%
August81.9%13.1%3.0%2.0%5.0%
September78.6%14.1%4.1%3.2%7.3%
October69.9%18.7%5.5%5.9%11.4%
November66.6%22.4%5.3%5.7%11.0%
December61.6%25.4%6.7%6.4%13.1%

The rest of each month is VFR. Hover or tap a bar for the full split.

Source: NOAA/NWS airport observations via Iowa Environmental Mesonet
VFR
Ceiling above 3,000 feet and visibility above 5 miles.
MVFR
Marginal VFR. Ceiling of 1,000 to 3,000 feet, or visibility of 3 to 5 miles.
IFR
Ceiling of 500 to under 1,000 feet, or visibility of 1 to under 3 miles.
LIFR
Ceiling under 500 feet, or visibility under 1 mile.

A ceiling counts only broken or overcast layers, or vertical visibility into fog or heavy precipitation. A few scattered clouds do not count.

Sky cover by month

Share of hours by the highest cloud cover reported.

0255075100%JanFebMarAprMayJunJulAugSepOctNovDec
0255075100%Jan100.1Feb99.9Mar100.0Apr100.0May100.0Jun100.1Jul100.0Aug100.0Sep100.0Oct100.0Nov100.0Dec100.0
  • Clear or few
  • Scattered
  • Broken
  • Overcast
View the numbers
Sky cover by month
MonthClear or fewScatteredBrokenOvercast
January14%8%22%56%
February15%10%25%49%
March12%11%30%46%
April15%14%31%40%
May18%15%32%35%
June19%17%34%31%
July42%16%23%20%
August36%17%26%21%
September31%14%27%28%
October22%11%27%41%
November15%10%26%49%
December12%8%24%56%
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

03

Weather by time of day

Each square is one month and one hour of the day (local time) and shows the share of hours that hit the condition you pick. The stronger the colour, the more likely.

Within January, the highest IFR-or-worse rate occurs 4 am to 5 am. The lowest occurs 6 pm to 7 pm.

Condition by month and hour of day

Local time. Pick a condition to repaint the grid.

12a3a6a9a12p3p6p9pJanFebMarAprMayJunJulAugSepOctNovDec
JFMAMJJASOND12a3a6a9a12p3p6p9p

Ceiling under 1,000 feet or visibility under 3 miles. Peak square: October, 7 am, 23.9% of hours.

Each square is one month and one hour, averaged over all years.

Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

04

Fog

1.62% of hours report fog, about 141 hours per year.

Fog has its highest monthly share in January and its lowest in June. Across all months, it is most frequent 7 am to 8 am.

The longest sequence of hourly fog reports lasts 35 hours. This counts routine reports, so short events between reports can be missed.

Share of hours with fog, by month

Fog reported by the station.

012345%4.72JanFebMarAprMay0.09JunJulAugSepOctNovDec
012345%Jan4.72Feb1.97Mar0.50Apr0.12May0.21Jun0.09Jul0.48Aug0.44Sep1.14Oct2.97Nov3.36Dec3.40
View the numbers
Share of hours with fog, by month
MonthValue (%)
January4.72
February1.97
March0.50
April0.12
May0.21
June0.09
July0.48
August0.44
September1.14
October2.97
November3.36
December3.40
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Fog by hour of day

All months combined, local time.

012345%4.47%12a3a6a9a12p3p6p9p
012345%4.47%12a3a6a9a12p3p6p9p
View the numbers
Share of hours with fog by hour of day
HourFog
12 am1.55%
1 am1.93%
2 am2.28%
3 am2.57%
4 am3.04%
5 am3.76%
6 am4.14%
7 am4.47%
8 am4.18%
9 am2.81%
10 am1.70%
11 am0.73%
12 pm0.44%
1 pm0.27%
2 pm0.17%
3 pm0.18%
4 pm0.20%
5 pm0.25%
6 pm0.35%
7 pm0.40%
8 pm0.56%
9 pm0.68%
10 pm0.85%
11 pm1.21%
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

05

Thunderstorms, precipitation and snow

Present-weather codes count thunderstorms at the airport.

August has the highest monthly thunderstorm rate, at 0.08% of hours.

November has the highest average precipitation total; July has the lowest. The annual average is 38.8 in.

The largest daily precipitation total in the downloaded station record is 5.02 in, on October 20, 2003.

February has the highest average snowfall total. Annual snowfall averages 4.5 in.

Share of hours with a thunderstorm at the airport

By month.

0.00.5%0.01JanFebMarAprMayJunJul0.08AugSepOctNovDec
0.00.5%Jan0.01Feb0.02Mar0.01Apr0.01May0.05Jun0.06Jul0.07Aug0.08Sep0.06Oct0.04Nov0.03Dec0.01
View the numbers
Share of hours with a thunderstorm at the airport
MonthValue (%)
January0.01
February0.02
March0.01
April0.01
May0.05
June0.06
July0.07
August0.08
September0.06
October0.04
November0.03
December0.01
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Average precipitation by month

Inches of rain and melted snow.

02468 inJanFebMarAprMayJun0.4JulAugSepOct6.2NovDec
02468 inJan5.7Feb3.6Mar4.0Apr2.9May1.9Jun1.5Jul0.4Aug0.9Sep1.8Oct4.1Nov6.2Dec5.8
View the numbers
Average precipitation by month
MonthValue ( in)
January5.7
February3.6
March4.0
April2.9
May1.9
June1.5
July0.4
August0.9
September1.8
October4.1
November6.2
December5.8
Source: NOAA GHCN-Daily

Average snowfall by month

Inches of snowfall depth, average over the years.

0.00.51.01.52.02.5 inJan2.0FebMar0.0AprMayJunJulAugSepOctNovDec
0.00.51.01.52.02.5 inJan0.8Feb2.0Mar0.2Apr0.0May0.0Jun0.0Jul0.0Aug0.0Sep0.0Oct0.0Nov0.2Dec1.3
View the numbers
Average snowfall by month
MonthValue ( in)
January0.8
February2.0
March0.2
April0.0
May0.0
June0.0
July0.0
August0.0
September0.0
October0.0
November0.2
December1.3
Source: NOAA GHCN-Daily

06

Wind and runway crosswinds

Runway axes and true headings come from OurAirports.

The most frequent wind sector is S, among reports with sustained wind of at least 3 kt.

Using the better aligned runway axis, the crosswind component stays at or below 13 kt in 97.9% of hours with a wind-speed report.

The share with wind or gusts of at least 25 kt is highest in December and lowest in July. Crosswind above 15 kt on every available axis is most frequent in December.

The largest sustained wind or reported gust in these hourly observations is 79 kt.

Where the wind comes from

Share of hours by direction the wind blows from and speed. Lines mark the runway axes.

5%10%15%20%1634NESW
  • 3 to 9 kt
  • 10 to 17
  • 18 to 24
  • 25 or more
  • Runway axes

Speed uses the stronger of sustained wind and gust. Calm hours (under 3 kt) are left out of the rose.

Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

SEA runways and crosswind exposure

Drawn to scale, north up. A stronger colour means crosswind above 15 kt in more hours.

1 mileN16C34C16L34R16R34L
View the numbers
Crosswind exposure by runway axis
Runway axisOver 15 ktOver 20 kt
16/341.4% of hours0.4% of hours

Runway positions from OurAirports. Terminals and taxiways are not shown.

Source: OurAirports runway data; NOAA/NWS airport observations via Iowa Environmental Mesonet

Share of hours with wind or gusts of 25 kt or more

By month.

01234%JanFebMarAprMayJun0.1JulAugSepOctNov3.6Dec
01234%Jan2.6Feb3.1Mar2.3Apr1.4May0.6Jun0.4Jul0.1Aug0.1Sep0.2Oct1.5Nov2.8Dec3.6
View the numbers
Share of hours with wind or gusts of 25 kt or more
MonthValue (%)
January2.6
February3.1
March2.3
April1.4
May0.6
June0.4
July0.1
August0.1
September0.2
October1.5
November2.8
December3.6
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Hours when even the best runway has over 15 kt of crosswind

Share of hours, by month.

0123%JanFebMarAprMayJun0.14JulAugSepOctNov2.89Dec
0123%Jan2.38Feb2.61Mar2.52Apr1.56May1.14Jun0.73Jul0.14Aug0.21Sep0.39Oct0.82Nov1.67Dec2.89
View the numbers
Hours when even the best runway has over 15 kt of crosswind
MonthValue (%)
January2.38
February2.61
March2.52
April1.56
May1.14
June0.73
July0.14
August0.21
September0.39
October0.82
November1.67
December2.89
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Which runway end the wind favours

Each hour is assigned to the numbered runway end with the largest headwind component. Parallel ends with the same heading are grouped. Ties go to the first sorted axis. This is not a record of runway use.

0255075100%JanFebMarAprMayJunJulAugSepOctNovDec
0255075100%Jan100.0Feb100.0Mar100.0Apr100.0May100.1Jun100.0Jul100.0Aug100.0Sep100.0Oct100.0Nov100.0Dec100.0
  • 16
  • 34
  • calm
View the numbers
Wind-only runway preference
Month1634calm
January63.3%23.8%12.9%
February60.8%28.3%10.9%
March66.5%22.9%10.6%
April61.8%27.0%11.2%
May53.8%33.7%12.6%
June52.9%34.5%12.6%
July43.1%42.4%14.5%
August43.2%40.8%16.0%
September45.3%38.9%15.8%
October54.0%30.7%15.3%
November62.8%24.9%12.3%
December65.6%22.9%11.5%
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

07

Temperature, humidity and daylight

Daily temperature comes from GHCN-Daily.

July has the highest average daily high; December has the lowest.

Dew points of at least 70°F are most frequent in January.

Mid-month daylight is longest in June and shortest in December. Sunrise and sunset use the configured US daylight saving rule.

Average high and low by month

Lines are the average. Shaded bands cover the middle 80% of days.

0°20°40°60°80°100°32°FHighLowJanFebMarAprMayJunJulAugSepOctNovDec
0°20°40°60°80°100°32°FHighLowJFMAMJJASOND
  • Daily high
  • Daily low
View the numbers
Temperature by month at SEA
MonthAverage highAverage lowDays 90F+Nights 32F or colderRecord highRecord low
January47°F37°F0.06.764°F (1981)0°F (1950)
February49°F37°F0.06.370°F (1968)1°F (1950)
March53°F39°F0.02.179°F (2019)11°F (1955)
April58°F43°F0.00.189°F (2016)29°F (1951)
May65°F48°F0.00.093°F (1963)28°F (1954)
June71°F53°F0.50.0108°F (2021)38°F (1952)
July78°F57°F1.80.0103°F (2009)43°F (1949)
August77°F57°F1.40.099°F (1960)44°F (1950)
September71°F54°F0.20.098°F (1988)35°F (1972)
October60°F47°F0.00.289°F (1987)28°F (1949)
November51°F40°F0.03.274°F (1949)6°F (1955)
December46°F37°F0.06.566°F (2014)6°F (1968)

Dashed line marks freezing.

Source: NOAA GHCN-Daily

Share of hours with a dew point of 70F or higher

By month.

0.00.5%0.0JanFebMarAprMayJunJulAugSepOctNovDec
0.00.5%Jan0.0Feb0.0Mar0.0Apr0.0May0.0Jun0.0Jul0.0Aug0.0Sep0.0Oct0.0Nov0.0Dec0.0
View the numbers
Share of hours with a dew point of 70F or higher
MonthValue (%)
January0.0
February0.0
March0.0
April0.0
May0.0
June0.0
July0.0
August0.0
September0.0
October0.0
November0.0
December0.0
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Sunrise and sunset

Local clock time. The shaded band is daylight; the small steps are the clocks changing.

4 am6 am8 am10 am12 pm2 pm4 pm6 pm8 pmJanFebMarAprMayJunJulAugSepOctNovDecLatest sunrise 7:57 amEarliest 5:11 am
4 am8 am12 pm4 pm8 pmJFMAMJJASOND
View the numbers
Sunrise, sunset and daylight, mid-month
MonthSunriseSunsetDaylight
January7:52 am4:43 pm8.8 hours
February7:16 am5:31 pm10.2 hours
March7:25 am7:13 pm11.8 hours
April6:22 am7:56 pm13.6 hours
May5:33 am8:37 pm15.1 hours
June5:11 am9:07 pm15.9 hours
July5:27 am9:03 pm15.6 hours
August6:04 am8:24 pm14.3 hours
September6:45 am7:24 pm12.7 hours
October7:26 am6:24 pm11.0 hours
November7:13 am4:35 pm9.4 hours
December7:50 am4:19 pm8.5 hours
Source: calculated by PilotPassion from the airport's position

08

Check a date

Use a seven-day window on each side of your date across 26 years.

October 15 at SEA

Chance of low cloud or poor visibility (IFR or worse)

  • Overnight12 am to 6 am15.9%
  • Morning6 am to noon21.6%
  • Afternoonnoon to 6 pm6.9%
  • Evening6 pm to midnight6.2%

The day

Typical high
60°F
Typical low
48°F
Sunrise
7:27 am
Sunset
6:22 pm
Measurable precipitation
51% of days
Snow of 0.1 in or more
0% of days
Wind or gusts 25 kt+
1.5% of hours

These historical frequencies are not a forecast.

09

Year to year

Each bar summarizes one local calendar year.

IFR-or-worse hours by year

Local calendar years.

051015%200020022004200620082010201214.320144.620162018202020222024average 7.8
051015%'00'01'02'03'04'05'06'07'08'09'10'11'12'1314.3'14'15'164.6'17'18'19'20'21'22'23'24'25
View the numbers
IFR-or-worse hours by year
YearShare of hours
20006.2%
20016.4%
20028.2%
20036.9%
20049.3%
20058.4%
20066.0%
20076.8%
20088.2%
20099.5%
20108.9%
20117.7%
20128.4%
201314.3%
20148.5%
20158.7%
20164.6%
20175.9%
20186.1%
20198.5%
20208.3%
20217.1%
20228.7%
20236.8%
20246.0%
20257.6%
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet

Precipitation by year

Local calendar years.

01020304050 in28.720002002200448.52006200820102012201420162018202020222024average 38.8
01020304050 in'0028.7'01'02'03'04'05'0648.5'07'08'09'10'11'12'13'14'15'16'17'18'19'20'21'22'23'24'25
View the numbers
Precipitation by year
YearInches
200028.7 in
200137.6 in
200231.4 in
200341.8 in
200431.1 in
200535.5 in
200648.5 in
200739.0 in
200830.8 in
200938.5 in
201047.0 in
201136.4 in
201248.3 in
201332.6 in
201448.5 in
201544.9 in
201645.2 in
201747.9 in
201835.8 in
201933.9 in
202041.3 in
202143.4 in
202241.0 in
202335.0 in
202432.2 in
202533.1 in
Source: NOAA GHCN-Daily

Snowfall by year

Local calendar years.

0510152025 in0.02000200220042006200820102012201420162018202021.620222024average 4.5
0510152025 in'000.0'01'02'03'04'05'06'07'08'09'10'11'12'13'14'15'16'17'18'19'20'2121.6'22'23'24'25
View the numbers
Snowfall by year
YearInches
20000.0 in
20010.0 in
20020.0 in
20030.0 in
20040.0 in
20050.0 in
20060.0 in
20070.0 in
200813.9 in
20099.5 in
20103.0 in
20114.8 in
201211.1 in
20131.1 in
20143.7 in
20150.0 in
20161.0 in
201713.2 in
20181.0 in
201921.0 in
20201.2 in
202121.6 in
20225.8 in
20232.3 in
20240.3 in
20252.3 in
Source: NOAA GHCN-Daily

10

SEA, RNT, BFI compared

The same hourly method and period apply to each station.

SEA's VFR share is lower than RNT's: 73.4% versus 75.0%.

SEA's VFR share is lower than BFI's: 73.4% versus 75.5%.

IFR-or-worse hours by month and airport

Same method and period for each station.

05101520%SEARNTBFIJanFebMarAprMayJunJulAugSepOctNovDec
05101520%JFMAMJJASOND
  • SEA
  • RNT
  • BFI
Source: NOAA/NWS airport observations via Iowa Environmental Mesonet
Airport comparison
MeasureSEARNTBFI
VFR hours73.4%75.0%75.5%
IFR or worse hours7.8%5.2%4.6%
Fog hours1.62%0.63%0.72%
Fog hours per year1415563
Thunderstorm hours per year323
Wind or gusts 25 kt+1.5%0.5%0.7%
Crosswind coverage at 13 kt97.9%99.1%96.3%

11

Best and worst months by hazard

Each row is a different weather problem. A stronger colour means a higher rate that month, and the three worst months for each hazard have the strongest colour.

Hazard calendar

The strongest-coloured cells are the three worst months for that row. A pale cell with a 0 means none at all.

JanFebMarAprMayJunJulAugSepOctNovDecLow cloud (IFR or worse)1595444557111113Fog4.72.00.50.10.20.10.50.41.13.03.43.4Thunderstorm at the airport<0.1<0.1<0.1<0.10.10.10.10.10.1<0.1<0.1<0.1Snow1.31.90.60.10.00.00.00.00.00.00.51.6Freezing rain or icepellets0.2<0.1<0.1<0.10.00.00.00.00.00.00.00.1Wind or gusts 25 kt+33211<1<1<1<1134Crosswind over 15 kt (allrunways)2.42.62.51.61.10.70.10.20.40.81.72.9Heat (days of 90F orhotter)0.00.00.00.00.00.51.81.40.20.00.00.0Frost (nights of 32F orcolder)762<100000<137Humid (dew point 70F+)000000000000
CloudFogStormSnowIceWindXwindHeatFrostHumidJan154.7<0.11.30.232.40.070Feb92.0<0.11.9<0.132.60.060Mar50.5<0.10.6<0.122.50.020Apr40.1<0.10.1<0.111.60.0<10May40.20.10.00.011.10.000Jun40.10.10.00.0<10.70.500Jul50.50.10.00.0<10.11.800Aug50.40.10.00.0<10.21.400Sep71.10.10.00.0<10.40.200Oct113.0<0.10.00.010.80.0<10Nov113.4<0.10.50.031.70.030Dec133.4<0.11.60.142.90.070
View the numbers
Hazard rates by month
HazardJanFebMarAprMayJunJulAugSepOctNovDec
Low cloud (IFR or worse)1595444557111113
Fog4.72.00.50.10.20.10.50.41.13.03.43.4
Thunderstorm at the airport<0.1<0.1<0.1<0.10.10.10.10.10.1<0.1<0.1<0.1
Snow1.31.90.60.10.00.00.00.00.00.00.51.6
Freezing rain or ice pellets0.2<0.1<0.1<0.10.00.00.00.00.00.00.00.1
Wind or gusts 25 kt+33211<1<1<1<1134
Crosswind over 15 kt (all runways)2.42.62.51.61.10.70.10.20.40.81.72.9
Heat (days of 90F or hotter)0.00.00.00.00.00.51.81.40.20.00.00.0
Frost (nights of 32F or colder)762<100000<137
Humid (dew point 70F+)000000000000

Weather-code, wind and humidity values are percentages of hourly reports. Heat and frost are days in an average year. A value shown as <0.1 or <1 is above zero but under that figure.

Source: NOAA/NWS airport observations via Iowa Environmental Mesonet; NOAA GHCN-Daily

12

Records and extremes

  • Hottest daily high108°FJune 28, 2021
  • Coldest daily low0°FJanuary 31, 1950
  • Largest daily precipitation5.0 inOctober 20, 2003
  • Largest daily snowfall20.0 inJanuary 13, 1950

Daily records cover the downloaded station history, starting 1948-01-01; hourly summaries cover 2000 to 2025.

13

Planning with SEA climate records

For travelers

  • April has the lowest historical IFR-or-worse rate. A monthly average does not predict weather on a particular trip.

For pilots

  • Use the charts to compare historical conditions. Get current METARs, TAFs and an official briefing before flying.

This page is for general information and trip planning. It is not an aviation weather briefing and must not be used for flight planning. Always get current weather from an official source such as aviationweather.gov or 1-800-WX-BRIEF before flying.

14

Questions about SEA weather

Which month has the most IFR-or-worse hours at SEA?

January has the highest share, at 14.9%. April has the lowest, at 3.5%.

When is fog most frequent at SEA?

January has the highest monthly share of fog reports. The annual share is 1.62%.

When are thunderstorms most frequent at SEA?

August has the highest share of hours with thunderstorms reported at the airport.

How much snowfall does SEA record?

Annual snowfall averages 4.5 in; February has the highest monthly average.

Is this a forecast?

No. The hourly summaries cover 2000 to 2025. Use current reports and forecasts for KSEA from aviationweather.gov.

15

Sources and method

Sources

Hourly weather
Iowa Environmental Mesonet archive of US National Weather Service routine hourly observations, report type 3, requested in UTC and filtered to local years 2000 to 2025.
Daily climate
NOAA NCEI GHCN-Daily station USW00024233. Menne et al. (2012), Global Historical Climatology Network Daily, doi:10.7289/V5D21VHZ.
Runways
OurAirports public domain runway data: source repository. Headings are degrees true. The first listed runway represents each numbered axis in crosswind calculations.
Time and daylight
Standard UTC offset -8 hours; US daylight saving rule, including the earlier rule before its statutory change. Solar times use the airport coordinates and NOAA equations.

Definitions

Sampling
One routine report per local clock hour. The first report is retained when hours repeat, including the autumn clock change.
Weather codes
Fog and thunderstorms exclude vicinity codes.
Wind
The stronger of sustained wind and gust is used for crosswind. Calm and variable direction count as zero crosswind.
Daily averages
Monthly totals and day counts are divided by the number of years in the analysis period.

Limits

  • Routine hourly sampling misses events between observations.
  • Wind above 100 kt, temperature outside -30 to 115 F and dew point outside -40 to 90 F are discarded as sensor glitches.
  • Wind-only runway preferences do not describe ATC assignments.

Weather data comes from the US National Weather Service and NOAA via IEM. PilotPassion is not affiliated with or endorsed by these agencies.

Aerial view of Seattle-Tacoma International Airport at dusk showing its three parallel runways
Seattle-Tacoma International Airport from the air, photographed in 2009 Photo: Jelson25, Public domain. Source

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