<p>Catastrophic flash flooding is usually a sign of poor city/road planning in flat areas or due to torrential downfall of rain.   The reality is that all the terrain in Washington allows water to drain, rather than be left standing (which causes flash flooding).  And let's be clear, it doesn't rain hard in WA very often, it's usually not torrential downpour, but rather a slow methodical drizzle that can easily drain away down rivers and streams.  A lot of development in the mid-west ignores known flood plains.</p>
<p>As for your comment about wildfires, WA gets its rain in the cold seasons.  So there is usually very dry weather in the summer when wildfires occur.</p>

CC BY-SA 4.0
2021-04-25T23:57:18.667Z
Seems harsh to blame city/road planning a lot of the time... many inches of rain in a day or hours is a lot to handle, after all many areas were once swampy from the same rain.  A city could probably put inordinate amounts of money and space to giant drainage systems to cover every possible extreme scenario, or they could balance cost with utility, deal with occasional floods, and spend the money on other important things. And while building locations aren't perfect, https://msc.fema.gov/portal/home shows most cities try to do a fair job. But yeah, not so much a concern in Washington state :-D
JeopardyTempest
CC BY-SA 4.0
2021-04-26T01:51:47.440Z
"Catastrophic flash flooding is usually a sign of poor city/road planning" Or the converse, the *lack* of flooding is the result of *good* city planning.
nick012000
CC BY-SA 4.0
2021-04-27T02:21:40.827Z
it says "or" torrential downfall... it can flash flood anywhere with enough rain in a short time.
f.thorpe
CC BY-SA 4.0
2021-04-22T22:19:12.233Z
2022-01-30T16:51:55.450Z
2022-01-30T16:51:55.450Z
f.thorpe
<p>We do get flooding in the Puget Sound lowlands, but it actually happens most often when a mid-winter warm front brings a moderate amount of rain to higher elevations, causing sudden, extensive snowmelt.</p>
<p>Those weather systems, like one in February 2020 that caused quite a bit of flooding, suddenly raise temps by 15-20 degrees C (20-30 °F), and raise the snow/rain threshold up by 1000 meters (a few thousand feet) or more overnight.  Even though the rainfall totals in those storms are usually not that great by comparison with the major storms in the South or the Plains, 5 cm/day (1-2 inches per day), the net effect is that a huge amount of water enters waterways all at once.</p>
<p>Even so, the steep slopes in the area generally mean that flooding is limited to a few river valleys.  Our elevation profile goes from 3000 meters (8000 feet) to sea level in about 50 km (30 miles), so that water heads downhill FAST.</p>

CC BY-SA 4.0
2021-04-25T11:38:51.503Z
@Earthworm: I loath & detest non Metric units & wish they would go away! I was introduced to the British version of such units when I was young & lived through a 10 year transition period to the adoption of Metric units. I have no intention of going backwards. Unfortunately, some people still use obscure obsolete units, even in my country. I wish there was still a ban on using non Metric units, but that legislation had a sunset clause.  In the 1980s television screen sizes were advertised in centimeters, they have since reverted back to inches, much to my chagrin.
Fred
CC BY-SA 4.0
2021-04-25T11:39:47.037Z
As to the numbers you mention in your comment, I simply put the original numbers back as a courtesy to the poster. I am simply adopting was has been discussed in the meta question: [Is the imperial measurement system still used in the geosciences?](https://earthscience.meta.stackexchange.com/questions/318/is-the-imperial-measurement-system-still-used-in-the-geosciences).
Fred
CC BY-SA 4.0
2022-04-07T00:20:16.987Z
Would you consider the Feb 1996 floods in Portland to be similar? i.e. a dump of snow on the Cascade foothills followed by an atmospheric river, raising temperatures enough to melt the snow, which in turn results in extensive river flooding
spillthrill
CC BY-SA 4.0
2021-04-23T22:27:55.000Z
2021-04-25T04:48:52.233Z
2021-04-25T04:48:52.233Z
juliaseid
<p><strong>Because soil drainage would be higher and the ground would take long to saturate</strong> Floods don't always happen in Rainy weather all the time because first the soil needs to be saturated (the point where it filled up with water) then the rain needs to continue, Flash floods are mostly produced this way.</p>
<p>So you would need lots of rain for a flood to occur in WA, I mean lots.</p>

CC BY-SA 4.0
2021-04-22T21:48:15.690Z
2021-04-22T21:48:15.690Z
Tardy
<p>To add some concrete data to some of the great answers already here:</p>
<p>Seattle is actually not particularly rainy, especially compared to other parts of WA, but also compared to other cities in the US. According to <a href="https://www.currentresults.com/Weather/US/average-annual-precipitation-by-city.php" rel="nofollow noreferrer">this chart of the largest 51 US cities</a>, Seattle is wetter than 18, drier than 31, and tied with 1. Yet, Seattle only has less rainy-days than 5 cities, and more rainy-days than 45 cities. This indicates that Seattle probably gets its rain as a constant drizzle (which seems confirmed from anecdotal evidence) which would allow for the area to store and drain water faster than it peaks.</p>
<p>Interesting side-note:</p>
<p>A unexpected city that does suffer from flash floods is Tucson, Arizona. It receives 11.6 inches (294.6 mm) of rain yearly and 2.4 inches (61 mm) in its peak month. It is, however, flat and apparently large parts of the city do not have storm sewers. Additionally, <a href="https://www.azcentral.com/story/news/local/arizona/2014/08/21/12-news-arizona-desert-cant-absorb-water/14361963/" rel="nofollow noreferrer">the Arizona habitat does not seem to naturally drain water very well</a>. This shows the importance both of city planning and natural drainage, which I'm sure Seattle, a wet city, has both in plenty.</p>

CC BY-SA 4.0
2021-04-25T16:24:53.627Z
2022-01-30T16:50:42.817Z
2022-01-30T16:50:42.817Z
stef
<p>Because Washington has many river channels.The rivers of Western Washington flood almost every year. Snohomish, Skagit and other rivers flood, Seattle is largely spared, city knowing full well floods would be an issue for a city that supports rainforest ecosystem...........has drainage.
Seattle is 53 meters (173 feet) above sea level and on mountainous terrain, so waters very seldom flood or inundate. Floods dominate flat terrain or valleys, which Seattle is Neither.........</p>

CC BY-SA 4.0
2022-02-05T13:37:15.473Z
the rainforest ecosystem is on the Olympic Peninsula, so you wouldn't get flow from it over in Seattle?
JeopardyTempest
CC BY-SA 4.0
2022-02-06T05:13:39.990Z
Seattle is 40 miles from Olympic Park....
LazyReader
CC BY-SA 4.0
2022-02-06T07:05:36.250Z
On the opposite side of Puget Sound. And the majority of it on the [windward side](https://www.researchgate.net/profile/Chris-Daly-5/publication/250220860/figure/fig2/AS:425515308851201@1478462163771/Mean-annual-19611990-precipitation-overlain-on-500-m-terrain-for-the-Olympic-Peninsula.png), which flows west. Some would classify the peaks of the Cascades as seasonal rainforests, but the rain isn't nearly the same level or area (see [this graphic](https://www.researchgate.net/figure/Mean-Annual-Precipitation-20-21-for-Washington-State-including-Eastern-Washington-Study_fig1_257497564)).
JeopardyTempest
CC BY-SA 4.0
2022-02-06T07:14:21.610Z
Olympic Park has basically no connection to Seattle's river levels or tides, since Puget Sound is open sea-level water.
JeopardyTempest
CC BY-SA 4.0
2022-02-05T07:55:22.573Z
2022-02-05T07:55:22.573Z
LazyReader
<p>Regarding climate, it does not rain in Seattle as much as people think; Seattle is in the snow shadow of the Olympic Mountains. It doesn't rain much in summer at all. Seattle gets rather dry in July and August.</p>
<p>Regarding flooding, the Skagit and Snohomish rivers north of Seattle flood regularly experience flooding. Some of the land in the flood plain is used for farming, and there are scattered households in the 100 year flood plain.</p>
<p>Regarding drought, drought severity is relative to the amount of precipitation and soil moisture levels typical for a specific locale. This means that even a rainforest can suffer drought. Because it's a relative concept, the rainfall during a drought in a rainforest would be a rainfall bonanza in arid climates.</p>
<p>Regarding forest fires, the Seattle area occasionally undergoes offshore flow. This occurs when the air pressure is lower in the Seattle area than it is east of the Cascades. This makes winds blow from the east, and if there's a forest fire east of the Cascades (which has a rather dry climate), that smoke can be carried westward toward the Seattle area by the offshore flow. That said, wildfires have occurred on the western slopes of the Cascades, and sometimes even in the temperate rainforest to the west of the Seattle area.</p>

CC BY-SA 4.0
2021-04-23T12:13:06.293Z
Another part of this is that much of the precipitation that Seattle receives is frequent small amounts, rather than multiple inches of rain all one time. Frequent small amounts are easier for the soil to absorb, reducing the chance of flash flooding.
ycartwhelen
CC BY-SA 4.0
2021-04-23T15:38:45.637Z
Yes - the Seattle area tends to experience "mist with delusions of grandeur" - it will be wet/damp, without much actual rainfall.  Which is why raincoats are popular compared to umbrellas.
Clockwork-Muse
CC BY-SA 4.0
2021-04-23T20:07:16.687Z
too small of a change to edit, but: s/Snowhomish/Snohomish/
Cody
CC BY-SA 4.0
2021-04-23T20:48:28.157Z
@Cody Thanks, fixed.
David Hammen
CC BY-SA 4.0
2021-04-24T16:44:31.720Z
Yeah, people think of Seattle as being impossibly rainy, but the absolute amount isn't actually that astonishing; the problem is just that it drizzles down slowly ALL THE TIME. Also, the entire Seattle area is surprisingly steep, so the kind of flooding seen in flatter areas just doesn't happen; the water all drains into the sea where it belongs.
Paul Z
CC BY-SA 4.0
2021-04-22T22:27:00.290Z
2021-04-23T20:35:57.957Z
2021-04-23T20:35:57.957Z
David Hammen
<p>The Puget Sound region is wedged between the Pacific and the Cascades...you'd think with all that rain (and snowmelt in the warmer months), there would be catastrophic flash flooding in lowland areas, of the magnitude seen in Oklahoma (<a href="https://www.weather.gov/oun/events-20130531-flooding" rel="noreferrer">1</a>, <a href="https://www.weather.gov/oun/events-20100614" rel="noreferrer">2</a>, <a href="https://www.weather.gov/tsa/1984may26_tulsamemorialdayflood" rel="noreferrer">3</a>), Texas (<a href="https://www.weather.gov/hgx/hurricaneharvey" rel="noreferrer">1</a>, <a href="https://www.hcfcd.org/Portals/62/Downloads/TS%20Imelda%20Flood%20Report/TS%20Imelda%20Flood%20Report-Final.pdf?ver=4JBzaMh-DydlHHx9_mlZgg%3D%3D&amp;timestamp=1619119442827" rel="noreferrer">2</a>, <a href="http://aipg-tx.org/_docs/TaxDayFlood_HGS.pdf" rel="noreferrer">3</a>, <a href="http://hurricane.egr.uh.edu/sites/hurricane.egr.uh.edu/files/files/2015/1-2015-MEMORIAL-DAY-FLOOD-8-4-2015.pdf" rel="noreferrer">4</a>) or Tennessee (<a href="https://www.weather.gov/ohx/20210327" rel="noreferrer">1</a>, <a href="https://www.weather.gov/ohx/lateFebruary2019flooding" rel="noreferrer">2</a>, <a href="https://www.weather.gov/ohx/may2010flood" rel="noreferrer">3</a>).</p>
<p>On the contrary, western WA is actually subject to <a href="https://1.bp.blogspot.com/-dtVzVuG-95Y/XV6PnEkANaI/AAAAAAAA3Vc/kAPFcCvfR3Q23SUyHUEIcL1h4CZysYNTgCEwYBhgL/s1600/20190820_WA_trd.png" rel="noreferrer">droughts</a> and <a href="https://static.seattletimes.com/wp-content/uploads/2017/08/08042017_moreseattlehaze_0645152-780x1170.jpg" rel="noreferrer">wildfires</a>, not something you'd expect from such a wet region with rainforests.</p>

CC BY-SA 4.0
2021-04-22T21:43:42.047Z
WA has a Rainforest?
Tardy
CC BY-SA 4.0
2021-04-22T21:46:45.090Z
https://en.wikipedia.org/wiki/Pacific_temperate_rainforests
spillthrill
CC BY-SA 4.0
2021-04-26T21:08:15.523Z
I see, I didnt know sorry.
Tardy
CC BY-SA 4.0
2022-02-02T16:57:07.453Z
Western Washington is somewhat wet a lot of the time.  Those other places are extremely wet for short periods of time.
Vikki
<meteorology><severe-weather><flooding>
With all the rain Seattle gets, why is widespread flooding relatively rare?
spillthrill
# With all the rain Seattle gets, why is widespread flooding relatively rare?

(Asked by: username_0 on 2021-04-22)

The Puget Sound region is wedged between the Pacific and the Cascades...you'd think with all that rain (and snowmelt in the warmer months), there would be catastrophic flash flooding in lowland areas, of the magnitude seen in Oklahoma ([1](https://www.weather.gov/oun/events-20130531-flooding), [2](https://www.weather.gov/oun/events-20100614), [3](https://www.weather.gov/tsa/1984may26_tulsamemorialdayflood)), Texas ([1](https://www.weather.gov/hgx/hurricaneharvey), [2](https://www.hcfcd.org/Portals/62/Downloads/TS%20Imelda%20Flood%20Report/TS%20Imelda%20Flood%20Report-Final.pdf?ver=4JBzaMh-DydlHHx9_mlZgg%3D%3D&timestamp=1619119442827), [3](http://aipg-tx.org/_docs/TaxDayFlood_HGS.pdf), [4](http://hurricane.egr.uh.edu/sites/hurricane.egr.uh.edu/files/files/2015/1-2015-MEMORIAL-DAY-FLOOD-8-4-2015.pdf)) or Tennessee ([1](https://www.weather.gov/ohx/20210327), [2](https://www.weather.gov/ohx/lateFebruary2019flooding), [3](https://www.weather.gov/ohx/may2010flood)).

On the contrary, western WA is actually subject to [droughts](https://1.bp.blogspot.com/-dtVzVuG-95Y/XV6PnEkANaI/AAAAAAAA3Vc/kAPFcCvfR3Q23SUyHUEIcL1h4CZysYNTgCEwYBhgL/s1600/20190820_WA_trd.png) and [wildfires](https://static.seattletimes.com/wp-content/uploads/2017/08/08042017_moreseattlehaze_0645152-780x1170.jpg), not something you'd expect from such a wet region with rainforests.

**Tags:** meteorology, severe-weather, flooding

> **Comments:**
> **username_1**: WA has a Rainforest?  
> **username_0**: https://en.wikipedia.org/wiki/Pacific_temperate_rainforests  
> **username_1**: I see, I didnt know sorry.  
> **username_2**: Western Washington is somewhat wet a lot of the time.  Those other places are extremely wet for short periods of time.  

---

## 6 answers

### Answer by username_10 on 2021-04-22. Score: 26 | Accepted answer

Regarding climate, it does not rain in Seattle as much as people think; Seattle is in the snow shadow of the Olympic Mountains. It doesn't rain much in summer at all. Seattle gets rather dry in July and August.

Regarding flooding, the Skagit and Snohomish rivers north of Seattle flood regularly experience flooding. Some of the land in the flood plain is used for farming, and there are scattered households in the 100 year flood plain.

Regarding drought, drought severity is relative to the amount of precipitation and soil moisture levels typical for a specific locale. This means that even a rainforest can suffer drought. Because it's a relative concept, the rainfall during a drought in a rainforest would be a rainfall bonanza in arid climates.

Regarding forest fires, the Seattle area occasionally undergoes offshore flow. This occurs when the air pressure is lower in the Seattle area than it is east of the Cascades. This makes winds blow from the east, and if there's a forest fire east of the Cascades (which has a rather dry climate), that smoke can be carried westward toward the Seattle area by the offshore flow. That said, wildfires have occurred on the western slopes of the Cascades, and sometimes even in the temperate rainforest to the west of the Seattle area.

> **Comments:**
> **username_11**: Another part of this is that much of the precipitation that Seattle receives is frequent small amounts, rather than multiple inches of rain all one time. Frequent small amounts are easier for the soil to absorb, reducing the chance of flash flooding.  
> **username_12**: Yes - the Seattle area tends to experience "mist with delusions of grandeur" - it will be wet/damp, without much actual rainfall.  Which is why raincoats are popular compared to umbrellas.  
> **username_13**: too small of a change to edit, but: s/Snowhomish/Snohomish/  
> **username_10**: @username_13 Thanks, fixed.  
> **username_14**: Yeah, people think of Seattle as being impossibly rainy, but the absolute amount isn't actually that astonishing; the problem is just that it drizzles down slowly ALL THE TIME. Also, the entire Seattle area is surprisingly steep, so the kind of flooding seen in flatter areas just doesn't happen; the water all drains into the sea where it belongs.  

---

### Answer by username_3 on 2021-04-22. Score: 19

Catastrophic flash flooding is usually a sign of poor city/road planning in flat areas or due to torrential downfall of rain. The reality is that all the terrain in Washington allows water to drain, rather than be left standing (which causes flash flooding). And let's be clear, it doesn't rain hard in WA very often, it's usually not torrential downpour, but rather a slow methodical drizzle that can easily drain away down rivers and streams. A lot of development in the mid-west ignores known flood plains.

As for your comment about wildfires, WA gets its rain in the cold seasons. So there is usually very dry weather in the summer when wildfires occur.

> **Comments:**
> **username_4**: Seems harsh to blame city/road planning a lot of the time... many inches of rain in a day or hours is a lot to handle, after all many areas were once swampy from the same rain.  A city could probably put inordinate amounts of money and space to giant drainage systems to cover every possible extreme scenario, or they could balance cost with utility, deal with occasional floods, and spend the money on other important things. And while building locations aren't perfect, https://msc.fema.gov/portal/home shows most cities try to do a fair job. But yeah, not so much a concern in Washington state :-D  
> **username_5**: "Catastrophic flash flooding is usually a sign of poor city/road planning" Or the converse, the *lack* of flooding is the result of *good* city planning.  
> **username_3**: it says "or" torrential downfall... it can flash flood anywhere with enough rain in a short time.  

---

### Answer by username_6 on 2021-04-23. Score: 7

We do get flooding in the Puget Sound lowlands, but it actually happens most often when a mid-winter warm front brings a moderate amount of rain to higher elevations, causing sudden, extensive snowmelt.

Those weather systems, like one in February 2020 that caused quite a bit of flooding, suddenly raise temps by 15-20 degrees C (20-30 °F), and raise the snow/rain threshold up by 1000 meters (a few thousand feet) or more overnight. Even though the rainfall totals in those storms are usually not that great by comparison with the major storms in the South or the Plains, 5 cm/day (1-2 inches per day), the net effect is that a huge amount of water enters waterways all at once.

Even so, the steep slopes in the area generally mean that flooding is limited to a few river valleys. Our elevation profile goes from 3000 meters (8000 feet) to sea level in about 50 km (30 miles), so that water heads downhill FAST.

> **Comments:**
> **username_7**: @Earthworm: I loath & detest non Metric units & wish they would go away! I was introduced to the British version of such units when I was young & lived through a 10 year transition period to the adoption of Metric units. I have no intention of going backwards. Unfortunately, some people still use obscure obsolete units, even in my country. I wish there was still a ban on using non Metric units, but that legislation had a sunset clause.  In the 1980s television screen sizes were advertised in centimeters, they have since reverted back to inches, much to my chagrin.  
> **username_7**: As to the numbers you mention in your comment, I simply put the original numbers back as a courtesy to the poster. I am simply adopting was has been discussed in the meta question: [Is the imperial measurement system still used in the geosciences?](https://earthscience.meta.stackexchange.com/questions/318/is-the-imperial-measurement-system-still-used-in-the-geosciences).  
> **username_0**: Would you consider the Feb 1996 floods in Portland to be similar? i.e. a dump of snow on the Cascade foothills followed by an atmospheric river, raising temperatures enough to melt the snow, which in turn results in extensive river flooding  

---

### Answer by username_8 on 2021-04-25. Score: 5

To add some concrete data to some of the great answers already here:

Seattle is actually not particularly rainy, especially compared to other parts of WA, but also compared to other cities in the US. According to [this chart of the largest 51 US cities](https://www.currentresults.com/Weather/US/average-annual-precipitation-by-city.php), Seattle is wetter than 18, drier than 31, and tied with 1. Yet, Seattle only has less rainy-days than 5 cities, and more rainy-days than 45 cities. This indicates that Seattle probably gets its rain as a constant drizzle (which seems confirmed from anecdotal evidence) which would allow for the area to store and drain water faster than it peaks.

Interesting side-note:

A unexpected city that does suffer from flash floods is Tucson, Arizona. It receives 11.6 inches (294.6 mm) of rain yearly and 2.4 inches (61 mm) in its peak month. It is, however, flat and apparently large parts of the city do not have storm sewers. Additionally, [the Arizona habitat does not seem to naturally drain water very well](https://www.azcentral.com/story/news/local/arizona/2014/08/21/12-news-arizona-desert-cant-absorb-water/14361963/). This shows the importance both of city planning and natural drainage, which I'm sure Seattle, a wet city, has both in plenty.


---

### Answer by username_1 on 2021-04-22. Score: 4

**Because soil drainage would be higher and the ground would take long to saturate** Floods don't always happen in Rainy weather all the time because first the soil needs to be saturated (the point where it filled up with water) then the rain needs to continue, Flash floods are mostly produced this way.

So you would need lots of rain for a flood to occur in WA, I mean lots.


---

### Answer by username_9 on 2022-02-05. Score: 0

Because Washington has many river channels.The rivers of Western Washington flood almost every year. Snohomish, Skagit and other rivers flood, Seattle is largely spared, city knowing full well floods would be an issue for a city that supports rainforest ecosystem...........has drainage.
Seattle is 53 meters (173 feet) above sea level and on mountainous terrain, so waters very seldom flood or inundate. Floods dominate flat terrain or valleys, which Seattle is Neither.........

> **Comments:**
> **username_4**: the rainforest ecosystem is on the Olympic Peninsula, so you wouldn't get flow from it over in Seattle?  
> **username_9**: Seattle is 40 miles from Olympic Park....  
> **username_4**: On the opposite side of Puget Sound. And the majority of it on the [windward side](https://www.researchgate.net/profile/Chris-Daly-5/publication/250220860/figure/fig2/AS:425515308851201@1478462163771/Mean-annual-19611990-precipitation-overlain-on-500-m-terrain-for-the-Olympic-Peninsula.png), which flows west. Some would classify the peaks of the Cascades as seasonal rainforests, but the rain isn't nearly the same level or area (see [this graphic](https://www.researchgate.net/figure/Mean-Annual-Precipitation-20-21-for-Washington-State-including-Eastern-Washington-Study_fig1_257497564)).  
> **username_4**: Olympic Park has basically no connection to Seattle's river levels or tides, since Puget Sound is open sea-level water.  

---

