<p>This event is "super historic" only because of its proximity to the coast.  It is fairly common to get flash flooding in the mountains and deserts of Socal at least a few times each summer, due to the Southwest Monsoon.  This event was different in that a dying tropical system moving north off of the coast of Mexico interacted with a trough off of the Northern California coast.  The combination of these two essentially funneled tropical moisture north directly into the coastal regions of Southern California.</p>

<p>Linking single events to long term global change is virtually impossible to do reliably, so I won't speculate. However one could argue that rising sea surface temperatures could allow tropical systems to stay more organized near Southern California, and increase the probability of events like this. But again, it is never a good idea to try and link a localized extreme event with a global phenomenon.</p>

<p>In terms of drought relief and reservoir storage these rains have virtually zero impact.  They impacted the southern third of California, while the majority of water storage is in the central and northern part of the state along the Sierras. The rain came down pretty quick and didn't soak in to any of the soils, so vegetation will still be just as dry as before the rain. California needs heavy snows in the Sierras for any serious drought relief. Although these rains have given many people a false sense of security.</p>

CC BY-SA 3.0
2015-07-21T05:32:17.203Z
Its more visible if you look at 500hPa on the 18th. Have a look at this link:  http://earth.nullschool.net/#2015/07/18/0600Z/wind/isobaric/500hPa/orthographic=-119.87,25.47,676  
the trough is the weak counter-clockwise circulation off the socal coast around 32 N, the tropical storm is the stronger circulation to the south around 20 N
pythonismyjam
CC BY-SA 3.0
2015-07-21T02:03:16.617Z
2015-07-21T02:03:16.617Z
pythonismyjam
<p>On July 19, 2015 there was record rainfall over the Los Angeles and San Diego areas.  This is amidst a historic drought and the rain is needed.</p>

<p>This article:
<a href="http://www.weather.com/storms/hurricane/news/southwest-flood-threat-july-2015-tropical-storm-hurricane-dolores">http://www.weather.com/storms/hurricane/news/southwest-flood-threat-july-2015-tropical-storm-hurricane-dolores</a></p>

<p>states that</p>

<blockquote>
  <p>Widespread showers and thunderstorms across the Desert Southwest are being fueled by moisture from former Hurricane Dolores.</p>
</blockquote>

<p>and</p>

<blockquote>
  <p>Los Angeles and San Diego set all-time rainfall records for the month of July on Saturday.</p>
</blockquote>

<p>and</p>

<blockquote>
  <p>National Weather Service meteorologist called [it] "super historic."</p>
</blockquote>

<p>What is the significance of the "super historic" rainfall for July in California (July 19, 2015) in terms of climate change and water reservoirs used for municipalities?  In other words, what is the likelihood that climate change could bring more of these types of rain events in the future?  Related, what is the relative impact on water reservoirs and how much relief from the drought does such an event provide?  Does California have a long-term plan to capture more of this type of flash-flood rainfall in the future?</p>

CC BY-SA 3.0
2015-07-20T23:07:39.113Z
@gansub: Even in El Nino years, it's not really normal to get much beyond scattered thunderstorms in much of the Western US.  There's also been much more rain than usual in the northern Sierra Nevada & neighboring Great Basin areas.
jamesqf
CC BY-SA 3.0
2015-07-21T17:50:21.530Z
@gansub: No, it's observation from someone who has lived here for 40+ years, and paid fairly close attention to weather patterns.  Also from talking to older people, like my neighbor (who'll be 101 in September).
jamesqf
CC BY-SA 3.0
2015-07-22T05:09:41.837Z
@gansub: Interesting, but basically what I've been saying.  We're seeing unusual amounts of summer rain/Tstorms in the west.  Your link shows an unusually strong El Nino developing.  Correlation, and maybe causation.  Just hope it lasts into the winter!
jamesqf
<climate><climate-change><rain><california><drought>
What is the significance of the "super historic" rainfall for July 2015 in southern California?
f.thorpe
# What is the significance of the "super historic" rainfall for July 2015 in southern California?

(Asked by: username_0 on 2015-07-20)

On July 19, 2015 there was record rainfall over the Los Angeles and San Diego areas. This is amidst a historic drought and the rain is needed.

This article:
<http://www.weather.com/storms/hurricane/news/southwest-flood-threat-july-2015-tropical-storm-hurricane-dolores>

states that

> Widespread showers and thunderstorms across the Desert Southwest are being fueled by moisture from former Hurricane Dolores.

and

> Los Angeles and San Diego set all-time rainfall records for the month of July on Saturday.

and

> National Weather Service meteorologist called [it] "super historic."

What is the significance of the "super historic" rainfall for July in California (July 19, 2015) in terms of climate change and water reservoirs used for municipalities? In other words, what is the likelihood that climate change could bring more of these types of rain events in the future? Related, what is the relative impact on water reservoirs and how much relief from the drought does such an event provide? Does California have a long-term plan to capture more of this type of flash-flood rainfall in the future?

**Tags:** climate, climate-change, rain, california, drought

> **Comments:**
> **username_1**: @gansub: Even in El Nino years, it's not really normal to get much beyond scattered thunderstorms in much of the Western US.  There's also been much more rain than usual in the northern Sierra Nevada & neighboring Great Basin areas.  
> **username_1**: @gansub: No, it's observation from someone who has lived here for 40+ years, and paid fairly close attention to weather patterns.  Also from talking to older people, like my neighbor (who'll be 101 in September).  
> **username_1**: @gansub: Interesting, but basically what I've been saying.  We're seeing unusual amounts of summer rain/Tstorms in the west.  Your link shows an unusually strong El Nino developing.  Correlation, and maybe causation.  Just hope it lasts into the winter!  

---

## 1 answers

### Answer by username_2 on 2015-07-21. Score: 6

This event is "super historic" only because of its proximity to the coast. It is fairly common to get flash flooding in the mountains and deserts of Socal at least a few times each summer, due to the Southwest Monsoon. This event was different in that a dying tropical system moving north off of the coast of Mexico interacted with a trough off of the Northern California coast. The combination of these two essentially funneled tropical moisture north directly into the coastal regions of Southern California.

Linking single events to long term global change is virtually impossible to do reliably, so I won't speculate. However one could argue that rising sea surface temperatures could allow tropical systems to stay more organized near Southern California, and increase the probability of events like this. But again, it is never a good idea to try and link a localized extreme event with a global phenomenon.

In terms of drought relief and reservoir storage these rains have virtually zero impact. They impacted the southern third of California, while the majority of water storage is in the central and northern part of the state along the Sierras. The rain came down pretty quick and didn't soak in to any of the soils, so vegetation will still be just as dry as before the rain. California needs heavy snows in the Sierras for any serious drought relief. Although these rains have given many people a false sense of security.

> **Comments:**
> **username_2**: Its more visible if you look at 500hPa on the 18th. Have a look at this link:  http://earth.nullschool.net/#2015/07/18/0600Z/wind/isobaric/500hPa/orthographic=-119.87,25.47,676   the trough is the weak counter-clockwise circulation off the socal coast around 32 N, the tropical storm is the stronger circulation to the south around 20 N  

---

