Storm Door Opens In Western U.S.

By: Shaun Tanner , 6:46 AM GMT on November 28, 2012

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I have been watching models for the past week or so in disbelief as both the GFS and ECMWF have both been consistently predicting a very wet period for the West Coast. Perhaps this disbelief is the reason I am writing this blog so close to the beginning of the wet period.

It has been quite some time since the West Coast has seen rain like what is expected for the next several days, so let's break down what is to be expected.

The first storm will slam into the coast Wednesday, lasting into Thursday. This storm will likely be the weakest in the series, which is a testament to how intense these storms will be. This is because nearly 2 inches of rain is possible in the wettest areas in Northern California, as noted in the precipitation forecast for Wednesday through Thursday morning.



The good people at the NWS have also posted various watches and warnings mostly in California in anticipation of this precipitation. Wind Advisories are posted for parts of the Northern California as southeast winds will gust to 40 mph. Winter Weather Advisories are also posted for the western slopes of the Sierra Nevadas, but snow levels will be a relatively high 6,000 feet. In fact, this will be a theme for this wet period as these storms will be rather warm in nature. So while the rain is certainly a blessing for dry areas of California that are in the brink a more serious drought (see below), it would have been great is some more of this precipitation would fall as snow. Not only would this help the water supply, it would also help the skiing industry in the Sierra Nevadas that has suffered greatly over the past 12 months.



The next storm to slam into the coast will arrive Thursday and last through much of Friday. This storm will be considerably wetter, as the first storm will do a great job in priming the atmosphere. The wettest areas (see below) could see over 7 inches of rain. This will be on top of the rain that has already arrived on Wednesday.



This is just the first two storms. Needless to say, the West Coast will be rather wet and wild through the first week of December. There are some interesting notes I want to bring to your attention.

First, if you look at the 5 day precipitation forecast from Wednesday through Sunday, you will see that there is a bulls eye of rain expected for Northern California. The storm track has consistently pointed directly at the California coast north of the San Francisco Bay Area. It is safe to say that if nearly 11 inches of rain fall on this area over the next 5 days, there will be some flooding issues for the mountainous areas of Northern California. The good news is that the streams in the area are fairly low at this time of year.



Second, one of the reasons I have been in disbelief at the amount of rain expected from this parade of storms is that a significant amount of subtropical moisture is needed. For these types of storms, the subtropical moisture can usually be seen on satellite as a thick line of clouds that extends from near Hawaii and is pointed directly at the West Coast. When this type of pattern sets up, California can receive days upon days of heavy rain. This is often called the "Pineapple Express", or more scientifically, the "Atmospheric River". If you are interested in watching this atmospheric river set up, watch the satellite on WunderMap.

Third, while the heavy rain from these storms is expected through the weekend, I still question slightly the actual location of the heavy rain. Certainly, the heaviest rain is likely in the hills of Northern California, but any southward movement of this deep moisture could bring the bulls eye closer to the San Francisco Bay Area. However, a more northward track would bring significantly less rainfall to San Francisco. This is only worth a mention at this point.

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14. WunderAlertBot (Admin)
6:42 AM GMT on November 29, 2012
shauntanner has created a new entry.
13. Luisport
10:15 PM GMT on November 28, 2012
Darren Peck‏@WeatherAnchor

Rain coming to an end right on schedule with just over half an inch in most Sac gauges. Friday a.m. is the next soaker. Bigger than today.
Member Since: October 27, 2012 Posts: 0 Comments: 2026
12. Luisport
10:11 PM GMT on November 28, 2012
PG&E‏@PGE4Me

#CentralCoast Outage Update (2 PM): Monterey County – 700; #SantaCruz County – 2,500; San Benito County – 190; Central Coast Total – 3,390
Member Since: October 27, 2012 Posts: 0 Comments: 2026
11. Luisport
10:07 PM GMT on November 28, 2012
PG&E‏@PGE4Me

#BayArea Outage Update (2 PM): North Bay – 40; #EastBay – 380; #SF – 30; Peninsula – 190; South Bay – 730 Bay Area Total – 1,370 #CAWx
Member Since: October 27, 2012 Posts: 0 Comments: 2026
10. Luisport
10:06 PM GMT on November 28, 2012
ABC7 News‏@abc7newsBayArea

The strongest part of the rain and wind has passed through the Bay Area but scattered showers continue in the North & East Bay. #BayAreaRain
Member Since: October 27, 2012 Posts: 0 Comments: 2026
9. Luisport
10:03 PM GMT on November 28, 2012
Jim Cantore‏@JimCantore

Squall Peak, CA had a peak gust to 90 mph within the last 2hours per @NWSMedford #CAwx


6 minJim Cantore‏@JimCantore

2 ESE Hayward, CA -- CHP reports areas of minor road flooding in several locations in Alameda county. #CAwx

7 minJim Cantore‏@JimCantore

5 NW Santa Cruz, CA -- Power lines down across Santa Cruz Mountains including a line down on highway 9 blocking traffic. #CAwx
Member Since: October 27, 2012 Posts: 0 Comments: 2026
8. Luisport
10:03 PM GMT on November 28, 2012
PG&E‏@PGE4Me

#CentralCoast Outage Update (1 PM): #Monterey County – 830; #SantaCruz County – 1,800; San Benito County – 190 #CentralCoast Total – 2,820

4 minPG&E‏@PGE4Me

#BayArea Outage Update (1 PM): #NorthBay – 50; #EastBay – 480; #SF – 60; Peninsula – 850; South Bay – 180; #BayArea Total – 1,620 #CAWx
Member Since: October 27, 2012 Posts: 0 Comments: 2026
7. Luisport
10:02 PM GMT on November 28, 2012
Ryan Maue‏@RyanMaue

After lull, next wave of energy into CA/OR border coast will have winds > hurr force just above surface layer Thur http://twitter.com/RyanMaue/status/273863416538599 425/photo/1/large
Member Since: October 27, 2012 Posts: 0 Comments: 2026
6. Luisport
10:01 PM GMT on November 28, 2012
NWSBayArea‏@NWSBayArea

12 hour rainfall total from #Venado -- 2.00" #bayarearain
Member Since: October 27, 2012 Posts: 0 Comments: 2026
5. Luisport
10:01 PM GMT on November 28, 2012
Jim Cantore‏@JimCantore

Mini bow (wind threat) heading towards Placerville, CA: http://radar.weather.gov/radar.php?rid=dax&product =N0R&overlay=11101111&loop=yes …No warning at the time of this tweet #CAwx
Member Since: October 27, 2012 Posts: 0 Comments: 2026
4. AndyEnglish
8:17 PM GMT on November 28, 2012
Be careful what you wish for. These storms are projected to cause similar flooding and damage as Sandy on the East Coast. This disruption could cause the frail California economy to falter again.
Member Since: November 28, 2012 Posts: 0 Comments: 0
3. lightning10
7:22 PM GMT on November 28, 2012
So Cal is getting shafted like usual.
Member Since: November 24, 2005 Posts: 41 Comments: 630
2. ycd0108
4:22 PM GMT on November 28, 2012
I'm well north of the heaviest rain forecast but 6.3" will test my aging shingles. My metal roof is sitting on a pallet about a kilometer away (not because of wind - I just got a call from the supplier).
The problem is:
When it is forecast to storm and rain it is not the time to be tearing off a roof no matter how bad the shingles look.
I want to thank you for weather information that will actually affect my area.
Member Since: January 1, 2008 Posts: 177 Comments: 4621
1. RockyMtnBreeze
1:48 PM GMT on November 28, 2012
Hopefully, the "Pineapple Express" will progress to us here in Colorado. We need it badly!
Member Since: November 23, 2012 Posts: 0 Comments: 0

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About shauntanner

Shaun Tanner has been a meteorologist at Weather Underground since 2004.

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