Over the past week, the west coast of the US has been getting absolutely hammered by severe winter storms. The pacific jet stream has been very active, with storm after storm after storm rolling into the region. These have produced absolutely ridiculous amounts of precipitation across California. Much of the state, especially the central and southern half, was in an exceptional drought no more than a week ago.
In the past week, multiple plumes of anomalous precipitable water values have moved northeastward out of the central Pacific to affect the west coast. This moisture streamed directly into the Sierra Nevada Mountains in California, and the Cascades in Oregon and Washington. In addition to already favorable synoptic scale ascent foster by strong low pressure systems, the strong onshore flow was aided by orographic ascent, which is just air that is forced to rise along geographical boundaries, such as mountains.
All of this has combined to create one of the most ridiculous weeks of winter storms in several years in that region. Heavy rainfall has plagued the central California valleys, with extremely heavy snowfall impacting the mountains. In fact, some of the snowfall levels even rose above what they normally would be in a storm like this, creating heavy rainfall on top of a thick snowpack in the mountains. This only enhanced the flooding threat in the valleys.
WOW! #CAstorm brought impressive 7-day precipitation totals across #NorCal. 20”+ over the Sierra! #CAFlood #cawx pic.twitter.com/EyIEThSEsF
— NWS Sacramento (@NWSSacramento) January 11, 2017
Dry Creek in West Roseville/Antelope is anything but dry! Beware of normally small creeks like this flooding roads tonight! #cawx #CAflood pic.twitter.com/p6CcqdosFI
— NWS Sacramento (@NWSSacramento) January 11, 2017
Sacramento Weir, looking downstream into the Yolo Bypass. Currently 7 gates open. #CAstorm pic.twitter.com/HU1sWUdBIt
— NWS CNRFC (@NWSCNRFC) January 10, 2017
Storms over the past week have brought just about everything you can think of in terms of weather. There was a weak tornado in northern California, damaging wind gusts across much of the region, heavy snowfall, freezing rain, etc. The past week truly has been crazy in that region.
More info on the EF0 tornado in Natomas, CA (a few minutes after midnight, 1/11/17) #cawx #CAstorm pic.twitter.com/X42Ofakcds
— NWS Sacramento (@NWSSacramento) January 11, 2017
The Sierra Nevada has seen some insane snowfall over the past 7 days, with some areas seeing upwards of 144″ of snowfall. Many mountain roads that traverse this region have been impacts, and even closed for several days. Snow continues to fall across the region.
The most recent storm brought warm temperatures and a largely moisture rich atmospheric column. This system caused widespread impact, but really caused some major heavy, wet snow to fall in the Sierra Nevada. One reporting station reported over 8″ of liquid precipitation, that yielded 29″ of snow. That is approximately a 3:1 snowfall ratio, which is incredibly low snowfall ratio. Usually it is 10″ of snow is equal to 1″ of liquid precip.
Portland, Oregon has been hit very hard with all of this, as well. Portland saw the second significant ice storm to impact Orgeon within a couple months over the weekend. Many areas saw ice accumulation in the 0.5″ range, with some areas seeing a higher amount.
@NWSPortland the ice is continuing to accumulate out in Goose Hollow! pic.twitter.com/28Ip4NANzT
— Malena Wood (@malenawood) January 9, 2017
I84 at Fairview Parkway. Still windy, still frozen, still super chilly. pic.twitter.com/Z9IqMKDSx9
— Ken McCormick (@kgwken) January 8, 2017
Earlier this AM around Salem RT @KandraKPTV: Ice-skating rink pic.twitter.com/916LkigdeV
— NWS Portland (@NWSPortland) January 8, 2017
With very little time to recover from this, a major storm system rolled into the region yesterday afternoon and into last night. This storm was initially forecast to produced heavy amounts of snow, but nothing like what they received. The NWS in Portland had a warning out for 1-4″ of snowfall, but the storm wellllll over-produced.
The dynamics associated with it led to heavy convective bands of snowfall developing, and then a strong deformation band developed to the north of the low pressure system, aiding in the longevity of the snowfall across the region as well. This led to high snowfall rates, and amounts. Travel was significantly impacted, as was life in general. The snowfall was heavy and wet, and caused tree limbs to fall on power lines and for power outages. Additionally, this snowfall was associated with thundersnow, just indicating the dynamical support for the snow.
@NWSPortland SW Portland checking in with a video! pic.twitter.com/OCRUjddCEH
— Malena Wood (@malenawood) January 11, 2017
@NWSPortland @Oregonian At the top Highway 99 just past I-5 exit heading down the hill. At least two dozen cars stranded/stuck. pic.twitter.com/nCiT8e9Cry
— Wade Zelazny (@tbird_05) January 11, 2017
Several reports of thundersnow in north Portland. A sign of jow how heavy the snow is. https://t.co/qSJ6CR8jnM
— NWS Portland (@NWSPortland) January 11, 2017
.@NWSPortland Heavy snow and flashes of lightning in at NW 22 & Overton pic.twitter.com/qYh1kc6eE6
— Steven Masters (@TheSteveMasters) January 11, 2017
Regenerating/training convective snow in Portland OR resulting in extreme rates/amounts [radar 4pm PST Tue – 6am Wed] #orwx pic.twitter.com/ldK5UTWbON
— Stu Ostro (@StuOstro) January 11, 2017
The west coast has been dealing with a lot, and hopefully it will let up soon. I would love a good winter storm in our region, but what they have gone through has been a bit too much at once.