Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 12:39 PM GMT op 20 januari 2012
A state of emergency has been declared in Oregon and Washington, where a powerful winter storm brought deadly floods, heavy snows of up to 4 feet, a severe ice storm, and damaging winds Wednesday and Thursday. Heavy rains of 3 - 8 inches have fallen over a wide swath of Western Oregon since Monday, causing major to record flooding on multiple rivers and creeks. In Albany, Oregon, a family of four drove out of a supermarket parking lot and into a flooded Perwinkle Creek Wednesday night, and were swept away. Two people were rescued, but a 20-month-old boy and his mother drowned. The Marys River in Philomath rose to its highest flood on record yesterday, and will remain at major flood stage today before gradually receding tonight. The rains have tapered off over much of the region today, but renewed rains are expected later today and intermittently into early next week. The storm also brought strong winds to Reno, Nevada, fanning a brush fire that tore through the Reno area, destroying more than 20 homes and forcing thousands to evacuate. Reno experienced sustained winds of 44 mph, gusting to 70 mph, during the afternoon Thursday. The city didn't get any precipitation, and has received just 0.03" of precipitation this year. That fell on Monday, breaking a 56-day streak with no precipitation--the longest wintertime dry streak in city history. Strong winds gusting to 55 mph are expected during the day today, keeping the fire danger high, but heavy rain is expected tonight, which should ease the fire danger. The storm also brought a significant freezing rain event to northern Oregon and Western Washington yesterday, and up to an inch of ice accumulated in some areas, contributing to power outages that affected at least 275,000 people.
Figure 1. Satellite image taken at 7 pm EST Thursday, January 19, of the West Coast winter storm. A second storm, now approaching the coast, can be seen at the left of the image. Image credit: NASA/GSFC.
Some select snow amounts between 2 pm PST Monday January 16, and 1am PST Friday January 20, as compiled in the latest NOAA/NCEP/HPC Storm Summary:
COVINGTON MILL 23.5
JUNCTION CITY 12.0
KETCHUM 22 NW 38.5
STANLEY 28 NE 32.9
BURLEY 30 SW 22.2
COPPER CAMP 13.0
MANY GLACIER 13.0
MT. HOOD MEADOWS 50.0
BEAR GRASS 32.0
ALTA 16.0 9662 FT
SNOWBIRD 11.0 8100 FT
PARK CITY JUPITER PEAK 5.0
JUNE LAKE 31.0
SURPRISE LAKE 30.0
LONE PINE 25.0
SOUTH ENTRANCE YELLOWSTONE 11.0
And some select rainfall amounts from the same time period:
CRESCENT CITY/MC NAMARA FIELD 5.87
ARCATA AIRPORT 3.63
SWISS HOME 15.50
PORT ORFORD 5 E 11.47
FALLS CITY 10.20
SILVERTON 9 SE 8.83
SALEM/MCNARY FIELD 6.82
PHILOMATH 5 SW 6.68
CAVE JUNCTION 2 N 6.25
N MYRTLE POINT 6.10
CORVALLIS MUNI ARPT 5.98
BROOKINGS 5 NNW 5.50
PORTLAND INTL ARPT 1.75
Figure 2. The Marys River in Philomath, Oregon crested at its highest flood height on record Thursday, and remains at major flood level today. Image credit: NOAA.
The short-term forecast
The storm door will remain open for California and the Pacific Northwest through the weekend and into mid-week, as two more moisture-laden storm systems pound the region. By the time the active weather pattern calms down by mid-week, rainfall totals of 10 - 20 inches are expected along the Oregon coast. Snowfall totals of 4 - 6 feet are likely in the Cascade Mountains of Washington and Oregon, in the Northern Sierra and Shasta/Siskiyou Mountains in California, in the Northern Wasatch and Uinta Ranges of Utah, and in the Northern Rockies from far eastern Idaho/Western Wyoming through Central and Northern Idaho, Northwestern Montana, and Northeastern Oregon. Damaging strong winds will affect the coast from Northern California to Northern Washington during the weekend and into early next week, as well.
Record dry spell ends for California and Nevada
In San Francisco, the first significant rains since November 20 fell yesterday, a modest 0.08". The two-month period November 20 - January 19 saw just 0.26" of rain fall in the city, making it the longest two-month winter dry period in the city since records began in 1850, according to wunderground's weather historian, Christopher C. Burt. More rain is expected Friday through Saturday.
The long-range forecast
A major atmospheric pattern shift is responsible for the big storm in the Western U.S. The ridge of high pressure that brought Northern California its driest two-month winter period on record Nov 20 - Jan 19 has retreated to the northwest towards Alaska, allowing the subtropical jet stream to dive underneath the ridge and bring a plume of moisture called an "atmospheric river" to the coast. This shift was possible thanks to a weakening of a pressure pattern known as the Arctic Oscillation (AO). During December and the first half of January, the AO took on its second most extreme configuration on record. The pressure difference between the Azores High and the Icelandic Low reached its most extreme value since records began in 1865, keeping the winds of the jets stream flowing very rapidly. This pattern bottled the jet stream far to the north in Canada, and prevented cold Arctic air from spilling southwards into the U.S . The combination of a near record-strength AO and a borderline weak/moderate La Ninña event in the Eastern Pacific combined to keep a powerful ridge in place over the Western U.S., deflecting all the winter storms into Canada and Southern Alaska. The AO index has become much less extreme over the past two weeks, though, and is now close to average strength. This has allowed the polar jet stream to sag southwards from Canada into the northern U.S., giving the northern tier of states their first real sustained winter-like weather of the season this week (it's about time!) However, the polar jet is expected to remain far enough north so that no major snow storms will occur in the U.S. during the remainder of January--except perhaps in the Pacific Northwest. It's likely that the lack of storms will make January 2012 one of the top five driest January months on record. This month is also likely to be a top-ten warmest January, but won't be able to challenge January of 2006 for the top spot. That January was an incredible 8.5°F above average in the contiguous U.S., and so far, we are running about 4 - 5°F above average. The AO index is predicted to remain near average or potentially change signs and go negative by the beginning of February, which would allow cold air to spill southwards into the U.S. bringing more typical winter-like weather.
It's too early to say what type of winter weather February might bring, but it might be instructive to look at the last time we had winter like this year's. Like the winter of 2011 - 2012, the winter of 2006 - 2007 started out exceptionally warm, with the AO index reaching its all-time most extreme positive value on record during December and early January. New York City hit 72°F on January 6, 2007, the city's all-time warmest January day. The rest of January 2007 saw a gradual lessening of the extreme AO pattern, much like we are seeing this year, and the AO returned to normal in February 2007. That month was a classic winter month, ranking as the 34th coldest February on record, with several notable snow storms.
Auroras possible this weekend
From spaceweather.com: Active sunspot 1401 erupted Jan. 19th, for more than an hour around 16:00 UT. The long-duration blast produced an M3-class solar flare and a Coronal Mass Ejection that appears to be heading toward Earth. Forecasters say strong geomagnetic storms are possible when the cloud arrives during the late hours of Saturday, Jan. 21st. High-latitude (and possibly middle-latitude) sky watchers should be alert for auroras this weekend.
Wunderground's weather historian Christopher C. Burt has a new post titled, The Pacific Northwest’s Greatest Storm: The ‘Storm King’ of January 1880.
Have a great weekend everyone, and I'll be back with a new post on Monday.
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