Storm Summary Number 1 for Western U.S. Winter Storm System
NWS Weather Prediction Center College Park MD
700 AM PST Mon Dec 13 2021

...Atmospheric River to bring significant heavy rain and snow to
California as a broader high wind threat continues across the
western and central U.S.... 

Winter Storm Warnings are in effect for the northern Coast Ranges,
Sierra Nevada, and Transverse ranges of California; the coastal
ranges and southern Cascades in Oregon; portions of the Sierra
Nevada and Great Basin in Nevada, and the Sawtooth Mountains in
Idaho.

High Wind Warnings are in effect for the Southern Coast Ranges,
Transverse Ranges, and Peninsular Ranges of California, the Sierra
Nevada of Nevada, and the Wyoming Basin.

Winter Weather Advisories are in effect for northern portions of
the Cascades and Okanogan Highlands in Washington, the Coast
Ranges and Cascades in Oregon, northern Great Basin of Nevada,
Northern Rockies of Idaho and Montana, and the Mongolian Rim and
northeastern Arizona.

High Wind Watches are in effect for portions of the western Great
Basin of Utah; the Mongolian Rim and other portions of northern
Arizona; the Sangre De Cristo Mountains and Eastern Plains of
Colorado and New Mexico; the Wyoming Basin; the High and Central
Plains of the Texas Panhandle and western Oklahoma, Kansas, and
Nebraska, and the Mid-Missouri Valley.

Wind Advisories are in effect for large portions of California,
western Arizona, Nevada, southern Oregon, southwestern Idaho.

For a detailed graphical depiction of the latest watches, warnings
and advisories, please see www.weather.gov

At 600 AM PST...A broad upper-level trough continued to approach
and move inland over the West Coast. At the surface, a slowly
meandering frontal boundary extended across the western U.S., from
the northern Plains west through the Northern Rockies before
turning south through southeastern Oregon and Northern California.
Significant moisture associated with an Atmospheric River
continued to spread inland behind and across this boundary.
Several areas of snow showers were ongoing across the Northern
Rockies in Montana and Idaho, the Cascades of Washington and
Oregon, and the Sierra Nevada and Coastal Ranges of California. In
addition, a broad area of heavy rain continued along the West
Coast, with particularly heavy rain currently falling along the
Coastal Ranges of California. 

...Selected preliminary Storm Total Snowfall in inches from 800 AM
PST Sat Dec 11 through 600 AM PST Mon Dec 13...

...CALIFORNIA...
MOUNT SHASTA 6 ENE                   13.0                    

...IDAHO...
DONNELLY 3 SSW                       20.0                    
NEW MEADOWS 2 NNW                    19.5                    
ELK RIVER                            15.0                    
HORSESHOE BEND 11 SSE                13.0                    
PIONEERVILLE 9 ESE                   12.0                    

...MONTANA...
DUPUYER 23 SW                        12.0                    
NOXON 12 NE                          12.0                    

...OREGON...
HALFWAY 9 NNW                        18.0                    
CRATER LAKE 1 SW                     16.0                    
TOLLGATE                             13.0                    
CRESCENT 1 W                         10.0                    
SUMPTER 6 N                           9.0                    

...WASHINGTON...
WINTON 3 NW                          14.0                    
LUCERNE 9 W                          10.5                    
MAZAMA 2 NW                           8.3                    
EASTON 6 NNW                          7.0                    

...Selected preliminary Storm Total Rainfall in inches from 800 AM
PST Sat Dec 11 through 600 AM PST Mon Dec 13...

...CALIFORNIA...
MOUNT TAMALPAIS                      8.74                    
SCOTTS VALLEY                        6.05                    
SCOTT CREEK                          5.84                    
WOODACRE                             5.84                    
BEN LOMOND                           5.68                    
KENTFIELD                            5.36                    
GASQUET                              4.86                    
RED MOUND                            4.56                    
FLYNN PRAIRIE                        4.37                    
SPRING VALLEY                        3.86                    
SAN FRANCISCO                        2.37                    

...Selected preliminary Peak Wind gusts in miles per hour earlier
in the event...

...IDAHO...
GRANGEVILLE 2 N                        60                    
WINCHESTER 5 NW                        59                    

...MONTANA...
EAST GLACIER PARK 8 SE                 92                    
BYNUM 14 W                             86                    
WILSALL 17 NE                          78                    
SUNBURST                               75                    
DENTON 7 ENE                           68                    
LIVINGSTON 2 WSW                       68                    
ZORTMAN 10 ESE                         65                    
GREAT FALLS 5 WSW                      62                    

...OREGON...
LINCOLN CITY                           93                    
YAQUINA BAY BRIDGE                     78                    
HEBO 5 ESE                             75                    
YACHATS 2 SE                           72                    
ASTORIA 1 W                            68                    
ROCKHOUSE RAWS                         61                    
GARIBALDI 2 WNW                        59                    
SALEM AIRPORT                          47                    
PORTLAND                               45                    

...WASHINGTON...
RICHLAND 22 NNW                        78                    
WALLA WALLA AIRPORT                    62                    
POMEROY                                58                    
LOOMIS 5 S                             49                    
SPOKANE SOUTH HILL                     42                    

...WYOMING...
BORDEAUX 1 SSE                         88                    
ARLINGTON 7 ESE                        85                    
CENTENNIAL 2 WNW                       77                    
CHEYENNE 1 NW                          64                    
BIG HORN 17 WSW                        60                    
GELNROCK 1 S                           58                    


Heavy precipitation in the form of both rain and snow will
continue across California, Oregon, and the Great Basin through
the early week as an upper-level trough continues inland across
the western U.S. and the Atmospheric River brings in additional
surges of significant moisture. Broad, significant snow totals of
1-3 feet are forecast for the Cascades, Sierra Nevada, and Great
Basin mountains. Locally, some snow totals may exceed 3-6 feet in
the Sierra Nevada. The heavy rain threat will also continue
through the next couple of days. There is a Moderate Risk of
Excessive Rainfall for Monday for the Big Sur Coast of California
with a broader Slight Risk for the Southern Coast Ranges. Rainfall
of 3-5 inches is likely with higher amounts of 6-8 inches possible
bringing the threat of flash flooding to the Coastal Ranges as
well as debris flows across burn scars. There is a Slight Risk of
Excessive Rainfall for Tuesday for portions of Southern California
including the Los Angeles and San Diego metro areas. Forecast
rainfall of 2-4 inches is expected along the higher terrain of
surrounding mountain ranges, with 48 hours totals potentially
approaching 3-6 inches. Debris flows along burn scars in the area
remains the primary impact. In addition to the heavy
precipitation, high winds will continue across a broad portion of
the western and central U.S. as the frontal system and strong
upper-level trough continue eastward, from the West Coast today
into the Central Plains by Wednesday. 

The next Storm Summary will be issued by the Weather Prediction
Center at 700 PM PST. Please refer to your local National Weather
Service office for additional information on this event.

Putnam