US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
330 PM EST Thu Dec 09 2021
 
Valid Sunday December 12 2021 - Thursday December 16 2021
 
Hazards:
- Heavy precipitation from coastal Washington southward into the northern half of California, 
Sun-Mon, Dec 12-Dec 13.
- Heavy precipitation across a large portions of California including the Sierra Nevada, as well as 
portions of Nevada and Utah, and parts of southwestern Colorado, Tue-Wed, Dec 14-Dec 15.
- Heavy snow across portions of the higher elevations in Idaho and northeastern Oregon, Sun, Dec 12.
- Heavy snow across portions of the northern Rockies, Tue, Dec 14.
- Heavy snow across portions of the central Rockies, Wed, Dec 15.
- High winds over portions of the northern and central Rockies, and across the northern Plains into 
the upper Midwest, Wed-Thu, Dec 15-Dec 16.
- High winds across portions of eastern Wyoming, Sun, Dec 12.
- Much above normal temperatures across portions of the central Plains to the upper Midwest, 
Tue-Wed, Dec 14-Dec 15.
- High winds across portions of the Alaska Peninsula as well Kodiak Island, Sun, Dec 12.
- Much below normal temperatures for the southern half of Alaska including the Alaska Peninsula, 
Sun-Mon, Dec 12-Dec 13.
 
Detailed Summary:

An amplified upper-level trough will likely to continue digging down just off the West Coast of the 
U.S. as the medium-range period begins on Sunday.  Rain and mountain snow over the Pacific 
Northwest should become less heavy behind a cold front.  However, heavy coastal rain and heavy 
mountain snows will likely surge into northern California ahead of the cold front Sunday into 
Monday.  Meanwhile, the Sierra Nevada will likely see big snowfall totals as this heavy 
precipitation event pushes further to the south into Tuesday.  From Tuesday onward, the upper 
trough is forecast to move onshore and into the western U.S. This will increase the threat of heavy 
precipitation to spread from southwest to northeast through the Great Basin and across the northern 
and central Rockies into Wednesday, bringing the threat of heavy snow across higher elevations and 
rain/snow for the lower elevations.  Depending on the strength and timing of the trough, the 
central to southern Rockies into the High Plains could be impacted by high winds starting next 
Wednesday.  Looking further ahead, models are indicating the potential of a rather robust low 
pressure system to track northeastward across the central Plains later on Wednesday into Thursday.  
High winds along with a swath of wintry precipitation are possible from the northern/central 
Rockies and across the northern U.S. although the specific details are uncertain at this time.  
Another moisture plume approaching the West Coast could bring the next round of heavy precipitation 
into northern California next Wednesday into Thursday.

As the upper trough works its way through the western U.S., an anomalous warm ridge of high 
pressure is forecast to build over the mid-section of the country.  A large area of well above 
normal temperatures is forecast to emerge over the central U.S. and then spread toward the Midwest 
and upper Midwest midweek next week after a swath of moderate to heavy snow is forecast to fall 
during the next couple of days.  The area highlighted represents regions with temperatures more 
than 25 degrees above normal (maximum approaching 40 degrees) for this time of the year.

Over the Northeast, a low pressure system moving further away into the Canadian Maritimes on Sunday 
will result in result in diminishing winds across northern New England.  Behind the exiting low, a 
rather pronounced upper ridge is forecast to build and extend across the western U.S. toward the 
Great Plains. This pattern will encourage downslope winds to develop on the lee side of the 
northern Rockies under strong pressure gradient during the weekend.  Parts of eastern Wyoming will 
remain under an enhanced threat of strong Chinook winds on Sunday before subsiding Sunday night.

In Alaska, a large cyclone lingering near the south coast of Alaska will continue to sustain the 
threat of high winds from the Alaska Peninsula to Kodiak Island into Sunday morning before 
subsiding considerably as the cyclone drifts farther south and weaken. Prior to the departure of 
the cyclone, much below normal temperatures will overspread the southern half of mainland Alaska, 
where daytime highs 20-30+ degrees below normal are expected. By early next week, model guidance 
continues to indicate another significant storm to enter the Bering Sea and then impact parts of 
the Aleutians with rain and strong gusty winds, followed by snowy and windy weather across 
southwestern Alaska.  These conditions appear to linger into midweek with additional disturbances 
pushing into western Alaska.

Kong