US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
247 PM EST Mon Dec 07 2020
 
Valid Thursday December 10 2020 - Monday December 14 2020
 
Hazards:
- Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Sat-Sun, Dec 12-Dec 13.
- Heavy snow across portions of the Central/Northern Great Basin and the Central/Northern Rockies, 
Sun-Mon, Dec 13-Dec 14.
- High winds across portions of mainland Alaska and the Aleutians, Thu, Dec 10.
- High winds across portions of mainland Alaska, Sat-Sun, Dec 12-Dec 13.
 
Detailed Summary:

Over the medium range period (Thursday, Dec 10 - Monday, Dec 14), periods of precipitation are 
likely across the Northwest. Precipitation amounts are expected to get heavier by the weekend in 
the Pacific Northwest and northern California as Pacific moisture increases and a frontal system 
approaches. Generally higher amounts of precipitation should occur in the terrain of the Coastal 
Range and Cascades, with higher elevation snow and lower elevation rain. Snow is forecast to spread 
into the Northern Rockies toward the Wind River Mountains/Tetons early next week, and amounts could 
be heavy there as well. There is also some chance of gusty winds across the Central/Northern 
Rockies this weekend into Monday.

Something else to watch during the period is a surface low pressure system deepening in the Plains 
late week and then track northeastward across the Great Lakes region by the weekend, ahead of an 
upper-level trough moving eastward across the CONUS. Ahead of the cold front associated with this 
low, Gulf of Mexico moisture could stream in and interact with the front and cause rain and 
thunderstorms, with highest rain amounts currently expected in and around the Lower Mississippi 
Valley. Since the front should be moving fairly quickly, and this area has seen below normal 
rainfall in the past month or so, the rainfall does not currently appear to pose widespread 
hazards. Then on the backside of the low track, wintry weather/snow is possible over parts of the 
north-central U.S., but enough uncertainty in the location and amounts of snow precluded drawing a 
hazard area there for now. Warmer than average temperatures by 10 to 20 degrees are forecast to 
push from the central U.S. Thursday/Friday into the eastern U.S. over the weekend ahead of the 
upper-level trough. 
Near average temperatures (with maximum temperatures maybe slightly below) are expected for the 
Intermountain West through Saturday. 

Over Alaska, a deep surface low over the Bering Sea Thursday should gradually weaken through the 
end of the week. But the tight pressure gradient could cause strong southerly winds across portions 
of the Aleutians and Alaska Peninsula on Thursday, along with some potential for precipitation for 
that area--model guidance varies with amounts, however. Then, some gusty winds are possible 
Saturday around the Alaska Peninsula/Kodiak Island area with another surface low, but does not 
appear to rise to the level of high winds. Areas of interior Alaska also may have a threat for high 
winds over the weekend with another tight pressure gradient. The winds could cause blowing snow and 
lower visibility. Below normal temperatures are expected for the western half of mainland Alaska 
Thursday, spreading into eastern parts of the interior for the end of the week.

Tate