US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
351 PM EST Wed Dec 09 2020
 
Valid Saturday December 12 2020 - Wednesday December 16 2020
 
Hazards:
- Heavy precipitation from across portions of northern California into the Pacific Northwest, 
Sat-Sun, Dec 12-Dec 13.
- Heavy precipitation across portions of the Pacific Northwest, Sat-Wed, Dec 12-Dec 16.
- Heavy precipitation across portions of northern Maine, Sun-Mon, Dec 13-Dec 14.
- Heavy snow across portions of Idaho into northeastern Oregon, Sun, Dec 13 and Tue-Wed, Dec 15-Dec 
16.
- Heavy snow across portions of northwestern Wyoming into eastern Idaho, Sun-Mon, Dec 13-Dec 14 and 
Wed, Dec 16.
- Heavy snow across portions of the upper Midwest into the northern part of lower Michigan, Sat, 
Dec 12.
- Flooding likely across portions of northeastern Montana.
- High winds across the central portions of mainland Alaska, Sat-Wed, Dec 12-Dec 16.
 
Detailed Summary:

An active pattern in the northeastern Pacific will continue to direct low pressure/frontal systems 
toward the Pacific Northwest during the medium range period (Saturday, Dec 12 - Wednesday, Dec 16). 
 Lower-elevation rain and mountain snow will likely be heavy through much of the weekend from 
northern California to the Pacific Northwest before spreading well inland across Idaho and into the 
northern Rockies on Sunday into Monday.  Generally the highest amounts of precipitation should 
occur along the Coastal Ranges and the Cascades.  Gusty winds will likely accompany the passage of 
a warm front followed by a cold front across the Pacific Northwest this weekend into Monday.  A 
lull in the precipitation should occur on Monday before the next wave of moisture arriving by 
Tuesday, with heavy precipitation continuing across western Washington and the Cascades into 
Wednesday.  Meanwhile, the moisture will penetrate farther inland and bring mountain snow across 
the northern Rockies Tuesday and Wednesday.

Meanwhile, a deepening surface low pressure system will likely track across the Midwest into the 
lower Great Lakes on Saturday.  Cold air wrapping around the backside of the cyclone will likely 
change the precipitation from rain to snow near and just north of the cyclone track.  A heavy snow 
area is indicated on the map where this changeover is forecast to occur.  There is still some 
uncertainty regarding the storm track but the models appear to have settled into the present 
forecast track.  The system will also bring a decent amount of wintry precipitation for northern 
Maine on Sunday which should become mostly snow later on Sunday before ending on Monday.

It is worth mentioning that the ECMWF has been indicating the possibility of a rapidly intensifying 
cyclone early next week across the Southeast and the Mid-Atlantic.  This scenario has not been 
incorporated into the current hazards map.  The latest (12Z) ECMWF has now switched to a 
non-development solution, which is supported by the 00Z EC ensemble mean.  Nevertheless, an 
immediate solution depicting a developing frontal wave moving off the East Coast is reasonable 
(such as the Canadian model).  Some wintry precipitation is possible along the central Appalachians 
early on Monday as the wave is forecast to move off the Mid-Atlantic coast.

Over Alaska, a persistent high pressure system centered in the Arctic Ocean will be contrasted with 
deep cyclones over the northeastern Pacific to create a tight pressure gradient across mainland 
Alaska.  Interior central Alaska will likely see the highest threat for high winds late in the 
weekend into early next week.  These winds could cause blowing snow and lowering of visibility.  By 
next Wednesday, there appears to be an increasing chance of precipitation moving into the Alaska 
Panhandle.  However, models have not yet come into a general agreement on the precipitation amounts 
for this area.

Kong