US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
404 PM EST Mon Dec 21 2020
 
Valid Thursday December 24 2020 - Monday December 28 2020
 
Hazards:
- Heavy precipitation across portions of California, the Pacific Northwest, and the 
Northern/Central Great Basin, Sat-Mon, Dec 26-Dec 28.
- Heavy precipitation across portions of California, the Central Great Basin, the Pacific 
Northwest, and the Southwest, Thu-Fri, Dec 24-Dec 25.
- Heavy precipitation across portions of the Northern Rockies and the Northern Great Basin, Sun, 
Dec 27.
- Heavy rain across portions of the Northeast, the Central/Southern Appalachians, the Great Lakes, 
the Mid-Atlantic, California, the Southeast, the Pacific Northwest, and the Ohio Valley, Thu-Fri, 
Dec 24-Dec 25.
- Heavy snow across portions of the Central Rockies, the Northern Rockies, and the Northern/Central 
Great Basin, Sun, Dec 27.
- Heavy snow across portions of the Northeast, the Central/Southern Appalachians, the Tennessee 
Valley, the Mid-Atlantic, the Great Lakes, and the Ohio Valley, Thu, Dec 24.
- Flooding occurring or imminent across portions of the Pacific Northwest.
 
Detailed Summary:

A deep low over Central Ontario, Canada, will move northeastward to Northeast Canada by Saturday.  
On Christmas Eve, the associated front extending from the Great Lakes to the Central Gulf Coast 
will move off the East Coast by Christmas.  Moisture from the Western Gulf of Mexico will pool 
along the boundary, aiding in the development of heavy rain from parts of the Northeast to the 
Mid-Atlantic and Southern Appalachians on Christmas Eve into Christmas.  Heavy snow will develop 
along the northwest side of the precipitation shield over parts of the Ohio Valley, Central 
Appalachians, the Lower Great Lakes, and parts of the interior Northern Mid-Atlantic on Christmas 
Eve. 

The pressure gradient associated with low pressure will be strong enough to produce robust and 
steady wind over the region from the Upper Midwest to the Northeast, but the wind will not meet the 
criteria for high wind.  Furthermore, the wind will be the highest over the Great Lakes' open 
waters on Christmas Eve and Christmas. It will begin to taper off later on Christmas. The wind will 
also be strong over parts of the Northwest and the Northern/Central Rockies on Christmas Eve and 
Christmas, but will not reach high wind criteria.

In the meantime, a front approaching the West Coast will move onshore overnight on Christmas.  The 
boundary will include moisture and will produce heavy rain over parts of Northern California and 
Oregon Coast as well as heavy precipitation over the Sierra Nevada Mountains on Christmas Eve and 
Christmas.

Upper-level energy will move over the West Coast in the wake of the front that will aid in 
producing heavy precipitation (rain and snow) over the Cascades, Olympic Peninsula, and the Sierra 
Nevada Mountains from Saturday into Monday.  As the front and associated upper-level energy moves 
into the Northern Intermountain Region/Northern Rockies, heavy precipitation (rain and snow) will 
develop over parts of Idaho and heavy snow will develop over the Tetons and Wind River mountain 
Ranges on Sunday.  Additionally, strong wind will develop over parts of the Central/Southern 
Rockies on Saturday and Sunday, tapering off on Monday.  The wind will be lower than the criteria 
for high wind on the Hazards Map.
 
Over Alaska, no hazards are depicted on the Hazards Chart.  However, an area of deep low pressure 
will move over the Aleutians and into the Bering Sea from the North Pacific on Saturday into 
Sunday.  The deep low pressure will have strong wind associated with it, but the wind will be just 
below the criteria for high wind over the Aleutians, e.g., 50 knots or greater, this time of the 
year. 

Ziegenfelder