US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
313 PM EST Thu Dec 20 2018
 
Valid Sunday December 23 2018 - Thursday December 27 2018
 
Hazards:
Heavy rain across portions of California and the Pacific Northwest, Sun-Tue, Dec 23-Dec 25.
Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee 
Valley, the Great Lakes, the Middle Mississippi Valley, the Mid-Atlantic, the Southern 
Appalachians, the Upper Mississippi Valley, the Southeast, the Southern Plains, and the Ohio 
Valley, Wed-Thu, Dec 26-Dec 27.
Heavy snow across portions of California, the Central Great Basin, the Pacific Northwest, the 
Northern Rockies, and the Northern Great Basin, Sun-Tue, Dec 23-Dec 25.
Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, 
and the Central Plains, Tue, Dec 25.
Heavy snow across portions of the Central Rockies, the Central Plains, the Middle Mississippi 
Valley, the Upper Mississippi Valley, and the Northern Plains, Wed-Thu, Dec 26-Dec 27.
Flooding possible across portions of the Southern Appalachians, the Mid-Atlantic, the Northeast, 
and the Central Appalachians.
Flooding occurring or imminent across portions of the Southeast and the Mid-Atlantic.
Flooding likely across portions of the Southeast.
High winds across portions of the Central Plains, the Central Rockies, the Central Great Basin, the 
Northern Plains, the Southern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, 
the Southern Plains, and the Southwest, Wed-Thu, Dec 26-Dec 27.
High winds across portions of mainland Alaska and the Aleutians, Mon, Dec 24.
High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Mon-Tue, 
Dec 24-Dec 25.
 
Detailed Summary:

A series of systems will move across the Pacific Northwest, Intermountain West and northern 
California through Dec the 23-25 time frame. These systems will bring copious amounts of moisture 
that could lead to have rainfall along the coast from Washington State southward into northern 
California. Furthermore, heavy snow along the Cascades and into parts of the Sierra Nevada 
mountains can also be expected. While there is a chance for rainfall each day, the most significant 
impacts are expected on Dec 24-25. These storm systems could also bring gusty winds and waves. 
Given the timing over the Holiday weekend, both road and air travel delays are expected.

A digging upper trough over the western U.S. will push eastward toward the Plains in the beginning 
of next week. A surface low will set up in the Plains late on the 26th and will strengthen as it 
moves northward into the Upper Midwest by the 27th. North of the low, significant/heavy snowfall is 
possible--particularly from the central High Plains eastward into the Upper Midwest. Pressure 
gradient may also lead to high winds with this heavy snowfall and could cause blowing snow and 
other hazards. Later on the 27th, as precipitation begins to spread across the Upper Great Lakes 
and approaches the central Appalachians--rain and possible freezing rain accumulations will be 
possible. However, the exact placement of the heaviest axis of snow along with the areas that could 
be impacted by freezing rain still remain uncertain. Models continue to show enough consensus on a 
heavy snow area on the hazards chart, but a freezing rain area could be added later on. To the 
south, deep southerly flow ahead of the digging trough along with a frontal system will lead to the 
possibility of heavy rainfall from the southern and central Plains eastward to the 
Southeast/southern Appalachians and into parts of the Ohio Valley Expect the heavy rainfall in the 
Plains/Mississippi Valley on the 26th, shifting eastward to the Ohio Valley/Southeast by the 27th. 
High winds associated with this trough is also possible from the Southwest to the western portions 
of the southern Plains along with the central Rockies on Dec 26-27. 

In Alaska, a couple of deep surface cyclones are forecast to move over or south of the Aleutians 
towards the Gulf. This may result in significant waves (>20 ft) or high winds (>50 knots) across 
portions of the Aleutians into the western part of the Panhandle Sunday-Monday.

Reinhart