US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
317 PM EST Fri Dec 21 2018
 
Valid Monday December 24 2018 - Friday December 28 2018
 
Hazards:
Heavy rain across portions of California and the Pacific Northwest, Mon, Dec 24.
Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee 
Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Upper 
Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, Wed-Fri, Dec 26-Dec 28.
Heavy snow across portions of California, the Central Great Basin, the Pacific Northwest, the 
Northern Rockies, and the Northern Great Basin, Mon, Dec 24.
Heavy snow across portions of the Central Plains, the Central Rockies, the Northern Plains, the 
Great Lakes, the Southern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, and 
the Southern 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, the Mid-Atlantic, the Northeast, and the Central 
Appalachians.
High winds across portions of the Central Plains, the Central Rockies, the Central Great Basin, the 
Northern Plains, the Great Lakes, 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, Fri, Dec 28.
High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Fri, Dec 
28.
 
Detailed Summary:

A large system will move across the Pacific Northwest, Intermountain West and northern California 
on Dec 24th. This system will bring copious amounts of moisture that could lead to rainfall along 
the coast from Washington State southward into northern California. Furthermore, heavy snow along 
parts of the Cascades and portions of the Sierra Nevada mountains can also be expected. Gusty winds 
and waves could also be expected. 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 southern/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. 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 and the 28th. 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 deep surface cyclone is forecast to move over or south of the Aleutians towards the 
Gulf on the 28th. This may result in significant waves (>20 ft) or high winds (>50 knots) across 
portions of the Aleutians and possibly into parts of the western Panhandle.

Reinhart