US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
211 PM EST Wed Dec 18 2019
 
Valid Saturday December 21 2019 - Wednesday December 25 2019
 
Hazards:
- Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Sat-Sun, Dec 21-Dec 22.
- Heavy rain across portions of the Southeast and the Lower Mississippi Valley, Sat-Mon, Dec 21-Dec 
23.
- Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sun-Tue, 
Dec 22-Dec 24.
- Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat, Dec 21.
- Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, 
and the Southwest, Tue-Wed, Dec 24-Dec 25.
- Flooding possible across portions of the Central Plains, the Pacific Northwest, and the Northern 
Plains.
- Flooding occurring or imminent across portions of the Ohio Valley and the Northern Plains.
- Flooding likely across portions of the Pacific Northwest and the Northern Plains.
- High winds across portions of the Southeast, Sat-Sun, Dec 21-Dec 22.
- High significant wave heights for coastal portions of the Southeast, Sun-Mon, Dec 22-Dec 23.
- Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Dec 
23-Dec 24.
- High winds across portions of the Aleutians, Sun-Mon, Dec 22-Dec 23.
- Much below normal temperatures across portions of mainland Alaska, Sat-Mon, Dec 21-Dec 23.
- High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Mon-Tue, 
Dec 23-Dec 24.
 
Detailed Summary:

The biggest threat in the medium range period the day 3-7 hazards for the continental U.S. will be 
a persistent atmospheric river funneling moisture into the West.  The moisture plume is expected to 
focus in the Pacific Northwest slowly move south on Saturday into Northern California.  Heavy snow 
is forecast in higher elevations of the Cascades and Northern Rockies, with heavy rain in lower 
elevations. 

A surface low over the North-Central Gulf of Mexico will move eastward across Florida and contimue 
to move eastward out over the Western Atlantic by Tuesday.  The system will produce locally heavy 
rainfall along the Atlantic coast of Florida and the Carolinas into parts of the Cenral Gulf Coast 
on Saturday into Monday.

A general upper-level troughing pattern over Alaska is expected to cause below average temperatures 
there, which has been unusual this year.  The largest cold temperature anomalies will be south of 
the Brooks Range into the central part of the state.  Low pressure in the Gulf of Alaska will lead 
to heavy precipitation for the Alaska Panhandle on Monday and Tuesday.  Then, there is potential 
for a strong low to cause high winds over 50 knots for the Aleutians on Sunday and Monday. There is 
uncertainty with the track of this low, with the GFS model runs tracking north of the Aleutians 
with a deeper low, and the ECMWF/CMC tracking just south of the islands with a slightly weaker, yet 
still robust low. In addition, significant waves will impact the Aleutuans on Monday into Tuesday.

In Hawaii, strong trade winds are likely Saturday into Sunday morning as a anomalously strong 
surface high pressure system sets up north of the islands. Then there is the possibility of heavy 
rain coming in ahead of a cold front Tuesday, Christmas Eve, there.

Ziegenfelder