US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
336 PM EST Mon Dec 20 2021
 
Valid Thursday December 23 2021 - Monday December 27 2021
 
Hazards:
- Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Thu-Mon, Dec 23-Dec 27.
- Heavy rain across portions of California, Thu-Mon, Dec 23-Dec 27.
- Heavy snow across portions of the Central Great Basin, and California, Thu-Mon, Dec 23-Dec 27.
- Flooding occurring or imminent across portions of the Pacific Northwest.
- Flooding likely across portions of the Pacific Northwest.
- Much below normal temperatures across portions of the Northern Plains and the Northern Rockies, 
Fri-Mon, Dec 24-Dec 27.
- High winds across portions of mainland Alaska, Thu-Fri, Dec 23-Dec 24.
- Much below normal temperatures across portions of the Alaska Panhandle, Mon, Dec 27.
 
Detailed Summary:

The medium range period (Thursday, December 23rd - Monday, December 27th) will center around a 
drawn out heavy precipitation event across the West Coast with other temperature hazards likely 
across portions of the central CONUS and Alaska's panhandle. The upper-level pattern will be quite 
stagnant during the medium range with troughing in the West, ridging over the Central third of the 
country and quasi-zonal flow over the East. A short wave trough will arrive over the West Coast 
this Thursday, bringing with it a round of much needed heavy rain to the entire coast and lower 
elevations, as well as heavy snow to the Olympics, Cascades and Sierra ranges. While day-to-day 
totals will be greatest at the beginning of the period, persistent onshore moisture flow will allow 
for continued hazards such as; flash flooding, mud/rock slides etc. Snow will be measured in feet 
while multiple inches of rain will fall across the West Coast by early next week.

Downstream from this, temperatures will rise significantly across much of the Southern/Central 
Plains, Mississippi Valley and Midwest between Thursday and Monday as an Upper-ridge builds over 
the region. High temperatures may only reach the 70s and 80s for these areas which doesn't warrant 
a 'much above normal' hazard area. A bit of energy will break off from the larger troughing in the 
West and send a pair of surface low pressure systems across Canada and the northern tier of the 
CONUS through the medium range. This will lead to higher winds for the Central part of the country 
on Friday as well as anomalously cold temperatures for much of the Montana foothills and western 
North/South Dakota on the backside of the low pressure systems between Friday and Monday. High 
temperatures will be between 20-30 degrees below average for these areas. These systems may go on 
to produce heavy precipitation over parts of the Northeast on Christmas. Model uncertainty dictates 
that a hazard area not be issued for this region just yet, though.

Troughing along Alaska's southern mainland coast will lead to high wind hazards on Thursday and 
Friday. The encroachment of high pressure into the Panhandle and troughing off the coast will 
contribute to much below average temperatures by Monday.

Kebede