US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
328 PM EST Thu Dec 23 2021
 
Valid Sunday December 26 2021 - Thursday December 30 2021
 
Hazards:
- Heavy precipitation across portions of California and the Pacific Northwest, Sun, Dec 26.
- Heavy snow across portions of California, the Great Lakes, the Pacific Northwest, the Upper 
Mississippi Valley, and the Northern Plains, Sun, Dec 26.
- Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sun-Mon, 
Dec 26-Dec 27.
- Flooding occurring or imminent across portions of the Pacific Northwest.
- High winds across portions of the Southern Rockies, the Central Rockies, the Southern Plains, the 
Central Plains, and the Southwest, Sun, Dec 26 and Tue, Dec28.
- Much below normal temperatures across portions of California, the Central Great Basin, the 
Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Thu, Dec 27-Dec 30.
- Much below normal temperatures across portions of the Northern Plains and the Northern Rockies, 
Sun-Thu, Dec 26-Dec 30.
- Much below normal temperatures across portions of the Upper Mississippi Valley and the Northern 
Plains, Tue-Thu, Dec 28-Dec 30.
- Heavy snow across portions of mainland Alaska, Sun, Dec 26 and Tue, Dec 28.
- Much below normal temperatures across portions of the Alaska Panhandle, Sun-Tue, Dec 26-Dec 28.
 
Detailed Summary:

Over the lower 48 during the upcoming medium range period (Sunday, December 26 - Thursday, December 
30), upper troughing will remain deeply entrenched over the western states, resulting in a 
prolonged period of below normal temperatures and unsettled weather. Meanwhile, ridging and mostly 
dry/mild conditions will predominate across much of the Southeast. Separating these different air 
masses will be an active set of frontal boundaries stretching across the central and eastern U.S 
which will feature several waves of low pressure as short waves rotate through and eject out of the 
western trough.

One of the big stories this period will be the extremely cold weather over the north-central and 
northwestern states. Arctic air will take hold of the northern High Plains this weekend and likely 
persist through the end of next week. This prolonged cold outbreak will be centered over central 
and eastern Montana, but will build south and eastward across the Dakotas and upper Mississippi 
Valley during next week. The bitterly cold air will also spill westward over the Rockies and 
encompass the Pacific Northwest and parts of the Intermountain Region. High temperatures in the 
core of the coldest air (Montana/North Dakota) will remain at or below zero through the entire 
week, with lows dipping into the 20s and 30s below zero. In the Pacific Northwest, temperatures 
will range from 10-20 degrees below normal, resulting in many of the major cities west of the 
Cascades remaining below freezing much of the week, along with the threat for periods of light snow 
or snow showers.

Downstream of the western trough axis, the first of a series of frontal lows will form in the lee 
of the Colorado Rockies Sunday and promote gusty winds to its south across a fairly large area from 
central/eastern New Mexico into western Texas and Oklahoma, along with sections of southern 
Colorado and western Kansas. Given the dry conditions in this region, visibilities across the 
region may be reduced due to blowing dust, and potentially an enhanced fire weather risk. As this 
low moves out into the Plains and tracks toward the Upper Mississippi Valley, snow is expected to 
break out during Sunday from the Dakotas eastward into the upper Great Lakes region. At the moment, 
the most impactful snow (near warning criteria) will probably be confined to northern/central 
Minnesota and northern Wisconsin, while lighter amounts fall farther to the west and east.

The next system will push into the central Plains by early Tuesday and again be accompanied by a 
high wind threat across much of the same region that experiences windy conditions on Sunday. The 
low that rides along this front is not expected to be as strong, so while some snow is likely in 
the Upper Mississippi Valley/Great Lakes region, amounts should generally be light. Farther south, 
there will definitely be a better influx of Gulf of Mexico moisture into the front than the 
previous system, and strong frontal convergence ahead of the low will result in widespread rainfall 
breaking out from the mid-Mississippi Valley eastward into the Mid-Atlantic states on Tuesday, 
which will then shift southward with the front Wednesday. Total rainfall amounts appear to be only 
marginally heavy, and along with some uncertainty with the timing of low pressure and the frontal 
position, opted not to draw a hazard area. But will monitor this going forward.

In the West, while unsettled and showery weather is likely through much of next week, the general 
trend will be that the bulk of the precipitation shifts southward as the core of the trough begins 
to slide inland, but leaves behind a southern stream system near or off the coast. The highest 
likelihood for significant amounts will be with a system moving onshore Sunday into Monday. Heavy 
snow is expected from the Oregon Cascades southward across the Sierra Nevada range, with rains 
mostly confined to coastal locations and lowest elevations inland as snow levels with this feature 
are expected to be quite low. The majority of heavy snow over Oregon will fall Sunday into early 
Monday, then shift mostly into the Sierra Monday-Tuesday where one-week total accumulations will 
top several feet. During the middle to latter part of next week, there are some indications that 
the aforementioned southern stream trough will bring heavy precipitation into southern California 
and the Southwest, but the high degree of uncertainty precludes drawing any hazard areas at this 
time.

Across Alaska, Arctic air will bring much below normal temperatures to the Panhandle through early 
next week. By mid-week, however, the coldest air will begin shifting inland, leading to 
temperatures moderating closer to normal levels. Across the mainland, there appear to be at least 
two very good chances at significant snowfall during the period as a couple of systems move through 
the amplified upper ridge parked in the eastern Pacific. The models are in excellent agreement that 
a storm system and associated cold front will bring a significant snowstorm to northern/central 
Alaska Sunday. Deep moisture preceding the front will allow heavy snow to quickly spread from the 
west coast of northern Alaska east-southeastward through the southern part of the Brooks Range and 
the Yukon-Tanana Uplands during Sunday. Amounts of 5-10 inches should be common with locally over a 
foot in heavier bands or favored terrain. The next storm will bring another slug of deep moisture 
into the Interior and a renewed threat of heavy snow Tuesday-Wednesday. The details are more 
uncertain, but heavy snow may impact much of the same region as Sunday's storm. This feature has 
the potential to then spread heavy snow into South-Central Alaska toward the end of the period.

Klein