US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
325 PM EST Mon Dec 27 2021
 
Valid Thursday December 30 2021 - Monday January 03 2022
 
Hazards:

Detailed Summary:

An active weather pattern is expected for many parts of the country as we close out 2021 and ring 
in the New Year.  The extremely persistent upper trough that has dominated much of the western U.S. 
will finally move eastward later this week through the weekend.  The respite for the West will be 
brief, however, as it's likely another powerful system will amplify off the coast early next week.  
Before the trough exits, a few features will bring some impactful weather.  The first is a 
fast-moving short wave crossing the northern High Plains Thursday, which will induce low pressure 
over Wyoming and the potential for high winds over southern/western Wyoming and favored terrain in 
northern Colorado. The second is a fairly potent short wave and surface low pushing into the 
Pacific Northwest Thursday; onshore flow will support some heavy snowfall (local amounts up to a 
foot) for the Washington and Oregon Cascades.  The third is a southern stream system that will 
spread precipitation into southern California and the Southwest Thursday-Friday.  The heaviest 
precipitation Thursday will focus over southern California, though right now the amounts appear 
mostly to stay below criteria levels.  Regardless, there is a threat for localized flooding, 
particularly in any burn scar locations.  As the storm moves inland Friday, favored terrain in 
central Arizona (Mogollon Rim area) and southwestern Colorado will likely see the most significant 
precipitation.  Much of this will be rain (with upwards of 1-1.5 inches) in Arizona, with moderate 
to heavy snowfall likely in Colorado.

Later Friday into Saturday, the southern stream system will eject into the Plains and spin up a 
fairly deep area of low pressure over the central High Plains.  This low will then track 
northeastward along a very strong frontal boundary, reaching the Upper Midwest by late Saturday 
before lifting across the Great Lakes States and toward New England Sunday.  Broad southwesterly 
flow out ahead of this low will draw significant Gulf of Mexico moisture northward, with widespread 
rainfall breaking out Friday night over the mid-Mississippi and Tennessee Valleys, then expanding 
in coverage and intensity on Saturday along with a threat for severe weather.  Rainfall amounts of 
1-3 inches with locally higher amounts are expected over the Tennessee and lower Ohio Valleys, the 
mid-Atlantic states and into the Southeast.  To the north of this low track, widespread snowfall is 
likely, mainly from Friday through Saturday nights.  There has been some uncertainty with the 
track/strength of this low, so confidence has been fairly low pinpointing where the heaviest may 
fall.  At the moment, believe the best chance for warning criteria snowfall will extend from 
southern Wisconsin across the northern part of lower Michigan.  On Sunday, there are indications 
that another low will spin up along the front as it continues pressing eastward.  This would 
maintain moderate to heavy precipitation for parts of the mid-Atlantic region and central 
Appalachians through Sunday, but overall confidence is lower with this feature.

Another notable hazard associated with this front will be to its north, where Arctic air will 
maintain much below normal temperatures into the beginning of 2022 from the Upper Mississippi 
Valley westward across the northern Rockies and sections of the Pacific Northwest.  The core of the 
coldest air will sit over Montana and North Dakota, where temperatures through Saturday will 
average 20-30+ degrees below normal, which translates to highs in the minus teens and lows well 
down into the minus 20s.  As the previously mentioned low moves out into the Plains late 
Friday-Saturday, northerly winds behind it will allow the Arctic air to push southward through the 
central Plains for the weekend. However, ridging will build in early next week, allowing 
temperatures to finally begin to moderate back toward more normal levels.   

Early next week, another strong trough setting up off the Pacific Northwest coast may lead to a 
renewed round of heavy precipitation.  While there's still a lot of uncertainty with the specifics 
at this time range, it appears that the main threat for significant coastal/valley rain and 
mountain snow will extend from western Washington southward into northern California. 

For Alaska, a surface low tracking through the Bering Sea will bring gusty winds up to 50-60 mph to 
the Aleutians on Thursday.  Precipitation with this feature will spread inland across southwest and 
south-central Alaska, bringing mostly light-moderate snow accumulations (with the exception of the 
Alaska Peninsula where precipitation will likely fall as rain or a mix of rain/snow).  Farther 
east, however, a good fetch of deeper Pacific moisture will overrun an Arctic air mass and support 
heavy snowfall for much of the Panhandle Friday into Saturday.  Amounts of up to or exceeding a 
foot are possible, though right along the coast, totals may be lighter as precipitation mixes with 
rain.  Behind this feature, strong gap/outflow winds are likely to develop over the weekend across 
sections of the Alaska Peninsula eastward through Cook Inlet and the Kenai Peninsula Saturday, then 
extend toward Yakutat during Sunday.  Localized gusts over 60-70 mph are possible, especially 
Saturday night through Sunday.  Also behind this feature and downstream of an amplifying upper 
ridge, a very cold Arctic air mass will spread below normal temperatures across eastern sections of 
Interior Alaska, much of southwestern and south-central Alaska and possibly into the Panhandle for 
early next week.

Klein