US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
332 PM EST Wed Jan 27 2021
 
Valid Saturday January 30 2021 - Wednesday February 03 2021
 
Hazards:
- Heavy precipitation across portions of the Mid-Atlantic and the Central Appalachians, Sun-Tue, 
Jan 31-Feb 2.
- Heavy rain across portions of California and the Pacific Northwest, Sun-Tue, Jan 31-Feb 2.
- Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Wed, Feb 3.
- Heavy rain across portions of the Central Plains, the Southeast, the Middle Mississippi Valley, 
the Mid-Atlantic, and the Ohio Valley, Sat-Sun, Jan 30-Jan 31.
- Heavy snow across portions of California, the Pacific Northwest, the Northern Rockies, and the 
Northern Great Basin, Sat-Mon, Jan 30-Feb 1.
- Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat-Tue, 
Jan 30-Feb 2.
- Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Mon-Tue, Feb 
1-Feb 2.
- Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, 
and the Northern Great Basin, Tue-Wed, Feb 2-Feb 3.
- Heavy snow across portions of the Central Rockies, the Central Great Basin, and the Southwest, 
Wed, Feb 3.
- Heavy snow across portions of the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, 
and the Upper Mississippi Valley, Sat-Sun, Jan 30-Jan 31.
- Heavy snow across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the 
Southern Appalachians, the Great Lakes, and the Ohio Valley, Sun-Tue, Jan 31-Feb 2.
- Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great 
Lakes, Sat-Sun, Jan 30-Jan 31.
 
Detailed Summary:

A climactic end to January features medium range hazards along the West Coast extending into 
Mountain West and Mid-Atlantic regions. In the west, digging energy in the Northern Pacific will 
amplify an area of low pressure in the Pacific Northwest with an ample supply of Pacific moisture 
to siphon northeastward ahead of a frontal system this weekend. Although precipitable water 
anomalies are only marginally above normal ahead of the system, the sheer duration of the 
atmospheric river event only serves to exasperate ongoing effects from recent heavy rain and heavy 
mountain snow in the region. As the trough moves inland early next week, additional high-elevation 
heavy snow is likely across portions of the Mountain West which may provide beneficial water to 
drought stricken areas there. Meanwhile, a deep Colorado low develops and quickly races eastward 
Saturday as the trough digs into the Southern Plains. As the storm taps into a fetch of Gulf 
moisture, areas of heavy rain and snow develop over the Midwest. Hazardous travel conditions may 
arise with blowing snow in the heavy snow area as the low deepens. Farther east, "much below 
normal" temperatures are expected in New England Saturday and Sunday as strong cold air advection 
on the back end of a deep low pressure system in the Northwest Atlantic pulls down frigid Canadian 
air, with minimum temperature anomalies around fifteen degrees below normal.   

This wedge of cold air spills down the spine of the Appalachians Sunday and sets the stage for a 
clash between rich Gulf of Mexico moisture ahead of the Midwest storm system and sub-freezing air 
at low levels in the Mid-Atlantic. As the upper low approaches, precipitation looks to fall in the 
form of snow from the Ohio Valley and central Appalachians early Sunday to the Mid-Atlantic I-95 
corridor later in the day. Ensemble guidance remain at odds over the the speed of the approaching 
upper trough with the GEFS remaining on the faster side of guidance. The Euro ensemble is slower 
while also having a closed upper low tracking over Virginia by Monday afternoon. The subtle 
differences can mean drastically different positions where the axis of heavy snow becomes oriented. 
This is especially true in the Mid-Atlantic, because the longer the coastal low takes to develop 
and the main low in the Ohio Valley stays dominant (i.e. GFS/GEFS) the better the chances a warm 
nose aloft and/or dry slot may limit snow totals. The Euro ensemble makes the transition faster and 
farther south, leading to a greater signal for heavier snowfall in the Mid-Atlantic region. While 
these aspects of the forecast are still murky this much is clear: confidence is growing that a 
potentially significant winter storm may impact much of the Mid-Atlantic and Northeast late Sunday 
and into the first half of next week with hazards that would include heavy snow, treacherous ice 
(central Virginia into central North Carolina most notably), heavy rain (Southeast), gusty winds, 
and coastal flooding.

In Alaska, a passing cold front delivers a shot of below normal temperatures to most of the western 
regions, but departures appear to fall short of "much below normal" criteria. The next potential 
weather maker comes in the form of a strong cyclone west of the Aleutians. Gusty winds are likely 
Sunday and into Monday but do not appear to reach excessive levels. Ensemble guidance does suggest 
a plume of rich Pacific moisture streams north towards the Gulf shores by early next week, but high 
spread in ensemble members continue to keep confidence in totals low at this time. Will revisit 
this tomorrow to see if confidence improves enough to add a "heavy precipitation" area on Thursday.
  

Mullinax/Asherman