US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
351 PM EST Tue Dec 07 2021
Valid Friday December 10 2021 - Tuesday December 14 2021
- Heavy precipitation across portions of the Pacific Northwest, Fri-Sat, Dec 10-Dec 11.
- Heavy precipitation across portions of southwestern Oregon into the northern half of California
as well as the Sierra Nevada, Sun-Mon, Dec 12-Dec 13.
- Heavy precipitation along the Sierra Nevada and into portions of southern California, Tue, Dec 14.
- Heavy rain from the interior Deep South to the Tennessee and Ohio Valleys mainly west of the
spine of the Appalachians, Fri-Sat, Dec 10-Dec 11.
- Heavy snow across portions of the northern Rockies, Sat-Sun, Dec 11-Dec 12.
- Heavy snow from the northern/central Plains through the upper Midwest into the upper Great Lakes,
Fri-Sat, Dec 10-Dec 11.
- High winds across portions of the southern Rockies to the southern High Plains, Fri, Dec 10.
- High winds across portions of northwestern Montana, Sat, Dec 11.
- High winds across portions of eastern Wyoming, Sat-Sun, Dec 11-Dec 12.
- Heavy precipitation along the Alaska Panhandle to portions of the south coast of Alaska, Fri, Dec
- High winds across portions of southwestern Alaska and into the Aleutians, Sat-Sun, Dec 11-Dec 12.
- High winds across central Aleutians, Fri, Dec 10.
- Much below normal temperatures across the southern half of mainland Alaska and the Alaska
Peninsula, Sat-Mon, Dec 11-Dec 13.
An intensifying low pressure system exiting into the Plains on Friday will spread a variety of
weather hazards across portions of central and eastern U.S. through the weekend. Cold air already
in place across the northern Plains will likely support a swath of moderate to heavy snowfall with
gusty winds across the central to northern Plains and then through the upper Midwest into the upper
Great Lakes from Friday and into early on Saturday. Meanwhile, warm and moist air converging ahead
of a cold front will likely support heavy rainfall from the interior Deep South through the
Tennessee and Ohio Valleys mainly west of the spine of the Appalachians Friday and into Saturday.
As the front moves further into the East Coast later on Saturday, the threat of heavy rain should
generally decrease, although pockets of heavy rain are possible with some of the embedded
thunderstorms. There is some timing uncertainty with the eastward motion of the front but latest
model guidance appears to support a steady and faster progression of the front through the East
Coast into Saturday night.
Behind this intensifying low, portions of the southern Rockies to the southern High Plains will be
under the threat of high winds on Friday before the system moves farther away into the upper
Midwest Friday night. By Saturday, a rather pronounced upper ridge is forecast to build and extend
across the western U.S. This pattern will encourage downslope winds to develop on the lee side of
the northern Rockies under strong pressure gradient during the weekend. The highest threat of
strong Chinook winds should appear in northwestern Montana during the day on Saturday, with another
of enhanced threat across eastern Wyoming. The threat of high winds should decrease by Sunday
although eastern Wyoming could see these strong downslope winds to continue a bit longer on Sunday.
Meanwhile, amplified troughing digging down through the west coast of North America will likely
bring the next wave of heavy coastal rain and heavy mountain snows through much of the medium-range
period. Moderate to significant rain/mountain snow is expected to first reach the Olympic
Peninsula Friday night/early Saturday before steadily spreading from north to south through the
West Coast during the next few days. The Cascades, and especially the Sierra Nevada, will likely
see big snowfall totals as this heavy precipitation event unfolds through the first half of next
week. Some of the heavy snowfall will likely impact portions of the northern Rockies this weekend
In Alaska, a large cyclone lingering near the south coast of Alaska will continue to sustain the
threat of high winds across the Aleutians, the Alaska Peninsula and into portions of coastal
southwestern Alaska on Friday and through the weekend. These winds should finally subside on
Monday as the cyclone should drift farther south and weaken. Prior to the departure of the
cyclone, much below normal temperatures will overspread the southern half of mainland Alaska, where
daytime highs 20-30+ degrees below normal are possible. Heavy precipitation along the south coast
of Alaska and the Panhandle initially on Friday will likely wane Friday night. By early next week,
the guidance continues to show the potential for another significant storm to enter the Bering Sea
and then impact parts of the Aleutians with rain and strong gusty winds followed by snowy and windy
weather across southwestern Alaska. This situation will need to be further monitored as the models
come into better agreement on the strength and timing associated with this next storm.
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