Atmospheric Rivers

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Sat Nov 23 2024
Valid 12Z Sat Nov 23 2024 – 12Z Mon Nov 25 2024

…Very strong Atmospheric River to produce heavy snow across the Sierra
Nevada before winding down over north/central California today…

…Above average temperatures expand across the Central U.S. this
weekend…

Moisture associated with a highly impactful and dangerous atmospheric
river event will diminish as it sags south and east through central
California today. Heavy snow is likely over much of the Sierra Nevada this
morning where anywhere between 1-2 feet are expected to accumulate when
all said and done. Upslope portions of the Sierra below 7000 feet may
experience isolated instances of flash flooding this morning before snow
levels drop on the backside of the cold front pushing through the West
this afternoon. Snow showers spread into Northern/Central Rockies this
afternoon and the Intermountain West on Sunday. Snowfall totals of 6-12
inches are probable for the aforementioned areas by the end of the weekend.

Surface high pressure extending from central Canada down to the Gulf Coast
will support below average temperatures for those regions through tonight.
Parts of the Southeast will experience low temperatures in the mid to
upper 30s which may lead to some frost/freezes. A deepening upper trough
over the north-central U.S.and Ridge over Mexico will promote above
average temperatures across the Great Plains today and Sunday before
expanding into the East by Monday. Elsewhere, mixed precipitation can be
expected to continue across portions of upstate New York and New England
today.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Fri Nov 22 2024
Valid 12Z Fri Nov 22 2024 – 12Z Sun Nov 24 2024

…Atmospheric river will produce one last round of heavy rain/mountain
snow and strong wind gusts across the Pacific Northwest today…

…Moderate to heavy snow for portions of the Central Appalachians today...

…Above average temperatures expand across the Central U.S. this
weekend…

Anomalous moisture supported by a deep low pressure system will continue
impacting the Pacific Northwest today. Life threatening flooding is likely
across portions of northern California, where additional amounts of 3-5″
are expected, mainly over coastal areas. As much as 4-10″ of rain are
possible for the northern Sierra Nevada. Dangerous flooding, rock slides
and debris flows remain likely today. A Moderate Risk of Flash Flooding is
in effect for upslope portions of the northern Sierra below 5000′. The
flooding risk will decrease from north to south by later today and into
tonight. Heavy mountain snow is expected over the Washington Cascades and
Northern Rockies through Saturday. Multiple feet of snow are likely to
accumulate over portions of the northern Sierra (above 7000′) by Saturday
evening. Strong winds will continue across coastal areas of northwest
California into western Washington, and over south-central Oregon. These
winds may blow down trees and power lines, and additional power outages
are possible.

A deep upper low will pivot over the Northeast and reinforce a cooler
airmass along with a relatively shallow bit of moisture into the region
today. Some rain and snow showers are expected across much of the
Northeast/northern Mid-Atlantic as a result. Heavier snow will likely
remain confined to the higher terrain of the Central Appalachians, where
between 6-12 inches are expected with locally higher amounts possible.
Snow chances diminish as the day progresses and temperatures rise. Upper
ridging over the Intermountain West and Rockies will shift eastward into
the Central U.S. this weekend where above average temperatures are likely
to follow.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Thu Nov 21 2024
Valid 12Z Thu Nov 21 2024 – 12Z Sat Nov 23 2024

…Strong atmospheric river continues to impact northern California with
heavy rain and life-threatening flooding through Friday…

…Developing storm system forecast to bring another round of gusty winds
to the Pacific Northwest on Friday with heavy mountain snow spreading
toward the northern Rockies this weekend...

…Unsettled weather expected across much of the Northeast and Great Lakes
over the next few days, including the likelihood of heavy snow in the
central Appalachians and higher elevations of northeastern Pennsylvania
and southern New York…

Impactful and for some place dangerous weather conditions will continue
through early this weekend as two separate storm systems impact the Lower
48. Starting in the West, a strong atmospheric river currently impacting
northern California is forecast to remain relatively stationary over the
next few days and produce an additional 6-12 inches of rainfall over
regions with already saturated terrain. The atmospheric river is expected
to peak in intensity today, but with moderate bouts of rain lingering
through much of Friday and snow levels finally lowering somewhat on
Saturday. In the meantime, dangerous flooding, rock slides, and debris
flows are likely, which has prompted a High Risk (level 4/4) of Excessive
Rainfall to be issued across the northern California coastline today. Be
sure to check conditions before traveling and never drive across flooded
roadways.

Aiding the surge of atmospheric moisture into northern California and the
Northwest through the end of the week is a developing storm system
forecast to swing off the Oregon and Washington coastline on Friday. A
punch of gusty winds are expected, mainly along coastal regions, could
produce rough surf and additional isolated power outages. As precipitation
lifts northward and inland along a draped stationary boundary stretching
from the northern Rockies to British Columbia, heavy snow is possible from
the Washington Cascades to the western Montana, Idaho, and northwestern
Wyoming mountain ranges through early Sunday.

November snowfall is also in the forecast for parts of the Northeast and
Great Lakes thanks to a potent upper-level low swinging over the region.
At the surface, a compact area of low pressure is currently looping around
the Great Lakes with an eventual southward trajectory over Lake Michigan
later today. Parts of eastern Wisconsin could see precipitation fall as
snow along with wind gusts up to 40 mph. Winter Weather Advisories have
been issued for snowfall amounts up to 3-4 inches. Meanwhile, a separate
area of low pressure developing near Long Island tonight is also expected
to track in a looping orientation across the Northeast through Friday,
while also producing periods of heavy snow. The greatest chances for at
least 6 inches of snowfall is found across northeast Pennsylvania and
southern New York, including the Pocono and Catskill mountains.
Additionally, a long-duration upslope snow event is underway across the
central Appalachians and anticipated to linger through at least early
Saturday. Up to a foot of snow is possible across the higher terrain of
West Virginia, Maryland, and southwest Pennsylvania. Light snow is also
expected to reach as far south as the higher ranges of North Carolina.

The central and southern U.S. can expect much more tranquil conditions as
high pressure creates a void in the unsettled weather impacting both the
East and West coasts. However, below average temperatures are forecast
from the Mississippi Valley to the Southeast as breezy northwest flow
ushers in a colder airmass. This may lead to early morning frost and/or
freeze potential across the Southeast and Lower Mississippi Valley.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Wed Nov 20 2024
Valid 12Z Wed Nov 20 2024 – 12Z Fri Nov 22 2024

…Back-to-back powerful Pacific storm systems to impact the West Coast
through the end of this week with heavy rain, life-threatening flooding,
strong winds, and higher elevation mountain snow…

…Near blizzard conditions are possible through this evening across the
northern Plains…

…Heavy snow is likely throughout parts of the central Appalachians
beginning on Thursday, with a separate burst of snowfall possible across
northeast Pennsylvania and neighboring regions of the Northeast Thursday
night into Friday...

The active November weather pattern impacting CONUS is forecast to
continue through the end of this week and bring hazardous rain, wind, and
snow for several regions. A significant Pacific storm system and strong
atmospheric river have already started pummeling the West Coast and
Northwest this morning. The very deep low pressure system churning about
300 miles off the coast of Washington is responsible for high winds
impacting much of northern California, Oregon, and Washington. These winds
have already produced numerous power outages, reports of tree damage, and
are expected to create blizzard conditions throughout the Cascades.
Fortunately these winds are expected to gradually subside by midday as the
low pressure system swings away from the region. However, a continuous
plume of ample atmospheric moisture content entering northern California
this morning is forecast to linger through the end of the week and lead to
extreme rainfall totals. Over 10 inches of rainfall across the northern
California coast and inland mountain ranges are likely to increase the
threat of life-threatening flash flooding, rock slides, and debris flows.
As this corridor of heavy rainfall lingers along a stationary boundary
extending into the Pacific Ocean, a separate area of low pressure is
forecast to develop and rapidly strengthen off the Northwest coast on
Friday. This storm will help amplify the atmospheric river streaming into
northern California through Friday morning, exacerbating the flooding
threat. WPC has issued a High Risk (level 4/4) of Excessive Rainfall on
Thursday in order to further highlight this concern. Additionally, another
round of strong winds are anticipated from this second low pressure system
throughout the Northwest to end the week. Residents and visitors residing
or traveling between northern California and Washington are advised to
check road conditions before venturing out, listen to advice from local
officials, review emergency plans, and have multiple ways of receiving
warnings.

For the central U.S. the main weather story will be found throughout the
northern Plains as heavy snow and gusty winds create near blizzard
conditions today. These hazardous weather conditions are resulting from a
slow-moving and gradually weakening low pressure system just north of the
Minnesota-North Dakota border. The greatest snowfall amounts are forecast
across North Dakota, eastern South Dakota, and northwest Minnesota, but
with additional totals today generally under 4 inches. Wind impacts should
be more widespread and extend into eastern Montana and Nebraska as maximum
gusts could exceed 60 mph through tonight. This area of low pressure is
anticipated to rapidly weaken tonight and lead to calmer conditions on
Thursday.

After an extended period of dry and tranquil weather across the Northeast,
the upper level system exiting the northern Plains today will slide
eastward and produce a chance for heavy precipitation in the form of both
rain and snow. The evolution of surface features over the next few days
are forecast to begin with a developing strong and compact low pressure
system over the Great Lakes today, while a cold front quickly pushes
eastward to the Mid-Atlantic by tonight. Showers and maybe a rumble of
thunder may accompany this cold front as rain possibly mixes with snow
spreading across the Great Lakes. By Thursday, a separate area of low
pressure forming along the aforementioned cold front is expected to deepen
and lift northward into the Northeast, while also leading to a blossoming
precipitation shield. Rain is most likely across New England where warmer
air surges from the Atlantic Ocean, but the higher elevations and area
directly underneath the cold upper low pressure system may see
precipitation fall as heavy snow. Probabilities for at least 4 inches of
snow by Friday night are high (70-90%) across northeast Pennsylvania and
the southern Catskill mountains of New York. Impactful snowfall is also
likely to be experienced throughout the Allegheny mountains of West
Virginia, Maryland, and Pennsylvania through the end of the week due to a
longer duration favorable upslope snow setup. Total snowfall amounts in
these higher elevations could add up to a foot.

Elsewhere, high pressure building into the south-central U.S. will create
dry conditions from the lower Mississippi Valley to much of the Plains,
Rockies, and Southwest. The temperature outlook features one final day of
widespread 60s and 70s along the East Coast before a strong cold front
knocks afternoon highs below average through the start of the weekend. The
coldest temperatures when compared to climatology over the next few days
are forecast across the northern Plains (highs in the 20s) and Ohio Valley
(highs in the 30s and 40s).

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Tue Nov 19 2024
Valid 12Z Tue Nov 19 2024 – 12Z Thu Nov 21 2024

…Powerful Pacific low pressure system to produce significant high wind
impacts and heavy mountain snow across the Northwest, while a strong
atmospheric river takes aim at northern California by Wednesday…

…Potent storm system over the northern Plains to produce gusty winds and
locally heavy snow throughout the region before a redeveloping area of low
pressure brings unsettled weather to the Great Lakes, central
Appalachians, and Northeast from midweek onward…

…Heavy rain and flash flooding potential continues throughout portions
of the central and eastern Gulf Coast today…

No shortage of active weather across the Nation this week as two separate
strong low pressure systems produce hazardous conditions in the form of
high winds, heavy rain, and snowfall. Starting with the Pacific Northwest,
a rapidly strengthening and extremely powerful low pressure system
forecast to pass roughly 300 miles west of the Olympic Peninsula tonight
is anticipated to begin impacting the region today. Damaging winds with
gusts up to 70 mph are possible across northern California, as well as
parts of Oregon and Washington, with the highest winds expected along the
coast and high terrain. These winds are likely to produce numerous power
outages and tree damage in the most impacted regions. When combined with
heavy snowfall at the higher elevations, blizzard conditions are in the
forecast throughout the Washington Cascades. As an associated frontal
boundary slides southeastward and stalls near northern California on
Wednesday, a deep and continuous plume of anomalous atmospheric moisture
content will flow into the Redwood Coast of California and northern
mountain ranges of the Golden State. Heavy rain and rising snow levels
will increase the threat of numerous floods and potential mudslides,
exacerbated by the duration of heavy rainfall through the end of the week.
In fact, WPC has issued a High Risk (level 4/4) of Excessive Rainfall
across parts of northwest California on Thursday in order to further
highlight this flooding threat. Residents and visitors throughout the
Northwest are urged to have multiple ways to receive warnings, listen to
advice from local officials, and avoid traveling through hazardous weather
conditions if possible.

In the north-central U.S. another potent low pressure system is lifting
northward and producing unsettled weather of its own across the Upper
Midwest and northern Plains today. A tight pressure gradient being
produced by the storm is forecast to create strong winds across much of
Nebraska, eastern Montana, and the Dakotas through Wednesday with maximum
wind gusts up to 65 mph possible. Strong winds may also overlap with
moderate to locally heavy snow throughout North Dakota and northwest
Minnesota as the storm system stalls tonight over south-central Canada.
Probabilities for at least 6 inches of total snowfall are high (>70%)
across northern North Dakota. Meanwhile, scattered showers are forecast to
spread eastward into the Midwest, Great Lakes, and eventually the
Mid-Atlantic ahead of an advancing cold front today. By Wednesday night, a
redeveloping low pressure system rapidly strengthening over the Great
Lakes will help produce another round of precipitation over the Great
Lakes, central Appalachians and Northeast through the end of the week. The
greatest impacts from this precipitation is expected throughout the higher
elevations of West Virginia and western Maryland, where up to a foot of
snowfall is possible through Friday.

Elsewhere, heavy rain and a risk for scattered flash floods remains a
concern across the central and eastern Gulf Coast as a cold front, weak
area of low pressure, and ample atmospheric moisture content spark
numerous showers and thunderstorms capable of containing intense rainfall
rates through tonight. The greatest risk for flash flooding specifically
exists from far eastern Louisiana to the western Florida Panhandle, with
urban and poor drainage regions most susceptible to rapid water rises.

Temperatures will be on a roller coaster ride this week as well above
average temperatures are found in the East before an advancing cold front
knocks readings down below average by Thursday. Meanwhile, cooler
temperatures over much of the West are forecast to return to near normal
as upper ridging builds into place.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Nov 18 2024
Valid 12Z Mon Nov 18 2024 – 12Z Wed Nov 20 2024

…A potent storm system over the central U.S. today will create chances
for heavy rainfall, severe thunderstorms, and gusty winds, while moderate
snowfall is possible across the northern Plains by Tuesday…

…Heavy rain and flash flooding potential exists throughout the central
and eastern Gulf Coast over the next few days…

…Powerful Pacific low pressure system to impact the Northwest with high
winds and heavy mountain snow, while an atmospheric river takes aim at
northern California by Wednesday…

An amplified weather pattern and two separate strong storm systems are set
to impact the Nation during the first half of this week. First, a deep low
pressure system ejecting out of West Texas early this morning is
anticipated to further organize over the central U.S. today and produce
areas of heavy rain, severe weather, and gusty winds to the
southern/central Plains. Thunderstorms forming along an attached cold
front may contain damaging winds and perhaps a few tornadoes between
central Oklahoma and North Texas today. This region is where the Storm
Prediction Center has hoisted a Slight Risk (level 2/5) of severe
thunderstorms. As the system progresses northward into the Upper Midwest
on Tuesday, showers are also forecast to spread north throughout parts of
the Midwest and Great Lakes. Meanwhile, cold air working into the western
side of the storm will likely allow for precipitation to fall as snow
across parts of North Dakota and northern Minnesota into Wednesday.
Snowfall may also be accompanied by gusty winds, leading to lower
visibility on roadways. Current snowfall probabilities for at least 4
inches of snow are greatest (70-90%) across north-central North Dakota.

As the associated cold front pushes eastward through Tuesday, numerous
showers and thunderstorms interacting with a surge of moisture being
lifted northward from the Gulf of Mexico could contain intense rainfall
rates capable of producing flash flooding. Heavy rainfall is most likely
tonight across eastern Louisiana and southern Mississippi, with the threat
expanding east to the Florida Panhandle on Tuesday. Scattered flash floods
are most likely throughout low-lying and urban regions. Residents and
visitors are reminded to have multiple ways to receive warnings and never
drive across flooded roadways.

For much of the Northwest, northern Great Basin, and northern Rockies, a
cold front pushing across the region today and enhanced onshore flow will
allow for unsettled weather to continue ahead of a powerful storm system
forecast to develop off the coast of the Northwest on Tuesday. This
appetizer of precipitation to start the workweek will mainly include the
potential for moderate to heavy snowfall across the Cascades and northern
Rockies. However, by Tuesday night the rapidly strengthening Pacific low
pressure system will aid in producing high winds across the Pacific
Northwest and increasing precipitation intensity. Wind gusts up to 70 mph
are possible across parts of northern California and Oregon, with strong
winds also expected over parts of western Washington. These winds will
have the potential to knock down trees and produce power outages. Heavy
snowfall with amounts potentially exceeding two feet are possible over the
northern California ranges and Cascades. By Wednesday, an associated
atmospheric rive event is expected to take shape and direct continuous
Pacific moisture towards northern California and southwest Oregon.
Widespread rainfall amounts of 4 to 7 inches are expected through
Wednesday across this region, which could produce areas of river flooding
and increase the risk of mudslides. Heavy rain and the associated weather
hazards from this atmospheric river event are also expected to continue
beyond midweek.

Below average temperatures are forecast to remain over much of the western
U.S. over the next few days while gradually spreading eastward into the
Great Plains. Meanwhile, high pressure over the East will continue to
create mild and dry conditions through Tuesday as rainfall chances enter
the Mid-Atlantic and Northeast on Wednesday.