Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Fri Jan 15 2021

Valid 00Z Sat Jan 16 2021 - 00Z Mon Jan 18 2021

...A large storm produces snow and rain over parts of the Midwest into the
Northeast Through Sunday...

...Record-breaking warmth along with an elevated to critical fire weather
threat is expected over Southern California on Saturday...

A large storm over the Midwest will slowly move Northeastward to
Southeastern Canada by Sunday evening. The system will produce light snow
over parts of the Midwest through Sunday evening. As the associated front
moves eastward, rain will move into the Lower Great Lakes, the
Mid-Atlantic, and the Southeast on Friday evening. Light snow will
continue over most of the Midwest, moving into parts of the Central
Appalachians and parts of the Tennessee Valley. Overnight Friday, rain
and snow will move into the Northeast, continuing into Saturday. There
will be heavy lake effect snow down wind from Lakes Erie and Ontario and
into the Northern Green and White Mountains of New Hampshire and Vermont .
The light snow will continue over the Midwest and parts of the Northeast
through Sunday evening. The snow will produce hazardous driving
conditions.

Meanwhile, high pressure builds over the Northwest through Saturday night.
Above-average to record-breaking temperatures are expected across much of
Southern California into Nevada and Arizona on Saturday. Gusty winds and
low humidities are prompting Red Flag Warnings for portions of Southern
California. Temperatures will likely remain well above average, with dry
conditions persisting through Saturday and Sunday. Overnight Saturday, a
front will move onshore over the Northwest, producing rain and higher
elevation snow over the Pacific Northwest and also snow over parts of the
Northern Intermountain Region into parts of the Northern Rockies. By
Sunday evening, the system will move inland to the Northern High Plains
producing mainly snow and some lower elevation rain. The snow will create
hazardous driving conditions.

Ziegenfelder

Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
347 PM EST Fri Jan 15 2021

Valid 12Z Mon Jan 18 2021 - 12Z Fri Jan 22 2021

...Heavy rainfall event likely for portions of the interior South
next week...

...An anomalous upper low expected to bring unsettled weather over
parts of the Desert Southwest for much of next week...

...Pattern Overview and Guidance/Predictability Assessment...

An increasingly complex synoptic pattern appears to be in store
for much of next week as many of the southern tier states will
likely experience an extended period of unsettled weather. Model
consensus continues to indicate a trend toward more robust
amplification of an upper-level trough dipping across the Desert
Southwest, and possibly developing into a closed low by the time
it reaches the northern Baja. This anomalous upper low will
likely bring unsettled weather from the central Rockies down into
the Southwest on Monday into Tuesday, as moisture from the Gulf
returns into Texas. The GFS and ECMWF agree quite well with this
general scenario. The CMC, on the other hand, continues to take
the upper low further off the coast of Baja into the subtropical
Pacific--a scenario being ruled out at this point. A consensus of
the 00Z ECMWF/00Z EC mean with the 06Z GFS/06Z GEFS formed the
basis for this morning's WPC forecast charts. This brings the
anomalous upper low slowly eastward into northern Mexico for the
latter part of next week, keeping a good chance of unsettled
weather over the Desert Southwest while a threat of heavy rain
lingers from eastern Texas across the interior Deep South into the
interior Southeast.

...Weather/Threats Highlights...

The main weather story next week will be the potential for a
multi-day heavy rainfall event, extending from central Texas to
the southern Appalachians, mainly during the Tuesday-Thursday time
period. A prolonged period of moist southerly flow from the Gulf
and Caribbean ahead of a slow moving low pressure system over
southern Texas, in combination with moisture convergence along a
quasi-stationary front, may result in several inches of rainfall
for parts of this region and some potential for flooding.
Moderate to heavy snow is likely for portions of the central and
northern Rockies early in the week. Meanwhile, there appears to
be an increasing chance of wintry precipitation spreading into the
higher elevations of central Arizona and rain over the lower
elevations of southeastern Arizona and southwestern New Mexico.
By Thursday and Friday, the chance for snow returns to the
Northeast, the Great Lakes, as well as the Cascades as the next
storm systems arrive.

In terms of temperatures, readings should be near to slightly
above normal for most areas to begin the week, and some 10-20
degree positive anomalies are possible across the northern Plains
by Wednesday ahead of the next front. By the end of the week,
there are some hints of an Arctic airmass affecting the
northwestern quadrant of the U.S., although the core of the Arctic
high should remain north of the Canadian border.

Kong/Hamrick


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

Hazards:
- Flooding occurring or imminent across portions of the Southeast
and the Pacific Northwest.
- High winds across portions of the Central Great Basin,
California, and the Southwest, Mon-Tue,
Jan 18-Jan 19.
- High winds across portions of the Northern Plains and the
Northern Rockies, Tue, Jan 19.
- High winds across portions of the Central Rockies and the
Central Plains, Wed, Jan 20.
- Heavy rain across portions of the Southern Plains, the Lower
Mississippi Valley, the Tennessee
Valley, the Southern Appalachians, and the Southeast, Thu-Fri, Jan
21-Jan 22.
- Enhanced wildfire risk across portions of California, Mon-Tue,
Jan 18-Jan 19.

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
150 AM EST Fri Jan 15 2021

Valid 00Z Sat Jan 16 2021 - 00Z Sat Jan 23 2021

The weather pattern over the Hawaii domain will initially be
uneventful through this weekend with surface high pressure
centered to the northeast of the state. There will also be a
slightly weaker than normal pressure gradient, and thus modest
trades that are mainly easterly early in the period, and gradually
veer more towards a southeasterly direction. Typical trade wind
induced showers should be the rule through Sunday.

Major changes are becoming more likely by the beginning to middle
of next week as an anomalous upper trough, and potentially closed
low, develops near the Islands and moves rather slowly. This
would result in a noteworthy inverted surface trough and well
developed cold front over the region. The GFS indicates that the
best tropical moisture surge would likely be east of the Big
Island, whilst the ECMWF is more impactful with periods of heavy
rainfall across the state. The event could last for a few days
before upper level ridging eventually builds in to the north by
the end of the week.

Hamrick

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
720 PM EST Fri Jan 15 2021

Day 1
Valid 01Z Sat Jan 16 2021 - 12Z Sat Jan 16 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Petersen


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EST Fri Jan 15 2021

Day 2
Valid 12Z Sat Jan 16 2021 - 12Z Sun Jan 17 2021

...A Marginal Risk of Excessive Rainfall Exists Across Portions of
Coastal New England...

...Parts of New Hampshire into Maine...
Maintained the Marginal Risk area over parts of coastal New
England as low pressure over New York begins to occlude and spread
widespread precipitation across the region on Saturday.
Circulation around the low will draw deep-layered moisture across
the region, and southeasterly low level flow up to 70 kts at 850
mb will direct that moisture inland across the coastal areas into
the foothills and upslope region of the White Mountains.
Precipitable water values above an inch would be near record
values for mid-January according to the sounding climatology at
Gray, Maine. The strong low-level flow and high precipitable water
values will combine to yield IVT values above the 90th percentile.
This is a synoptic setup conducive for moderate to heavy rainfall
along the coast and areas as far inland as the foothills and
upslope region of the interior mountains. However, there are
several factors mitigating the risk of excessive rainfall. WPC
deterministic QPF values were generally in the 1 to 1.75 inch
range, with only part of the area near the coast and nearby
foothills expected to receive all of the precipitation in the form
of rain. It will also help that rain will not be falling on a deep
snowpack and that the system will be progressive. Rainfall rates
according to the high res models should generally remain under
half an inch an hour. As a result, the risk of flooding should be
limited to minor flooding of smaller streams and tributaries of
the mountains or flooding/ponding in regions of poor drainage or
low lying areas.

Bann/Tate


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 PM EST Fri Jan 15 2021

Day 3
Valid 12Z Sun Jan 17 2021 - 12Z Mon Jan 18 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Tate


Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 PM EST Fri Jan 15 2021

Valid 00Z Sat Jan 16 2021 - 00Z Tue Jan 19 2021

Days 1 to 3...

...Midwest/OH Valley to the Great Lakes/Central Appalachians and
Northeast...

A slow-moving and vertically stacked low pressure system currently
over the Midwest will shift gradually east across the OH Valley
tonight and cross the central Appalachians, northern Mid-Atlantic
and lower Great Lakes region on Saturday. As the strong height
falls approach the East Coast later tonight, a robust shortwave
will lift out of the base of the upper trough and up along the
Mid-Atlantic coast which will foster secondary cyclogenesis along
the attendant cold front edging offshore. This low center will
then lift inland across southern/central New England by Saturday
evening and then through central/eastern Maine by early Sunday. As
all of this occurs, deep layer south to southeast flow will ride
northeast up across New England bringing strong warm-air advection
and a robust fetch of Atlantic moisture for widespread moderate to
heavy precipitation. While there will be little in the way of cold
air initially in place to support widespread snow, the thermal
profiles do appear to be conducive for locally heavy, wet, and
elevation-dependent snowfall for portions of NY and New England.
The main focus should on elevations especially above 1500 feet in
the Adirondacks, the Berkshires, and the Green and White
mountains. Adjacent areas of western Maine will also be a focus
for heavy snowfall. The strong and mild Atlantic inflow should
keep snow levels somewhat elevated at least through midday
Saturday across the Northeast, but as the stronger height falls
arrive and low-level cold air begins arriving around the back side
of departing low pressure, the snow levels will begin to fall and
reach some of the interior valley locations across NY and New
England later in the day. The current forecast is for as much as 6
to 12+ inches of snow for the aforementioned higher elevations of
the Northeast going through early Sunday, with the heaviest
accumulations generally over the Green and especially White
mountains where storm totals of 12 to 18+ inches will be possible.

Meanwhile, the deep layer cyclonic flow coupled with multiple
embedded shortwave impulses will continue to favor broken areas of
light to occasionally moderate snow across portions of the Midwest
this evening and then spreading into the OH Valley by Saturday
morning. This energy coupled with cold and relatively moist low to
mid-level upslope flow into the central Appalachians should favor
an axis of heavier accumulating snowfall from central WV into far
western MD and southwest PA. Locally some areas of central WV may
see in excess of 6 inches of snowfall going through Sunday as the
focus will transition increasingly from synoptically forced
snowfall to more of a lake-enhanced snowfall threat as the
boundary layer winds gradually involve more of the flow over the
Great Lakes going through Saturday night and early Sunday.
Portions of western NY involving the Tug Hill plateau will also
see an increasing focus of heavy lake-enhanced snowfall Saturday
night and Sunday around the departing low center over the
Northeast with a highly favorable cold, moist and convergent
low-level fetch coming off the relatively warm waters of Lake
Ontario. As much as 6 to 12 inches of snow will be possible here.
Elsewhere, the broad deep-layer cyclonic envelope of this system
will also maintain the threat of accumulating lake-effect snowfall
for even areas of the U.P. of MI where north to northeast
low-level flow over Lake Superior will support locally 6+ inches
of additional snow for areas east of the Keweenaw Peninsula.

As the main closed low/trough pushing into the Northeast begins to
pull away by late Sunday, there will be a new vigorous upper
trough/closed low center dropping southeast across the Midwest and
the OH Valley going through early Monday. This may bring locally a
few additional inches of snow to the central Appalachians and
portions of western NY.


...Northern/Central Rockies...

Multiple shortwave troughs will be advancing southeast down across
the northern/central Rockies going through this weekend and early
next week, with one impulse sliding progressively southeast
tonight and early Saturday, and then a stronger shortwave digging
southeast and into Intermountain West by Monday. Stronger
jet-aided forcing associated with the shortwave impulses coupled
with relatively moist mid-level flow should favor heavy snowfall
for portions of the Bitterroots and Sawtooth where as much as 6 to
12 inches will be possible going through Monday. However, somewhat
stronger upslope flow should tend to favor even heavier snowfall
totals that may exceed 1 foot across the Belts, Beartooths and
Bighorns. Some of this heavier snowfall should make it farther
south down into south-central WY and far northern CO with the
Medicine Bow mountains likely to see as much as 1 foot of snow as
well.


For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Orrison

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
347 PM EST Fri Jan 15 2021

Valid 12Z Mon Jan 18 2021 - 12Z Fri Jan 22 2021

...Heavy rainfall event likely for portions of the interior South
next week...

...An anomalous upper low expected to bring unsettled weather over
parts of the Desert Southwest for much of next week...

...Pattern Overview and Guidance/Predictability Assessment...

An increasingly complex synoptic pattern appears to be in store
for much of next week as many of the southern tier states will
likely experience an extended period of unsettled weather. Model
consensus continues to indicate a trend toward more robust
amplification of an upper-level trough dipping across the Desert
Southwest, and possibly developing into a closed low by the time
it reaches the northern Baja. This anomalous upper low will
likely bring unsettled weather from the central Rockies down into
the Southwest on Monday into Tuesday, as moisture from the Gulf
returns into Texas. The GFS and ECMWF agree quite well with this
general scenario. The CMC, on the other hand, continues to take
the upper low further off the coast of Baja into the subtropical
Pacific--a scenario being ruled out at this point. A consensus of
the 00Z ECMWF/00Z EC mean with the 06Z GFS/06Z GEFS formed the
basis for this morning's WPC forecast charts. This brings the
anomalous upper low slowly eastward into northern Mexico for the
latter part of next week, keeping a good chance of unsettled
weather over the Desert Southwest while a threat of heavy rain
lingers from eastern Texas across the interior Deep South into the
interior Southeast.

...Weather/Threats Highlights...

The main weather story next week will be the potential for a
multi-day heavy rainfall event, extending from central Texas to
the southern Appalachians, mainly during the Tuesday-Thursday time
period. A prolonged period of moist southerly flow from the Gulf
and Caribbean ahead of a slow moving low pressure system over
southern Texas, in combination with moisture convergence along a
quasi-stationary front, may result in several inches of rainfall
for parts of this region and some potential for flooding.
Moderate to heavy snow is likely for portions of the central and
northern Rockies early in the week. Meanwhile, there appears to
be an increasing chance of wintry precipitation spreading into the
higher elevations of central Arizona and rain over the lower
elevations of southeastern Arizona and southwestern New Mexico.
By Thursday and Friday, the chance for snow returns to the
Northeast, the Great Lakes, as well as the Cascades as the next
storm systems arrive.

In terms of temperatures, readings should be near to slightly
above normal for most areas to begin the week, and some 10-20
degree positive anomalies are possible across the northern Plains
by Wednesday ahead of the next front. By the end of the week,
there are some hints of an Arctic airmass affecting the
northwestern quadrant of the U.S., although the core of the Arctic
high should remain north of the Canadian border.

Kong/Hamrick


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

Hazards:
- Flooding occurring or imminent across portions of the Southeast
and the Pacific Northwest.
- High winds across portions of the Central Great Basin,
California, and the Southwest, Mon-Tue,
Jan 18-Jan 19.
- High winds across portions of the Northern Plains and the
Northern Rockies, Tue, Jan 19.
- High winds across portions of the Central Rockies and the
Central Plains, Wed, Jan 20.
- Heavy rain across portions of the Southern Plains, the Lower
Mississippi Valley, the Tennessee
Valley, the Southern Appalachians, and the Southeast, Thu-Fri, Jan
21-Jan 22.
- Enhanced wildfire risk across portions of California, Mon-Tue,
Jan 18-Jan 19.

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml