Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Sat Jan 18 2020

Valid 00Z Sun Jan 19 2020 - 00Z Tue Jan 21 2020

...Winter storm to persist another day followed by very cold weather from
the Plains to the East Coast...

The ongoing winter storm across the Great Lakes and the Eastern U.S. is
expected to persist through Sunday across New England as a second low
develops near the coast Saturday night. A broken band of showers and a
few thunderstorms are expected from the central Gulf Coast to the
Carolinas ahead of the cold front, and a cold rain across much of the
Mid-Atlantic region and some freezing rain across portions of Maryland,
West Virginia, and Pennsylvania. Farther to the north across the Great
Lakes and much of New York and northern New England, the depth of cold air
will be sufficient to support mainly snow, including some lake enhanced
snow. Snowfall totals on the order of 6 to 12 inches are likely from
northern New York to central Maine. The blizzard conditions across the
Dakotas and Minnesota are expected to abate overnight as high pressure
continues building southward across that region.

An arctic airmass will be settling southward in the wake of the winter
storm across much of the central and northern Plains, with temperatures as
much as 20 degrees below average for Sunday and into Monday. Although
this airmass will modify some before reaching the East Coast to begin the
work week, readings will still be below average by 5 to 15 degrees in most
cases.

Dry conditions can be expected from California to the Ohio Valley over the
next couple of days with no significant storm system expected after the
current storm departs the East Coast, other than onshore flow and showers
for western Washington and Oregon.

Hamrick

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Sat Jan 18 2020

Valid 12Z Tue Jan 21 2020 - 12Z Sat Jan 25 2020

...Overview...

As upper troughing exits the Southeast on Tuesday, another will
approach the Pacific Northwest. This will dig through the Rockies
and into the Southern Plains by Thursday, increasing the threat of
rainfall and northern fringe snow for the eastern half of the
CONUS through Saturday. A couple other Pacific fronts will bring
some snow/rain to the Northwest late next week.

...Guidance/Predictability Assessment...

The models/ensembles were in generally good synoptic agreement in
showing a progressive and modestly amplified longwave flow
pattern. Models have seemed to come into much better agreement
over the Southeast coast on Tuesday. The next system enters the
Northwest late Tuesday, reaching the Plains by early Thursday.
Models show generally good agreement with this early in the
period, but continue to struggle with the north-south location of
low pressure in the Lower MS Valley or northern Gulf Coast region
Friday-Saturday. The ECMWF is farthest south, with the GFS the
strongest/deepest and farthest north. The ensemble means would
generally favor a location somewhere in between (which ends up
close to the 00z CMC). Given the continued uncertainty, opted to
stay fairly close to WPC continuity while blending in some of the
latest model runs.


...Weather/Hazard Highlights...

Lingering below normal temperatures over the Upper Midwest/Corn
Belt (owing to new snowfall in the short term) will moderate
Wednesday onward as southerly flow brings in milder air (5-15 deg
above normal). This will work its way to the East Coast by Friday
into Saturday ahead of the Gulf system.

Precipitation in the Northwest Tuesday will be a nearly daily
occurrence with several systems to push through. Thursday may be
the rainier/snowier day of the 5-day period which will see several
inches of precipitation in favored areas. Rainfall will expand
over Texas and points eastward/northeastward starting Tuesday with
help from leftover mid/high-level moisture from a weak Pacific
system racing across Mexico. Then as the surface cold front
organizes over Texas Thursday, some Gulf inflow will help realize
modest rainfall totals along the Gulf coast with uncertainty to
its northward extent. Some amounts could be locally heavy. The
system may have some wintry weather on its northern side from the
Central Plains to the Great Lakes.

Santorelli/Fracasso


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

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
248 AM EST Sat Jan 18 2020

Valid 00Z Sun Jan 19 2020 - 00Z Sun Jan 26 2020

Trades will increase to breezy in the wake of a cold front out of
the NE to ENE through Monday as a surface high slides eastward
between 25-30N this weekend. Models/ensembles generally show below
normal precipitable water values (around an inch or less) next
week with light windward/mauka showers. Trades will weaken and
veer to the SE late next week as a front slides eastward past
30N/160W Thursday. This front may approach Kauai by the end of the
week but the consensus favors keeping it just to the north.


Fracasso

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
750 PM EST Sat Jan 18 2020

Day 1
Valid 01Z Sun Jan 19 2020 - 12Z Sun Jan 19 2020

...Lower Texas Coast...
The Marginal Risk area was dropped here as minimal shower and
thunderstorm activity has formed this far and what has developed
in a linear/organized fashion is near and offshore Padre Island
and progressing east of due south at a decent clip. While there
is a non-zero chance of storms causing heavy rainfall in the
region, radar trends have been suggested minimal risk so the
marginal risk was eliminated.

Roth


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
206 PM EST Sat Jan 18 2020

Day 2
Valid 12Z Sun Jan 19 2020 - 12Z Mon Jan 20 2020

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

Campbell

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Sat Jan 18 2020

Day 3
Valid 12Z Mon Jan 20 2020 - 12Z Tue Jan 21 2020

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Campbell


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
328 PM EST Sat Jan 18 2020

Valid 00Z Sun Jan 19 2020 - 00Z Wed Jan 22 2020


...Great Lakes/Northeast...
Warm advection and moisture advection on the nose of a 700 mb jet
forecast to be near 50 kt as it crosses southern VT, southern NH
and Maine combines to produce snow across VT, NH and Maine.
Snow get enhanced in downeast Maine along the mid level
deformation zone associated with developing low pressure near the
coast tonight. The event winds down Sunday as the low and ascent
depart.

In addition to the larger scale forcing, orographic enhancement is
expected to bolster amounts in the Green Mountains to the White
Mountains and ranges of western Maine.

The initial low level warm front combines with southerly flow this
evening to produce snow from the Tug Hill region eastward into the
southern Adirondacks. The flow veers across Lake Ontario tonight
to become westerly by morning. The moisture convergence along the
eastern shore line and upslope flow favors heavy snow in the Tug
Hill to the western Adirondacks. Around a foot of snow is possible
tonight into Sunday in the Tug Hill. The flow veers with time
Sunday afternoon, shifting the band south to the southern shore of
Lake Ontario.

The west southwest flow developing across Lake Erie leads to
leeshore convergence in southwest NY and northwest PA, with a
prolonged period of moderate to heavy snow tonight into early
Sunday. The flow veering late Sunday allows bands to shift and
develops further south along the lake into northeast Ohio. Where
bands persist, clusters of 8-12 inches of snow are expected in
southwest NY and northwest PA in counties adjacent to Lake Erie.

Strongly confluent flow off Lake Superior leads to well defined
moisture convergence over western lake Superior with a vertical
velocity maxima in the western UP of MI leading to a burst of
heavy snow tonight. The lift spreads into the central UP, where
several inches are also expected into early Sunday where winds
become north Sun morning. Activity tapers later Sunday as drier
air aloft moves across the lake.

Boundary layer west winds tonight favors snow showers across
southwest lower MI. Once the sfc trough passes later Sun, the
flow veers and snow showers focus further south in southwest lower
MI and develop Sunday evening in northern IN. Drier air aloft
cross lake on Mon should lead to a decrease in snow shower
coverage/intensity.

...Pacific Northwest/California...
Snow coverage and amounts tonight into Monday should be minimal
the next few days as the mid level flow back and the region has
only light QPF.
On Tue, a large, slow moving circulation over the northeast
Pacific drifts east, driving a cold front towards the Pacific
northwest and northern CA. A band of enhanced moisture and lift
precedes the front, with precip breaking out in a band of low-mid
level convergence and moving inland into he WA/OR Cascades and the
Shasta/Siskiyou ranges of northern CA. Locally heavy mountain
snows are possible at higher elevations, as southerly flow ahead
of the front warms the region. Snow elevations gradually drop as
the front arrives Tue.

The probability of greater than 0.25 inches of freezing rain is
less than 10 percent.

Petersen

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Sat Jan 18 2020

Valid 12Z Tue Jan 21 2020 - 12Z Sat Jan 25 2020

...Overview...

As upper troughing exits the Southeast on Tuesday, another will
approach the Pacific Northwest. This will dig through the Rockies
and into the Southern Plains by Thursday, increasing the threat of
rainfall and northern fringe snow for the eastern half of the
CONUS through Saturday. A couple other Pacific fronts will bring
some snow/rain to the Northwest late next week.

...Guidance/Predictability Assessment...

The models/ensembles were in generally good synoptic agreement in
showing a progressive and modestly amplified longwave flow
pattern. Models have seemed to come into much better agreement
over the Southeast coast on Tuesday. The next system enters the
Northwest late Tuesday, reaching the Plains by early Thursday.
Models show generally good agreement with this early in the
period, but continue to struggle with the north-south location of
low pressure in the Lower MS Valley or northern Gulf Coast region
Friday-Saturday. The ECMWF is farthest south, with the GFS the
strongest/deepest and farthest north. The ensemble means would
generally favor a location somewhere in between (which ends up
close to the 00z CMC). Given the continued uncertainty, opted to
stay fairly close to WPC continuity while blending in some of the
latest model runs.


...Weather/Hazard Highlights...

Lingering below normal temperatures over the Upper Midwest/Corn
Belt (owing to new snowfall in the short term) will moderate
Wednesday onward as southerly flow brings in milder air (5-15 deg
above normal). This will work its way to the East Coast by Friday
into Saturday ahead of the Gulf system.

Precipitation in the Northwest Tuesday will be a nearly daily
occurrence with several systems to push through. Thursday may be
the rainier/snowier day of the 5-day period which will see several
inches of precipitation in favored areas. Rainfall will expand
over Texas and points eastward/northeastward starting Tuesday with
help from leftover mid/high-level moisture from a weak Pacific
system racing across Mexico. Then as the surface cold front
organizes over Texas Thursday, some Gulf inflow will help realize
modest rainfall totals along the Gulf coast with uncertainty to
its northward extent. Some amounts could be locally heavy. The
system may have some wintry weather on its northern side from the
Central Plains to the Great Lakes.

Santorelli/Fracasso


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

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