Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Thu Jan 23 2025

Valid 12Z Thu Jan 23 2025 - 12Z Sat Jan 25 2025

...Very Cold Winter temperatures continue from the Rockies to the East
Coast with a slow warm up anticipated heading into the weekend....

...Periods of lake-effect snow expected downwind of the Great Lakes with
some moderate accumulations possible...

...There is a Critical Risk of fire weather over parts of Southern
California Thursday...

Well below average, very cold temperatures will continue for most of the
country from the Rockies east to the East Coast the next couple of days,
with some of the most notable departures from average over the Southeast.
Forecast highs Thursday generally range from the teens and 20s for the
northern Plains and Midwest, the 20s and 30s from the Rockies and central
Plains east through the Ohio Valley to the Northeast, and the 30s and 40s
from the southern Plains east to the Southeast. Although winds have come
down compared to recent days, wind chills will still be quite frigid and
make temperatures feel around 10 degrees colder. Some of the more adverse
impacts from these temperatures will be for portions of the Gulf Coast and
Southeast where snow and ice linger on roads and keep travel hazardous
after the historic winter storm. It may take a few more days for these
road conditions to improve. Morning lows are also expected to drop below
freezing again Friday and Saturday along the Gulf Coast and into northern
Florida, keeping sensitive vegetation at risk. Conditions will moderate
some on Friday, especially for portions of the Plains where warm westerly
winds will bring temperatures up by 10-20 degrees and to average to above
average levels. Most areas will continue to slowly moderate into the
weekend.

A clipper system passing through the Great Lakes and into the Interior
Northeast/Appalachians will bring some snow showers Thursday. Some
moderate accumulations are possible with lake-effect snow bands for
favorable downwind locations of the Great Lakes. Another clipper system
following quickly in its wake will bring another round of light snow
showers to the northern Plains/Upper Midwest on Friday and the Great Lakes
again by Friday evening. To the west, passage of an upper-level
wave/surface cold front will bring some light to moderate snow showers to
the northern Rockies Thursday and into the central Rockies/eastern Great
Basin Friday.

Very gusty offshore Santa Ana winds will continue into the day Thursday
for Southern California, with gusts as high as 70 mph for some of the area
mountain ranges. These winds in combination with very low humidity and dry
antecedent conditions have prompted the Storm Prediction Center to
continue a Critical Risk of Fire Weather (level 2/3). Wind gusts are
expected to come down in strength heading into Friday, reducing the fire
risk, though an elevated threat will still exist given dry humidity and
conditions. Elsewhere in the West, conditions will be mostly dry with
generally at or above average temperatures. Forecast highs the next couple
of days range from the 30s and 40s in the Interior West and Pacific
Northwest and the 60s and 70s for California and the Desert Southwest.

Putnam


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Jan 23 2025

Valid 12Z Sun Jan 26 2025 - 12Z Thu Jan 30 2025


...Overview...

The start of the period on Sunday will feature an upper level
closed low diving southward along the California coast, and only
very slowly moving eastward with time next week. This should bring
beneficial precipitation to parts of southern California that have
been dealing with devastating wildfires. Organized rains/terrain
snows should make their way downstream into the Southwest as well.
Meanwhile, northern stream mean troughing, and reinforcing
shortwaves will cross from the northern Plains into the Great Lakes
and Northeast into next week. Moderate to locally heavy rainfall
will develop to the south across the Lower Mississippi Valley
Sunday and Monday as a slow moving frontal boundary moves through
the region. Additional frontal wave genesis over the Southern
Plains into the middle of next week given Southwest low slow
approach may again increase lead return flow and emerging rainfall
to monitor.

...Guidance/Predictability Assessment...

On the large scale, the guidance continues to show reasonable
agreement, but there remains plenty of uncertainty in the details
and timing of individual systems. Through early next week, models
show good clustering of the low as it slowly moves south through
California. After Tuesday though, there is some uncertainty in
timing into the Southwest/Four Corners and also with less
predictable energy that may shear off from the low. Ensemble mean
guidance provides a good middle ground for this feature in the late
period. To the north, mean northern stream troughing over the
Northern Plains- Great Lakes-Northeast continues to show
uncertainty in the amplitude of individual shortwaves dropping
through, especially next Wednesday and Thursday.

Accordingly, WPC guidance used a general model blend for the first
half of the period. For days 6 and 7, transitioned to a 60/40
split between the ensemble means and the deterministic GFS and
ECMWF which seemed to provide the best starting point amidst the
uncertainties.

...Weather/Hazards Highlights...

The slow moving upper low through California on Sunday will
continue to allow for much needed rain to southern California. Even
though QPF amounts are not too high, given sensitivity especially
in fresh burn scar locations, it may not take much to cause
flooding concerns. For this reason, a small marginal risk was added
to parts of Southern California on the Day 4 Excessive Rainfall
Outlook. Modest snows are possible across the terrain of southern
California, with rain and mountain snow into parts of the Southwest
as well. A tightened gradient behind the cold front dropping south
may produce some gusty winds along parts of the Rockies late this
week and California and Nevada on Saturday with offshore flow and
modestly favorable fire weather conditions possible again behind
the upper low next week to keep an eye on.

Farther east, Gulf moisture will interact with a front approaching
the Lower Mississippi Valley to Tennessee and Ohio Valleys by this
coming weekend/early next week. Latest guidance continues to show
heavy rainfall totals over parts of the southern U.S., with the
potential for heavy rain and thunderstorms on Sunday across the
Lower Mississippi Valley. A marginal risk was carried into the new
Day 4/Sunday Excessive Rainfall Outlook from eastern Texas into
Mississippi where storms may train along a slow moving frontal
boundary. Snow or a wintry mix is possible on the northern side of
this precipitation shield mainly over the Ohio Valley, south-
central Appalachians, and possibly the Tennessee Valley and
vicinity. Precipitation may spread towards the East Coast early
next week as the frontal system progresses with some rainfall
redevelopment across the Southern Plains and lower Mississippi
Valley as well. This signal is increasing with development of an
organized frontal wave with Southwest upper system approach.

Much of the East should finally be back up towards normal
temperatures early next week, though readings a few degrees below
normal are possible across the Southeast. Anomalously cold
temperatures will also develop in the High Plains, Rockies, and
much of the West under the influence of upper troughing. The
coldest anomalies will be in the High Plains and Rockies to
Southern High Plains where high temperatures could be 10-20 degrees
below normal. Late period ridging over the northern tier could
allow temperatures to rise above normal next week, gradually
shifting south and east with time.


Santorelli


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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EST Thu Jan 23 2025

Valid 00Z Fri Jan 24 2025 - 00Z Fri Jan 31 2025

A cut off low north of Hawaii will linger until about Friday when
it lifts north and weakens. Behind this, another amplified trough
or upper low will develop again to the north. Rounds of enhanced
precipitation is expected with associated cold fronts, with some
moderate to locally heavy rainfall at times and some gusty winds
within and overall wet and windy pattern for Hawaii. The guidance
shows good agreement on the first upper low lifting out in the
next day or so, but a lot of uncertainty in the timing and
placement of the next feature.

Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
716 PM EST Wed Jan 22 2025
Day 1
Valid 01Z Thu Jan 23 2025 - 12Z Thu Jan 23 2025


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

Bann


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
237 AM EST Thu Jan 23 2025
Day 1
Valid 12Z Thu Jan 23 2025 - 12Z Fri Jan 24 2025


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

Hamrick


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
237 AM EST Thu Jan 23 2025
Day 2
Valid 12Z Fri Jan 24 2025 - 12Z Sat Jan 25 2025

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

Hamrick


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
237 AM EST Thu Jan 23 2025
Day 3
Valid 12Z Sat Jan 25 2025 - 12Z Sun Jan 26 2025

A developing closed low over central California late Saturday is
expected to advect enough moisture from the Pacific to generate
scattered to numerous showers that should start around 00Z Sunday,
with most guidance indicating QPF on the order of 0.25 to 0.50 of
an inch, with most of this within the last 6 hours of Day 3.

After collaboration with WFO Los Angeles, a Marginal Risk area has
been introduced for the Transverse Ranges and the surrounding
valleys. Even though the next round of rain appears to be mainly
moderate in intensity for the 00Z-12Z Sunday time period, the new
burn scar areas are extremely sensitive to run-off, and thus a
normally beneficial and modest rainfall could become problematic
and easily lead to flooding, with potentially serious impacts if
rainfall is heavier than expected and concentrated over a burn scar
near populated areas. There is still uncertainty regarding this
event, so please monitor future forecasts and outlooks as details
become better refined.

Hamrick

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Jan 23 2025


The slow moving upper low through California on Sunday will
continue to allow for much needed rain to southern California. Even
though QPF amounts are not too high, given sensitivity especially
in fresh burn scar locations, it may not take much to cause
flooding concerns. For this reason, a small marginal risk was added
to parts of Southern California on the Day 4 Excessive Rainfall
Outlook. Modest snows are possible across the terrain of southern
California, with rain and mountain snow into parts of the Southwest
as well. A tightened gradient behind the cold front dropping south
may produce some gusty winds along parts of the Rockies late this
week and California and Nevada on Saturday with offshore flow and
modestly favorable fire weather conditions possible again behind
the upper low next week to keep an eye on.

Farther east, Gulf moisture will interact with a front approaching
the Lower Mississippi Valley to Tennessee and Ohio Valleys by this
coming weekend/early next week. Latest guidance continues to show
heavy rainfall totals over parts of the southern U.S., with the
potential for heavy rain and thunderstorms on Sunday across the
Lower Mississippi Valley. A marginal risk was carried into the new
Day 4/Sunday Excessive Rainfall Outlook from eastern Texas into
Mississippi where storms may train along a slow moving frontal
boundary. Snow or a wintry mix is possible on the northern side of
this precipitation shield mainly over the Ohio Valley, south-
central Appalachians, and possibly the Tennessee Valley and
vicinity. Precipitation may spread towards the East Coast early
next week as the frontal system progresses with some rainfall
redevelopment across the Southern Plains and lower Mississippi
Valley as well. This signal is increasing with development of an
organized frontal wave with Southwest upper system approach.

Much of the East should finally be back up towards normal
temperatures early next week, though readings a few degrees below
normal are possible across the Southeast. Anomalously cold
temperatures will also develop in the High Plains, Rockies, and
much of the West under the influence of upper troughing. The
coldest anomalies will be in the High Plains and Rockies to
Southern High Plains where high temperatures could be 10-20 degrees
below normal. Late period ridging over the northern tier could
allow temperatures to rise above normal next week, gradually
shifting south and east with time.


Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Jan 23 2025


The slow moving upper low through California on Sunday will
continue to allow for much needed rain to southern California. Even
though QPF amounts are not too high, given sensitivity especially
in fresh burn scar locations, it may not take much to cause
flooding concerns. For this reason, a small marginal risk was added
to parts of Southern California on the Day 4 Excessive Rainfall
Outlook. Modest snows are possible across the terrain of southern
California, with rain and mountain snow into parts of the Southwest
as well. A tightened gradient behind the cold front dropping south
may produce some gusty winds along parts of the Rockies late this
week and California and Nevada on Saturday with offshore flow and
modestly favorable fire weather conditions possible again behind
the upper low next week to keep an eye on.

Farther east, Gulf moisture will interact with a front approaching
the Lower Mississippi Valley to Tennessee and Ohio Valleys by this
coming weekend/early next week. Latest guidance continues to show
heavy rainfall totals over parts of the southern U.S., with the
potential for heavy rain and thunderstorms on Sunday across the
Lower Mississippi Valley. A marginal risk was carried into the new
Day 4/Sunday Excessive Rainfall Outlook from eastern Texas into
Mississippi where storms may train along a slow moving frontal
boundary. Snow or a wintry mix is possible on the northern side of
this precipitation shield mainly over the Ohio Valley, south-
central Appalachians, and possibly the Tennessee Valley and
vicinity. Precipitation may spread towards the East Coast early
next week as the frontal system progresses with some rainfall
redevelopment across the Southern Plains and lower Mississippi
Valley as well. This signal is increasing with development of an
organized frontal wave with Southwest upper system approach.

Much of the East should finally be back up towards normal
temperatures early next week, though readings a few degrees below
normal are possible across the Southeast. Anomalously cold
temperatures will also develop in the High Plains, Rockies, and
much of the West under the influence of upper troughing. The
coldest anomalies will be in the High Plains and Rockies to
Southern High Plains where high temperatures could be 10-20 degrees
below normal. Late period ridging over the northern tier could
allow temperatures to rise above normal next week, gradually
shifting south and east with time.


Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
218 AM EST Thu Jan 23 2025

Valid 12Z Thu Jan 23 2025 - 12Z Sun Jan 26 2025

...Great Lakes...
Days 1-3...

Cyclonic flow across the east will be amplified by a shortwave
moving through the flow which will push a cold front eastward
across the Great Lakes late Thursday into Friday, followed by
renewed CAA. This CAA will be somewhat short lived as a brief
period of shortwave ridging follows in its wake, primarily
resulting in subtle WAA D2, before a second, but weaker and
displaced farther north, shortwave digs across the region driving
another cold front eastward. This will result in two rounds of CAA
across the now cold lakes (GLERL total ice coverage up to 24%), so
despite steepening lapse rates the duration and intensity of any
subsequent lake effect snow (LES) will be modest.

This results in the heaviest snow likely occurring D3 as reflected
by WPC probabilities for more than 6 inches reaching 30-50% east of
Lake Ontario and across the Keweenaw Peninsula, but D1
probabilities for 4+ inches are also high (70%) in the eastern
U.P., along the eastern shore of Lake Michigan, and east of Lake
Ontario. 3-day total snowfall may eclipse 12 inches in the most
prolonged snow bands.


...The West...
Days 1-3...

An upper ridge dominating the flow across much of the West will
quickly be replaced by an amplifying trough beginning the latter
half of D1. This will occur in response to a shortwave trough
digging across British Columbia/Alberta and connecting with
secondary energy from the Pacific moving into the Pacific
Northwest. Together, these will force a longwave trough to deepen,
with height falls rapidly beginning Friday across the Pacific and
Interior Northwest as secondary energy digs southward through the
trough. With time, this feature is progged to become even more
impressive, taking on a negative tilt near CA Saturday and then
potentially closing off into an amplified low as reflected by both
ECMWF and GFS deterministic 500mb fields, and supported by NAEFS
700-500mb height anomalies falling to below the 10th percentile
over CA and portions of the Great Basin.

This synoptic evolution will help push a cold front southward
through the Central Rockies and Great Basin, while the placement of
the upper low results in downstream divergence and pronounced SW
flow atop the sinking front. The result of this will be increasing
isentropic ascent and expanding precipitation, generally in the
form of snow as the swath of precip pivots south from the Northern
Rockies through the Great Basin, accompanied by snow levels falling
from 1500-3000 ft ahead of the front to less than 500 ft below it.
Most of the precipitation should be light to moderate as PW
anomalies are generally normal to below normal, but some heavier
snowfall is possible, especially D3 as a stripe of fgen develops in
the LFQ of a strengthening jet streak collocated with the
WAA/isentropic ascent from the Great Basin east to the Front Range
of CO. Some enhanced ascent will also occur in this area due to
increasing upslope flow on the NE flow around a high pressure to
the north.

This evolution will spread a swath of snowfall southward each day.
On D1, WPC probabilities for 4+ inches are moderate (50-70%) across
some of the higher terrain of central Montana. By D2 the coverage
of moderate probabilities increases and spread across the
Absarokas, NW WY ranges, and into the CO Rockies including the Park
Range. By D3, WPC probabilities for 4 inches or more are highest
across the Front Range and Park Range of CO, with some lower
probabilities as far east as the Sierra. Days 2-3 snowfall could
exceed 1 foot in parts of the Colorado Rockies.


For the days 1-3 period, the probability of significant icing
greater than 0.10" is less than 10 percent.


Weiss



...Winter Storm Key Messages are in effect. Please see current
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Jan 23 2025

Valid 12Z Sun Jan 26 2025 - 12Z Thu Jan 30 2025


...Overview...

The start of the period on Sunday will feature an upper level
closed low diving southward along the California coast, and only
very slowly moving eastward with time next week. This should bring
beneficial precipitation to parts of southern California that have
been dealing with devastating wildfires. Organized rains/terrain
snows should make their way downstream into the Southwest as well.
Meanwhile, northern stream mean troughing, and reinforcing
shortwaves will cross from the northern Plains into the Great Lakes
and Northeast into next week. Moderate to locally heavy rainfall
will develop to the south across the Lower Mississippi Valley
Sunday and Monday as a slow moving frontal boundary moves through
the region. Additional frontal wave genesis over the Southern
Plains into the middle of next week given Southwest low slow
approach may again increase lead return flow and emerging rainfall
to monitor.

...Guidance/Predictability Assessment...

On the large scale, the guidance continues to show reasonable
agreement, but there remains plenty of uncertainty in the details
and timing of individual systems. Through early next week, models
show good clustering of the low as it slowly moves south through
California. After Tuesday though, there is some uncertainty in
timing into the Southwest/Four Corners and also with less
predictable energy that may shear off from the low. Ensemble mean
guidance provides a good middle ground for this feature in the late
period. To the north, mean northern stream troughing over the
Northern Plains- Great Lakes-Northeast continues to show
uncertainty in the amplitude of individual shortwaves dropping
through, especially next Wednesday and Thursday.

Accordingly, WPC guidance used a general model blend for the first
half of the period. For days 6 and 7, transitioned to a 60/40
split between the ensemble means and the deterministic GFS and
ECMWF which seemed to provide the best starting point amidst the
uncertainties.

...Weather/Hazards Highlights...

The slow moving upper low through California on Sunday will
continue to allow for much needed rain to southern California. Even
though QPF amounts are not too high, given sensitivity especially
in fresh burn scar locations, it may not take much to cause
flooding concerns. For this reason, a small marginal risk was added
to parts of Southern California on the Day 4 Excessive Rainfall
Outlook. Modest snows are possible across the terrain of southern
California, with rain and mountain snow into parts of the Southwest
as well. A tightened gradient behind the cold front dropping south
may produce some gusty winds along parts of the Rockies late this
week and California and Nevada on Saturday with offshore flow and
modestly favorable fire weather conditions possible again behind
the upper low next week to keep an eye on.

Farther east, Gulf moisture will interact with a front approaching
the Lower Mississippi Valley to Tennessee and Ohio Valleys by this
coming weekend/early next week. Latest guidance continues to show
heavy rainfall totals over parts of the southern U.S., with the
potential for heavy rain and thunderstorms on Sunday across the
Lower Mississippi Valley. A marginal risk was carried into the new
Day 4/Sunday Excessive Rainfall Outlook from eastern Texas into
Mississippi where storms may train along a slow moving frontal
boundary. Snow or a wintry mix is possible on the northern side of
this precipitation shield mainly over the Ohio Valley, south-
central Appalachians, and possibly the Tennessee Valley and
vicinity. Precipitation may spread towards the East Coast early
next week as the frontal system progresses with some rainfall
redevelopment across the Southern Plains and lower Mississippi
Valley as well. This signal is increasing with development of an
organized frontal wave with Southwest upper system approach.

Much of the East should finally be back up towards normal
temperatures early next week, though readings a few degrees below
normal are possible across the Southeast. Anomalously cold
temperatures will also develop in the High Plains, Rockies, and
much of the West under the influence of upper troughing. The
coldest anomalies will be in the High Plains and Rockies to
Southern High Plains where high temperatures could be 10-20 degrees
below normal. Late period ridging over the northern tier could
allow temperatures to rise above normal next week, gradually
shifting south and east with time.


Santorelli


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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw