Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
358 PM EDT Tue Oct 29 2024

Valid 00Z Wed Oct 30 2024 - 00Z Fri Nov 01 2024

...Mountain snow continues over parts of the central and northern Rockies
through Wednesday...

...Record warmth expands into the Eastern U.S. through Thursday...

...Severe thunderstorms are likely across portions of the central and
southern Plains as well as the middle and lower Mississippi Valley on
Wednesday...

A potent storm system located over the central and northern Rockies will
continue to produce moderate to heavy snow across the high elevations of
Utah, Wyoming, and Colorado tonight into Wednesday. An injection of colder
air combined with a tap of significant moisture will result in snow
accumulations up to a foot for many mountain ranges in the region. The
snow will make for difficult travel over the high mountain passes,
especially during the nighttime and early morning hours tonight into
Wednesday. Numerous Winter Storm Warnings and Winter Weather Advisories
remain in effect. Be prepared for winter driving conditions and slower
travel should you need to venture out into the high country. In the wake
of the storm, much colder air will lead to frost and freeze concerns for
the lower elevations tonight and again on Wednesday night, likely marking
an end to the growing season for many locations.

Out ahead of the storm and cold front that is bringing snow to parts of
the central and northern Rockies is a surge of unseasonable warmth that is
gradually expanding eastward from the Central U.S. to the Eastern U.S.
through Thursday. High temperatures will soar into the 70s and 80s across
a large portion of the eastern half of the country the next couple of
days, with highs eclipsing the 90 degree mark across parts of the southern
Plains, lower Mississippi Valley, and Southeast. Temperatures will remain
quite mild at night as well, with overnight lows dropping only into the
50s and 60s. Compared to climatology, temperatures that warm this late in
the year are easily 25 to 35 degrees above normal... and are likely to set
many daily high and high minimum temperature records through Thursday. In
fact, many places across the Northeast and Mid-Atlantic are likely to
experience their warmest Halloween on record, making for rather pleasant
conditions for trick-or-treating Thursday evening.

The period of record warmth will come to an end across much of the Central
U.S. by Wednesday night into Thursday as a passing cold front is forecast
to bring much cooler temperatures into the region. Before that comes to
fruition, the cold front will be responsible for sparking widespread
showers and thunderstorms across a large portion of the nation's
midsection Wednesday afternoon, evening, and night. Some of the storms
that develop will have the potential to become severe, with damaging
winds, large hail, and a few tornadoes possible. As a result, The Storm
Prediction Center has issued an Enhanced Risk of severe thunderstorms
(level 3 of 5) for southeast Nebraska, Northwest Missouri, much of eastern
Kansas, and parts of northeast Oklahoma. Outside the Enhanced Risk lies a
Slight Risk of severe thunderstorms (level 2 of 5) which extends from
southwest Iowa parts of northern Texas. In addition to the severe threat,
a few stronger storms could produce heavy rainfall. Despite recent
dryness, isolated instances of flash flooding cannot be completely ruled
out... and the anomalous moisture in play was enough for the Weather
Prediction Center to issue a Marginal Risk (level 1 of 4) of excessive
rainfall from central Wisconsin south to northeastern Texas.


Miller



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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 29 2024

Valid 12Z Fri Nov 01 2024 - 12Z Tue Nov 05 2024

...Heavy Rain Threat from the Southern Plains to the Mid-
Mississippi Valley to develop this weekend...


...General Overview...

An upper trough and moderate surface low will eject through the
Northeast and eastern Canada Friday overtop a warm ambient upper
ridge held over the Southeast. A cold front will swing through the
eastern U.S. to focus lingering showers and usher in moderating
post-frontal high pressure. The trailing portion of the front is
forecast to slow, but offer some convective focus. An emerging
heavy rainfall pattern then eminates up through the south-central
U.S. with return flow in a deepening moisture channel between the
Southeast upper ridge and the approach of upper trough energy and
front from the West. Towards that end, aforementioned upstream
upper trough energy will dig sharply into an unsettled West, with
moderate rains and elevation snows over the Northwest and
uncertainly southward to California along with less organized
activity to the Intermoutain West/Rockies. This pattern may lead to
closed low development at the base of a main trough.

...Guidance/Predictability Assessment...

Models have trended slower and deeper with an anomalous trough that
may dig into the West beginning this weekend. A general model
blend consisting of the deterministic 00z EC/CMC/UKMET and 06z GFS
were used on days 3 and 4, with heavy weighting placed on the EC
and GFS solutions on day 3, because they are both more progressive
and in line with the ensemble means with their depiction of a
closed mid- level low dropping into the Northwest from the Gulf of
Alaska.

Weighting shifts to the GFS on day 4 because it, much like all of
the ensemble means, avoids closing off a mid-level low over the
Northwest while maintaining a positively tilted trough axis along
the West Coast. The 00z ECE/CMCE and 06z GEFS are introduced to the
blend on day 5 in place of the deterministic CMC and UKMET which
are comparatively much more bullish with the western trough than
the deterministic EC/GFS and ensemble means. The ensemble means are
favored through the rest of the period as they cluster fairly well
on a slow moving trough over the central U.S., despite some timing
spread, particularly found in the ECE and CMCE.

The 06z AIFS resembles more of a 00z CMC solution with a closed
positively tilted mid-level low over the Southwest on day 6
(Monday). The GraphCast looks more like the 06z GEFS mean, which is
more progressive than the rest of the deterministic, ensemble and
ML models (FuXi, Pangu, FourCastNet).

...Weather/Hazards Highlights...

A heavy rainfall pattern seems likely on tap by the weekend over
the southern Plains and vicinity. A WPC Day 4/Friday Excessive
Rainfall Outlook (ERO) Marginal Risk area is in place to address
potential, with the new Day 5/Saturday ERO introducing Marginal
and Slight Risk areas given consistent guidance signals. Expect
activity to expand and focus along a southwest to northeast axis
ahead of additional frontal boundaries this weekend and into early
next week as robust upper trough/closed low energy digs upstream
into the West Coast to re-amplify the flow over the Lower 48 and
vicinity. Multiple days of southerly, moist Gulf flow look to
increase the chances of more widespread, heavy rainfall with
flooding concerns despite dry antecedent conditions, especially
from the south-central Plains to the Middle Mississippi Valley.

Precipitation associated with Pacific system approach as enhanced
by terrain and moderate long-fetch moisture is forecast to focus
and with much uncertainty work southward over the West Coast later
in the week and through the weekend, with high- elevation snow
reaching into favored terrain of the northern Intermountain
West/Rockies and enhanced rains reaching down into California.
Regardless, the cold frontal surge and possible closed low
development at the southern base of the main upper trough will
bring in cooler temperatures to much of the West.

Kebede/Schichtel


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
326 AM EDT Tue Oct 29 2024

Valid 00Z Wed Oct 30 2024 - 00Z Wed Nov 06 2024

Models and ensembles reasonably agree that high pressure will be
periodically reinforced while bridging to the north and settling
well to the northeast of the state over the next week. This favors
strengthened island trades in a relatively drier and stable
pattern with windward terrain favored showers into midweek.
However, some enhanced shower activity may redevelop through the
southern islands later week pending influx and passage of deeper
moisture with a current eastern Pacific tropical disturbance. A
drier pattern should re-emerge by the weekend.

Schichtel

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
834 PM EDT Tue Oct 29 2024
Day 1
Valid 01Z Wed Oct 30 2024 - 12Z Wed Oct 30 2024

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

Chenard


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
834 PM EDT Tue Oct 29 2024
Day 2
Valid 12Z Wed Oct 30 2024 - 12Z Thu Oct 31 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE
SOUTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY/UPPER MIDWEST...

A deep layered trough is expected to eject into the Plains by
Wednesday morning, which in turn results in surface troughing that
draws Gulf moisture northward ahead of an approaching cold front.
Cooler air filtering in from the west/north will encounter the warm
air advection associated with the low- level jet. Convection over
the region is expected to increase in both coverage and intensity
with the set up becoming more favorable for isolated heavy
rainfall amounts/rates and localized flooding concern.

The 12Z global and ensemble guidance continues to show two
distinct areas swaths of higher QPF. The first remains focused near
the juncture of Oklahoma, Texas and Arkansas state borders amid
areas of higher instability...on the order of 1500 to 2500 J per kg
of surface based CAPE. The second area from northeast Kansas to
northern and central Wisconsin still inched westward in this model
cycle close the the greatest mid- and upper-level height falls
which was roughly co-located near a region of sloped frontogenesis
in the 800 mb to 600 mb layer late in the period. At the same
time...the 29/12Z NAM accelerates low level flow to the 45 kt to 65
kt range acting to enhance moisture transport into the area as
early as 31/03Z in a few spots. The Marginal Risk area needed only
a minor nudge after the shape was altered more noticeably in the
previous outlook.

Antecedent conditions are quite dry...as reflected by the very high
flash flood guidance. That should mitigate any widespread threat
of excessive rainfall as well as progressive cells. Even so...the
Marginal Risk area still seemed appropriate based on what the
magnitude of the instability and mesoscale forcing from the coarser
numerical guidance with room to adjust with future guidance
(including the CAM guidance).

Campbell/Bann


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
834 PM EDT Tue Oct 29 2024
Day 3
Valid 12Z Thu Oct 31 2024 - 12Z Fri Nov 01 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY...

2030Z Excessive Rainfall Update...
Instability remains the highest in portions of the Lower
Mississippi Valley while the flow pattern/mesoscale forcing weakens
farther north. The previous outlook had that pretty well handled
so no change was made.

Bann

083-Z Excessive Rainfall Discussion...

The upper level trough will continue to advance through the Upper
Midwest which will send the cold front through the eastern portions
of the Southern Plains and mid-Mississippi Valley. Strong to
severe thunderstorms will persist for areas along and ahead of the
advancing frontal boundary per SPC (Marginal Risk); which will
shift the heavy rain potential to the central Gulf Coast to
western Kentucky where there is a Marginal Risk area for excessive
rainfall. Areal averages will be in the 1 to 2 inch range with
locally higher amounts possible.

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 29 2024


A heavy rainfall pattern seems likely on tap by the weekend over
the southern Plains and vicinity. A WPC Day 4/Friday Excessive
Rainfall Outlook (ERO) Marginal Risk area is in place to address
potential, with the new Day 5/Saturday ERO introducing Marginal
and Slight Risk areas given consistent guidance signals. Expect
activity to expand and focus along a southwest to northeast axis
ahead of additional frontal boundaries this weekend and into early
next week as robust upper trough/closed low energy digs upstream
into the West Coast to re-amplify the flow over the Lower 48 and
vicinity. Multiple days of southerly, moist Gulf flow look to
increase the chances of more widespread, heavy rainfall with
flooding concerns despite dry antecedent conditions, especially
from the south-central Plains to the Middle Mississippi Valley.

Precipitation associated with Pacific system approach as enhanced
by terrain and moderate long-fetch moisture is forecast to focus
and with much uncertainty work southward over the West Coast later
in the week and through the weekend, with high- elevation snow
reaching into favored terrain of the northern Intermountain
West/Rockies and enhanced rains reaching down into California.
Regardless, the cold frontal surge and possible closed low
development at the southern base of the main upper trough will
bring in cooler temperatures to much of the West.

Kebede/Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 29 2024


A heavy rainfall pattern seems likely on tap by the weekend over
the southern Plains and vicinity. A WPC Day 4/Friday Excessive
Rainfall Outlook (ERO) Marginal Risk area is in place to address
potential, with the new Day 5/Saturday ERO introducing Marginal
and Slight Risk areas given consistent guidance signals. Expect
activity to expand and focus along a southwest to northeast axis
ahead of additional frontal boundaries this weekend and into early
next week as robust upper trough/closed low energy digs upstream
into the West Coast to re-amplify the flow over the Lower 48 and
vicinity. Multiple days of southerly, moist Gulf flow look to
increase the chances of more widespread, heavy rainfall with
flooding concerns despite dry antecedent conditions, especially
from the south-central Plains to the Middle Mississippi Valley.

Precipitation associated with Pacific system approach as enhanced
by terrain and moderate long-fetch moisture is forecast to focus
and with much uncertainty work southward over the West Coast later
in the week and through the weekend, with high- elevation snow
reaching into favored terrain of the northern Intermountain
West/Rockies and enhanced rains reaching down into California.
Regardless, the cold frontal surge and possible closed low
development at the southern base of the main upper trough will
bring in cooler temperatures to much of the West.

Kebede/Schichtel

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Tue Oct 29 2024

Valid 00Z Wed Oct 30 2024 - 00Z Sat Nov 02 2024


...Central Rockies onto High Plains....
Day 1...

A late October winter storm is underway across the Central Rockies
and High Plains largely due to an unusually strong upper level
trough (500mb and 700mb heights as low as the 2.5 climatological
percentile in parts of the central Rockies) and strong upper level
ascent beneath dual-divergent channels of 250mb jet streaks aloft.
Vertical cross sections depict excellent 700-550mb frontogenesis
aligning over east-central Montana this afternoon and evening,
which will coincide with the the heaviest snow bands that generate
1-2"/hr snowfall rates according to the 12Z HREF. The lack of a
frigid air-mass will keep the heaviest snowfall totals to the
typical mountain ranges and where the heaviest snowfall rates ensue
across Wyoming and South Dakota's Black Hills. Farther south and
west, closer to the lower/colder heights/temperatures at 700mb,
periods of snow over the Wasatch, Uinta, and Colorado Rockies will
persist this evening but snowfall rates will gradually dissipate as
the strongest synoptic-scale forcing heads into the Northern
Plains tonight. While some lingering snow showers may stick around
in Wyoming and the Black Hills Wednesday morning, additional
snowfall will be minor as temperatures in the boundary layer warm
and moisture aiding in producing snow departs.

From 00Z this evening onward, WPC probabilities show moderate-to-
high chances (50-80%) for additional snowfall totals >8" in most
mountain ranges in central Wyoming and the Black Hills. Similar
probabilities are present but for >4" in parts of the Uinta and
Colorado Rockies. The Probabilistic WSSI between 00Z Wed -
00Z Thurs shows high chances (>70%) for Minor Impacts in the Black
Hills and along the Front Range in Wyoming. Minor Impacts will also
be felt in parts of the Central Rockies in southern Wyoming and
central Colorado. Impacts are likely to included snow covered roads
and reduced visibilities in complex terrain, making for dicey
travel in affected areas.

...Northwest to the Northern Rockies...
Days 2-3...

Following a mostly dry Tuesday in the Pacific Northwest, a potent
storm system arrives on Wednesday that will direct the next round
of unsettled weather into the region. NAEFS does show the upper
low barreling into the the Pacific Northwest and southern British
Columbia Wednesday night does sport 500mb and 700mb heights that
are below the 10th climatological percentile and a narrow IVT
channel peaking up to 400 kg/m/s that will supply modest moisture
into the region. That said, there is not much in the way of a sub-
freezing air-mass either in front of the storm or arriving in its
wake. This will keep heavy snow to elevations above 5,000ft in the
Cascades and Olympics. By Thursday morning, the upper low
continues to deepen and moves into western Oregon, resulting in
snow levels falling as low as 3,000ft in some parts of the Cascade
Range. In addition, moisture from the initial round of mountain
snow in the Pacific Northwest on Wednesday will reach the northern
Rockies where periods of light-to-moderate snow will engulf the
Sawtooth, Boise, Bitterroots, and Teton ranges. The heaviest snow
arrives on Thursday in the Oregon Cascades, northern Sierra Nevada,
Siskiyou, and Blue Mountain ranges, then late Thursday into Friday
in the northern Rockies.

WPC PWPF does show moderate-to-high chances (50-70%) for > 12" of
snowfall for the event in the Oregon Cascades while the tallest
peaks have low-to-moderate chances (30-50%) for >18". Meanwhile,
there are high chances (>70%) for snowfall >8" in the peaks of the
Blue Mountains, the Siskiyou, and northern Sierra Nevada above
6,000ft. The Probabilistic WSSI shows moderate chances (40-60%)
for Moderate Impacts in the Oregon Cascades and Siskiyou Mountains
at elevations above 5,000ft. These mountains and elevations would
have the best odds of seeing impacts that would cause impacts to
daily life that include hazardous travel and potential road
closures. Elsewhere, the other mountain ranges mentioned above are
sporting moderate-to- high chances for Minor Impacts as a result of
this impending winter storm Wednesday and through Friday morning.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 29 2024

Valid 12Z Fri Nov 01 2024 - 12Z Tue Nov 05 2024

...Heavy Rain Threat from the Southern Plains to the Mid-
Mississippi Valley to develop this weekend...


...General Overview...

An upper trough and moderate surface low will eject through the
Northeast and eastern Canada Friday overtop a warm ambient upper
ridge held over the Southeast. A cold front will swing through the
eastern U.S. to focus lingering showers and usher in moderating
post-frontal high pressure. The trailing portion of the front is
forecast to slow, but offer some convective focus. An emerging
heavy rainfall pattern then eminates up through the south-central
U.S. with return flow in a deepening moisture channel between the
Southeast upper ridge and the approach of upper trough energy and
front from the West. Towards that end, aforementioned upstream
upper trough energy will dig sharply into an unsettled West, with
moderate rains and elevation snows over the Northwest and
uncertainly southward to California along with less organized
activity to the Intermoutain West/Rockies. This pattern may lead to
closed low development at the base of a main trough.

...Guidance/Predictability Assessment...

Models have trended slower and deeper with an anomalous trough that
may dig into the West beginning this weekend. A general model
blend consisting of the deterministic 00z EC/CMC/UKMET and 06z GFS
were used on days 3 and 4, with heavy weighting placed on the EC
and GFS solutions on day 3, because they are both more progressive
and in line with the ensemble means with their depiction of a
closed mid- level low dropping into the Northwest from the Gulf of
Alaska.

Weighting shifts to the GFS on day 4 because it, much like all of
the ensemble means, avoids closing off a mid-level low over the
Northwest while maintaining a positively tilted trough axis along
the West Coast. The 00z ECE/CMCE and 06z GEFS are introduced to the
blend on day 5 in place of the deterministic CMC and UKMET which
are comparatively much more bullish with the western trough than
the deterministic EC/GFS and ensemble means. The ensemble means are
favored through the rest of the period as they cluster fairly well
on a slow moving trough over the central U.S., despite some timing
spread, particularly found in the ECE and CMCE.

The 06z AIFS resembles more of a 00z CMC solution with a closed
positively tilted mid-level low over the Southwest on day 6
(Monday). The GraphCast looks more like the 06z GEFS mean, which is
more progressive than the rest of the deterministic, ensemble and
ML models (FuXi, Pangu, FourCastNet).

...Weather/Hazards Highlights...

A heavy rainfall pattern seems likely on tap by the weekend over
the southern Plains and vicinity. A WPC Day 4/Friday Excessive
Rainfall Outlook (ERO) Marginal Risk area is in place to address
potential, with the new Day 5/Saturday ERO introducing Marginal
and Slight Risk areas given consistent guidance signals. Expect
activity to expand and focus along a southwest to northeast axis
ahead of additional frontal boundaries this weekend and into early
next week as robust upper trough/closed low energy digs upstream
into the West Coast to re-amplify the flow over the Lower 48 and
vicinity. Multiple days of southerly, moist Gulf flow look to
increase the chances of more widespread, heavy rainfall with
flooding concerns despite dry antecedent conditions, especially
from the south-central Plains to the Middle Mississippi Valley.

Precipitation associated with Pacific system approach as enhanced
by terrain and moderate long-fetch moisture is forecast to focus
and with much uncertainty work southward over the West Coast later
in the week and through the weekend, with high- elevation snow
reaching into favored terrain of the northern Intermountain
West/Rockies and enhanced rains reaching down into California.
Regardless, the cold frontal surge and possible closed low
development at the southern base of the main upper trough will
bring in cooler temperatures to much of the West.

Kebede/Schichtel


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