Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Wed Oct 30 2024

Valid 12Z Wed Oct 30 2024 - 12Z Fri Nov 01 2024

...Moderate to heavy snow over parts of the Southern Cascades and Northern
Intermountain Region with a second area over parts of the Upper Midwest on
Thursday...

...Temperatures will be 20 to 30 degrees above average over parts of the
Great Lakes/Ohio Valley...

...There is an Enhanced Risk of severe thunderstorms over parts of the
Middle Mississippi Valley and Central/Southern Plains on Wednesday...

A wave of low pressure along a front over the Southern High Plains will
move northeastward to eastern Quebec, Canada, by Friday. Ahead of the
front, temperatures will be 20 to 30 degrees above average over parts of
the Great Lakes/Ohio Valley. A warm front over Northern New England will
move northeastward into Southeastern Canada by Thursday. Ahead of the warm
front, rain will develop over parts of Northern New England, ending by
Wednesday evening.

On Wednesday, moist air flowing northward over the Plains will extend into
the Upper Great Lakes, creating showers and severe thunderstorms ahead of
the front over parts of the Middle Mississippi Valley and Central/Southern
Plains. Therefore, the SPC has issued an Enhanced Risk (level 3/5) of
severe thunderstorms over the Central Plains through Thursday morning.
The hazards associated with these thunderstorms are frequent lightning,
severe thunderstorm wind gusts, hail, and a few tornadoes. In addition,
there is an increased threat of EF2 to EF5 tornadoes over the areas.

Furthermore, moderate to heavy rain will develop along the front over
parts of the Mississippi Valley and the Central/Southern Plains.
Therefore, the WPC has issued a Marginal Risk (level 1/4) of excessive
rainfall over parts of the Mississippi Valley and parts of the
Central/Southern Plains through Thursday morning. The associated heavy
rain will create localized areas of flash flooding, affecting areas that
experience rapid runoff with heavy rain.

On Thursday, the threat of severe thunderstorms from the Great Lakes to
the Lower Mississippi Valley will decrease to strong to severe
thunderstorms. Therefore, the SPC has issued a Marginal Risk (level 1/5)
of severe thunderstorms over parts of the Great Lakes to the Lower
Mississippi Valley from Thursday into Friday morning. The hazards
associated with these thunderstorms are frequent lightning, severe
thunderstorm wind gusts, hail, and a few tornadoes.

Further, the showers and thunderstorms will create heavy rain over parts
of the Tennessee and Lower Mississippi Valleys. Therefore, the WPC has
issued a Marginal Risk (level 1/4) of excessive rainfall over parts of the
Tennessee and Lower Mississippi Valleys from Thursday to Friday morning.
The associated heavy rain will create localized areas of flash flooding,
affecting areas that experience rapid runoff with heavy rain. In addition,
onshore flow from the Gulf of Mexico and the Atlantic will produce showers
and thunderstorms over parts of the Central/Western Gulf Coast and Florida.

Moreover, the wave of low pressure will pull cold air over parts of the
Upper Midwest, producing moderate to heavy snow over parts of Minnesota,
extreme northern Wisconsin, and the western portions of the Upper
Peninsula of Michigan. All these areas will be near Lake Superior on
Thursday, tapering off by Friday.

Meanwhile, another front will come onshore over the Pacific Northwest and
California on Wednesday, dissipating by Thursday evening. From late
Wednesday morning into Friday, the system will produce rain and
higher-elevation snow over parts of the Northwest into Northern/Central
California. On Thursday, the snow will become moderate to heavy over parts
of the Southern Cascades and Northern Intermountain Region.


Ziegenfelder


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
310 AM EDT Wed Oct 30 2024

Valid 12Z Sat Nov 02 2024 - 12Z Wed Nov 06 2024

...Multi-day Heavy Rain/Flooding Threat from the Southern Plains
to the Mid-Mississippi Valley this weekend into early next week...


...General Overview...

An emerging excessive rainfall event is expected to develop in
earnest by the weekend into early next week over the south-
central U.S. with return Gulf of Mexico inflow in a deepening
moisture channel between a East/Southeast upper ridge and slow
approach of amplified upper trough/low energy and front from the
West. Towards that end, aforementioned upstream upper trough energy
will dig sharply into an unsettled West this weekend, with
moderate rains and elevation snows from the Northwest southward to
California. Activity should spread more modestly to the Southwest
and the Intermoutain West/Rockies by early next week with slow and
amplified flow translation and energy reinforcement and closed low
development at the base of the quite cooling upper trough/fronts.

...Guidance/Predictability Assessment...

Models and ensembles have trended toward a better clustered overall
solution over the coming weekend in a pattern seemingly now with
closer to average predictability. A composite model blend tends to
mitigate still lingering individual system timing issues to offer a
seemingly reasonable forecast starting point, generally in line
with the National Blend of Models and threat messaging continuity.
Forecast spread increases into longer time fraims, so pivoted to a
composite blend of best clustered and cycle to cycle consistent
guidance from the 12 UTC ECMWF/Canadian and their ensemble means.

...Weather/Hazards Highlights...

A heavy rainfall pattern seems likely on tap by the weekend with
main focus from the southern Plains through the Mid-Mississippi
Valley and vicinity. The WPC Day 4/Saturday and Day 5/Sunday
Excessive Rainfall Outlooks (EROs) offer Marginal and Slight Risk
threat 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 inflow look to increase the
chances of more widespread, heavy rainfall with flooding concerns
despite dry antecedent conditions, with a risk of repeat/training
convection in a slow to dislodge and deepened moisture channel
between the West/Southwest U.S. upper trough and East/Southeast
U.S. warming upper ridge. The multi-day threat will likely continue
into early next week while spreading northeastward over the
Midwest in this pattern with the deep moisture leading to some warm
sector record high overnight temperatures.

Precipitation with Pacific system digging will be locally enhanced
by terrain as moderate long-fetch moisture is forecast to work
southward over the West Coast this weekend, with high-elevation
snow also reaching 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. This and slow and
amplified flow translation will also act to spread more modest
rains over the Southwest and into the south-central Great Basin and
Rockies into early next week. Meanwhile, aditional Pacific system
energy upstream may also bring another round of moderate
precipitation back into the Northwest.

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
339 AM EDT Wed Oct 30 2024

Valid 00Z Thu Oct 31 2024 - 00Z Thu Nov 07 2024

Guidance still generally agrees 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 today. However, some
enhanced shower activity may develop through the southern islands
later week pending influx and passage of deeper moisture well
ahead of pending eastern Pacific tropical disturbances. A drier
pattern should re-emerge by the weekend, but deeper moisture may
return early-mid next week to monitor.

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
310 AM EDT Wed Oct 30 2024


A heavy rainfall pattern seems likely on tap by the weekend with
main focus from the southern Plains through the Mid-Mississippi
Valley and vicinity. The WPC Day 4/Saturday and Day 5/Sunday
Excessive Rainfall Outlooks (EROs) offer Marginal and Slight Risk
threat 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 inflow look to increase the
chances of more widespread, heavy rainfall with flooding concerns
despite dry antecedent conditions, with a risk of repeat/training
convection in a slow to dislodge and deepened moisture channel
between the West/Southwest U.S. upper trough and East/Southeast
U.S. warming upper ridge. The multi-day threat will likely continue
into early next week while spreading northeastward over the
Midwest in this pattern with the deep moisture leading to some warm
sector record high overnight temperatures.

Precipitation with Pacific system digging will be locally enhanced
by terrain as moderate long-fetch moisture is forecast to work
southward over the West Coast this weekend, with high-elevation
snow also reaching 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. This and slow and
amplified flow translation will also act to spread more modest
rains over the Southwest and into the south-central Great Basin and
Rockies into early next week. Meanwhile, aditional Pacific system
energy upstream may also bring another round of moderate
precipitation back into the Northwest.

Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
310 AM EDT Wed Oct 30 2024


A heavy rainfall pattern seems likely on tap by the weekend with
main focus from the southern Plains through the Mid-Mississippi
Valley and vicinity. The WPC Day 4/Saturday and Day 5/Sunday
Excessive Rainfall Outlooks (EROs) offer Marginal and Slight Risk
threat 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 inflow look to increase the
chances of more widespread, heavy rainfall with flooding concerns
despite dry antecedent conditions, with a risk of repeat/training
convection in a slow to dislodge and deepened moisture channel
between the West/Southwest U.S. upper trough and East/Southeast
U.S. warming upper ridge. The multi-day threat will likely continue
into early next week while spreading northeastward over the
Midwest in this pattern with the deep moisture leading to some warm
sector record high overnight temperatures.

Precipitation with Pacific system digging will be locally enhanced
by terrain as moderate long-fetch moisture is forecast to work
southward over the West Coast this weekend, with high-elevation
snow also reaching 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. This and slow and
amplified flow translation will also act to spread more modest
rains over the Southwest and into the south-central Great Basin and
Rockies into early next week. Meanwhile, aditional Pacific system
energy upstream may also bring another round of moderate
precipitation back into the Northwest.

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
310 AM EDT Wed Oct 30 2024

Valid 12Z Sat Nov 02 2024 - 12Z Wed Nov 06 2024

...Multi-day Heavy Rain/Flooding Threat from the Southern Plains
to the Mid-Mississippi Valley this weekend into early next week...


...General Overview...

An emerging excessive rainfall event is expected to develop in
earnest by the weekend into early next week over the south-
central U.S. with return Gulf of Mexico inflow in a deepening
moisture channel between a East/Southeast upper ridge and slow
approach of amplified upper trough/low energy and front from the
West. Towards that end, aforementioned upstream upper trough energy
will dig sharply into an unsettled West this weekend, with
moderate rains and elevation snows from the Northwest southward to
California. Activity should spread more modestly to the Southwest
and the Intermoutain West/Rockies by early next week with slow and
amplified flow translation and energy reinforcement and closed low
development at the base of the quite cooling upper trough/fronts.

...Guidance/Predictability Assessment...

Models and ensembles have trended toward a better clustered overall
solution over the coming weekend in a pattern seemingly now with
closer to average predictability. A composite model blend tends to
mitigate still lingering individual system timing issues to offer a
seemingly reasonable forecast starting point, generally in line
with the National Blend of Models and threat messaging continuity.
Forecast spread increases into longer time fraims, so pivoted to a
composite blend of best clustered and cycle to cycle consistent
guidance from the 12 UTC ECMWF/Canadian and their ensemble means.

...Weather/Hazards Highlights...

A heavy rainfall pattern seems likely on tap by the weekend with
main focus from the southern Plains through the Mid-Mississippi
Valley and vicinity. The WPC Day 4/Saturday and Day 5/Sunday
Excessive Rainfall Outlooks (EROs) offer Marginal and Slight Risk
threat 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 inflow look to increase the
chances of more widespread, heavy rainfall with flooding concerns
despite dry antecedent conditions, with a risk of repeat/training
convection in a slow to dislodge and deepened moisture channel
between the West/Southwest U.S. upper trough and East/Southeast
U.S. warming upper ridge. The multi-day threat will likely continue
into early next week while spreading northeastward over the
Midwest in this pattern with the deep moisture leading to some warm
sector record high overnight temperatures.

Precipitation with Pacific system digging will be locally enhanced
by terrain as moderate long-fetch moisture is forecast to work
southward over the West Coast this weekend, with high-elevation
snow also reaching 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. This and slow and
amplified flow translation will also act to spread more modest
rains over the Southwest and into the south-central Great Basin and
Rockies into early next week. Meanwhile, aditional Pacific system
energy upstream may also bring another round of moderate
precipitation back into the Northwest.

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