Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
254 PM EST Wed Nov 06 2024

Valid 00Z Thu Nov 07 2024 - 00Z Sat Nov 09 2024

...Heavy rain threat emerging over the interior Southeast late today into
Thursday as tropical moisture associated with weak low over southeastern
Gulf of Mexico lifts northward...

...Increasing threat for heavy snow to impact the central to southern
Rockies and nearby High Plains through the next couple of days...

...Watching the Florida Keys for impacts associated with Hurricane Rafael
forecast to pass not far too to the west tonight...

...Record warmth expected for the Mid-Atlantic and southern New England
today...

Tropical moisture associated with a weak low pressure circulation centered
over southeastern Gulf of Mexico is lifting north toward the Florida
Panhandle under a broad channel of southerly flow aloft. This weak low is
a system somewhat separate from Hurricane Rafael farther south in the
Caribbean Sea. The tropical moisture associated with the weak low is
forecast to be drawn northward today, leading to heavy rainfall tonight
into Thursday morning across the interior section of the Southeast. WPC
currently places a moderate risk of heavy rain across central Georgia into
portions of South Carolina for this upcoming heavy rain event.

Hurricane Rafael continues to intensify over the northwestern Caribbean
Sea while heading northwest toward western Cuba. The latest forecast from
the National Hurricane Center has Rafael tracking just to the west of Key
West as category-2 hurricane tonight into Thursday morning. Tropical
Storm Warning is in effect for the western portion of the Florida Keys
where increasing winds with passing squally downpours associated with
rainbands from Rafael can be expected by tonight and may lead to isolated
flood concerns.

Meanwhile, a winter storm is brewing across the Southern Rockies. A
vigorous upper-level trough is plunging south ushering a surge of polar
air into the region while developing an area of snow over the Central
Rockies into the central High Plains. The snow is expected to expand in
coverage and pickup intensity through the day. The compact and vigorous
nature of this upper low will help sustain the snow in the general
vicinity of Central/Southern Rockies into the nearby High Plains (mostly
within Colorado and New Mexico) as the upper low rotates and lingers. If
the upper low deepens more than expected, the associated snow could linger
in the same area farther out in time. There is potential for a foot of
snow to fall across the Front Range of Colorado, while a few feet of wet
snow is possible farther south across the higher elevations near the
Colorado-New Mexico border and into northern New Mexico. Winter Storm
Watches and Warnings as well as Winter Weather Advisories have been issued
for much of the aforementioned areas. In addition to producing snow, this
vigorous upper low could have changeable influences on the future track of
Rafael in the Gulf of Mexico. Please refer to NHC for the latest forecast
track on Rafael.

Much colder temperatures are expected across the West behind the cold
front; with 30s and 40s across the valleys and dipping into the single
digits in the cool spots for overnight lows. Make sure to bundle up.
Strong wind gusts along with lower moisture will increase the risk for
wildfires over the next few days. Critical wildfire conditions persist
across California where Red flag warnings are in effect for portions of
coastal and interior California. The Storm Prediction Center has Critical
Fire Conditions highlighted for southern California today with an extreme
area in the vicinity of Santa Clarita which will carry over into Thursday.
In contrast, high temperatures are forecast to challenge or break records
today across the Mid-Atlantic into southern New England as well as
scattered locations in the South ahead of the weakening cold front moving
across the Mississippi Valley.

Campbell/Kong


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Nov 6 2024

Valid 12Z Sat Nov 09 2024 - 12Z Wed Nov 13 2024

...Watching Hurricane Rafael as it tracks into the Gulf of
Mexico...


...Overview...

The National Hurricane Center continues to issue advisories for
Hurricane Rafael as it tracks across the Gulf this weekend into
early next week while weakening as it interacts with a mean upper
ridge stretching from the Bahamas. Models and the NHC forecast have
trended farther south with Rafael, keeping it offshore well south
of the central Gulf Coast while it weakens. But the combination of
Rafael's moisture and a frontal system supported by an upper low
ejecting northeast from the Plains may produce some areas of
locally heavy rainfall from the Gulf Coast northward especially
this weekend. Meanwhile, a series of Pacific systems will increase
coverage of rain and higher elevation snow over the West from the
weekend into early next week. Much of the East should see above
normal temperatures through the period while the southern Rockies
will start the weekend on the chilly side and cooler temperatures
will spread across the West next week.


...Guidance/Predictability Assessment...

For Hurricane Rafael, recent model runs have generally trended to
the south, showing the surface low weakening over the Gulf rather
than making landfall in the central Gulf Coast as some previous
runs had showed. The 00Z ECMWF, UKMET, and many EC ensemble members
were particularly aggressive with this southwestward shift as
Rafael does not get picked up by the upper trough to track it
northward. GFS runs are indicating this trend but not to the extent
of the EC/UKMET that take Rafael so far south it goes into central
Mexico. The 12Z CMC does have Rafael track north into the central
Gulf Coast, along with some GEFS members and the bulk of the AI/ML
models initialized at 00Z, so there remains uncertainty with this
trend. Continue to monitor latest NHC products for additional
information on Rafael.

Farther north, the first system of note is a closed upper low
starting the period Saturday atop the central High Plains and
tracking northeast Sunday-Monday while opening up. Model guidance
is rather agreeable with this feature especially over the weekend,
but guidance has been more erratic with details of a shortwave that
enters western North America during the weekend and may have some
influence on the remaining upper low energy by early next week. The
00Z CMC in particular seemed like an eastern outlier with this
shortwave for more interaction with the preexisting upper
low/trough. This leads to lingering uncertainty for some details of
the frontal system reaching the Northeast.

There are continued timing and amplitude differences for the
larger scale trough moving into/through the West early next week
and toward the central U.S. by midweek, with GFS runs leaning
slower and ECMWF faster. Latest ML models show a similar spread,
arguing for a blend/compromise approach. This also mitigates issues
for how energy may be distributed within the upper trough by the
middle of next week, with individual solutions ranging between
greater dynamics in the northern part of the trough, or farther
south, to an evenly phased trough. A compromise also looks best for
the next system that may come into the picture over the
northeastern Pacific by next Wednesday.

Overall a blend favoring the 06Z GFS and 00Z ECMWF with lesser
portions of the UKMET and GEFS/EC ensemble means early in the
period, with an increasing proportion of the ensemble means as the
period progressed given increasing uncertainty.


...Weather/Hazards Highlights...

The combination of the Plains system pushing into the Mississippi
Valley and moisture from Rafael, which is forecast to be south of
the central Gulf Coast by the weekend, will lead to the potential
for some areas of heavy rainfall from the central Gulf Coast to the
Ohio Valley this weekend. On Saturday, maintained the Marginal
Risk in the ERO with generally minor changes from the previous
forecast. By Sunday, good moisture and some limited instability
should continue to spread into similar regions, shunted just a bit
eastward. This forecast cycle, WPC has stretched the Marginal Risk
well north across parts of the Lower Mississippi Valley to Mid-
South to the Ohio Valley where moderate to heavy rainfall rates may
train in the vicinity of the frontal system. The areal coverage
may be able to shrink with time if models converge. Dry antecedent
conditions in the Ohio Valley in particular may limit the extent of
impacts of flash flooding from heavy rain, but a 5 percent risk
(Marginal) seems warranted. Some rainfall may linger beyond Sunday
but most of the East should trend drier by Monday-Tuesday. Also of
note, a wave tracking from the southern Bahamas into the eastern
Gulf may increase rainfall over Florida around Sunday-Monday.

The West will see a wetter regime with high elevation snow,
starting in the Pacific Northwest and then spreading farther south
into parts of California and east into the Rockies. Highest totals
should be in the Sunday-Monday time frame with a vigorous upper
trough and frontal system approaching/reaching the area. While
there is still a fair amount of spread for QPF magnitudes, first-
guess guidance is showing enough of a signal to introduce a
Marginal Risk area in the Day 5 ERO over parts of the Pacific
Northwest where initial soil conditions are neutral to damp. Higher
elevation snow is likely for the Cascades, Sierra Nevada, and
northern/central Rockies. Another system is likely to bring
additional focused precipitation to the Pacific Northwest next
Wednesday. Depending on western upper trough progression, some
rainfall may develop over the central U.S. by the middle of next
week.

Except for the Great Lakes into New England during the weekend,
the eastern half of the country will likely see above normal
temperatures through the period. Warmest anomalies should be for
morning lows, reaching 20-25F above normal on one or more days over
the South and extending a little farther northeastward at times.
Coverage of plus 10-15F anomalies for highs should increase going
from the weekend into the first half of next week. Corresponding to
these relative anomalies, there will be better potential for some
record warm lows versus more isolated records for daytime highs.
The northern Plains will also be well above normal until a cooling
trend Tuesday-Wednesday, while the southern Plains will be warmest
early next week. Chilly temperatures over the southern Rockies/High
Plains will gradually moderate while much of the West will be near
normal during the weekend. Then the upper trough pushing into the
West next week should expand the coverage of below normal
temperatures from west to east.


Tate/Rausch


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
257 AM EST Wed Nov 06 2024

Valid 00Z Thu Nov 07 2024 - 00Z Thu Nov 14 2024

A cold front now reaching the region should stall and dissipate,
while strong northeasterly winds prevail late this week. Expect
trades to remain brisk while turning more easterly during the
weekend as high pressure passes by to the north. Then winds
should be easterly or east-southeasterly through the early-middle
part of next week. Central Pacific pattern differences arise
toward midweek, with dynamical/machine learning (ML) guidance
split as to how much of a front/inverted trough there may be off
to the west of the main islands--affecting the orientation of
trades over the state. At the very least, 18Z/00Z GFS runs may be
a little too far east with their feature by next Wednesday.

It took a number of days, but the 00Z ECMWF finally resembles
other guidance more closely for shearing trough energy that likely
consolidates into a weak upper low over/south of the state from
late week onward. However the latest ML runs and most other
dynamical solutions advertise a slightly farther south and west
low track versus the ECMWF, favoring an evolution closer to the
GFS. Windward/mountain-focused showers should trend lighter late
this week as moisture declines to below climatology, followed by
some increase around the weekend and/or early next week due to
flow around the upper low. Precipitable water values may decline
a bit thereafter.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 PM EST Wed Nov 6 2024
Day 1
Valid 16Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST...

1600Z Update...

A Marginal Risk area has been added to portions of central to
northeast LA and also a small part of southwest MS to account for
the ongoing slow-moving areas of heavy showers and thunderstorms
across the region that are focusing along and out ahead of a
quasi-stationary front. Please consult MPD #1131 for more details
on this. Convective trends across this region will continue to be
closely monitored through the afternoon hours for additional
convective development.

Elsewhere, the 12Z HREF guidance and recent HRRR guidance continues
to support the development and expansion of broken areas of heavy
showers and thunderstorms across the interior of the Southeast
beginning later this afternoon and heading into the overnight
hours. However, there has been a trend to concentrate the heaviest
convective rainfall threat a bit farther south and east and a bit
deeper into the coastal plain of southern and eastern GA and the SC
Lowcountry. Additionally, there are multiple HREF models that are
quite heavy with the rainfall potential across parts of the FL
Panhandle. Regionally, the potential exists for as much as 4 to 8
inches of rain, with some isolated 10+ inch totals being supported
by 12Z/Thursday. The 12Z HREF guidance shows 50 to 80 percent
probabilities of seeing 5+ inches of rain from eastern parts of the
FL Panhandle northeastward into the SC Lowcountry, and in a focused
manner across parts of east-central GA and along the SC border,
there are 60 to 80 percent probabilities of seeing 8+ inch
rainfall totals. The heavy rains are again expected to be the
result of increasing moisture transport poleward of Hurricane
Rafael and interaction with an inverted surface trough, and with
right-entrance region upper-level jet dynamics providing deeper
layer ascent. Given the setup, which will favor rainfall rates of 2
to 3+ inches/hour and these impressive totals, there will be a
strong concern for areas of high-impact flash flooding. These
latest trends have necessitated the need to adjust the Slight and
Moderate Risk areas farther south and east.

Related to Hurricane Rafael, there may be some potential for outer bands
of convection to impact portions of the lower FL Keys going through
tonight, and as a result the Marginal Risk area has been maintained
for this area.

Orrison


Previous discussion...

In coordination with CAE/Columbia, SC and FFC/Peachtree City, GA
forecast offices, a Moderate Risk upgrade was introduced with this
update.

A plume of deep tropical moisture, indirectly associated with
Hurricane Rafael will continue overspreading portions of the
Southeast today. The moisture plume will run into a developing
front over Georgia and South Carolina. An upper level jet streak
will add lift to the atmosphere. Late today into this evening, the
nocturnal low level jet's strengthening will kick the moisture
advection into high gear. Frontogenesis occurring over Georgia and
South Carolina will act to focus the heavy rain over the narrow
Moderate Risk corridor. Expect training convection to develop
during the evening which will persist through the overnight and
while slowly weakening in the pre-dawn hours, is likely to continue
into western South Carolina into Day 2/Thursday.

HREF probabilities show a 20 to 25 percent chance of a 100 year
rainfall event in the Moderate Risk area. FFGs are very high in the
area due to recent dry conditions with only very light rain. This
has likely made some of the clay soils quite hydrophobic. The
hydrophobic soils will likely increase the runoff from the heavy
rain, which will likely quickly exceed FFGs as the heavy rain
likely persists for multiple hours.

Wegman

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 PM EST Wed Nov 6 2024
Day 2
Valid 12Z Thu Nov 07 2024 - 12Z Fri Nov 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST AS WELL AS PORTIONS OF TEXAS PANHANDLE AND WESTERN
OKLAHOMA...

20z Update: Slight risk reasoning still holds over GA and SC. Only
adjustment was to expand the risk towards the coast following
model trends.

Convection Thursday evening into the overnight hours should drive
at least some flash flood risk over portions of TX and OK. Plenty
of large scale forcing and moisture in place to drive a widespread
convective risk...with the main uncertainty more relating to the
degree of instability present. The inherited Slight risk was
shifted southward with this update into more of TX. This is
supported by the 12z HREF probabilities and the 12z GEFS based
machine learning ERO guidance. The area encompassed by the Slight
risk should see slightly better instability which will allow for
the potential of higher rainfall rates.

Chenard

...Previous Discussion...

...Southeast...

Heavy rain will be ongoing across Georgia and especially South
Carolina at the start of the period Thursday morning. While the
rainfall will be diminishing in intensity, it's expected after the
much heavier rains of Wednesday night, that the lighter totals
forecast for Thursday will still be influential since antecedent
conditions will be radically different by then as compared to where
they are now. The Slight Risk threat largely is for the Thursday
morning period with lingering rainfall from Wednesday night. Expect
the rain to continue diminishing through the day as the moisture
plume shifts westward with Hurricane Rafael.

...Texas Panhandle and Western Oklahoma...

A positively tilted longwave trough and associated upper level
energy in the form of jet streaks and shortwave energy will support
the development of a strong low over the southern Plains. To the
west, a significant amount of the low's moisture will fall in the
form of snow. Where the precipitation will remain as rain, expect
steady heavy rain across the Texas Panhandle and western Oklahoma.
While rates are not generally expected to be notably heavy, the
flood threat will be primarily focused on the long duration of
steady rain, as well as the fact that much of this area was hit
very hard with heavy rain a few days ago, so soils and rivers
remain elevated in this region. Thus, low FFGs support the Slight
Risk upgrade.

Wegman

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 PM EST Wed Nov 6 2024
Day 3
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS...

20z Update: The Slight risk over the Plains was adjusted a bit
southward with this update. This aligns well with the forecast
overlap of instability and moisture convergence. We continue to
carry higher end Slight risk probabilities across portions of TX
into western OK. Given the above average soil saturation already
in place, and the forecast overlap of rainfall Thursday and Friday
over this area, some instances of flash flooding are becoming
increasingly likely. Still some uncertainty with exactly where the
best overlap of convection and thus highest 2 day rainfall totals
will be...with the favored axis currently from north central TX
into southwest OK, where 3-5" is forecast. If confidence in this
area increases and/or totals trend up over 5" then a MDT risk
upgrade may eventually be needed.

Chenard

...Previous Discussion...

The upper level low over the Southwest will eject into the Plains
on Friday. There will be significant upper level energy associated
with the low, which combined with strong frontogenesis, plentiful
Gulf moisture advecting up the Plains on the low level jet, and a
strengthening surface low...expect heavier rainfall amounts across
Oklahoma and Kansas on Friday as compared with Wednesday. While
north Kansas didn't see as much rain a few days back compared with
areas further south...much of the rest of the Slight risk area does
overlap with both the heavy rain from a few days ago but continued
rainfall from Day 2/Thursday. Thus, added an internal higher-end
Slight for western Oklahoma into south Kansas. Depending on how
much rain the area gets on Day 2, there is some potential for a
Moderate Risk upgrade in this area with future updates.

Wegman

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Nov 6 2024


The combination of the Plains system pushing into the Mississippi
Valley and moisture from Rafael, which is forecast to be south of
the central Gulf Coast by the weekend, will lead to the potential
for some areas of heavy rainfall from the central Gulf Coast to the
Ohio Valley this weekend. On Saturday, maintained the Marginal
Risk in the ERO with generally minor changes from the previous
forecast. By Sunday, good moisture and some limited instability
should continue to spread into similar regions, shunted just a bit
eastward. This forecast cycle, WPC has stretched the Marginal Risk
well north across parts of the Lower Mississippi Valley to Mid-
South to the Ohio Valley where moderate to heavy rainfall rates may
train in the vicinity of the frontal system. The areal coverage
may be able to shrink with time if models converge. Dry antecedent
conditions in the Ohio Valley in particular may limit the extent of
impacts of flash flooding from heavy rain, but a 5 percent risk
(Marginal) seems warranted. Some rainfall may linger beyond Sunday
but most of the East should trend drier by Monday-Tuesday. Also of
note, a wave tracking from the southern Bahamas into the eastern
Gulf may increase rainfall over Florida around Sunday-Monday.

The West will see a wetter regime with high elevation snow,
starting in the Pacific Northwest and then spreading farther south
into parts of California and east into the Rockies. Highest totals
should be in the Sunday-Monday time frame with a vigorous upper
trough and frontal system approaching/reaching the area. While
there is still a fair amount of spread for QPF magnitudes, first-
guess guidance is showing enough of a signal to introduce a
Marginal Risk area in the Day 5 ERO over parts of the Pacific
Northwest where initial soil conditions are neutral to damp. Higher
elevation snow is likely for the Cascades, Sierra Nevada, and
northern/central Rockies. Another system is likely to bring
additional focused precipitation to the Pacific Northwest next
Wednesday. Depending on western upper trough progression, some
rainfall may develop over the central U.S. by the middle of next
week.

Except for the Great Lakes into New England during the weekend,
the eastern half of the country will likely see above normal
temperatures through the period. Warmest anomalies should be for
morning lows, reaching 20-25F above normal on one or more days over
the South and extending a little farther northeastward at times.
Coverage of plus 10-15F anomalies for highs should increase going
from the weekend into the first half of next week. Corresponding to
these relative anomalies, there will be better potential for some
record warm lows versus more isolated records for daytime highs.
The northern Plains will also be well above normal until a cooling
trend Tuesday-Wednesday, while the southern Plains will be warmest
early next week. Chilly temperatures over the southern Rockies/High
Plains will gradually moderate while much of the West will be near
normal during the weekend. Then the upper trough pushing into the
West next week should expand the coverage of below normal
temperatures from west to east.


Tate/Rausch

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Nov 6 2024


The combination of the Plains system pushing into the Mississippi
Valley and moisture from Rafael, which is forecast to be south of
the central Gulf Coast by the weekend, will lead to the potential
for some areas of heavy rainfall from the central Gulf Coast to the
Ohio Valley this weekend. On Saturday, maintained the Marginal
Risk in the ERO with generally minor changes from the previous
forecast. By Sunday, good moisture and some limited instability
should continue to spread into similar regions, shunted just a bit
eastward. This forecast cycle, WPC has stretched the Marginal Risk
well north across parts of the Lower Mississippi Valley to Mid-
South to the Ohio Valley where moderate to heavy rainfall rates may
train in the vicinity of the frontal system. The areal coverage
may be able to shrink with time if models converge. Dry antecedent
conditions in the Ohio Valley in particular may limit the extent of
impacts of flash flooding from heavy rain, but a 5 percent risk
(Marginal) seems warranted. Some rainfall may linger beyond Sunday
but most of the East should trend drier by Monday-Tuesday. Also of
note, a wave tracking from the southern Bahamas into the eastern
Gulf may increase rainfall over Florida around Sunday-Monday.

The West will see a wetter regime with high elevation snow,
starting in the Pacific Northwest and then spreading farther south
into parts of California and east into the Rockies. Highest totals
should be in the Sunday-Monday time frame with a vigorous upper
trough and frontal system approaching/reaching the area. While
there is still a fair amount of spread for QPF magnitudes, first-
guess guidance is showing enough of a signal to introduce a
Marginal Risk area in the Day 5 ERO over parts of the Pacific
Northwest where initial soil conditions are neutral to damp. Higher
elevation snow is likely for the Cascades, Sierra Nevada, and
northern/central Rockies. Another system is likely to bring
additional focused precipitation to the Pacific Northwest next
Wednesday. Depending on western upper trough progression, some
rainfall may develop over the central U.S. by the middle of next
week.

Except for the Great Lakes into New England during the weekend,
the eastern half of the country will likely see above normal
temperatures through the period. Warmest anomalies should be for
morning lows, reaching 20-25F above normal on one or more days over
the South and extending a little farther northeastward at times.
Coverage of plus 10-15F anomalies for highs should increase going
from the weekend into the first half of next week. Corresponding to
these relative anomalies, there will be better potential for some
record warm lows versus more isolated records for daytime highs.
The northern Plains will also be well above normal until a cooling
trend Tuesday-Wednesday, while the southern Plains will be warmest
early next week. Chilly temperatures over the southern Rockies/High
Plains will gradually moderate while much of the West will be near
normal during the weekend. Then the upper trough pushing into the
West next week should expand the coverage of below normal
temperatures from west to east.


Tate/Rausch

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
222 PM EST Wed Nov 6 2024

Valid 00Z Thu Nov 07 2024 - 00Z Sun Nov 10 2024


...Central/Southern Rockies and Adjacent High Plains...
Days 1-3...

Upper low at the base of a larger western CONUS trough lies over
the Four Corners this afternoon and will continue sinking
southward tonight into eastern AZ. It will slowly detach from the
northern stream and cut off as it wobbles southward then eastward
into southern NM by early Friday. Then, feeling the push of the
subtropical jet, it will lift northeastward across the northern TX
Panhandle and far western OK Panhandle to the CO/KS border by early
Saturday. The slow movement of the upper low combined with a
fairly steady stretch of moisture as well as upslope enhancement
will lead to significant snow accumulations in parts of the NM
mountains and across the CO line along the Sangre de Cristo range.
Impacts may be major to extreme in some locations and exaggerated
by the fact that this is the first significant winter storm of the
season for this region.

For early D1, frontal boundary slowly sinking southward from
western KS to northeast NM on the edge of the height falls will
continue to promote light to modest snow through this evening over
northeast CO and border regions of KS and NE in an area of surface
convergence and beneath bouts of PVA. Through the evening, as the
upper low tucks farther southwest of CO, heights should rise and
the snow should lessen. Nevertheless, snowfall rates near 1"/hr
should yield an additional few inches near/south of DEN and
eastward over the High Plains.

Farther south over NM, closer to the stream of moisture and vort
maxes rotating around the upper low center, snow will increase in
intensity over much of the NM terrain on D1 and last through D2
with similar intensity before the upper low lifts north and weakens
by D3. The slow movement of the upper low will allow for continued
heavy snowfall to its east via persistent IVT values near/above
the 90th percentile. This could result in 1-3ft of snow over the NM
terrain (WPC probabilities for at least 12 inches are >90% over
much of northeastern NM and southeastern CO) along with areas of
blowing/drifting snow eastward into the far western OK Panhandle.
Snow will continue over northern NM into southern CO along the
Sangre de Cristos and onto the High Plains as the upper low sloshes
toward the TX/OK Panhandles. Moisture source will add in then
largely switch to the western Gulf, wrapping around the upper low
and capitalizing on upslope from the northeast through the column.
Snow will finally start to taper off by the end of the period
(early Saturday).

The greatest uncertainty remains along the eastern gradient of
snowfall where low-level warmth creeps into the High Plains and
leads to a transition toward rain from the KS/CO border to eastern
NM and the TX/OK Panhandles. A brief period of sleet is possible
as a warm nose aloft ebbs and flows across the High Plains during
the event. Exactly where this rain/snow/mix line occurs is still a
question, with today's guidance trending westward and a gradually
warming transition as the storm weakens by Saturday.


All told, 3-day WPC probabilities for at least 24 inches of snow
are >50% above 6000-7000ft over the Sangre de Cristos and Raton
Mesa, with a large footprint of at least 6 inches over much of
eastern CO southward into central NM. Latest WSSI shows these
snowfall values as producing widespread Major to Extreme impacts
across much of central and northern NM as well as south-central
Colorado.


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


Fracasso/Snell




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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Nov 6 2024

Valid 12Z Sat Nov 09 2024 - 12Z Wed Nov 13 2024

...Watching Hurricane Rafael as it tracks into the Gulf of
Mexico...


...Overview...

The National Hurricane Center continues to issue advisories for
Hurricane Rafael as it tracks across the Gulf this weekend into
early next week while weakening as it interacts with a mean upper
ridge stretching from the Bahamas. Models and the NHC forecast have
trended farther south with Rafael, keeping it offshore well south
of the central Gulf Coast while it weakens. But the combination of
Rafael's moisture and a frontal system supported by an upper low
ejecting northeast from the Plains may produce some areas of
locally heavy rainfall from the Gulf Coast northward especially
this weekend. Meanwhile, a series of Pacific systems will increase
coverage of rain and higher elevation snow over the West from the
weekend into early next week. Much of the East should see above
normal temperatures through the period while the southern Rockies
will start the weekend on the chilly side and cooler temperatures
will spread across the West next week.


...Guidance/Predictability Assessment...

For Hurricane Rafael, recent model runs have generally trended to
the south, showing the surface low weakening over the Gulf rather
than making landfall in the central Gulf Coast as some previous
runs had showed. The 00Z ECMWF, UKMET, and many EC ensemble members
were particularly aggressive with this southwestward shift as
Rafael does not get picked up by the upper trough to track it
northward. GFS runs are indicating this trend but not to the extent
of the EC/UKMET that take Rafael so far south it goes into central
Mexico. The 12Z CMC does have Rafael track north into the central
Gulf Coast, along with some GEFS members and the bulk of the AI/ML
models initialized at 00Z, so there remains uncertainty with this
trend. Continue to monitor latest NHC products for additional
information on Rafael.

Farther north, the first system of note is a closed upper low
starting the period Saturday atop the central High Plains and
tracking northeast Sunday-Monday while opening up. Model guidance
is rather agreeable with this feature especially over the weekend,
but guidance has been more erratic with details of a shortwave that
enters western North America during the weekend and may have some
influence on the remaining upper low energy by early next week. The
00Z CMC in particular seemed like an eastern outlier with this
shortwave for more interaction with the preexisting upper
low/trough. This leads to lingering uncertainty for some details of
the frontal system reaching the Northeast.

There are continued timing and amplitude differences for the
larger scale trough moving into/through the West early next week
and toward the central U.S. by midweek, with GFS runs leaning
slower and ECMWF faster. Latest ML models show a similar spread,
arguing for a blend/compromise approach. This also mitigates issues
for how energy may be distributed within the upper trough by the
middle of next week, with individual solutions ranging between
greater dynamics in the northern part of the trough, or farther
south, to an evenly phased trough. A compromise also looks best for
the next system that may come into the picture over the
northeastern Pacific by next Wednesday.

Overall a blend favoring the 06Z GFS and 00Z ECMWF with lesser
portions of the UKMET and GEFS/EC ensemble means early in the
period, with an increasing proportion of the ensemble means as the
period progressed given increasing uncertainty.


...Weather/Hazards Highlights...

The combination of the Plains system pushing into the Mississippi
Valley and moisture from Rafael, which is forecast to be south of
the central Gulf Coast by the weekend, will lead to the potential
for some areas of heavy rainfall from the central Gulf Coast to the
Ohio Valley this weekend. On Saturday, maintained the Marginal
Risk in the ERO with generally minor changes from the previous
forecast. By Sunday, good moisture and some limited instability
should continue to spread into similar regions, shunted just a bit
eastward. This forecast cycle, WPC has stretched the Marginal Risk
well north across parts of the Lower Mississippi Valley to Mid-
South to the Ohio Valley where moderate to heavy rainfall rates may
train in the vicinity of the frontal system. The areal coverage
may be able to shrink with time if models converge. Dry antecedent
conditions in the Ohio Valley in particular may limit the extent of
impacts of flash flooding from heavy rain, but a 5 percent risk
(Marginal) seems warranted. Some rainfall may linger beyond Sunday
but most of the East should trend drier by Monday-Tuesday. Also of
note, a wave tracking from the southern Bahamas into the eastern
Gulf may increase rainfall over Florida around Sunday-Monday.

The West will see a wetter regime with high elevation snow,
starting in the Pacific Northwest and then spreading farther south
into parts of California and east into the Rockies. Highest totals
should be in the Sunday-Monday time frame with a vigorous upper
trough and frontal system approaching/reaching the area. While
there is still a fair amount of spread for QPF magnitudes, first-
guess guidance is showing enough of a signal to introduce a
Marginal Risk area in the Day 5 ERO over parts of the Pacific
Northwest where initial soil conditions are neutral to damp. Higher
elevation snow is likely for the Cascades, Sierra Nevada, and
northern/central Rockies. Another system is likely to bring
additional focused precipitation to the Pacific Northwest next
Wednesday. Depending on western upper trough progression, some
rainfall may develop over the central U.S. by the middle of next
week.

Except for the Great Lakes into New England during the weekend,
the eastern half of the country will likely see above normal
temperatures through the period. Warmest anomalies should be for
morning lows, reaching 20-25F above normal on one or more days over
the South and extending a little farther northeastward at times.
Coverage of plus 10-15F anomalies for highs should increase going
from the weekend into the first half of next week. Corresponding to
these relative anomalies, there will be better potential for some
record warm lows versus more isolated records for daytime highs.
The northern Plains will also be well above normal until a cooling
trend Tuesday-Wednesday, while the southern Plains will be warmest
early next week. Chilly temperatures over the southern Rockies/High
Plains will gradually moderate while much of the West will be near
normal during the weekend. Then the upper trough pushing into the
West next week should expand the coverage of below normal
temperatures from west to east.


Tate/Rausch


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