Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Tue Nov 28 2023

Valid 12Z Tue Nov 28 2023 - 12Z Thu Nov 30 2023

...Active lake-effect snowfall downwind of the Great Lakes will continue
Tuesday, producing locally heavy snowfall amounts...

...Below average temperatures continue for the East Coast and South with
freeze-related advisories in effect from the Florida Panhandle to coastal
South Carolina...

...Mostly dry conditions for the western and central U.S. as a warm up
comes to the Plains/Mississippi Valley...

Embedded shortwaves in northwesterly cyclonic flow rounding a deep
upper-level low over Canada will continue to produce snow downwind of the
Great Lakes Tuesday, particularly Lakes Erie and Ontario. Here, additional
forecast snow totals of 8-16 inches, with locally higher amounts, are
expected through Wednesday morning, bringing storm total snowfall well
above 2 feet for some locations. Heavy snow rates and gusty winds will
make travel treacherous. Some lighter amounts of around 2-4 inches will
remain possible downwind of Lakes Superior and Michigan. Much of the rest
of the country will remain dry over the next couple of days. One exception
will be in coastal California where an approaching upper-level
trough/Pacific system will bring some light to moderate showers. As this
upper-level trough continues southeastward, some lower elevation/valley
rain and higher elevation snow will be possible by late Wednesday for the
Four Corners region. Any snow accumulations look to remain light and
limited to higher mountain peaks, at least through Thursday morning.
Increasing moist southerly flow from the Gulf ahead of this system should
also bring some showers and thunderstorms to portions of the Southern
Plains/Lower Mississippi Valley Wednesday night.

The other main story over the next couple of days will be the chilly,
below average temperatures for the East Coast and portions of the South.
Forecast highs Tuesday and Wednesday will be in the 20s and 30s for New
England, 30s and 40s for the Mid-Atlantic, 40s and 50s for the Carolinas,
and 50s and 60s from southern Texas along the Gulf Coast into the
Southeast and all but south Florida. The coldest morning lows of the
season so far are expected from the Mid-Atlantic through the Southeast
Wednesday morning, with widespread 20s forecast. Temperatures may dip to
near or below freezing as far south as the Florida Panhandle/north
Peninsula northeastward through coastal South Carolina. A Freeze Watch has
been issued for the region as these temperatures may damage and kill
sensitive crops and vegetation. Meanwhile, upper-level ridging moving
eastward over the western Plains as upper-level troughing gives way over
the Midwest will bring a warm-up to central portions of the country. Highs
will be well above average and in the 40s and 50s for the Northern and
Central Plains. After one more chilly day Tuesday, temperatures will warm
into the 40s and 50s for much of the Middle and Upper Mississippi Valley
Wednesday. Conditions will be mostly seasonable across the West, with 30s
and 40s for the Rockies and Great Basin, 40s and 50s for the Pacific
Northwest, 50s and 60s for California, and 70s for 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
206 AM EST Tue Nov 28 2023

Valid 12Z Fri Dec 01 2023 - 12Z Tue Dec 05 2023

...Overview...

An upper-level shortwave will lift from the Middle Mississippi
Valley to the Northeast Friday into Saturday, while at the same
time, a couple of short waves into the West act to amplify mean
troughing which should translate eastward with time, reaching the
East Coast by early next week. Upper ridging will build over the
East this weekend and the West by early next week. This overall
pattern would bring daily bouts of moderate to heavy rainfall to
the Southeast as well as the Pacific Northwest. Widespread but
lighter rain should spread up the East Coast as well next Monday
into Tuesday.


...Guidance Evaluation/Predictability Assessment...

The latest model guidance remains in very good agreement for the
medium range time period, though still with plenty of uncertainty
in the details. The greatest uncertainty continues with individual
shortwaves into the West, acting to reinforce a building amplified
trough over the region. There is some considerable run to run
variability with timing/location of Western U.S. energies, but
there is an overall consensus on a more amplified and active
pattern. A possible atmospheric river looks to impact the West
around Sunday-Monday time frame, and the ECMWF is by far the
strongest, indicating a possible moderate to strong AR, according
to the CW3E AR scale tool. The new 00z ECMWF came in just as
strong (if not stronger) but about 12 hours faster. At this point,
the ECMWF is a strong outlier, but the potential is there so this
should be monitored. The guidance shows similar timing as the
trough shifts into the East early next week, just with
considerable differences in the details. For tonights WPC blend, a
purely deterministic model blend was used for days 3-5, with
increasing amounts of the ensemble means by days 6-7 (still only
to about 50% of the overall blend) to account for the increased
uncertainty late period. This maintains good continuity with the
previous WPC forecast as well.


...Weather/Hazards Highlights...

Upper-level shortwave energy will move over the Mid-South while a
warm front lifts north out of the Gulf of Mexico late this week,
and an amplified trough shifts out of the West this weekend
providing a renewed surge of moisture. This will support daily
widespread moderate to heavy rainfall for the Gulf Coast and
Southeast. There is a Marginal Risk of Excessive Rainfall for this
region valid Days 4 and 5 (Friday and Saturday) as anomalous
moisture (PWs 2-3 standard deviations above normal) and
instability will be present. It is possible an embedded slight
risk will be needed at some point but there is still some
uncertainty on exact amounts. The heavy rainfall threat across the
Southeast will linger into Sunday as well, with less intense
rainfall also lifting northward up the East Coast on Monday. Out
West, precipitation will increase Thursday through the weekend as
a couple shortwaves move through the region, with some
precipitation reaching southward into California and the Southwest
Friday-Saturday and possibility for accumulating snows in the
higher elevations. The heaviest precipitation (coastal rain and
mountain snow) will be across the Washington/Oregon coast and
Cascades Sunday into Monday, where some models indicate a
potential atmospheric river to impact the region. Modest snowfall
looks to impact parts of the northern Rockies as well this weekend
into early next Week.

The interior West should stay cooler than normal underneath
reinforced troughing through the weekend. Temperatures for the
rest of the country should be closer to normal late this week, but
trend warmer with time across the Northern Plains into the Midwest
and eventually the East by the weekend. Daytime highs could be
5-10 degrees above average across this region. The Western U.S.
may finally trend back towards normal, or above normal in some
places, early next week with well above normal temperatures (on
the order of +10-15F) returning to the North-Central Plains next
Tuesday.

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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key
Messages are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#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
259 AM EST Tue Nov 28 2023

Valid 00Z Wed Nov 29 2023 - 00Z Wed Dec 06 2023

...Heavy Rain and Flash Flooding possible this week across much of
Hawaii...

There continues to be excellent agreement that a Kona low will set
up west of Hawaii this week, bringing potential for widespread
heavy rainfall and thunderstorms Tuesday-Friday to much of the
state. The guidance shows precipitable water values surging up to
two or more standard deviations above normal, increasing the
threat for flooding and flash flooding. Despite the large scale
agreement, there continues to be quite a bit of uncertainty in the
details which has implications for total rainfall amounts with
some of the guidance suggesting the heaviest rains may actually
stay north of the island chain. The 00z run of the CMC is
displaced a bit east of the better consensus, but not totally out
of the realm of possibilities. Still, at this point, prefer a
non-CMC solution. The upper low should weaken and slowly begin to
drift east Friday-Saturday. Rainfall this weekend should trend
lighter across Hawaii, but still some potential for locally heavy
rain as the upper low lingers. Trade winds should shift back
easterly and strengthen early-mid next week.

Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Tue Nov 28 2023

Day 1
Valid 12Z Tue Nov 28 2023 - 12Z Wed Nov 29 2023

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

Campbell

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Tue Nov 28 2023

Day 2
Valid 12Z Wed Nov 29 2023 - 12Z Thu Nov 30 2023

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

Campbell



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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Tue Nov 28 2023

Day 3
Valid 12Z Thu Nov 30 2023 - 12Z Fri Dec 01 2023

...THERE IS A MARGINAL RISK AREA FROM THE CENTRAL GULF COAST TO
THE MID-MISSISSIPPI/OHIO RIVER VALLEY...

Shortwave energy exiting the Rockies into the Southern Plains will
help a surface low pressure system to develop, sending a cold
front into the Plains and Mississippi Valley. Convection is
expected to fire up over eastern Texas and the Gulf Coast then
increase coverage and intensity as the front advances, spreading
northeast into the Mid-Mississippi/Ohio Valley. Hourly rates of
0.5 inch/hr or greater will be possible along with areal averages
of 1 to 3 inches from the Texas Coast to southern Indiana. At this
time the heaviest QPF is favoring southwest/southern Louisiana.
Recent precipitation has increased soil saturation across portions
of the south-central and central U.S. so there may be isolated
areas where the expected precipitation may reach or exceed local
flash flood guidance. A Marginal Risk is in effect from eastern
Texas/Central Gulf Coast north and east to southwest Indiana.

Campbell

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Tue Nov 28 2023


Upper-level shortwave energy will move over the Mid-South while a
warm front lifts north out of the Gulf of Mexico late this week,
and an amplified trough shifts out of the West this weekend
providing a renewed surge of moisture. This will support daily
widespread moderate to heavy rainfall for the Gulf Coast and
Southeast. There is a Marginal Risk of Excessive Rainfall for this
region valid Days 4 and 5 (Friday and Saturday) as anomalous
moisture (PWs 2-3 standard deviations above normal) and
instability will be present. It is possible an embedded slight
risk will be needed at some point but there is still some
uncertainty on exact amounts. The heavy rainfall threat across the
Southeast will linger into Sunday as well, with less intense
rainfall also lifting northward up the East Coast on Monday. Out
West, precipitation will increase Thursday through the weekend as
a couple shortwaves move through the region, with some
precipitation reaching southward into California and the Southwest
Friday-Saturday and possibility for accumulating snows in the
higher elevations. The heaviest precipitation (coastal rain and
mountain snow) will be across the Washington/Oregon coast and
Cascades Sunday into Monday, where some models indicate a
potential atmospheric river to impact the region. Modest snowfall
looks to impact parts of the northern Rockies as well this weekend
into early next Week.

The interior West should stay cooler than normal underneath
reinforced troughing through the weekend. Temperatures for the
rest of the country should be closer to normal late this week, but
trend warmer with time across the Northern Plains into the Midwest
and eventually the East by the weekend. Daytime highs could be
5-10 degrees above average across this region. The Western U.S.
may finally trend back towards normal, or above normal in some
places, early next week with well above normal temperatures (on
the order of +10-15F) returning to the North-Central Plains next
Tuesday.

Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Tue Nov 28 2023


Upper-level shortwave energy will move over the Mid-South while a
warm front lifts north out of the Gulf of Mexico late this week,
and an amplified trough shifts out of the West this weekend
providing a renewed surge of moisture. This will support daily
widespread moderate to heavy rainfall for the Gulf Coast and
Southeast. There is a Marginal Risk of Excessive Rainfall for this
region valid Days 4 and 5 (Friday and Saturday) as anomalous
moisture (PWs 2-3 standard deviations above normal) and
instability will be present. It is possible an embedded slight
risk will be needed at some point but there is still some
uncertainty on exact amounts. The heavy rainfall threat across the
Southeast will linger into Sunday as well, with less intense
rainfall also lifting northward up the East Coast on Monday. Out
West, precipitation will increase Thursday through the weekend as
a couple shortwaves move through the region, with some
precipitation reaching southward into California and the Southwest
Friday-Saturday and possibility for accumulating snows in the
higher elevations. The heaviest precipitation (coastal rain and
mountain snow) will be across the Washington/Oregon coast and
Cascades Sunday into Monday, where some models indicate a
potential atmospheric river to impact the region. Modest snowfall
looks to impact parts of the northern Rockies as well this weekend
into early next Week.

The interior West should stay cooler than normal underneath
reinforced troughing through the weekend. Temperatures for the
rest of the country should be closer to normal late this week, but
trend warmer with time across the Northern Plains into the Midwest
and eventually the East by the weekend. Daytime highs could be
5-10 degrees above average across this region. The Western U.S.
may finally trend back towards normal, or above normal in some
places, early next week with well above normal temperatures (on
the order of +10-15F) returning to the North-Central Plains next
Tuesday.

Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Tue Nov 28 2023

Valid 12Z Tue Nov 28 2023 - 12Z Fri Dec 01 2023

...Great Lakes...
Days 1-2...

Today will continue the ongoing and impressive lake effect snow
(LES) event, especially downwind of lakes Erie and Ontario. The
core of the cyclonic gyre centered south of Hudson Bay will slowly
advect eastward today in response to one final potent shortwave
shifting from the Great Lakes through the Ohio Valley, and
eventually off the New England coast by Wednesday morning. This
feature will provide additional synoptic ascent and produce at
least subtle additional moisture, but will primarily act to
enhance the CAA once again to enhance LES potential. 850mb temps
will crash to below -15C in some areas, which when moving across
the still warm lake waters will result in robust SBCAPE of
500-1000 J/kg and inversion depths that will persist as high as
15kft through D1. This should allow for focused LES bands in the
favored W/NW snow belts downwind of lakes Erie, Ontario, Superior,
and Michigan, with an upstream connection enhancing snow rates and
amounts in some areas. The snow bands will likely fluctuate in
position a little more today than they did Monday due to shifting
winds from NW early, to W, and eventually SW as shortwave ridging
develops ahead of the next vorticity maxima. This secondary
shortwave/vort on Wednesday is expected to be much weaker and
shallower than the previous, and will quickly be followed by more
zonal flow, so additional LES beyond D1 is expected to be much
lighter.

WPC probabilities for today/tonight are above 80% for the Tug Hill
Plateau , areas near Syracuse NY, and south of Buffalo, where
locally an additional 12 inches is possible. WPC probabilities for
more than 6 inches are more modest, 30-60%, along the Chautauqua
Ridge and near Traverse Bay. By D2 the greatest risk for more than
6 inches of additional LES shifts northward off Lake Ontario to
near Watertown where WPC probabilities are as high as 50%.


...Northeast and Mid-Atlantic...
Day 1...

An arctic cold front which moved across the Great Lakes and
Northeast Monday will continue to exit to the east across the
Mid-Atlantic today. Behind this front, the guidance has come into
better agreement that widespread snow showers with at least
scattered snow squalls are possible, especially late this morning
through early evening as a potent shortwave rotates through the
cyclonic mid-level flow atop the region. During this time, the
snow squall parameter reaches above 1 (favorable for snow squalls)
from western MD through northern NJ and into much of New England.
This is coincident with the high res simulated reflectivity (most
notably in the HRRR) suggesting widespread cellular activity which
will likely manifest as snow showers and snow squalls. Despite
that, there remains uncertainty into the coverage of squalls (vs
snow showers) as antecedent air is quite dry and 0-2km RH is
forecast to remain less than 60% for the eastern half of the
region. The synoptic level trough moving overhead may add some
additional moisture, which could also increase from lake
enhancement on the upstream connection to the Great Lakes. Where
moisture is sufficient, steep lapse rates will produce SBCAPE of
50-250 J/kg, highest across PA, upstate NY, and into VT,
coincident with pockets of enhanced 925mb fgen and plenty of wind
to mix through the PBL. Snow showers that develop could become
dangerous squalls despite producing minimal snow accumulation as
heavy rates and gusty winds lower visibility to near zero at
times. While the snow squall potential farther east is less
significant, heavy snow showers are possible and may reach the
coast later this evening, also producing periods of hazardous
travel.


...Southern Rockies and Four Corners...
Day 3...

A shortwave dropping along the coast of CA Wednesday night is
progged to amplify into a closed low near the Four Corners
Thursday before continuing to advect rapidly east and opening into
a wave once again over Texas on Friday. The amplification of this
feature into a closed low over the Desert Southwest will produce
increased mid-level divergence downstream, with height falls
additionally aiding in ascent towards the Four Corners on D3. At
the same time, a back door type surface front will drop SW out of
the High Plains and into the Four Corners, providing additional
ascent through convergence and post-frontal upslope flow. There is
still considerable spread as to the timing of this front, but with
at least modest increasing moisture both through elevated PW
advection from the WSW and modest theta-e ridging downstream of
the upper low, moderate snowfall is likely in the higher terrain
above 6000 ft. WPC probabilities for more than 4 inches on
Thursday reach as high as 30-50%, especially in the San Juans,
southern Sangre de Cristos, and Jemez Mountains.


...Cascades through the Sierra...
Day 3...

A shortwave ejecting from the Pacific will arc onshore Thursday
night into Friday morning while amplifying into a longwave trough
draped from British Columbia through California. This trough will
demarcate the leading edge of an incoming Pacific jet streak which
is progged to reach 110 kts and place its favorable LFQ portion
atop the Pacific Northwest the latter half of D3. Current PW and
IVT from the NAEFS ensemble tables suggest near normal moisture,
and the progressive nature of the flow will result in a relatively
transient period of high 700-500mb RH. However, snow levels will
be below many of the passes in the Cascades at 2000-3000 ft,
rising to around 4000-5000 ft in the Sierra, so any moisture wrung
out by the brief but favorable ascent will result in impactful
snow. Still some uncertainty into the amplitude and timing of this
trough, but WPC probabilities currently reflect a 40-70% chance
for more than 4 inches, highest in the OR Cascades and central
Sierra.


Weiss

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Tue Nov 28 2023

Valid 12Z Fri Dec 01 2023 - 12Z Tue Dec 05 2023

...Overview...

An upper-level shortwave will lift from the Middle Mississippi
Valley to the Northeast Friday into Saturday, while at the same
time, a couple of short waves into the West act to amplify mean
troughing which should translate eastward with time, reaching the
East Coast by early next week. Upper ridging will build over the
East this weekend and the West by early next week. This overall
pattern would bring daily bouts of moderate to heavy rainfall to
the Southeast as well as the Pacific Northwest. Widespread but
lighter rain should spread up the East Coast as well next Monday
into Tuesday.


...Guidance Evaluation/Predictability Assessment...

The latest model guidance remains in very good agreement for the
medium range time period, though still with plenty of uncertainty
in the details. The greatest uncertainty continues with individual
shortwaves into the West, acting to reinforce a building amplified
trough over the region. There is some considerable run to run
variability with timing/location of Western U.S. energies, but
there is an overall consensus on a more amplified and active
pattern. A possible atmospheric river looks to impact the West
around Sunday-Monday time frame, and the ECMWF is by far the
strongest, indicating a possible moderate to strong AR, according
to the CW3E AR scale tool. The new 00z ECMWF came in just as
strong (if not stronger) but about 12 hours faster. At this point,
the ECMWF is a strong outlier, but the potential is there so this
should be monitored. The guidance shows similar timing as the
trough shifts into the East early next week, just with
considerable differences in the details. For tonights WPC blend, a
purely deterministic model blend was used for days 3-5, with
increasing amounts of the ensemble means by days 6-7 (still only
to about 50% of the overall blend) to account for the increased
uncertainty late period. This maintains good continuity with the
previous WPC forecast as well.


...Weather/Hazards Highlights...

Upper-level shortwave energy will move over the Mid-South while a
warm front lifts north out of the Gulf of Mexico late this week,
and an amplified trough shifts out of the West this weekend
providing a renewed surge of moisture. This will support daily
widespread moderate to heavy rainfall for the Gulf Coast and
Southeast. There is a Marginal Risk of Excessive Rainfall for this
region valid Days 4 and 5 (Friday and Saturday) as anomalous
moisture (PWs 2-3 standard deviations above normal) and
instability will be present. It is possible an embedded slight
risk will be needed at some point but there is still some
uncertainty on exact amounts. The heavy rainfall threat across the
Southeast will linger into Sunday as well, with less intense
rainfall also lifting northward up the East Coast on Monday. Out
West, precipitation will increase Thursday through the weekend as
a couple shortwaves move through the region, with some
precipitation reaching southward into California and the Southwest
Friday-Saturday and possibility for accumulating snows in the
higher elevations. The heaviest precipitation (coastal rain and
mountain snow) will be across the Washington/Oregon coast and
Cascades Sunday into Monday, where some models indicate a
potential atmospheric river to impact the region. Modest snowfall
looks to impact parts of the northern Rockies as well this weekend
into early next Week.

The interior West should stay cooler than normal underneath
reinforced troughing through the weekend. Temperatures for the
rest of the country should be closer to normal late this week, but
trend warmer with time across the Northern Plains into the Midwest
and eventually the East by the weekend. Daytime highs could be
5-10 degrees above average across this region. The Western U.S.
may finally trend back towards normal, or above normal in some
places, early next week with well above normal temperatures (on
the order of +10-15F) returning to the North-Central Plains next
Tuesday.

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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key
Messages are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#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