Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Tue Sep 3 2024

Valid 12Z Fri Sep 06 2024 - 12Z Tue Sep 10 2024

...Hazardous heat likely late week across parts of the Southwest
and California with heavy rainfall threats across the Lower
Mississippi Valley to the Southeast during the weekend...

...Overview...

An amplified upper-level pattern with an upper low slowly moving
through the Northeast will support a period of enhanced rainfall
over portions of New England this weekend, with a surge of fall-
like dry and cool air mass behind it across much of the eastern
half of the country. A lingering front will keep decent rain
chances from central Gulf Coast eastward to Florida, with heavy
rain most likely Friday and Saturday along central to eastern Gulf
Coast. Meanwhile, a ridge shifting slowly east across the western
U.S. will increase the threat of excessive heat over portions of
the Southwest and California late this week. Tropical moisture
moving into the southwestern Gulf could bring heavy rain into
southern Texas by early next week.


...Guidance/Predictability Assessment...

Models continue to indicate the likelihood for a deep upper low to
form over the Great Lakes region by this weekend as a ridge axis
shifts slowly eastward across the western U.S., allowing the next
trough from the Gulf of Alaska to approach the Pacific Northwest
early next week. There has been a tendency for the models to slow
down the eastward progress of the upper low out of the Great Lakes
this weekend in response to a trend for a deeper and more closed-
off upper low circulation.

Along the Gulf Coast, there has been a trend to slow down the
motion of a frontal wave late this week into the weekend, allowing
heavier rainfall to fall along the coast but this did not affect
the timing and location of the heavy rain just of the Southeast
coast all that much. Elsewhere, models have not shown too drastic
of a change lately.

The WPC medium-range products were derived based on 40% from the
00Z EC/EC mean, 40% from the 06Z GFS/GEFS, and 20% from the CMC/CMC
mean, and leaning toward the consensus of the ensemble means for
Days 6 and 7.


...Weather/Hazards Highlights...

The main heavy rainfall focus during the period will be across the
Southeast on Friday as shortwave energy interacts with a lingering
surface front along/near the Gulf coast. Precipitation coverage
and totals remain somewhat uncertain, but the overall dynamics and
anomalous moisture support a heavy to excessive rainfall threat as
highlighted by a broad marginal risk on the Day 4 Excessive
Rainfall Outlook. A Slight Risk area has been introduced along the
central to eastern Gulf Coast due to a general increase of model
QPFs with a slowing frontal wave. Models continue to suggest a
southward trend with the overall threat and so compared to
yesterdays Day 5 ERO, trimmed the northern extent of the marginal a
bit for the new update. There may be a need for an eventual
upgrade to a slight risk, particularly for the central to eastern
FL panhandle where the stronger instability should be, but decided
to hold off on that with this cycle given continued uncertainty in
placement. The front should linger across northern FL for a few
days, with some pockets of heavier rainfall possible so did
maintain a narrow marginal across this area for the Day 5/Saturday
ERO as well. Farther north, some heavier rainfall may accompany the
cold front as it passes through the Northeast, aided by wrap back
moisture from a surface low along the coast. Covered this with a
marginal risk on the Day 5 ERO for now, with a possibility for an
embedded Slight Risk. From Sunday into early next week, much of
the country should dry out, though shortwave energy within and
around western U.S. upper ridging may produce isolated to scattered
rainfall with mostly light amounts. Meanwhile, tropical moisture
moving into the southwestern Gulf could bring an increasing threat
of heavy rain into southern Texas by early next week.

Above normal temperatures with hazardous heat over the West should
be most pronounced on Friday, with HeatRisk showing widespread
major threats across the Southwest and central valleys of
California and moderate to locally major into the Pacific
Northwest. California highs may reach up to 10-15F above normal
while the Pacific Northwest could see readings up to 15-20F or so
above normal. Some daily records are possible. Heat should persist
to some degree into the weekend over the Northwest and slowly
expand into the northern High Plains. In contrast, a much cooler
airmass will filter eastward from the northern Plains and Great
Lakes into the East this weekend and early next week, with daytime
highs 10-20 degrees below normal.

Kong/Santorelli


Additional 3-7 Day Hazard information can be found on the WPC
medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

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

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
239 PM EDT Wed Sep 4 2024

Valid 12Z Sat Sep 07 2024 - 12Z Wed Sep 11 2024

...Heavy rainfall threats to impact Northern Florida and the
Northeast on Saturday...

...Overview...

An amplified upper-level pattern will be in place by the weekend
with an upper ridge over the West that sluggishly shifts east with
time, and as a mean upper low slowly works through the Northeast.
This will support a lingering period of enhanced rainfall over
portions of New England this weekend, with a fall-like dry and
cool air mass filtering in behind it across much of the eastern
half of the country. A lingering and wavy front will keep rain
chances across the Gulf Coast to Florida, with the best chance for
heavy rain on Saturday across Northern Florida. Tropical moisture
moving into the southwestern Gulf could bring heavy rain into
southern Texas by early next week.

...Guidance/Predictability Assessment...

One main areas of system uncertainty during the period continues
to surround the deep upper low/trough as it shifts out of the Great
Lakes/Northeast. There are also timing inconsistencies with the
next amplified trough in the Eastern Pacific next week, which
guidance shows potential for a cutoff low off the West Coast with a
possible slow shift of the larger scale trough to/into the West.

A composite blend of model and ensemble guidance offered a
seemingly reasonable forecast basis. However, given amplified flow
tends to linger on the slower side of the full envelope of
guidance, opted to apply slightly greater weighting to those
components. This stays in line with the National Blend of Models.

...Weather/Hazards Highlights...

One heavy rainfall focus during the period will be across the
Northeast on Saturday as the upper low/associated trough pivots
through the Northeast, aided by wrap back moisture from a surface
low along the coast. The WPC Day 4 Excessive Rainfall Outlook
shows a Marginal Risk. Farther south, a lingering front across
northern Florida and along the Gulf Coast will continue to focus
showers and storms, locally heavy, through at least the weekend.
The better chance for heavier QPF is on Saturday, as covered by a
WPC Marginal risk on the Day 4 ERO. Depending on what falls where
during the short range period, a marginal risk may eventually be
needed on the Day 5/Sunday ERO as well, but the QPF signal still
does not show sufficient focus. From Sunday into early next week,
much of the country should dry out, though shortwave energy within
and around western U.S. upper ridging may produce isolated to
scattered rainfall with mostly light amounts. Meanwhile, tropical
moisture moving into the southwestern Gulf may bring an increasing
threat of heavy rain into southern Texas by early next week. Some
guidance show potential of locally significant amounts to monitor.

Hazardous heat across the Southwest and into California during the
short range period should be waning by this weekend as the upper
ridge begins to shift out of the West. Above normal temperatures
will also slide east with time from the West into the Central U.S.,
however it does not look to be particularly hazardous at this
time. In contrast, a much cooler airmass will filter eastward from
the northern Plains and Great Lakes into the East this weekend and
early next week, with daytime highs 10-20 degrees below normal.

Santorelli/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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 PM EDT Thu Sep 5 2024

Valid 12Z Sun Sep 08 2024 - 12Z Thu Sep 12 2024


...Overview...

An amplified upper-level pattern will be in place this weekend
with an upper ridge over the West that shifts east with time, as a
mean upper low/trough slowly works through the Northeast. This will
usher in a fall-like dry and cool air mass across much of the
eastern half of the country. Elsewhere, a lingering and wavy front
will keep rain chances across the Gulf Coast to Florida, while
tropical moisture moving into the southwestern Gulf could bring
heavy rain into South Texas by early next week.


...Guidance/Predictability Assessment...

Models have been very consistent with the upper level pattern in
the eastern and southern U.S., but they have been struggling with
an amplified trough that's forecast to move into the West during
the second half of the period. The 00Z ECMWF seems to deviate the
most from the consensus and yesterday's ECMWF runs, it splits the
trough energy, resulting in a much weaker wave in the West
compared to other guidance like the GFS and CMC. Today's 12Z ECMWF
run was not available at the time the forecast was made, but it
has fallen back into line with the consensus, having a stronger
trough move into the West mid/late next week.

For the WPC afternoon forecast, a blend of the deterministic
GFS/CMC/UKMET/ECMWF was used for the first half of the period,
opting to use yesterday's 12Z ECMWF run instead of the 00Z run.
Ensemble means were added gradually to make up to 50% of the blend
for the second half of the period, which helped to smooth out
differences in the West by Days 6 and 7.


...Weather/Hazards Highlights...

A lingering front across North Florida and along the Gulf Coast
will continue to focus showers and storms, locally heavy, into next
week. Heavy rain that is forecast across North Florida and
southern Georgia in the short term period will likely saturate
soils and could make this region more prone to flooding with any
locally heavy rain that may fall on days 4 and 5 (Sunday and
Monday). A Marginal Risk area will likely be introduced in the Day
4/Sunday ERO, and an additional Marginal Risk may eventually be
needed on day 5/Monday.

Tropical moisture moving into the southwestern Gulf may bring an
increasing threat for heavy rain to South Texas, which is covered
by a Marginal Risk on the Day 5/Monday ERO. Some guidance shows
potential for locally significant amounts that will need to be
monitored. Otherwise, much of the country should be quiet and dry,
although shortwave energy within and around the western U.S. upper
ridging may produce isolated to scattered rainfall with mostly
light amounts. Rainfall ahead of the next Western U.S. trough
should begin to move into the region late Tuesday.

Above normal temperatures across the Northwest on Sunday will
shift into the Northern Plains early next week and into the
Midwest by mid-next week. Daytime highs are forecast to be 10-20
degrees above normal, but this may only equate to a moderate
HeatRisk threat. In contrast, a much cooler airmass will be in
place across the East this weekend, but may trend back towards
normal next week. Below normal temperatures should also develop
along the West Coast mid-next week as an upper trough moves
onshore.

Santorelli/Dolan


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 PM EDT Fri Sep 6 2024

Valid 12Z Mon Sep 09 2024 - 12Z Fri Sep 13 2024

...Multi-day Western Gulf Coast States Heavy Rainfall/Flooding
Threat through early-mid next week also being monitored by NHC...


...Overview...

Heavy rain and thunderstorms will continue to make weather
headlines for the western Gulf Coast states as another resurgence
of deep Gulf of Mexico/tropical moisture feeds inland through
early-
mid next week as a warm front lifts toward the region in advance of
a tropical feature being monitored by NHC for possible development.

Elsewhere, the start of next week will be featured with an upper
level trough across the Northeast U.S. and a large Canadian surface
high. This will result in a high quality airmass across much of
the Eastern U.S. with a hint of fall in the air, but a moderation
trend ensues going into the middle of the week. Out West, the
persistent upper ridge and widespread anomalous warmth should abate
by the end of the week as an upper trough with precipitation works
over the West Coast and Northern Intermountain West/Rockies. The
pattern should be mainly benign for the rest of the nation.

...Guidance/Predictability Assessment...

The latest model guidance continues to feature good overall
synoptic scale agreement across the nation as the work week begins
Monday, even though there are characteristic lingering timing
differences with shortwave perturbations and surface features
detail. The models have trended stronger with the large scale
trough/upper low that works across the West Coast/Intermountain
West compared to past cycles.

Accordingly, the WPC medium range product suite was primarily
derived from a model and ensemble mean composite as highlighted by
solutions that at this time are less robust and detailed with Gulf
of Mexico tropical development given continued NHC uncertainties.

...Weather/Hazards Highlights...

Tropical moisture deepening over the southwestern Gulf of Mexico
over the next few days is expected to bring an increasing threat
for heavy rain to the coastal areas of the Texas Gulf Coast by
early next week, which is covered by a Marginal Risk on the WPC
Day 4/Monday ERO. Guidance signals are solidifying in support for
potential of impactful rainfall totals that will need to be
monitored going into the Day 5/Tuesday time period when a Slight
Risk of excessive rainfall is indicated along much of the Texas
coast to Lake Charles, Louisana. There is a still uncertain threat
for tropical system development being monitored by NHC that could
further enhance this threat. This region will likely have
noteworthy rainfall leading up to this over the next few days, and
this will make conditions more susceptible to potential flooding
concerns. Otherwise, much of the country should be relatively
uneventful and dry, although shortwave energy pivoting around the
western-central U.S. upper ridging may produce isolated to
scattered rainfall with mostly light amounts. Upstream, light to
locally moderate precipitation ahead of a Western U.S. trough
will begin to move into/across the region into mid-late next week.

Temperatures are expected to be unseasonably warm by September
standards across much of the north-central U.S., with highs
running about 5 to 15 degrees above average from the Front Range of
the Rockies to the western Great Lakes for much of the week. The
hot weather expected across much of the West Coast and
Intermountain West during the short range period is expected to
improve going into the middle of next week as the upper trough
builds southward and heralds the arrival of a cold front, bringing
temperatures of 5-15 degrees below normal for portions of the West
Coast states and into Nevada. Slightly below average readings are
also likely for the Gulf Coast region (but still humid) owing to
increased cloud cover and rain.

Hamrick/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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 PM EDT Sat Sep 7 2024

Valid 12Z Tue Sep 10 2024 - 12Z Sat Sep 14 2024

...Multi-day western to central Gulf Coast States heavy
rainfall/flooding threat through early-mid next week, with
possible tropical system development being monitored by NHC...


...Overview...

Widespread and protracted heavy rain/thunderstorms with flooding
issues will make weather headlines for the western to central Gulf
Coast states with inland return resurgence of deep Gulf moisture
with a slowly lifting warm front early to mid-later next week.
This threat could be significantly enhanced with possible tropical
system development and approach as currently monitored by NHC.

Elsewhere, it generally remains the case that the beginning of
next week will be featured with an upper level trough exiting the
Northeast U.S. and a large surface high. The initially fall-like
airmass will undergo a moderation trend going into the middle to
end of the week with widespread 80s for highs returning. Out West,
the persistent upper ridge and widespread anomalous warmth is
forecast to abate for the second half of next week as an upper
trough and light to moderate precipitation focus works across the
West Coast, the Intermountain West and then eventually out through
the northern Rockies/Plains.

...Guidance/Predictability Assessment...

Latest model guidance still features good overall synoptic scale
agreement across the nation into Tuesday/Wednesday, with
differences slowly increasing through longer time frames. Guidance
has shown measured cycle to cycle uncertainty with the amplifying
trough over the northwestern U.S., but a favored composite has
trended toward the more amplified side of the full envelope of
solutions. Importantly, the forecast signal continues to increase
in favor of possible tropical system development over the Gulf of
Mexico with likely impacts for the western to central Gulf coast.

The WPC medium range product suite was primarily derived from a 00
UTC ECMWF/NAEFS ensemble mean blend along with the 13 UTC National
Blend of Models and WPC overnight continuity. This solution works
well with latest NHC guidance and also has good composite model
support over much of the rest of the country for next week.

...Weather/Hazards Highlights...

Increasing tropical moisture over the southwestern Gulf of
Mexico/Bay of Campeche in the short term is expected to bring an
increasing threat for heavy rain and strong storms to the coastal
areas of the Gulf Coast states through next week. This disturbance
is also being monitored by the National Hurricane Center for
possible development of a tropical depression or storm as the
system gets closer to the Texas Coast. For the Day 4 period
Tuesday, the guidance generally keeps the heaviest rain close to
the coast or just offshore the Texas Coast. Owing to wet antecedent
conditions from heavy rain in the days leading up to this, a
Slight Risk remains valid from South Texas to near Lake Charles,
where a multiple inches of rainfall will be possible for some of
these areas. Going into the Day 5 period Wednesday, there is a
decent overall model signal for a swath of enhanced rainfall
moving inland
across southeast Texas and into central Louisiana, with
potentially a sharp western gradient of the QPF inland from the
Texas
Gulf Coast. A Slight Risk remains from the cental Texas coast to
near Baton Rouge. A Moderate Risk upgrade was considered and may
be needed pending future NHC updates.

Otherwise, the trough arriving over the West will likely produce
mainly light to moderate showers across portions of the Pacific
Northwest and into the Rockies through Thursday night. The heaviest
QPF from this will likely be over northern Wyoming and into
Montana, with snow for the highest mountain ridges. Showers and
some storms then reach the central/northern Plains by Friday, while
the northeastern quadrant of the nation remains dry.

Temperatures are expected to be unseasonably warm by September
standards across much of the north-central U.S., with highs
running about 5 to 15 degrees above average from the Front Range of
the Rockies to the western Great Lakes for much of the week. The
hot weather expected across much of the West Coast and
Intermountain West during the short range period is expected to
improve going into the middle of next week as the upper trough
builds southward and heralds the arrival of a cold front, bringing
temperatures of 5 to 15 degrees below normal for portions of the
West Coast states and into Nevada. Slightly below average readings
are also likely for the Gulf Coast region (but still humid) owing
to increased cloud cover and rain.

Hamrick/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