999
FXUS02 KWBC 091949
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Thu Oct 9 2025

Valid 12Z Sun Oct 12 2025 - 12Z Thu Oct 16 2025


...A strong coastal low could bring significant coastal flooding,
beach impacts, wind gusts, and heavy rain to the East Coast...

...Heavy rain and flash flooding is a continued concern across the
Southwest early next week...


...Overview...

As the medium range period begins early next week, a strengthening
low pressure system is forecast to move slowly north in the
western Atlantic near the East Coast. This coastal low is forecast
to bring strong onshore winds causing coastal flooding, rip
currents, beach erosion, and heavy rain in the Mid-Atlantic and
Northeast. Meanwhile, upper troughing in the West will draw
tropical moisture and remnant tropical energy northward and bring
potentially widespread heavy rain and some flash flooding into the
Southwest early next week. This trough and another round of
troughing in the West will maintain cooler than average
temperatures as well as precipitation chances, including higher
elevation snow. Upper ridging should prevail farther east in the
central U.S., allowing for unseasonably warm temperatures, and
rounds of rain in the north-central U.S. directed around the ridge.


...Guidance/Predictability Assessment...

An active medium range period begins Sunday across the CONUS
including consolidating upper-energy over the eastern U.S. and
associated coastal low development as well as deep upper-troughing
over the western U.S., with an upper-ridge in between. Model
guidance has continued to come into generally good consensus on
both these regions for at least the early period. For the eastern
U.S., both the ECMWF and GFS are in good agreement on upper-energy
over the southern U.S. passing over the southwestern Atlantic
helping to trigger coastal low development along the Carolinas,
with reinforcing/consolidating upper-energy dropping southward from
the Midwest. The ECMWF has trended a bit weaker with the coastal
low compared to the GFS, but both models depict a path northward
close to the Mid-Atlantic coast through Monday, before the low
begins to shift eastward into the Atlantic by Tuesday. The updated
12Z guidance continued this trend favoring a track along the coast.
Similar to last night`s discussion, the CMC has remained an
outlier in depicting both a stronger low and one that takes an
eastern path further away from the coast. There also remains a lot
of uncertainty with regards to both the footprint and amount of
potential rainfall, with the GFS/ECMWF showing heavier amounts
earlier through the Mid- Atlantic given the track closer to the
coast, and the CMC shows much more significant amounts into New
England given the much stronger low that lingers for a longer
period of time. For now, felt the NBM represented the uncertainty
earlier in the period (Sunday- Monday) well by capturing the
amounts shown by the deterministic guidance but aligning with the
footprint of the ECens/GEFS mean through the Mid- Atlantic/southern
New England. However, the NBM remains a bit heavier further north
into New England Tuesday- Thursday timeframe compared to much of
the guidance, so prefer a more muted solution for the time being
given the uncertainty.

In the western U.S., the updated guidance was also in generally
good agreement with the depiction of mean upper-troughing over the
western U.S. and an initial shortwave ejecting over the north-
central U.S. Though, there is some notable difference in cold front
placement with this initial upper-wave, and high temperatures in
the central Plains vicinity vary greatly depending on which
solution is preferred (GFS south, ECMWF north). Guidance begins to
diverge in the mid- to late period with regards to additional
upper-energy upstream over the northeastern Pacific diving south
along the West Coast, and especially on the eventual progression of
this energy and/or additional northern stream energy eastward
towards the central U.S. This will have the potential for
significant timing/placement differences of precipitation across
the region, and for now relied heavily on the NBM which provided a
decent compromise on placement even if coverage/timing may
eventually change, especially across the Plains.

The updated WPC forecast began with a 50/50 blend of the 00Z
ECMWF/06Z GFS given their consensus on the overall pattern,
specifically over the eastern U.S., compared to the CMC. A
contribution from the ECens mean is added mid-period, with a
combination of the ECens/GEFS mean eventually compromising 60% of
the blend by the end of the period, as differences with regards to
the evolution of the western upper-trough and eventual progression
of upper-energy eastward to the Plains/associated surface frontal
system placement grow.



...Weather/Hazards Highlights...

At the start of the period Sunday, a low pressure system in the
western Atlantic is forecast to affect the East Coast. Heavy rain
is possible for the Mid-Atlantic and Northeast, especially coastal
areas like the Delmarva Peninsula into Long Island and coastal
southern New England. A Slight Risk was maintained for Day 4/Sunday
for coastal areas with a broader Marginal Risk in the Excessive
Rainfall Outlook. By Day 5/Monday there is more uncertainty with
rain amounts onshore. There could be potential heavier bands of
rain; models generally indicate that around Boston could see
heavier rain amounts, which combined with the urban area could
cause flooding issues, but will show just a Marginal Risk for the
coastal Mid- Atlantic to Northeast on Day 5 at this point and see
how models trend. In addition to heavy rain threats, the
combination of persistent and strong onshore winds, high surf, and
above normal tides may lead to significant coastal flooding impacts
along with strong rip currents and potential beach erosion. See
Key Messages being issued by WPC for the latest on this system.
Guidance suggests at least some rainfall may linger into mid-week
across New England but with significant uncertainty on
coverage/amounts.

Early next week, another round of tropical moisture and energy is
forecast to enter the Southwest as newly formed Raymond in the
Pacific follows in the wake of Priscilla. Precipitable water values
are likely to be near max values for this time of year, and PWs of
1.5 inches would even be in the 75th-90th percentile during the
typical peak of monsoon season in early-mid August. The Southwest
should also be in the right entrance region of the upper jet for
good dynamical support for heavy rain. However, a limiting factor
in terms of flash flooding could be somewhat limited instability
under widespread clouds and rain, which could limit rain rates.
Also, the current forecast shows the greatest rainfall totals to
the southeast of where the heaviest rain could fall in the short
range. Thus continue to hold off on any Moderate Risks at this
time, but Slight Risks are in place across portions of Arizona and
New Mexico for the Days 4-5 (Sunday and Monday) Excessive Rainfall
Outlooks, and WPC will continue to monitor for potential upgrades,
with the greatest current threat appearing to center across
southeastern Arizona.

Elsewhere, the rounds of upper troughing in the West will promote
precipitation, including higher elevation snow. Moderate to heavy
snow is likely for the Cascades/northern Rockies Sunday, and then
moving into the Sierra Nevada Monday-Tuesday. Lighter snow is
possible for the Intermountain West/northern Rockies with the
second trough as well. Additionally, a moisture plume/atmospheric
river is forecast to move across California Monday ahead of a cold
front. While it could be relatively fast- moving, some instability
could be present and rainfall rates could reach an inch per hour,
so have a Marginal Risk of excessive rainfall drawn up for parts of
northern California on Day 5/Monday. Farther east, rounds of
precipitation are possible in the Plains to Upper Midwest and Great
Lakes region.

Cooler than average temperatures are forecast particularly for
highs in the West through next week underneath renewing troughing.
Meanwhile, upper ridging in the central U.S. will lead to warmer
than average temperatures. Highs in the 70s reaching as far north
as the Dakotas Sunday will be 15-20 degrees above average.
Temperatures there should cool behind a cold front into the
workweek, but temperatures of 10 to 15 degrees above normal will
last several days farther south, as unseasonably warm highs in the
90s continue for Texas and Louisiana. Warmer than average
temperatures are forecast to stretch into the Midwest. Some cool
highs along the East Coast early week should moderate close to
normal as the week progresses.


Putnam/Tate


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





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