975
FXUS02 KWNH 090757
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
356 AM 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...

Model guidance shows okay agreement on the overall pattern but
with important differences in the details. In the East, the coastal
surface low shows some differences in position even as the period
begins on Sunday. The 12Z CMC and the newer 00Z CMC are both
farther east with the low compared to consensus, but then they
linger the low closer to the coast into later Monday-Tuesday than
consensus. GFS runs through the 12Z tended to be faster than
preferred, but the 18Z GFS showed better alignment with the ECMWF
runs. Overall leaned heavily toward the consistent ECMWF with some
18Z GFS inclusion. Models are trending toward having consolidated
upper energies (from the Great Lakes and from the Atlantic merging
in the Mid-Atlantic) by 12Z Monday, a little earlier than runs from
a day ago. The newer 00Z guidance still shows spread though,
including a slower 00Z GFS and faster 00Z ECMWF with the surface
low track, so continue to watch for forecast changes to the low
position and resulting QPF. The low should be gradually pulling
east/away by Tuesday and beyond.

In the West, upper troughing atop the Rockies Sunday is forecast
to quickly lift northeast by Monday, with good agreement. Meanwhile
another round of energy developing an upper low will be diving
along the West Coast Monday-Tuesday. There is more model spread
with this upper low position going forward. The 12Z CMC and UKMET
were west of consensus by Tuesday, while the 12/18Z GFS runs and
many GEFS ensemble members were east of the 12Z EC/EC ensemble
preferred middle ground. The 00Z GFS trended west and the 00Z CMC
trended east, fortunately for better model convergence. However, by
Wednesday-Thursday the new 00Z ECMWF splits energy and pulls some
west into the eastern Pacific into later week, whereas the GFS/CMC
have a consolidated trough remaining in the West. Will monitor if
other guidance like the 00Z AI/ML models follow suit, but for now
the 00Z ECMWF seems like an outlier. Upper ridging in between the
West and East troughs is at least agreeable, though its extent is
less certain from day to day.

The WPC forecast used a 12Z ECMWF/18Z GFS/12Z EC ensemble mean (in
decreasing order) model blend for the early part of the medium
range period, given the favorable ECMWF positions in the East and
West. As the period progressed, used more ensemble mean guidance to
a little over half the blend by days 6-7 given the increasing
spread.


...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. 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.

Early next week, another round of tropical moisture and energy is
forecast to enter the Southwest with a tropical system that is
likely to develop behind Priscilla per the National Hurricane
Center. 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.

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, with some
snow moving into the Sierra Nevada Monday-Tuesday, and 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.


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



$$