934
FXUS02 KWBC 161935
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
335 PM EDT Thu Oct 16 2025

Valid 12Z Sun Oct 19 2025 - 12Z Thu Oct 23 2025


...Guidance/Predictability Assessment...

The latest model runs continue to show reasonably good agreement
with their depiction of the large scale pattern through the medium
range period, particularly through Day 5. Uncertainty increases
heading into Days 6 and 7, but overall the pattern shows better
agreement than in previous forecasts. The period starts off with a
potent negatively tilted trough ejecting to the northeast from the
Ohio Valley to the Great Lakes into southeast Canada. Guidance is
fairly well clustered with this feature, with only minor
differences in phasing and timing. This trough forces the
development of strong cyclogenesis across the Great Lakes on Sunday
with possible secondary development near New England later Monday
into Tuesday. Models differ on exactly when and where secondary
development occurs, but the signal is strong enough that a
compromise between the EC/GFS/CMC looked reasonable. Expect more
adjustments to the surface reflection in coming forecasts. The
other feature we are tracking is a fast moving trough that quickly
scoots across the Pacific Northwest and northern Rockies Sunday
into Monday before tracking through the Upper Midwest, Great Lakes
and Northeast to round out the period. Guidance is well clustered
with this system through Day 5/6, with uncertainty regarding
possible phasing with a northern stream disturbance followed by
closing off into a large upper low.

The WPC forecast consisted of a composite blend of the 00Z/06Z
EC/GFS/CMC/UK through Day 4/5 before increasing weighting of the
EPS/GEFS/CMCE ensemble means in place of the CMC/UK for Days 5, 6,
and 7. This blend showed good continuity while offering stability
through the period.

...Weather/Hazards Highlights...

A lead main upper trough and deepening surface low pushing across
the Great Lakes region this weekend will draw anomalous moisture
and instability northward in advance of a cold front. The slowly
progressive nature of the upper-level and surface features will
then spread organized rainfall eastward into the East/Northeast
Sunday into early next week. Activity will also focus with
development of a deepening/consolidating coastal low pressure
system near New England. A WPC Day 4/Sunday Excessive Rainfall
Outlook Marginal Risk area was maintained from the central
Appalachians to the eastern Great Lakes/Ohio Valley. For Day 5, a
Marginal Risk was introduced for coastal regions of New England
given a decent QPF/instability signal and remarkable consistency
from machine learning models such as the EC-AIFS and Graphcast GFS.

Out West, a main/complex upper trough and surface low/frontal
system will approach and push across the Pacific Northwest and
northern Rockies over the weekend to produce a period of moderately
heavy coastal and valley rains along with higher mountain snow.
The WPC Day Winter Weather Outlook shows mountain snow potential
inland to the Northern Rockies into Monday. Downstream system
translation and some lead return flow looks to support moderate
rainfall emergence in an expanding pattern over the north-central
to east central U.S. into next Wednesday/Thursday to monitor.

Miller/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














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