541
FXUS02 KWBC 171951
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
351 PM EDT Fri Oct 17 2025

Valid 12Z Mon Oct 20 2025 - 12Z Fri Oct 24 2025


...Overview...

A couple of progressive upper troughs are forecast to move through
the eastern two-thirds of the country through the medium range
period, with a tendency for them to close off into upper lows as
they near the New England coast. Meanwhile, an upper low is
forecast to push onshore into the Southwest amid general ridging
across the Northwest before ridging takes over late next week while
progressing east into the northern High Plains. Precipitation
chances look to increase late next week across the Pacific
Northwest as an upper-trough/potential Atmospheric River
approaches, with heavy rain possible.


...Guidance/Predictability Assessment...

The medium range period beings Monday (Oct 20) with good consensus
in most of the guidance on a continued progressive pattern
featuring a couple upper-troughs over the eastern/central U.S.,
another upper-trough upstream over the northeastern Pacific, and a
southern stream upper-low off the coast of California. Most
guidance also remains in good agreement through at least the middle
part of the period, with the progression of both of the upper-
troughs/potential closed lows over the Great Lakes/Northeast
followed by the upper- trough over the northeastern Pacific
dropping southeastward across southwestern Canada and into the
north-central U.S., as well as with the upper-low moving eastward
over California. Guidance begins to diverge by later next week with
regards to the upper-low and the amplification of the overall
pattern, specifically indications that an upper-ridge will build
over the western/central U.S. Both the latest GFS and ECMWF, and to
a lesser degree the ECens mean, are relatively similar in bringing
the upper-low east, possibly as an open wave, over the
southwestern to south- central U.S. under the amplifying ridge,
while the CMC brings the wave east a bit faster and shows that it
merges with the northern stream upper- trough dropping
southeastward. The last several runs of the ECMWF/GFS also show
large run-to-run variability on timing. This will have implications
on the coverage and amount of potential rainfall over the south-
central U.S. For now, the agreement on this feature from the
GFS/ECMWF this run cycle, as well as the presence of this feature
regardless of exact timing in previous run cycles, at least signals
an increasing chance of precipitation from the central Rockies
east through the south- central U.S. Further upstream, some
uncertainty exists on the timing and coverage of precipitation
across the Pacific Northwest associated with another upper-
trough/potential atmospheric river depending on the amplification
of the upper-ridge downstream, but all guidance does reflect a
significant increase in precipitation chances by late next week.
The updated WPC forecast used a blend of the 00Z ECMWF/06Z GFS with
a component of the 00Z CMC through mid- period, with the CMC
removed and a contribution from the ECens and then GEFS means
ramped up to 50% of the blend by the end of the period as
uncertainty with respect to the evolution of the upper- low into
the southwest/south-central U.S. grows.


...Weather/Hazards Highlights...

The medium range period should begin with moderate to locally
heavy rain possibly with embedded thunderstorms across northern New
England ahead of the first trough that could develop into a closed
low. A marginal risk of flash flooding has been maintained for
this area. Meanwhile, another upper trough may develop into a
closed low over the Great Lakes on Tuesday but with modest amounts
of rainfall. The progressive pattern with consistent post-frontal
northwesterly flow over the Great Lakes will also bring the chance
of lake-effect showers through much of next week.

Out West, increasing chance of moderate to heavy precipitation is
seen near the Pacific Northwest coast toward the end of next week
ahead of an approaching upper trough and potential atmospheric
river. Meanwhile, there are increasing model signals for an
expanding area of rain across the south-central U.S. later next
week but with a fair amount of uncertainty in the amounts and
placement at this point in time. There is also a signal for some
precipitation in the Four Corners region/central Rockies vicinity,
with higher elevation snow possible.

High temperatures across the south-central U.S. look to remain
persistently above average next week, especially for Texas where
highs into the 90s may tie/break a few daily high temperature
records. There may be some periods of below average temperatures
for the Midwest/Northeast following cold frontal passages, though
highs in general look to remain near Fall averages through much of
next week. Highs across the northern- tier from the Rockies east to
the Plains will initially be below average before an amplifying
upper-ridge brings well above average highs by late next week.


Putnam/Kong


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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