019
FXUS02 KWBC 051941
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
341 PM EDT Sat Sep 5 2026

Valid 12Z Tue Sep 08 2026 - 12Z Sat Sep 12 2026


...Prolonged late-summer heat wave lingers for the central/
southern Plains to the Mid/Lower Mississippi Valley through much of
next week...


...Overview...

An upper low in south-central Canada on Tuesday will round the top
of a persistent southern tier ridge, tracking over the Canadian
Prairies to James Bay by Wednesday. This system brings showers to
parts of the Great Lakes to Northeast and Midwest ahead of it
Tuesday-Thursday. Marie and a closed low off the Pacific Northwest
coast will interact farther offshore, meaning less direct moisture
influx from Hurricane Marie. A stronger northern stream
disturbance over the Pacific Northwest will work with another
trough over southern Canada to generate a faster flow pattern over
the northern tier late week. Meanwhile, anomalous upper-ridging may
continue over much of the southern tier into the start of next
weekend.


...Guidance/Predictability Assessment...

Guidance remains in decent agreement regarding the upper-level
pattern through Day 4. Guidance has become better clustered
through Day 5 on future post-tropical Marie`s location, too. Where
model spread begins to increase is with the strength and
progression of the upper trough over British Columbia on Day 5,
then through the Northwest U.S. for Days 6-7. The source of the
differences come from the amplification and slowing of the 500mb
trough over the Northwest. The 12Z CMC does not deepen the 500mb
trough over the Northwest and the northern stream feature races
east over northern Saskatchewan on Day 6. It instead tries to bring
the remnant upper-level trough associated with Marie towards the
Northwest, which does not have much ensemble support. Meanwhile,
the 12Z ECMWF/GFS are generally in decent agreement on a deeper yet
positively- tilted trough over the Pacific NW. The 12Z ECMWF
slowed down from its faster 00Z run and looks closer to the 12Z
GFS, although the strength and axis of the embedded shortwave
troughs still differ to an extent. Still, both deterministic
members are not far off from the 00/12Z GEFS/ECENS ensemble means,
which led to those two ensembles being more favored for the Days
6-7 period.

The WPC forecast was a general model consensus through early Day 5,
then phased out the CMC and 00Z ECMWF beyond Day 5. Days 6-7 began
to use a increasing to 70 percent ensemble mean guidance based more
on the ECENS and GEFS. This kept the forecast closer to continuity,
while also accounting for subtle changes in the northern stream
that appears to be coming into focus per latest 12Z guidance.


...Weather/Hazards Highlights...

The long duration heat wave is expected to linger over Mid/Lower
Mississippi Valley to southern Texas through much of next week
though may wane in intensity by later in the week. Key Messages
remain in effect with several forecast record highs forecast.
Cooler than normal temperatures on tap for early next week under
the low/trough from the northern tier into the Northeast, but with
moderation by late week as some ridging builds back across the
South.

The upper low through southern Canada will bring Tuesday-Thursday
light to locally moderate rainfall along the main cold front as it
sinks through the Midwest and Northeast. This trough will also be
responsible for high winds in parts of the Northern Plains by
Tuesday and possibly into Wednesday. Monsoonal moisture will
continue for the Southwest and southern Rockies through the week.
Tropical moisture from Marie looks to generally remain offshore
from California, though some uncertainty still remains with this
plume as some residual moisture will still keep some showers and
thunderstorms in the forecast. Precipitation chances may expand
more across the Northwest late week with increasing troughing over
the region.


Mullinax/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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

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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