641
FXUS02 KWBC 050659
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM 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 near Montana 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. Energy dropping down the West Coast mid-week may cut off
from the main flow and meander off the West for much of the period,
likely meaning less direct moisture influx from Hurricane Marie.
This low eventually looks to get absorbed into another shortwave
into the Northwest late week, with deeper troughing over much of
the West by next weekend allowing for the southern ridge to finally
break down somewhat.

...Guidance/Predictability Assessment...

Guidance is fairly agreeable Days 4/5 with the low tracking from
Idaho Monday to Manitoba Tuesday with improving consensus on timing
from there with the latest guidance runs. There is still a fair
amount of uncertainty out West, though with trends now for a more
offshore low. But where this low sets up seems dependent on how
quickly what will be post-tropical Marie gets absorbed. Eventually
this energy should phase with additional shortwave into the
Northwest late week, but will plenty of uncertainty again on the
timing. GFS is faster with more troughing over the West by the end
of the period than the more offshore ECMWF. GFS and UKMET are most
aggressive with remnants of Marie moving towards the West Coast
early in the week.

The WPC forecast was based on a general non-UKMET consensus for
the early period, increasing to 60 percent ensemble mean guidance
with the ECMWF for late period. Overall maintains good continuity
with the previous shift as well.


...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. 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 uncertainty still remains with this plume.
Precipitation chances may expand more across the Northwest by next
weekend with increasing troughing over the region.


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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