439
FXUS02 KWBC 071741
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
141 PM EDT Mon Sep 7 2026

Valid 12Z Thu Sep 10 2026 - 12Z Mon Sep 14 2026


...Prolonged late-summer heat wave lingers for the southern Plains
through next weekend...

...Overview...

An upper level trough will push across the Northeast late this
week, accompanied by a cold front that will bring precipitation
chances from the Northeast to the Mid-Mississippi Valley. Upper
level troughing will also extend into the Northwest late this week
and be reinforced by shortwave energy next weekend. This feature
will gradually push east through early next week, resulting in
unsettled weather from the Northwest to the Plains, with some
winter weather potential for the northern Rockies. Meanwhile, upper
level ridging will persist across the southern tier, maintaining
hot conditions across the south-central U.S.


...Guidance/Predictability Assessment...

Model guidance remains in good agreement on the synoptic scale
pattern through the end of the week, with relatively flat/zonal
upper level flow leading to some minor timing differences. Model
spread increases significantly next weekend into early next week as
the models struggle to resolve upper level interactions between
various lows and troughs extending from Canada into the northern
tier of the lower 48 states. These interactions will ultimately
determine the evolution of the upper level trough/shortwave in the
Northwest next weekend.

Agreement among model solutions has somewhat improved since the
overnight forecast, now reflecting the most likely solution to be
slower with less interaction with energy in Canada. The 06Z runs of
the AI-GFS and EC-AIFS highlighted this trend and were even slower
than the other deterministic solutions, though the 12Z AI-GFS
is a bit too dramatic with this trend. The GFS runs have remained
consistently too progressive, but the 12Z run showed a significant
slow down and falls closer to the consensus. Ensemble means also
showed a large spread of solutions, further highlighting the
uncertainty surrounding the Northwestern trough evolution.

Given good agreement, a near even blend of the deterministic
guidance was used as a starting point for the forecast through the
end of this week. Ensemble means from the ECENS and GEFS were
added in increasing amounts through the weekend to help smooth out
model differences, and the GFS was phased out since it was too
progressive. This blend maintained continuity with the overnight
forecast and the National Blend of Models.


...Weather/Hazards Highlights...

The long duration heat wave is expected to linger over the
Mid/Lower Mississippi Valley and southern Plains through much of
the week with widespread Major to Extreme HeatRisk. Key Messages
remain in effect with several record minimum and maximum
temperatures in the forecast. The pattern becomes more uncertain
by the weekend, but there is some trend for relief to northern
areas, confining the greatest heat threat to the southern Plains.
Above normal heat may also build briefly across the Southwest and
parts of California mid-week as upper level ridging extends into
the region.

A low pressure system moving through eastern Canada will push a
cold front across the Midwest and Northeast, which will trigger
showers and thunderstorms from the Northeast and Mid-Atlantic to
the Ohio and Mississippi Valleys Wednesday into Thursday. Locally
heavy rainfall will be possible, especially in the Ohio Valley where
the front will encounter an anomalously moist air mass and in the
central Appalachians where terrain may enhance precipitation
totals. This frontal boundary should move relatively quickly, which
will help to limit flash flood potential.

The focus for precipitation will shift to the Northwest late this
week into next weekend as upper level troughing strengthens. This
trough will push a cold front south across the Northwest and
northern Plains late this week, which will bring unsettled weather
to these regions. Early next week, the front will continue to move
south across the Great Basin and Intermountain West while low
pressure strengthens along the boundary over the northern/central
Plains. Wintry weather will be possible in the northern Rockies
next weekend as cooler air moves in behind the cold front, and
heavy rainfall potential may develop over eastern Plains into the
Upper Midwest ahead of the strengthening low early next week.

Daily rounds of diurnal showers and thunderstorms are expected to
continue in the Southeast and Southwest. A couple of weak frontal
boundaries will move into the Southeast and dissipate, which will
focus moisture and instability across the region. In the
Southwest, monsoonal moisture will continue focus showers and
thunderstorms in the Four Corners region.


Dolan/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


$$