407
FXUS02 KWBC 301849
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Aug 30 2025

Valid 12Z Tue Sep 02 2025 - 12Z Sat Sep 06 2025


...Overview...

Troughing over the eastern 1/2 of the CONUS will be reinforced
midweek which will bring in well below normal temperatures to the
Plains/Great Lakes/Midwest. The Pacific Northwest will see upper
ridging and much warmer than normal temperatures during the week.
Rainfall will focus along/ahead of the strong cold front over the
East as well as across the Southeast/Mid-Atlantic as a southern
system lifts northward along the coast. Monsoonal moisture will
remain in place, albeit on the lighter side, though it may increase
by the end of the week.


...Guidance/Predictability Assessment...

Through the 00/06Z guidance, a blend of the GFS/ECMWF/UKMET offered
the best clustering with the overall amplified pattern. The 00Z
Canadian was offset in its handling of the upper low Wed and beyond
(farther southwest) and was not included. The ECMWF AIFS ENS was
notably sharper/deeper than its dynamical ensemble mean, which
clustered better with the deterministic consensus (GFS/ECMWF).
Thus, included a majority deterministic weighting through the
period.

Interesting to note that the ECMWF AIFS was much more aggressive
with shortwave energy rounding the upper trough than any other
dynamical model. This would introduce much more cloudiness/showers
than currently predicted over the Northern Plains/Corn Belt
Thu/Fri. Time will tell.


...Weather/Hazards Highlights...

Shortwave energy and a weak surface low along a front could
support storms with elevated rain rates centered over the Mid-South
on Tuesday. A Marginal Risk remains in place in the Day 4/Tuesday
ERO for that region with only minor changes to continuity. Farther
south, frontal boundaries are forecast to meander over Florida in
an unstable environment with above normal moisture, also allowing
for localized flash flooding potential there and Marginal Risks in
the Day 4/Tuesday and Day 5/Wednesday EROs. Additional frontal
boundaries atop Florida may help focus continued diurnal convection
in Florida into later next week, but with some signal for moisture
levels to decrease back toward normal.

Farther north, a cold front dropping into the north-central U.S.
ahead of the strong reinforcing upper trough could see some
convection ahead of it. On Tuesday, locally heavy rain amounts look
to focus around the Upper Midwest where the Marginal Risk remains
in the Day 4 ERO. Instability and moisture are not too high, but
the forcing is strong and the front may be moving a little slower
on Tuesday into Wednesday, and with an uptick in QPF we have added
a Marginal Risk on the Day 5 ERO over WI/U.P. of MI. Rain is
forecast to push into the East Thursday-Friday (after a dry
period), potentially influenced by a coastal system.

Meanwhile, monsoonal moisture is forecast to flow into the
southwestern U.S. underneath the mean upper ridge for scattered
showers and thunderstorms. Marginal Risks are in place across much
of Arizona and New Mexico (and clipping neighboring states) on Days
4/5 for locally heavy rainfall causing flooding concerns
especially in sensitive areas. Despite low deterministic QPF,
moisture anomalies are generally highest there and the weak energy
around northern California could provide a bit of lift. Some rain
and storms could also extend across the southern Rockies to
southern Plains next week.

The large trough covering the central and eastern U.S. next week
will promote below to well below average temperatures.
Temperatures around 5-10 degrees below normal will be fairly common
east of the Rockies into Tuesday, but the reinforcing energy
coming into the trough will push a strong cold front into the
north-central U.S. Wednesday and spreading into much of the Plains
and Midwest Thursday. Lows are forecast to be generally around
10-15 degrees below average, while highs may be around 15-20
degrees below normal. These cool highs could set daily records for
low maximum temperatures, as highs only reach the 50s in some
locations of the Upper Midwest and Great Lakes. While record
lows may be less expansive, there may be a concern for frost
around Lake Superior particularly Thursday morning, depending on
wind and cloud cover. On the other hand, the West can expect warm
to hot conditions under the upper ridge. Temperatures will be most
anomalous in the Northwest, with upper 90s and possibly reaching
100F east of the Cascades. Record high minimum and maximum
temperatures are possible, and the HeatRisk rebounds to Major to
locally Extreme in the northern Great Basin.


Fracasso/Tate


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



$$