267
FXUS02 KWBC 290746
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Fri Aug 29 2025

Valid 12Z Mon Sep 01 2025 - 12Z Fri Sep 05 2025


...Overview...

The overall pattern will remain fairly stagnant through the medium
range period with mean upper troughing over the East and ridging
over the West. A southern frontal boundary will maintain rain and
thunderstorm chances from the Southwest into the Gulf Coast states,
while shortwave energy will support some areas of modest rainfall
through the central U.S. into the Ohio and Tennessee Valleys
Monday-Tuesday. Into mid-next week, a strong reinforcing upper
shortwave/possible closed low is forecast to drop south towards the
Great Lakes and push a cold front across the central U.S.,
resulting in well below average temperatures across the Plains and
Midwest and some rain for the East ahead of it.


...Guidance/Predictability Assessment...

Model guidance shows good agreement with the amplified synoptic
scale pattern anchored by the ridge in the West and trough in the
East. Through the first half of next week, there is some minor
spread with shortwaves in the northeastern quadrant of the lower 48
within the broad trough, without much model consensus. Out West,
models are reasonably agreeable with an eastern Pacific upper low
getting shunted northward rather than penetrating the ridge, but
weak energy to the south reaching California shows more
variability. Additionally, problems with frontal placement
including QPF axis differences in Florida are seen. But these
issues are generally within typical spread for the medium range.

By midweek, models have been persistent with stronger energy
dropping south through the western side of the trough, reinforcing
and deepening the trough for the central and east-central CONUS.
What is less consistent is whether or not this energy will form a
closed low over the Upper Midwest and Great Lakes, which also
affects the depth of an associated surface low. The 18Z GFS as well
as the 12Z CMC trended toward not showing an upper low closing
off, while the 12Z GFS briefly showed a closed low but farther
north. Thus the 12Z ECMWF was the main operational model with a
closed low during the 12Z model cycle. While a closed low still
seemed reasonable and older models including some GFS runs had
suggested this, did not prefer the 12Z ECMWF in terms of the
aggressively deepening surface low into the 980s underneath the
upper low. The consensus of other operational and AI/ML models were
much weaker. The incoming 00Z models are now leaning toward a
closed low again, though the CMC seems to be on the fast/east side
with its position by later next week.

The WPC forecast was based on a multi-model deterministic blend
early in the forecast period. As the period progressed, lessened
the proportion of deterministic guidance (including removing the
12Z ECMWF) in favor of the ensemble means. The means reached just
over half the blend by Days 6 and 7.


...Weather/Hazards Highlights...

A surface front draped from the southern High Plains across the
Gulf Coast and through the Southeast will create a focus for
rainfall when combined with monsoonal and Gulf moisture into next
week. The upper jet reaching the Gulf Coast states, rather south
for early August, should provide lift for some thunderstorms and
isolated heavy rain. A broad Marginal Risk stretches from the
Southwest across parts of Texas and the Gulf Coast region into
Florida for Day 4/Monday for this activity. Did remove the Slight
Risk in southern New Mexico/Far West Texas during this forecast
cycle as models show the more widespread QPF falling in that area
on Sunday (Day 3 in the short range). By Day 5/Tuesday the front
may clear parts of the Gulf Coast, but Florida could still see
locally heavy rain, so will continue to delineate a Marginal Risk
there. Will note that where heavy rain will focus in Florida seems
particularly uncertain, with the potentially multiple frontal
boundaries moving through, and areas may need to be refined in
future cycles. Rain chances may linger in Florida through much of
next week. Meanwhile lingering monsoonal moisture seems to warrant
a Marginal Risk in parts of the Four Corners states on Tuesday,
with increasing moisture possible across the Southwest into the
south-central U.S. by midweek and beyond.

To the north, a frontal system and a shortwave or two aloft will
support storms with elevated rain rates across the Mid-Mississippi
Valley and into the Tennessee Valley and Southern Appalachians on
Monday, and Marginal Risks remain in the Day 4/Monday ERO for these
regions with only minor changes to continuity. By Day 5/Tuesday
convection is likely to focus across the Lower Ohio and Tennessee
Valleys, with a Marginal Risk to start the new Day 5 ERO. Meanwhile
enhanced moisture may push across the Upper Midwest on Tuesday
ahead of the strong cold front emerging. Will delineate a Marginal
Risk across the Upper Midwest for locally heavy rain potential in
this strongly forced environment. With the back end of the front
across the Dakotas, the rain should be lighter and likely move
quickly and lessen the flash flood risk. As the cold front pushes
eastward Wednesday, rain and storms are forecast to overspread the
east-central U.S. and reach the East on Thursday.

The large trough covering the central and eastern U.S. next week
will promote below average temperatures. Temperatures around 5-10
degrees below normal will be fairly common east of the Rockies
early next week, but the reinforcing energy coming into the trough
will push a strong cold front into the north-central U.S. Wednesday
and through much of the Plains into the Midwest Thursday. Lows are
forecast to be generally around 10-15 degrees below average, while
highs could 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. On the other hand, the West can expect warm 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 next week.


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



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