Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Fri Aug 8 2025

Valid 12Z Mon Aug 11 2025 - 12Z Fri Aug 15 2025

...Heat returns to the Midwest/Great Lakes/Northeast next week...


...Overview...
Central CONUS troughing will yield to strong downstream ridging
over southeastern Canada that will help usher in much warmer
temperatures to the Northeast 1/4 of the Lower 48. Strong upper
ridging over the northeastern Pacific is forecast to retrograde,
allowing digging troughing to settle into the Pacific Northwest.
Cooler than normal temperatures will replace the warmer than normal
temperatures by later in the week.


...Guidance/Predictability Assessment...

The 06/12z guidance was reasonable agreement as to the synoptic
evolution across the lower 48 next week. On day 3 a general model
blend consisting of the 00z ECMWF/CMC/UKMET and 06z GFS with more
weighting placed on the Euro and Canadian since they both diverge
from the GFS with respect to an inverted ridge over the West Coast.
The GFS also overamplifies and is more progressive with a trough
over the Plains compared to a more subdued trough in the UK/EC/CMC.

The overamplification in the GFS continues on day 4, but the
Canadian and UKMET also have a bubble high over the West, which is
why the Euro makes up 40% of the general model blend on this day. A
more equitable approach to the blend consisting of deterministic
and ensemble guidance is taken on days 5 and 6 before resorting to
a predominantly ensemble blend on day 7.


...Weather/Hazards Highlights...
A cold front over the Great Lakes (on Monday) back to the Plains
will be a focus for some locally heavy rain Monday into Tuesday as
it slowly pushes to the east and southeast into the Midwest. To the
south, a lingering stationary boundary draped along the I-10
corridor amid higher than normal moisture levels will also act as
an impetus for some heavier rain. Both of these areas, for Monday
and Tuesday, are denoted with a Marginal risk of flash flooding
(excessive rainfall). A targeted slight risk area was added to the
day 4 ERO with this afternoon's update to account for likely
antecedent heavy rainfall set to unfold over parts of eastern Iowa,
southern Wisconsin northern Illinois and northern Missouri. In
addition, much of New Mexico and into southeastern Arizona may see
some localized modest rainfall amid sensitive terrain. A Marginal
risk exists there for Monday. For the rest of the week, rainfall
chances will increase over the eastern 1/3 of the country as the
northern frontal boundary wavers over the region.

Temperatures will warm into the Northeast to near record levels
Mon-Wed with highs into the 90s. This will push HeatRisk levels
into the Moderate (level 2) to Major (level 3 out of 4) category
after a relatively cool/comfortable start to August. Lingering heat
over the Southwest will slowly subside through the period though
temperatures will remain slightly above normal.

On the flip side, increased troughing into the Pacific Northwest
will cool temperatures rather smartly from 5-15 degrees above
normal Monday to 5-10 degrees below normal by Thursday (WA/OR). To
the south through coastal CA, temperatures will hover near to below
normal as the cooler than normal summer carries on.

Kebede/Fracasso


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Aug 9 2025

Valid 12Z Tue Aug 12 2025 - 12Z Sat Aug 16 2025

...Overview...
Strong upper ridging over the northeastern Pacific will retreat
westward, favoring increased troughing into the Pacific Northwest
and above normal heights for much of the rest of the Lower 48 for a
time. Slow-moving frontal boundaries in the East will spark
convection and locally heavy rainfall in amid seasonably warm to
hot temperatures, with some signal for monsoon convection in the
Southwest.



...Guidance/Predictability Assessment...
The 00Z/06Z guidance offered reasonable clustering through the
period with the ensemble means. The pressures, fronts, 500 hPa
heights, and winds started out with an even split of the 00z ECMWF,
00z UKMET, 00z Canadian, and 06z GFS, with some 00z ECMWF ensemble
mean and 00z NAEFS mean input late in the period to account for
uncertainty. The remainder of the grids have a strong resemblance
to the 13z NBM, with some 06z EC AIFS inclusion.



...Weather/Hazards Highlights...
Near and ahead of a cold front moving through the Great Lakes,
Midwest, and portions of the Appalachians, locally heavy rain is
expected within a moist and unstable air mass. Locally heavy
rainfall is also possible near a returning warm front in and near
North Dakota. To the south, ample moisture and instability near a
dying front/surface convergence zone will also act as an impetus
for some heavier rain Tuesday into Wednesday near the central Gulf
coast and Lower MS Valley. These three areas are denoted with a
Marginal risk of flash flooding (excessive rainfall). Much of New
Mexico and into southeastern Arizona may see some localized modest
rainfall amid sensitive terrain and burn scars Tuesday, and a
Marginal risk exists there. For the rest of the week into the start
of the weekend, rainfall chances will be modestly high over the
eastern 1/3 of the country as the northern frontal boundary wavers
over the region (Great Lakes to Northeast).

Temperatures will start the period quite warm into the Northeast
to near record levels Tuesday with highs into the 90s. This will
push HeatRisk levels into the Moderate (level 2) to perhaps Major
(level 3 out of 4) category. Lingering heat over the Southwest with
record highs Tuesday will slowly subside through the period,
though temperatures will remain slightly above normal until later
in the week.

Over the Pacific Northwest, temperatures will trend cooler than
normal as troughing increases. Temperatures in the 70s/80s/90s
Tuesday will drop by 10-20 degrees late this week. Through coastal
CA, temperatures will hover near to below normal as the cooler
than normal summer carries on. Even inland locations will cool by
the end of the week as upper troughing takes a hold.

For Puerto Rico and the U.S. Virgin Islands, a broad tropical wave
with some rotation leaving the African coast is expected to track
west to west-northwest, ending up northeast of the Leeward Islands
Friday into next weekend. This could lead to a trailing trough from
its southwest side moving across the region which would focus
shower and thunderstorm activity and weaken the trade winds. The
system's track thereafter remains uncertain due to uncertainty
regarding the upper level pattern from the Appalachians east into
the western Subtropical Atlantic at that long time range. See
National Hurricane Center Tropical Weather Outlooks for more
concerning its potential for tropical cyclone development.

Roth/Fracasso


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Sun Aug 10 2025

Valid 12Z Wed Aug 13 2025 - 12Z Sun Aug 17 2025

19Z Update: The 12Z forecast models remain in good overall
agreement across the Continental U.S. for the middle to end of the
week, and a multi-deterministic model blend works as a starting
point in the forecast process. At the time of fronts/pressures
preparation, the 00Z CMC strayed from the consensus with the main
upper low/trough over southern Canada by Friday and into next
weekend, so more of the GFS/ECMWF was applied by Days 6 and 7, but
the 12Z CMC has trended closer to the consensus. The ensemble
means were gradually increased to about half by next Sunday amid
growing model differences across the Pacific Northwest and the
northern tier states. The previous forecast discussion is appended
below for reference. /Hamrick
-----------------

...Overview...

Increased troughing into the Pacific Northwest later this week
will linger through the upcoming weekend as above normal heights
dominate much of the rest of the Lower 48. Slow-moving frontal
boundaries in the East will spark convection and locally heavy
rainfall amid seasonably warm to hot temperatures, with at least
some signal for monsoon convection in the Southwest.

...Guidance/Predictability Assessment...

Through the 12Z/18Z guidance, most of the deterministic runs
offered reasonable clustering with the ensemble means except for
the 12Z Canadian over western Canada. The ECMWF AIFS EPS was a bit
slower/deeper than its dynamical counterpart which was more in line
with the ECMWF/GFS. Still, timing the shortwaves across Canada
exhibits lower confidence beyond day 3 as is typical in the summer.
Trended toward an even split between the ensembles and
deterministic GFS/ECMWF by the end of the period.

...Weather/Hazards Highlights...
Near and ahead (and south) of a frontal boundary astride the Great
Lakes, locally heavy rain is expected within a moist and unstable
air mass. The western end of this front over the High Plains will
push eastward as a warm front, igniting some locally heavier rain
across the Upper Midwest Wednesday into Thursday. Over the
Southwest, monsoonal moisture will make another attempt at pushing
northward midweek. These areas are denoted with a Marginal risk of
flash flooding (excessive rainfall) Wednesday-Thursday. For the
rest of the period (Fri-Sun), rainfall chances will be modestly
high over the Upper Midwest near a couple frontal boundaries, over
the Southeast, and across the Southwest.

Temperatures will start the period quite warm into the Northeast
to near record levels Wednesday with highs into the 90s. This will
push HeatRisk levels into the Moderate (level 2) to perhaps Major
(level 3 out of 4) category from DC northward into New England.
Temperatures will remain near to several degrees above normal over
much of the CONUS east of the Rockies, especially over the Midwest
into the Northeast/Mid-Atlantic (though likely below record
levels). Over the Pacific Northwest into California, temperatures
will trend cooler than normal as troughing digs into the West.


Fracasso


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
229 PM EDT Mon Aug 11 2025

Valid 12Z Thu Aug 14 2025 - 12Z Mon Aug 18 2025

...Overview...

Western troughing and eastern ridging will be the story for the
medium range period, with the jet stream mostly across southern
Canada. This will take the storm track into the Pacific Northwest
then through the northern tier of the Lower 48. Temperatures will
generally follow suit with cooler than normal readings for much of
the West but warmer than normal readings for most of the rest of
the CONUS. Rainfall will be favored in the Pacific Northwest, Upper
Midwest, Mid-South/Southeast, and increasingly in the Southwest as
the monsoon season finally shows some life.

...Guidance/Predictability Assessment...

Updated 00/06Z guidance remains in good agreement on the overall
Synoptic pattern through the medium range period covering the end
of this week and through the weekend (Thursday Aug 14 - Mon Aug
18). Run-to-run consistency is also well maintained suggesting
above average predictability in the pattern. All guidance shows the
storm track will lift northward over the central/eastern U.S. as
an upper- level high builds over the Southeastern and then south-
central U.S. following the departure of a mid-week system over the
Northeast. Meanwhile, mean upper- troughing will be in place over
the northeastern Pacific into the Pacific Northwest, with periodic
short-wave/system activity through the Northwest as well as east
into southern Canada/the northern-tier of the U.S. A composite
blend of the deterministic guidance (00Z ECMWF/CMC/UKMET and 06Z
GFS) remains a good starting point for the updated WPC forecast
through early next weekend given good overall agreement and
maintains consistency with the prior forecast. The blend for the
latter part of the period used the 00Z ECMWF/06Z GFS and the 00Z
ECens/06Z GEFS means as differences naturally begin to increase,
and the CMC diverges from the other guidance with a more aggressive
depiction of a short-wave breaking through the broad upper-ridging
over the central U.S.

...Weather/Hazards Highlights...

For Thursday and Friday, there are three areas with Marginal risks
for excessive rainfall/flash flooding -- the Upper Midwest, Mid-
South/Southeast, and Southwest. The first is due to an approaching
frontal system with another just to the south over the Plains --
showers/storms are likely ahead of the warm front. The Storm
Prediction Center has indicated the threat for severe weather in
the Upper Midwest this Thursday as well. The second area is due to
increased moisture in the Southeast 1/4 of the CONUS, coincident
with daytime heating which will spark mainly afternoon
showers/storms. The last area (Southwest) will see an increase in
moisture into the region out of Mexico Thursday with a nudge
eastward Friday. Potential exists for future upgrades to Slight
risks in each of these areas, but confidence is limited at this
range. Into the weekend and next Monday, rainfall may ease a bit in
the Southwest but increase over the Upper Midwest/Great Lakes and
eventually Northeast as the cold front moves eastward. The
Southeast will continue to see a daily chance of showers/storms in
typical summertime fashion.

Temperatures will be very warm/hot over the Plains Thursday
(approaching 100F) which will spread eastward into the weekend,
reaching the Midwest Friday and the Northeast/Mid-Atlantic this
coming weekend. Many areas will see temperatures into the 90s with
higher humidity. This will drive HeatRisk values into the the
Moderate (level 2) to perhaps Major (level 3 out of 4) category.
High temperatures and humidity will combine to make for very
uncomfortable conditions as well over Florida late this week and
and along the Gulf Coast into the weekend as an intensifying upper-
level high passes overhead. Over the Pacific Northwest into
California, temperatures will be cooler than normal as troughing
digs into the West. Coastal areas may only see highs into the 60s
and low 70s with inland areas only in the 80s to low 90s. Abundant
cloud cover with elevated rain chances over the Southwest will
likely keep temperatures cooler than normal as well
-- 90s to low 100s for the desert cities.


Putnam/Fracasso


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
202 PM EDT Tue Aug 12 2025

Valid 12Z Fri Aug 15 2025 - 12Z Tue Aug 19 2025

...Overview...

During this period troughing will be present over the West with
ridging over the East initially before slow retrogression westward
of the entire pattern into early next week. As this pattern is in
transition, the ridge is expected to build into the Southern
Plains/Rockies with troughing dipping into the Northeast. There
will be a stark temperature contrast with cool in the West and
warm/hot in the East that will moderate as the new week progresses.
With the ridge axis shifting westward so will the warming
temperatures. Rainfall will focus over the northern Tier (Upper
Midwest/Great Lakes) in association with the storm track, across
the Southeast, and over the Southwest. In addition, a modestly
strong cold front will bring appreciable rain to the Pacific
Northwest on Friday/Saturday.

...Guidance/Predictability Assessment...

The latest suite of guidance remains fairly clustered through the
extended period with the broad upper ridge and bookend troughs near
each coast. There continues to be timing differences with
individual embedded shortwave but nothing egregious for this time
period. The National Hurricane Center is tracking Tropical Storm
Erin, which may start to get close to the southeastern boundary of
the domain by next Tuesday per the latest forecast. Please see the
NHC website for the most up-to-date information.

...Weather/Hazards Highlights...

Over the weekend there are three regions where there may be
excessive rainfall and isolated areas of flash flooding -- the
Upper Midwest, Southern Appalachians/Southeast, and the Southwest.
Showers and thunderstorms will likely fire up along and ahead of
an approaching cold front. Persistent high moisture levels over
the Southeast, when combined with afternoon heating, will trigger
showers and storms development during the afternoon. The last area
(Southwest) will see an increase in moisture into the region.
Though amounts may be light overall, some storms will still be
capable of producing heavier rainfall that may fall over more
sensitive areas (steep terrain, in/around burn scars, etc.). For
the rest of the period, rainfall may ease a bit in the Southwest
remain widespread across the Upper Midwest/Great Lakes as the
frontal boundary stalls across the region.

Very warm temperatures will persist over much of the central and
eastern U.S. this weekend, with many areas climbing into the 90s
with heat indices around 100F. This will drive HeatRisk values
into the the Moderate (level 2) to Major (level 3 out of 4)
category from the Corn Belt through the Midwest into the Mid-
Atlantic. High temperatures and humidity will combine to make for
very uncomfortable conditions as well over Florida late this week
and along the Gulf Coast into the weekend. With the cold front
approaching from the north, cooler air filtering in will provide
some degree of relief from the Great Lakes to the Northeast. For
the West Coast, the weekend will be much cooler than seasonal
average for August however temperatures are expected to slowly
rebound as the troughing eases back westward. Coastal areas may
only see highs into the 60s and low 70s with inland areas only in
the 80s to low 90s. Even the Southwest will likely see temperatures
a bit cooler than normal -- 90s to low 100s for the desert cities
instead of 100-110F+. However, the heat may start to return over
the Four Corners region by Tuesday as the upper ridge moves into
the area from the east.


Campbell/Fracasso


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