956
FXUS02 KWBC 081900
PMDEPD

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




















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