954
FXUS02 KWBC 041856
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Wed Jun 4 2025

Valid 12Z Sat Jun 07 2025 - 12Z Wed Jun 11 2025


...Severe weather possible in the southern tier Saturday, with
heavy rain possible there through much of next week...

...Heat wave for the Interior West with some heat in South
Texas...


...Overview...

This weekend into early next week, reloading troughing centered
over the Great Lakes and vicinity will push fronts through the
Plains eastward, producing rounds of thunderstorms that may be
severe and/or cause flash flooding in the southern tier in
particular. Meanwhile, rounds of ridging over the West (though
interrupted by shortwaves) will lead to much above normal
temperatures.


...Guidance/Predictability Assessment...

Model guidance is generally agreeable for the large scale features
of the pattern, with more differences in the details. Broad
troughing is likely across the northern tier this weekend, while
more consolidated energy dives across south-central Canada to form
an upper low by Sunday that reaches the Upper Midwest/Great Lakes
on Monday and deepens the trough slightly across the east-central
U.S. Shortwaves ahead of this main upper low and the resulting
surface lows/fronts and QPF are more uncertain. Within general
spread, the 06Z GFS seemed to be the biggest outlier, as it put a
relatively deep surface low atop Ohio/Pennsylvania by early Sunday
and led to much more QPF along that axis compared to other models
and other GFS runs. Then with the main upper low, surface low
pressure had some minor to moderate spread in its depth and
position. 00/06Z individual models were a bit farther north over
the Great Lakes compared to the ensemble means with the surface low
by early Monday, but the newer 12Z models have jumped south and
are more consistent with the means now. There is good model
consensus for this trough axis to start moving more quickly east by
midweek.

Farther west, there is good agreement for northern stream upper
ridging to be atop the Northwest over the weekend, expanding and
moving east across the Intermountain West gradually next week as a
trough may reach the West Coast by Tuesday or Wednesday. A southern
stream low offshore California to start the period on Saturday
looks to shrink/weaken but perhaps drift inland early next week,
with more uncertainty.

The WPC forecast used a multi-model deterministic blend of the 00Z
GFS/ECMWF/UKMET/CMC for the weekend forecast. As the period
progressed, included some GEFS and EC ensemble means in the blend,
but was able to maintain a majority of deterministic models even
through Day 7 due to the broad scale agreement. Changes to the NBM
and continuity included less QPF in the Southeast overall and more
QPF/PoP in the southern Plains due to newer model trends.


...Weather/Hazards Highlights...

A frontal system will be working through the Northeast at the
start of the period Saturday, with above average moisture (likely
from the Gulf and Atlantic) and instability pooling along and ahead
of it. This should produce some convection possibly with heavy
rain rates over an inch per hour that could cause flash flooding
concerns over typically sensitive areas like terrain in the
Northeast. Thus a Marginal Risk is in place in the Day 4/Saturday
ERO in eastern New York into northern New England. This trend was
farther north than than the previous outlook showed.

This front will stretch back through the Lower Ohio/Tennessee
Valleys, Lower Mississippi Valley, and into the southern Plains.
Ample moisture and high instability is likely across this southern
tier with upper level support at the base of the trough. Rain and
thunderstorms are likely to be widespread with these parameters in
place. The Storm Prediction Center continues to show the potential
for severe weather Saturday across the south-central Plains east
into the Southeast. Meanwhile there is a threat for flash flooding
in much the same areas, but perhaps reaching the southern
Appalachians. The Day 4/Saturday ERO indicates a Marginal Risk,
with an embedded Slight along the Red River into the Ark-La-Tex
where convection may be ongoing Saturday morning, with another
round Saturday night. This Slight was shifted just a bit south
compared to the previous issuance per newer guidance. Did think it
was best to break the Day 4 Marginal Risk that previously stretched
across the central/northern Appalachians and remove those areas,
as rain there is generally expected to be less than half an inch
and not cause flash flooding concerns.

Into Sunday, the front will progress more quickly offshore of the
Northeast, but linger across the southern tier, pressing slightly
southward especially in the Southeast. A Day 5 Marginal Risk is in
place across the Lower Mississippi Valley and Southeast, with an
expansion back west across the southern Plains where models
indicate yet another MCS. Will continue to monitor if/how heavy
rain overlaps with previous days, with the ground being more
sensitive in areas where there has already been heavy rain ,
leading to enhanced flooding concerns. In other words, eventual
upgrades to Slight Risks are certainly possible especially where
antecedent conditions allow for it, and if/where models converge on
placement of heavy rain rates.

Meanwhile, another frontal system will track across the
Midwest/Great Lakes for some modest rain there over the weekend,
reaching the Northeast by Monday and Tuesday. The current forecast
continues to show the leading front dissipating while this
secondary front becomes dominant. The second front settling south
will once again promote rain and thunderstorms across the southern
Plains and Southeast through the first half of next week as the
moisture and instability lingers.

The trough aloft centered in the east-central U.S. will generally
lead to average to slightly below average temperatures there.
However, southern Texas will be a few degrees above already hot
averages, reaching well into the 100s with heat indices possibly
above 110F. But the largest temperature anomalies will be across
the Northwest U.S. through the weekend into early next week
underneath mean upper ridging. Temperatures are forecast to be 15
to 25 degrees above average across much of the Northwest, with
highs reaching well into the 90s in interior areas. Even cities
like Seattle look to reach the mid to upper 80s. Above normal
temperatures will stretch into the central Great Basin, and the
Desert Southwest can expect temperatures well into the 100s to 110
degrees. For safety information, see weather.gov/heat.


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



$$