328
FXUS02 KWBC 051904
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
304 PM EDT Wed Jun 5 2024

Valid 12Z Sat Jun 08 2024 - 12Z Wed Jun 12 2024

...Warmer than average temperatures continue for the West into the
weekend and early next week, though less extreme than the short
range period...


...Overview...

A reloading upper trough will be present in the eastern U.S. this
weekend into early next week, while mean upper ridging is forecast
for the western U.S. (though disrupted at times by shortwave
energies). Warm to hot temperatures will continue across the West
during the medium range period, though moderated a bit compared to
the short range. The forecast pattern should support multiple
rounds of showers/storms over the central or south-central Rockies,
Plains, and Mississippi Valley as systems ride the ridge and
frontal boundaries help to focus moisture. Rain chances should
eventually reach the Southeast into next week. Meanwhile, periods
of light to modest rain are likely in the northeastern U.S.
underneath the slow-moving trough/low.


...Guidance/Predictability Assessment...

Latest model guidance continues to generally agree on the overall
large scale pattern across the CONUS during the medium range
period, but there are some key differences in the details even in
the early-mid period that will affect sensible weather. Energy
digging southward from the western side of the trough into the
north-central U.S. continues to pose problems and plenty of
uncertainty. The 06z GFS run was the greatest outlier suggesting a
much stronger upper low across the Upper Midwest, while the
ECMWF/CMC/UKMET all suggest a weaker and faster shortwave into the
East. The 12z GFS however did trend away from this scenario, though
some of the AI/ML models continue to show a stronger solution,
keeping confidence low still. Otherwise, still some differences in
energy from a northeast Pacific trough traversing through the
West/north-central U.S. and eventual interaction with reloading of
the Eastern U.S. trough later in the period.

The WPC forecast was based on a blend of deterministic models in a
non-GFS consensus early in the period, but increased the
proportion of ensemble means in the blend Day 6 and Day 7 given the
increasing uncertainty. Overall, this maintained good agreement
with the previous WPC forecast.


...Weather/Hazards Highlights...

Ample moisture from the Gulf and Pacific moisture advecting around
the upper ridge will combine across the southern/central Rockies
and Plains this weekend, with one or more surface boundaries
helping to focus multiple rounds of showers and thunderstorms in an
environment with plenty of instability. While there is still some
uncertainty in the exact placement of convection on any given day,
the ingredients are in place for heavy rain amounts and rain rates
that could cause flooding concerns. For Day 4/Saturday, a Slight
Risk in the ERO remains in place across the
Oklahoma/Kansas/Missouri/Arkansas intersection, as models continue
to show a heavy rainfall axis of 3-5 inches in these areas. The
Marginal Risk expands back into the central High Plains. By Sunday,
the cold front should press south a bit and shift the flooding
risk south with it. For the Day 5/Sunday ERO, have a broad Marginal
Risk from the southern/central Rockies east into the southern
Plains and into the Mid-South. Southern parts of the Rockies and
High Plains around northeastern New Mexico or so have shown the
greatest consistency in moderate to heavy rain amounts, but was not
confident that the impacts would rise to the Slight Risk level
there. Farther east, the placement of embedded heavier convection
remains uncertain as there is not a lot of run-to-run continuity.
But an embedded Slight Risk is possible somewhere across the south-
central U.S. on Sunday if models converge better on a location of
focus, and if it overlaps areas that have seen significant rains
recently. The front should continue to press southeast into Monday
and could spread rain chances to the Gulf Coast and Southeast,
particularly the Florida peninsula as the front stalls. After some
light showers in the interior West Saturday, weak upper troughing
farther north will bring in modest rain to the northern Rockies
Sunday and continue rain chances across the central/southern
Rockies Monday. Meanwhile, rounds of rain and possible
thunderstorms are expected across the Lower Great Lakes to the
Northeast underneath the upper trough. These rainfall amounts look
to be sub-Marginal Risk levels.

The mean ridge in the West will continue to cause much warmer than
average temperatures there, but by the weekend some southern
stream troughing disrupting the ridge should moderate temperatures
(and HeatRisk) somewhat in the Southwest compared to the short
range period. Higher temperature anomalies of 15-20F above normal,
locally higher, will be in the Northwest Saturday and just a touch
below that by early next week when a northern stream shortwave
moves through. By Tuesday-Wednesday the warm anomalies look to
expand back south as well as east into the northern Plains though.
Meanwhile, most areas east of the Rockies should trend to slightly
below normal behind the cold front. This will eventually include
Texas and Florida after a hot weekend, where highs several degrees
above normal may lead to some daily records.


Santorelli/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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