868
FXUS02 KWBC 060657
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Thu Jun 6 2024

Valid 12Z Sun Jun 09 2024 - 12Z Thu Jun 13 2024

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


...Overview...

Into early next week, upper troughing is forecast for the eastern
U.S., which may get renewed into the middle of next week with
another shortwave. Periods of upper ridging are likely for much of
the western and central U.S., though could be disrupted by
shortwave energies at times. Warm to hot temperatures will continue
across the West during the medium range period, though moderated a
bit compared to the short range. A front should focus moisture
near the Rockies early next week, causing showers and storms there
and farther east across the southern tier. Rounds of rain and
storms are also possible across the Eastern Seaboard next week, and
heavy amounts may come into Florida by Tuesday-Wednesday.


...Guidance/Predictability Assessment...

Model guidance is finally coming into somewhat more reasonable
agreement with the forecast features described above. An upper low
meandering around Ontario/Quebec to start the period Sunday and
shortwave energy coming through the southwestern side will push
troughing through the eastern U.S. early in the week, with some
uncertainty for when it pushes into the western Atlantic around
midweek. For the past couple of model cycles, models have been more
agreeable with the track and timing of a shortwave likely forming
a closed low moving across south-central Canada, which looks to
combine with a shortwave moving through the Northwest Sunday to
expand troughing into the north-central U.S. by around Tuesday and
providing better predictability for a low/pressure frontal system
associated with it. This pushes into the eastern U.S. by Wednesday-
Thursday with typical levels of spread. Meanwhile in the West,
models continue to show support for mean ridging, though disrupted
on the northern side with the northwestern to north-central U.S.
shortwave mentioned above Sunday-Monday. By Wednesday-Thursday the
ridge may slowly be pushed east into the central U.S. as a larger-
scale upper low moves through the northeastern Pacific (with some
spread in timing/placement) while a southern stream upper low also
approaches the Southeast.

The WPC forecast was based on a blend of the 18Z GFS, 12Z ECMWF,
and 12Z CMC early in the forecast period. Included the GEFS and EC
ensemble means by Day 5 and increased their proportion to almost
half by the end of the period as spread increased.


...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 into Sunday, with a surface front helping to focus
showers and thunderstorms in an environment with plenty of
instability. For the Day 4/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. The
faster movement of the front will mostly preclude excessive rain
there, but the front continuing to stall across the central Rockies
to southern High Plains may produce additional rounds of
convection with potential for heavy rain rates, so a Marginal Risk
is delineated for Day 5/Sunday in those areas. Rounds of rain are
also possible for the Eastern Seaboard as fronts come through. The
heaviest rain is likely across Florida into Tuesday-Wednesday as
well above moisture pools along the stalling front.

The mean ridge in the West will continue to cause much warmer than
average temperatures there, albeit not quite as hot as in the
short range period. The highest temperature anomalies of 10-20F
above normal are forecast for the Great Basin, warming a bit and
expanding eastward as the week progresses into the northern Rockies
and Plains. Temperatures will also rise a few degrees in the
Desert Southwest to bring temperatures back above 110F in some
places. Meanwhile, most areas east of the Rockies should trend to
slightly below normal behind the cold front. Warmer than average
temperatures that could set daily records in the Florida peninsula
into Sunday will eventually moderate as rain chances increase.


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



$$