134
FXUS02 KWBC 061857
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 PM 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...

There remains some agreement on the large scale pattern featuring
a reloading Eastern U.S. trough and Western U.S. ridging eventually
pushing eastward, but plenty of uncertainty in the details. Run to
run continuity regarding a compact upper low over west-central
Canada continues to pose a problem. Models have flip flopped
between whether that energy gets pulled southward with the larger
Ontario/Quebec upper low or if it stays totally separate and
eventually gets pushed north and east with additional energy into
the Northwest/Northern Rockies. Through the 00z/06z guidance,
models were showing better agreement for it to hang back over
Canada, but recent 12z runs today (available after forecast
generation time) suggest it could get pulled more southward into
the north-central U.S.. So confidence is the details of this
remains very low. Otherwise, lots of uncertain timing of initial
energy through the Northwest Sunday-Monday and again as the main
East Pacific trough moves into the Coast late period. This impacts
how fast the upper ridge over the West moves out into the Plains.
The Gulf Coast and Florida remains an issue mid to late week
regarding strength/presence of upper troughing/shortwave energy and
weaker impulses.

Was able to use a general blend of the deterministic guidance to
get a good starting point for the first half of the period, but
given the new 12z guidance, even that forecast is low confidence.
Increased the ensemble means late period to about 50 percent of the
blend to help mitigate the differences in the deterministics.
Overall, maintained good continuity 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 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 still with
enough uncertainty to preclude a Slight Risk at this point. Farther
east, the placement of embedded heavier convection also 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 with some aid
from weak upper level impulses/energy.

The mean ridge in the West will continue to cause much warmer than
average temperatures, 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 next
week.


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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