538
FXUS02 KWBC 100640
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
240 AM EDT Thu Oct 10 2024

Valid 12Z Sun Oct 13 2024 - 12Z Thu Oct 17 2024


...Overview...

Guidance continues to show development of an amplified ridge-
trough pattern over the lower 48, downstream from a deep system
just south of Alaska. A shortwave diving through the north-central
U.S. this weekend will begin the process of amplifying eastern U.S.
troughing and support a Northeast surface system, with multiple
trailing impulses helping to reinforce the trough. Much below
normal temperatures and frost/freeze may be a concern over some
areas from the northern Plains into the East. The front leading the
colder trend should suppress this weekend`s central-southern U.S.
heat that may continue to challenge daily records at some locations
early in the period. The upper ridge over the Rockies will support
persistent warmth over the Interior West and Rockies, focusing
more over the northern Rockies/High Plains toward the middle of
next week. Expect the leading edge of a Pacific trough to push a
front and some accompanying rainfall into the Northwest by next
week.


...Guidance/Predictability Assessment...

Models continue to show pretty good agreement on the amplified
trough-ridge-trough pattern during the medium range period, but a
lot of uncertainty in the details especially late period. The main
area of spread is over the East next Tuesday-Thursday with whether
or not deeper energy down the west side of the established trough
with close off an upper low. The CMC continues to hold on to a
cutoff upper low over the East next Thursday, and while in the
minority of solutions, not out of the realm of possibilities on
this evolution. At this time, looking at the rest of the guidance
and AI/ML models, there seems to be better support for a more
elongated trough but the timing is very uncertain. Yesterdays 12z
ECMWF did show a CMC- like cutoff low over the East, but the 00z
run tonight trended faster with the trough, more like the GFS. Run
to run variance in the deterministic guidance is huge still, so a
blend towards the ensemble means seems prudent at this time.

The WPC forecast for tonight used a blend of the deterministic
guidance for days 3-5, which despite some disagreement by day 5,
still served as a good starting point. Given the evolution
uncertainty days 6 and 7 with the East, trended more heavily
towards the ensemble means.


...Weather/Hazards Highlights...

A large part of the lower 48 will see fairly dry weather for a
majority of the period. The amplifying upper trough and
accompanying surface system affecting the East late this weekend
into early next week should produce some areas of locally enhanced
rainfall across parts of the Great Lakes/Northeast, with some
possibility for snow during the colder overnight hours. Little if
any instability and fairly modest moisture anomalies suggest that
short- term rain rates will likely not be high enough to pose a
flash flood threat. A front lingering near south Florida may bring
some showers/instability, and it`s possible a localized flash flood
threat could develop, but still a lot of uncertainty in rain
amounts. Therefore the new Days 4-5 Excessive Rainfall Outlooks
continue to show no risk areas. The next trough/front into the West
should spread modest rain and higher elevations snows into the
Northwest/Rockies but is not expected to be too impactful.

An upper ridge aligned over/near the Rockies for most of the
period will maintain well above normal temperatures over the
Southwest/Interior West into Rockies, and extending into the
northern High Plains toward midweek as the ridge shifts eastward a
little. The central/southern Plains should remain warm into Sunday
before northern stream troughing and a cold front suppress above
normal readings to the south/southeast. Greatest anomalies of plus
10-20F should be over the northern Rockies multiple days and
eventually the northern High Plains, as well as the southern Plains
during the weekend. Daily records will be possible from the
Southwest through the southern Plains this weekend. Meanwhile, the
East should trend colder with time toward highs 5-15F below normal
next Monday- Wednesday underneath amplified upper troughing.
Morning lows next week may be a tad less anomalous but still cold
enough to raise some frost/freeze concerns from the north-central
U.S. through the Midwest/Great Lakes and Northeast/Appalachians.

Santorelli


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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