308
FXUS02 KWBC 250649
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Wed Sep 25 2024

Valid 12Z Sat Sep 28 2024 - 12Z Wed Oct 02 2024

...Pattern Overview and Guidance/Predictability Assessment...

Models and ensembles have come into better overall agreement from
the weekend into early next week. This generally includes the
latest guidance from the 00 UTC cycle. A blocky split flow pattern
develops across much of the country as highlighted aloft by a
warming Rockies/Southwest ridge and a low/trough lifting over the
Canadian Maritimes that sandwich a cutoff low settling over the
Mid-South. Post Tropical Cyclone Helene will weaken into the
weekend over the Mid-South entrained into the cutoff low, but
remains a slow translation rainfall/runoff threat there and with
trailing back moisture into the south- central Appalachians.

Meanwhile, forecast spread is less then stellar over time with
more progressive and energetic flow overtop from the northeast
Pacific through the Northwest and downstream. Guidance varies with
extent of potential southeastward digging of upper trough energy,
modest to moderate rain focusing wavy frontal surges and post-
frontal drying/cooling through the north-central/Midwest and
eastern U.S. into next week, replacing/kicking the leading Mid-
South cutoff low and lingering tropical moisture signature.

Overall, a composite of compatible guidance of the
GEFS/ECMWF/Canadian ensemble means, the National Blend of Models
and WPC continuity seems to offer a good compromise forecast,
albeit will smoothed detail through medium range time scales.

...Weather/Hazards Highlights...

The WPC Day 4/Saturday and Day 5/Sunday Excessive Rainfall Outlooks
show lingering and elongated Marginal Risk threat areas from the
Mid-South with pooled tropical moisture around the post-tropical
remains of Helene and with a trailing/lingering deepened moisture
back through the south-central Appalachians and onward with a
trailing wavy and slow moving front down over central Florida.
More certain local focus closer to occurrence may lead to Slight
Risk issuance upgrades given Helene moisture, especially given
earlier period heavy rainfall will create saturated soils.

Schichtel


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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