Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Fri Sep 22 2023

Valid 12Z Mon Sep 25 2023 - 12Z Fri Sep 29 2023

...Overview...
The pattern features an upper trough moving into the West and a
downstream Omega Block evolving into a Rex-like Block across the
eastern portion of North America and the adjacent northwest
Atlantic.


...Guidance Evaluation/Predictability Assessment...
The guidance shows reasonably good agreement.  For the 500 hPa
heights, pressures, winds, and QPF, used a compromise of the
deterministic 12z UKMET, 12z Canadian, 12z ECMWF, and 18z GFS
early before utilizing increasing amounts of the 12z ECMWF/12z
NAEFS ensemble means.  The remainder of the grids were more
heavily weighted on the 01z NBM.


...Weather/Hazards Highlights...
An early season storm system will bring unsettled and active
weather to the Pacific Northwest beginning late this weekend and
through early next week. A few rounds of heavier precipitation are
likely, favored for the coastal regions and upslope areas of the
Washington and Oregon Cascades into northern California/southwest
Oregon where some localized flooding may be possible with
repeating rounds of moderate rainfall, particular in burn
areas/burn scars near the western border of CA/OR Monday into
early Tuesday.

A fading front dropping into the southern Plains/western Gulf
coast is expected to reinforce the polar front across the Gulf of
Mexico as the parent upper trough slowly progresses from the
Midwest into the Southeast and lead to the potential for heavy
rainfall Monday into early Tuesday.  Rainfall could be excessive
in areas that have been wetter than average this past week and in
around portions of south-central and southeast TX.  The volume of
rainfall near and east of the Appalachians mid to late next week
remains a question mark as the guidance shows a variety of
possible scenarios.

Temperatures should be most above average across portions of the
Plains/Midwest -- moreso on overnight lows -- and below average
across portions of the Mid-Atlantic States and West, which will be
most noticeable for daytime highs.

Roth


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, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key
Messages are at:

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