Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Sat Sep 23 2023

Valid 12Z Tue Sep 26 2023 - 12Z Sat Sep 30 2023

...Overview...
The pattern through the middle to late parts of next week features
an amplifying upper trough over the Northwest through the entire
western U.S. with a downstream omega high centered over Ontario
before drifting east.


...Guidance Evaluation/Predictability Assessment...
Reasonable agreement among global guidance continues through
through Thursday with the 06Z GFS more amplified with the
Northwest trough. Thereafter, the 00Z ECMWF and 06Z GFS maintain
an amplified trough/becoming a closed low by the weekend. The 00Z
Canadian continues to flatten out the mid-level flow and be more
progressive to the northern Plains. The initial blend is a fairly
even blend of the 00Z ECMWF/UKMET/Canadian, and 06Z GFS through
Day 5. After Thursday morning, the blend increasingly relied on
the 00Z ECENS/06Z GEFS. QPF grids are from the 13Z NBM enhanced
with the ECMWF/GFS through about Day 5, then mainly the NBM for
Days 6/7 given increased uncertainty.


...Weather/Hazards Highlights...
No Excessive Rain Outlooks for Days 4/Tuesday or 5/Wednesday at
this time.

An early season storm system will bring active weather to the
Pacific Northwest through next week. Rounds of heavier
precipitation are expected, favored for the coastal regions and
upslope areas of the Washington and Oregon Cascades. However,
given current drought conditions and generally lower rainfall
rates suggests no excessive rainfall outlooks are needed.

A stalled front over the Florida Peninsula through much of next
week will bring periodic heavy rains Tuesday into next weekend. A
particular focus area will need to be looked for, but as of this
time there is insufficient confidence to warrant an excessive
rainfall outlook.

Increased ridging over the center of the country and troughing
farther west, will make for an increasing temperature trend in the
Plains/Great Lakes and decreasing across the West. Below normal
temperatures over the Mid-Atlantic States can be expected through
midweek before moderating on approach of the ridge.


Jackson/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