FXUS02 KWBC 230726
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
326 AM EDT Wed Oct 23 2024

Valid 12Z Sat Oct 26 2024 - 12Z Wed Oct 30 2024

...General Overview...

Predominantly zonal flow across the lower 48 at the beginning of
the period (this weekend) will give way to a more amplified pattern
toward the end. A closed upper low over the Gulf of Alaska will
fill and dig into the West Coast of the CONUS this weekend. This
system will bring cool temperatures, rain and snow to the Northwest
U.S. through early next week before developing a threat for heavy
rainfall and thunderstorms over parts of the central U.S. by mid-
week. A pronounced downstream ridge will generate above average
temperatures across the Plains and Mississippi Valley beginning
Monday.

...Guidance/Predictability Assessment...

Models are in reasonable agreement regarding the overall synoptic
pattern across the CONUS during the medium range period. The
deterministic Euro and GFS guidance have trended slower with the
digging East Pacific trough next week, while the ensemble means
still have some timing spread. There's pretty good clustering of
the ensembles on the depth of the trough, though.

On days 3 and 4 a general model blend consisting of equal parts 12z
ECMWF/CMC/UKMET and 18z GFS were utilized due to the predominantly
zonal flow across the lower 48 and large ridge over the southern
tier states/northern Mexico. The 12z ECE/CMCE and 18z GEFS were
introduced to the blend on day 5 and continued through the end of
the period to mitigate some deterministic solutions that signal the
formation of a closed mid-level low over the Four Corners region
by mid-week. There's some signal for another split flow pattern
over the central U.S. on day 7.

...Weather/Hazards Highlights...

A cold front, associated with a closed mid-level low over the Gulf
of Alaska, will focus rain and high elevation mountain snow
showers across much of the Pacific Northwest and Northern Rockies
this weekend. Snow showers will remain confined to the northern
Cascades and Olympic Mountains before expanding into the southern
Cascades and Northern Rockies on Sunday, the northern Sierra and
Yellowstone/Absarokas on Monday and Colorado Rockies by Tuesday.
Beneath the upper trough, temperatures will be well below average.
Portions of the Great Basin and Intermountain West may experience
minimum temperature anomalies between 10-20 degrees below average
from Monday to Wednesday.

Cyclogenesis is likely to occur on the lee side of the Rockies
while the digging upper-trough pulls moisture from the Gulf of
Mexico beginning on Tuesday. Showers and thunderstorms may focus
along a cold front slowly propagating through the central U.S..
There's some signal for a heavy rain event to unfold over parts of
the Lower Missouri Valley into the Upper Midwest mid-week, due to
the slow moving upper-level trough.

An upper ridge over the southern and central U.S. will promote
above average temperatures across portions of the Great Plains and
Upper Midwest beginning this weekend. Parts of the Northern Plains
and Upper Midwest will experience positive temperature anomalies
between 10-20 degrees above average.

Kebede


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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