FXUS02 KWBC 231858
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Wed Oct 23 2024

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

...General Overview...

A predominantly zonal pattern across the mainland U.S. will give
way to a more amplified pattern by next week. The prevailing
tranquil weather this weekend across much of the country will
become more unsettled across the western U.S. with periods of rain, high-
elevation snow and gusty winds. The trough that brings the
unsettled weather in the West early next week will likely be
pushing east against a warm high pressure system in the eastern
U.S., resulting in a sharp and wavy frontal boundary to drape
across the mid-section of the country where bands of moderate to
locally heavy rain appear possible.


...Guidance/Predictability Assessment...

Models are in reasonable agreement regarding the overall synoptic
pattern across the CONUS through the medium range period. The main
discrepancy among the guidance suite has to do with the timing of
the western U.S. trough and the associated precipitation. The
ECMWF and CMC tend to be faster with the eastward progression of
the trough compared with the GFS. Nevertheless, the spread is
relatively small given the predicted depth of the trough even out
to Day 7.

Therefore, the WPC medium-range forecasts are based on a general
consensus of 40% 00Z ECMWF/EC mean, 40% 06Z GFS/GEFS, and 20% 00Z
CMC/CMC mean, with higher percentages from the ensemble means for
Day 6 & 7. This blend yielded a solution that compares well with
the previous WPC forecasts.


...Weather/Hazards Highlights...

A cold front ahead of a closed mid-level low over the Gulf of
Alaska will reach the Pacific Northwest this weekend. This cold
front will gradually work its way through much of the western U.S.
by midweek next week, bringing unsettled weather with periods of
rain and lowering of snow levels across the higher elevations
behind the front along with gusty winds. The Pacific Northwest
will see the precipitation moving through this weekend, followed by
the northern to central Rockies early next week, with some snow
lingering over the central Rockies by midweek. With the passage of
the cold 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.

Meanwhile, an upper ridge with a broad southerly return flow at the
surface behind a large high pressure system will promote
increasingly warm temperatures first across much of the Plains this
weekend and especially by Monday. The warmth will then expand
eastward to encompass much of the Great Lakes into New England by
Wednesday.

The trough that will bring the unsettled weather across the West
will be pushing east against the warm high pressure system in the
eastern U.S., resulting in a sharp and wavy frontal boundary to
drape across the mid-section of the country by midweek. There is
some signal for an organized moderate to heavy rain event to unfold
over parts of the lower Missouri Valley into the upper Midwest
midweek if a low pressure wave is able to consolidate and remains
relatively slow-moving along the front, where bands of moderate to
locally heavy rain with embedded thunderstorms could develop
midweek.

In addition, some locally strong Chinook winds are possible as
modest cyclogenesis is currently forecast to occur on the lee side
of the northern Rockies late Sunday into Monday, as well as across parts
of the Intermountain West behind the cold front as far south as
interior southern California.


Kong


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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