Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Sun Oct 13 2024

Valid 12Z Wed Oct 16 2024 - 12Z Sun Oct 20 2024


...Overview...

A pattern change is forecast by midweek in the West, as upper
troughing and then reinforcing energy come in from the eastern
Pacific, leading to much cooler temperatures and increasing
precipitation chances, including higher elevation snow. Upper
ridging ahead of this trough will promote warmer than average
temperatures in the northern/central Plains to Midwest as it
gradually moves east, eventually displacing the chilly upper trough
and surface high in the East by late week into next weekend.


...Guidance/Predictability Assessment...

The latest suite of model guidance are in reasonably good agreement
regarding the overall synoptic pattern across the CONUS during the
early stages of the medium range period (Wednesday--Thursday). The
deterministic Euro's progressive and phased trough pattern in the
West continues to be an outlier, compared to the UKMET, GFS and
Canadian suites which have persistently developed a cut-off
low/split flow upper-level pattern. Elsewhere, the deterministic
06z GFS develops a closed mid-level low over the Mid- Atlantic
Coast on Wednesday night, which deviates significantly from the
rest of the other pieces of guidance and is inconsistent with past
runs, which maintain a ridge over the East Coast next weekend.

A non-06z GFS blend, consisting of the 00z GFS/EC/CMC/UKMET were
utilized on days 3 and 4 due to reasonable agreement across the
CONUS. The 00z CMCE and 06z GEFS were introduced to the blend on
day 5, but the deterministic guidance still carried most of the
weighting in that blend. By day 6, the 00z ECE is incorporated into
the blend while the deterministic Euro is removed. The 06z GEFS
and 00z CMCE are favored through day 7.

...Weather/Hazards Highlights...

The developing and reloading upper trough and multiple surface
fronts moving into the West will push precipitation across the
Northwest Wednesday, with enhanced precipitation totals in terrain
like the coastal ranges and Cascades into the northern Rockies.
Higher elevation snow is likely, which will be the first snow of
the season in some locations given the warm Fall in the West thus
far. Precipitation is forecast to spread across the Intermountain
West and Rockies Thursday and Friday. By Friday and into the
weekend, Gulf moisture could stream in just ahead of the upper
trough for increasing rain chances in the Plains to Upper Midwest.
The forecast details vary, but models generally show some moderate
to locally heavy rain totals in the south-central Plains.

In the northeastern U.S., cool westerly flow underneath the upper
trough to start the period Wednesday will lead to some continued
lake-enhanced and terrain-enhanced precipitation across the
central/northern Appalachians and the Great Lakes region into the
Interior Northeast. Colder temperatures should allow for snow
especially in the higher elevations. Precipitation should taper off
by Thursday, and the East is likely to be dry for later week as a
cool surface high sets up behind a secondary cold front. The
exception could be across South Florida, which is forecast to see
return flow of moisture by late week for increasing rain and
thunderstorm chances.

An upper ridge aligned over the central U.S. midweek and shifting
eastward later week will promote well above normal temperatures in
its vicinity. The biggest anomalies are forecast across the
northern Rockies and High Plains on Wednesday, where highs into the
70s and 80s are 15-25 degrees above average for mid-October. These
warm temperatures will shift into the central/northern Plains and
Midwest by Thursday-Friday. Meanwhile, temperatures are forecast to
be below average by 10-20 degrees on Wednesday in much of the
eastern U.S. under cool high pressure. Morning lows may cause
frost/freeze concerns from the north-central U.S. through the
Midwest/Great Lakes and Northeast/Appalachians. Some gradual
moderation/warming is likely there Thursday-Friday and even more so
into the weekend when upper ridging comes overhead, for
temperatures around 5-10 degrees above normal in the northeastern
tier. On the other hand, the upper trough and frontal surges coming
into the West will lead to below normal temperatures spreading
gradually inland for the latter half of the week. These colder
temperatures may also lead to additional frost/freeze concerns for
still susceptible growing areas.


Tate


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