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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1900Z Feb 28, 2024)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Feb 28 2024

Valid 12Z Sat Mar 02 2024 - 12Z Wed Mar 06 2024

...Heavy Snow and High Wind Threat for the Western and
North-Central U.S...
...Wet Pattern for the West Coast and The South...

...Guidance/Predictability Assessment...

A previously uncertain trough pattern in the East Pacific/Western
U.S. for this weekend has come into better focus over the last 24
hours. Thus, a general model blend consisting of the deterministic
00z EC/CMC/UKMET and 06z GFS was used for days 3 and 4. The Euro
tilts the trough negatively and flattens out into a long wave by
day 5. The GFS and UKMET evolve the trough into a wound up closed
low over south-central Canada/Northern Plains, while the ensemble
means depict a negatively tilted trough over the Central U.S. with
notable spread for a day 5 forecast. Therefore, the 00z ECE and
06z GEFS were introduced to the blend to mute some of the
inconsistencies displayed by the deterministic EC and CMC. On day
6, the ensemble means develop a notable amount of timing spread
with respect to the wound up upper low over southern Canada as
well as potential embedded energy responsible for heavy rainfall
over the Gulf Coast/Southeast. The 00z CMCE is introduced on day 6
and the ensembles make up almost the entire blend by day 7 with
plenty of uncertainty with respect to the trough pattern over the
West Coast.

...Overview and Weather/Hazards Highlights...

The main weather story concerns the evoltion of amplified upper
troughing set to dig into the eastern Pacific later this week and
then shift earnestly over the West this weekend. This and
subsequent but uncertain additional/varied Pacific systems will
support multiple chances for locally moderate precipitation foci
into the Pacific Northwest over this forecast period. A leading
long fetch moisture plume/Atmospheric River will shift down the
coast through southern California into Saturday while easing. The
WPC Day 4/Saturday Excessive Rainfall Outlook shows a Marginal
Risk area. There is also a significant threat for high winds and
very heavy snow to spread inland across the Intermountain West and
Rockies, especially for favored terrain/mountains as highlighted
in the WPC Winter Weather Outlook (WWO). Confidence continues to
increase in the risk for moderate to extremely disruptive high
snowfall rates/blowing snow, particularly for the Sierra Nevada.
Additionally, valley snowfalls may develop more over time as snow
levels decrease with upper system and wavy frontal push.  This
translation should also favor development of an emerging
precipitation shield over the cooling Rockies/Plains by
Sunday/Monday with Plains cyclo/fronto genesis. This may lead into
a chance for heavy wrap-back snows in quite windy flow across the
Northern Plains and Upper Midwest with Plains cyclogensis and the
digging of cold Canadian air southward in the wake of this main
system, as per the WWO. Downstream, widespread
showers/thunderstorms look to develop across the
Plains/Mississippi Valley then east-central U.S., with eventual
possible focus over vicinity of the Gulf Coast States into

A leading southern stream upper trough will finally exit the East
Coast Saturday to prompt modest/uncertain coastal frontal lows,
with a wavy trailing front with continued rain/showers lingering
back across the Southeast and the Gulf of Mexico. Uncertain but
gradually improving moisture return from the Gulf of Mexico and
lingering onshore fetch from the Atlantic may again combine to
fuel renewed areas with enhanced rain/convective chances broadly
over the South to monitor for any local runoff issues early next
week with downstream progression and direction of the active upper
flow pattern out from the West

Pacific upper trough amplification and inland progression this
weekend will cool temperatures over much of the West, leading to
the spreading of values as cold as 15 degrees below normal.
Downstream, expect much above normal pre-frontal warmth later week
over the north-central U.S. that will spread to much of the
central and eastern U.S. this weekend/early next week downstream
of the main upper trough position and associated frontal systems.
Pre-frontal springlike conditions for much of the central to
eastern U.S. will feature minimum and maximum temperatures ranging
upwards to 20-30+ degrees above normal over the Midwest/Great
Lakes to again challenge record values.


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:

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: