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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 2001Z Mar 29, 2023)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
401 PM EDT Wed Mar 29 2023

Valid 12Z Sat Apr 01 2023 - 12Z Wed Apr 05 2023

...Synoptic Overview...

Strong low pressure tracking from the Great Lakes through northern
New England into southeastern Canada this weekend will provide the
first weather headline of the period.  The upper trough associated
with this low will be quite progressive and the majority of
significant weather should exit the East Coast by Sunday morning,
though brisk winds could persist a little longer over New England.
 Meanwhile, energy ahead of the next upper level trough/closed low
dropping down from the Gulf of Alaska should reach the Pacific
Northwest by Saturday, and then the larger scale trough will
likely settle in over the West through early next week.  This
system will bring another cold front across much of the western
U.S. to reinforce the cool weather pattern and support multiple
days of rain and potentially heavy mountain snow from the Pacific
Northwest and northern California into the northern-central
Rockies.  This latter western system should support strengthening
surface low tracking from near the central Plains northeastward by
Tuesday-Wednesday, bringing another episode of cold sector snow,
warm sector rain/thunderstorms with some severe potential, and
strong winds over some areas.  Pattern uncertainty originating
from the North Pacific ultimately reaches the eastern
Pacific/western U.S. by next Tuesday-Wednesday, with some
influence on the timing/evolution of the expected central U.S.

...Model Guidance/Predictability Assessment...

A blend of 00Z/06Z models provided a reasonable depiction of
significant features for about the first half of the period. 
Guidance is fairly well clustered for the strong storm tracking
northeastward from the Great Lakes on Saturday while a model
average provides good continuity for the system tracking along the
U.S.-Canadian border.  For this latter system, the ECMWF/ECMWF
mean continue to lean on the faster side of the spread and the CMC
is on the slower side, with other solutions generally in the
middle to slower half of the spread.  The GFS becomes somewhat
faster/weaker than most other guidance with a southern tier
shortwave that could play a role in the rainfall forecast along
and north of the Gulf Coast.

By the early to middle part of next week, initial divergence of
the GFS/GEFS mean from most other guidance over and near the North
Pacific ultimately leads to significant pattern differences over
the eastern Pacific/western U.S.  Specifically, the GFS/GEFS mean
remain sheared with energy flowing southeastward from Alaska as
upper ridging builds into the eastern Pacific while the 00Z
ECMWF/CMC and their means (plus the 00Z UKMET through the end of
its run) suggest that the Alaskan energy will form an upper low
that reaches the northwestern U.S. while the Pacific ridge stays
farther westward.  Downstream impacts are for the GFS/GEFS to be
slower than the majority with the expected central U.S. storm
system along with somewhat later deepening.  Even with these
differences, the ensemble means as a whole have trended noticeably
deeper at the surface and aloft to provide increasing confidence
in the potential for a significant storm even though details are
more of a question mark.  Given the split of the guidance, along
with continuity that was closer in principle to the majority ECMWF
cluster, the updated forecast tilted more in that direction. 
Minority GFS/GEFS input transitioned to the 00Z run that was a
little closer to the other guidance versus the 06Z cycle.  Among
new 12Z guidance, the UKMET has made the most pronounced change as
it has switched to the GFS camp even though some of its upstream
details differ some from the GFS.  The CMC still falls in line
more with the 00Z ECMWF cluster.  However, the new 12Z ECMWF has
shifted more in the GFS direction, so the most likely scenario is
definitely in flux at the moment. 

...Weather/Hazards Highlights...

The strong low pressure system tracking from the Great Lakes to
southern Quebec will continue to result in impactful weather
across much of the East Coast on Saturday ahead of a quick moving
cold front.  Although the worst of the weather should occur on
Friday, there should still be enough forcing and instability
across the Southeast and parts of the Mid-Atlantic to fuel a
broken line of showers and thunderstorms, and should weaken going
through the day on Saturday.  However, it will likely be windy for
much of the eastern U.S. owing to a strong pressure gradient in
place.  Windy conditions may also continue into Sunday for New
England on the backside of the departing surface low.  Snow
showers are likely for the Upper Peninsula of Michigan and far
northern portions of Maine, and then some snow on the backside of
the low across northern New York and into northern Vermont and New
Hampshire Saturday night.  In terms of excessive rainfall
potential, it appears the threat of heavy rainfall and flooding
has decreased for the new Day 4 period (12Z Saturday-12Z Sunday),
with now a smaller Marginal Risk area across portions of the far
Southeast with some locally heavier rainfall on the southern end
of the front.  Progression should keep overall rainfall totals
from becoming too high but intense rainfall for a brief period
could still pose localized issues over areas that have recently
had heavy rain.  For the Day 5 outlook (12Z Sunday-12Z Monday), a
Marginal Risk exists from eastern Texas into the Lower Mississippi
Valley where return flow from the western Gulf increases moisture
and instability, with a stationary front beginning to lift north
as a warm front to provide some added focus.

Elsewhere across the nation, reloading of upper level troughing
over the northwestern U.S. by the weekend and continuing into
early next week will support multiple days of rain/mountain snow
with terrain enhancement from the Pacific Northwest and northern
California into the northern and central Rockies, with the
moisture shield pushing gradually farther southeast with time. 
Heavy snow is likely for the Cascades and the Olympic Mountains
where a few feet of snow accumulation is expected at higher
elevations.  Significant snow may reach the Sierra Nevada by early
next week.  Showers and thunderstorms are likely to make a return
to locations from the central Gulf Coast to the Ohio Valley again
Tuesday night and into Wednesday as the next storm system gets
better organized across the central Plains.  Recent model runs
suggest this could also be a significant event with heavy snow
northwest of the low track, with probabilities for at least 0.25
inch liquid in the form of snow steadily increasing along an axis
from the north-central High Plains northeastward.  Strong to
severe storms will be possible in the warm sector, with the Storm
Prediction Center already monitoring that possibility over the
east-central U.S.  Meanwhile the best potential for strongest
winds with this system extends from the southern Rockies/High
Plains into the Upper Midwest, with a much broader area of brisk
to windy conditions also possible over the central/eastern U.S.

Much of the western U.S. will continue to have cooler than normal
temperatures for most of this forecast period as the next upper
level trough becomes anchored over the region, though with some
uncertainty over details of trough progression/possible
replacement late in the period.  The best potential for highs 15
to 25 degrees below normal will be early-mid week from the Great
Basin to the Dakotas.  Scattered record cold highs may be
possible.  Upper level ridging extending from a Gulf of Mexico
upper high should maintain warm and humid conditions across the
south-central U.S. and extending into the East Coast region on
Saturday, with highs generally 5-15F above average and lows around
15-20F warmer than normal.  After a brief cooling trend, above
normal temperatures should again return to the central U.S. on
Sunday and into the rest of the East by Monday-Wednesday. 
Tuesday-Wednesday will offer the best potential for some daily
records, with warm lows tending to be more numerous than record
highs (which should be over parts of the South on Tuesday and
mainly the Florida Peninsula on Wednesday). 


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

- Heavy snow across portions of the Pacific Northwest and the
Northern Great Basin, Sat-Sun, Apr 1-Apr 2.
- Heavy snow across portions of the Northern Rockies and the
Northern Great Basin, Sat, Apr 1.
- Heavy snow across portions of the Central Great Basin, Mon, Apr
- Heavy snow across portions of the Central Rockies, the Central
Plains, and the Northern Plains, Mon-Tue, Apr 3-Apr 4.
- Heavy snow across portions of the Great Lakes, the Upper
Mississippi Valley, and the Northern Plains, Tue, Apr 4.
- Severe weather across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee Valley, the Great Lakes, the
Middle Mississippi Valley, the Southeast, the Southern Plains, and
the Ohio Valley, Tue, Apr 4.
- Flooding possible across portions of the Southeast and the Ohio
- Flooding occurring or imminent across portions of the Southeast,
the Middle Mississippi Valley, the Lower Mississippi Valley, and
the Ohio Valley.
- Flooding likely across portions of the Southeast and the Ohio
- High winds across portions of the Central Plains, the Central
Rockies, the Central Great Basin, the Southern Rockies, the
Southern Plains, and the Southwest, Mon-Tue, Apr 3-Apr 4.
- High winds across portions of the Central Plains, the Middle
Mississippi Valley, the Southern Plains, the Upper Mississippi
Valley, and the Northern Plains, Tue, Apr 4.
- High winds across portions of the Central Plains, the Upper
Mississippi Valley, and the Northern Plains, Tue-Wed, Apr 4-Apr 5.
- Enhanced wildfire risk across portions of the Southern Plains,
Mon, Apr 3.

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are