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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1900Z Mar 30, 2023)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Mar 30 2023

Valid 12Z Sun Apr 02 2023 - 12Z Thu Apr 06 2023

...Strong Plains through Upper Midwest storm early-mid week to
bring strong winds, northern Plains snow, heavy rainfall and
severe thunderstorms from the South into the Ohio Valley...

...Synoptic Overview...

The strong storm system over the eastern U.S. in the short range
period should be over eastern Canada by Sunday morning with
improving weather for the East Coast to conclude the weekend as a
surface high moves in from the west.  A progressive surface low
tracking eastward along the U.S./Canada border through Monday will
bring a colder airmass behind it across the northern Plains for
the beginning of the week.  The main weather story next week will
be the development of another strong low pressure system tracking
from the central High Plains northeastward as a potent upper
trough ejects from the western U.S.  By Wednesday-Thursday this
low may follow a path a little northwest of the one expected this
Friday/Saturday.  This storm should bring a broad area of
significant/hazardous weather to areas from the Rockies eastward
and a large area of well below normal temperatures in its wake,
from the West through the northern Plains.  In contrast, upper
ridging over the Gulf Coast should build northward over the
eastern U.S. and support anomalous warmth ahead of the storm's
associated cold front.

...Model Guidance/Predictability Assessment...

The 00Z/06Z guidance generally showed additional consolidation
from the prior cycles with respect to trends for handling upstream
North Pacific/Alaska flow and resulting effects on the amplifying
western U.S. upper trough along with subsequent ejection and
central U.S. storm evolution.  Latest consensus has the upstream
energy dropping into the back side of the larger scale trough in
sheared fashion, delaying ejection a bit compared to some guidance
in previous days.  New 12Z runs have nudged a bit stronger again
with this incoming energy but not nearly to the extent of what had
been a stronger/closed cluster.  The end result is gradually
improving clustering for the timing and track of the overall
system lifting northeastward across the northern tier by midweek. 
The new 12Z CMC is still a tad on the slower side but not to the
degree seen in the 00Z run.  Based on other guidance through 06Z,
an average among the slower or westward GFS/GEFS and faster
ECMWF/ECMWF mean seemed reasonable given recent guidance
spread/variability and typical errors by 5-7 days out in time. 
Behind this system there is a general consensus on some lingering
troughing over the West but with uncertainty in the details.   

By mid-late week a lot of model and ensemble member spread
develops for flow details over the eastern Pacific/West Coast. 
Operational GFS/CMC runs have been showing more pronounced
shortwave energy nearing the West Coast, with other models/means
suggesting this energy will be somewhat weaker and/or slower.  The
new 12Z GFS has trended to a less amplified shortwave while the
12Z GEFS mean/CMC hold onto more ridging into Thursday.

A operational model blend (with ECMWF input split between the 00Z
and 12Z/29 runs) provided a reasonable depiction of significant
features for about the first half of the period.  The forecast
then transitioned toward a blend of ECMWF runs/06Z GFS along with
the 06Z GEFS/00Z ECMWF means to depict an intermediate
track/timing for the northern tier into eastern Canada storm while
accounting for the guidance spread near the West Coast late in the

...Weather/Hazards Highlights...

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/Sierra Nevada 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 and significant snow may
reach central and northern portions of the Sierra Nevada by early
next week.  Also expect a period of heavy snow to extend across
favored terrain from the Great Basin eastward into the Rockies
during Sunday-Monday.  Well ahead of this system, a southern
stream shortwave interacting with a Gulf Coast warm front along
with sufficient moisture/instability may produce some locally
heavy rainfall from eastern Texas into the Lower Mississippi
Valley with the Day 4 Excessive Rainfall Outlook (12Z Sunday-12Z
Monday) depicting a Marginal Risk area across this region.  Some
of this activity could extend eastward into daytime Monday but
with too much uncertainty in details for a risk area at this time.
 There are also some signals that a stalling front over the
Midwest/Lower Great Lakes could begin to focus increasing rainfall
but again with enough ambiguity on the threat to preclude any risk
area in the Day 5 (12Z Monday-12Z Tuesday) outlook.

The big headline will be the deepening Plains low that develops
along a strong frontal boundary early next week.  Numerous showers
and thunderstorms are likely to make a return to locations from
the central Gulf Coast to the Ohio Valley Tuesday night and
especially into Wednesday as this storm system gets better
organized across the central Plains and advects copious Gulf
moisture northward.  Also the threat of strong to severe storms is
increasing in the expansive warm sector, with the Storm Prediction
Center already monitoring that possibility on Tuesday.  At the
same time recent model runs maintain/add confidence for the idea
of a significant cold sector snow event northwest of the low
track, with probabilities for at least three inches of snow
steadily increasing along an axis from eastern Wyoming across much
of South Dakota/portions of North Dakota and then northern
Minnesota Monday night into Wednesday.  Heavy snow will be
possible within portions of this band.  This storm will also
produce strong winds, with best potential for the highest wind
speeds extending from the Southwest through southern High Plains
and northward through the northern Plains.  Other areas farther
east may see brisk to strong winds even if to a less extreme

A pronounced temperature contrast will develop across the nation
early-mid week with well below average readings spreading across
much of the western U.S. and central/northern Plains, and well
above average temperatures expanding from the southern Plains/Gulf
Coast through much of the eastern U.S.  Tuesday-Wednesday look to
be the coldest days versus normal over the West/Plains with some
areas seeing highs 20-30F below normal.  The reverse will hold
true over the southern Plains early in the week and farther
eastward thereafter, with highs generally 10-20F above normal and
lows 15-25F above normal.  Daily records mainly for cold highs
will be possible over the West during the first half of the week. 
Farther east in the warm sector, Tuesday-Thursday will offer the
best potential for some daily records, with warm lows tending to
be more numerous than record highs.


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, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are