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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0749Z Mar 30, 2023)
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Extended Forecast Discussion...amended
NWS Weather Prediction Center College Park MD
349 AM EDT Thu Mar 30 2023

Valid 12Z Sun Apr 02 2023 - 12Z Thu Apr 6 2023

***Strong low pressure system develops over the Plains early next
week with heavy rain, strong winds, northern Plains snow, and
severe thunderstorms from the Deep South to the Ohio Valley***

...Synoptic Overview...

The strong storm system over the eastern U.S. in the short range
period should be over southeastern 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
tracks eastward along the U.S./Canada border through Monday with a
colder airmass settling in behind it across the northern Plains
for the beginning of the week.  The main weather story going into
next week will be the development of another strong low pressure
system as a potent upper trough from the western U.S. ejects
eastward across the Plains, spurring surface cyclogenesis over
eastern Colorado by Tuesday morning.  This low may follow a
similar path to the one expected this Friday/Saturday and cross
over the Upper Midwest on Wednesday and then over Ontario by
Thursday with a strong cold front trailing behind it.  The upper
ridge from the Gulf of Mexico builds northward across much of the
eastern U.S. ahead of this storm system and brings anomalous
warmth ahead of the front.

...Model Guidance/Predictability Assessment...

The 00Z model guidance suite has above average synoptic scale
agreement for this weekend and a general model compromise works
well as a starting point in the forecast process for Sunday and
Monday.  Developing differences with upstream Pacific/Alaska flow
start to influence progression of the upper trough moving into the
West and then the Plains early next week.  The CMC is on the slow
side of the model guidance in tracking the low from the central
Plains to the Upper Midwest, but agrees well with the model
consensus on the building upper ridge across the eastern states. 
The GFS has trended a bit more to the northwest with the surface
low across the eastern Dakotas with more of a negatively tilted
upper trough, and the ECWMF/ECENS are quicker in the low track. 
The GEFS mean is closest to the overall model consensus regarding
the location of the low, but the intensity is probably closer to a
compromise of the CMC/ECMWF/GFS solutions.  Looking ahead to next
Thursday, model differences become substantial across the eastern
Pacific regarding the next potential shortwave to approach the
Pacific Northwest coast.  The use of the ensemble means was
increased to about 50% by Thursday to account for these increasing

...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 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 central and northern portions of the Sierra Nevada by
early next week.  For the Day 4 outlook (12Z Sunday-12Z Monday), a
Marginal Risk of excessive rainfall 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 for convection that could be locally heavy, but no strong
signals for anything yet on the Day 5 outlook.

The big headline will be the developing low over the Plains 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 again
Tuesday night and especially into Wednesday as this storm system
gets better organized across the central Plains and advects
copious Gulf moisture northward.  Recent model runs suggest this
could also be a significant event with heavy snow 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 and then northern Minnesota Monday night through
early Wednesday.  There is also the potential for some 6-12 inch
totals in the core of this band.  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
as favorable kinematic and thermodynamic parameters are expected. 
Meanwhile the best potential for the 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.  

A temperature dichotomy will exist across the nation with well
below average readings across much of the western U.S. and
central/northern Plains, and well above average temperatures from
the Gulf Coast to much of the eastern U.S. going into the middle
of next week.  Widespread highs of 15 to 25 degrees below early
April climatology are expected from the Intermountain West and the
Rockies to the northern Plains, with the greatest coverage of this
expected during the Tuesday through Thursday time period.  The
reverse holds true east of the Mississippi River where upper level
ridging extending from a Gulf of Mexico upper high should maintain
warm and humid conditions ahead of the evolving storm system, with
highs 10-20 degrees above average and overnight lows 15-25 degrees
above average.  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