Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Sat Mar 25 2023

Valid 12Z Tue Mar 28 2023 - 12Z Sat Apr 01 2023

...Overview...

The medium range period begins Tuesday with potent surface and
upper low systems just off the West Coast that will lead to heavy
mountain snow in California as well as coastal rain that could
cause some flooding issues in sensitive areas. These systems
should then track eastward through the latter half of the week,
bringing some modest precipitation to the interior West around
Wednesday-Thursday and then pushing into the central and eastern
U.S. late week, with rain on the southern and eastern side and
perhaps some wintry weather on the northwestern side of the
system. Meanwhile in the East, the forecast remains somewhat
uncertain for Tuesday-Wednesday with some model variety in
shortwaves there and surface low positions in the western
Atlantic, but in general the forecast for impactful precipitation
has been decreasing.


...Model Guidance/Predictability Assessment...

There remain some differences from model to model and run to run
across the eastern U.S. and into the western Atlantic even as the
period begins Tuesday. These differences are smaller scale but
affect a round or two of QPF in the northeastern quadrant of the
U.S. as well as surface low positions in the Atlantic. In general
the trend has been for a more offshore surface low, and more
recently also for a more suppressed (farther south) and weaker low
shifting into the Atlantic compared to previous cycles.
Interestingly the 00Z/06Z deterministic models were on the whole
farther south than the bulk of the 00Z/06Z ensemble mean lows on
day 4/12Z Wednesday, with some spread in ensemble members. This
iteration of the WPC forecast thus decreased QPF from the previous
forecast and this trend will likely continue even more in the next
forecast, seeing the newer and drier 12Z guidance.

Farther west, models are quite agreeable with the existence and
positioning of the upper and surface lows just offshore and coming
into northern California Tuesday. Some minor to moderate
differences arise as the upper troughing tracks eastward. The
GFS/GEFS suite has remained on the faster side of tracking the
trough east, but is no longer quite as dramatically doing so. This
seems to have improved slightly in the newer 12Z GFS/GEFS mean
with a slight slowing trend, but the 12Z ECMWF looked slower than
its old run too. CMC deterministic and ensemble runs seem to be a
fair middle ground with the trough timing and thus the ridge
placement east of it as well. Considering the above, the WPC
forecast was based on a blend of deterministic models early but
with time incorporated the EC ensemble and CMC ensemble means to
find a middle ground solution and temper individual model
differences including the faster GFS and slower ECMWF.


...Weather/Hazards Highlights...

In the West, the storm system will direct a plume of moisture into
California especially Tuesday and continuing southward on
Wednesday. Though this would only be considered a weak atmospheric
river, especially compared to recent events, some heavy rain
totals may be possible along the coast and in higher elevations. A
Slight Risk remains embedded along the central coast of California
where conditions are particularly sensitive to flooding from wet
antecedent conditions, with a broader Marginal Risk in the lower
elevations. This is a colder system than previous recent ones for
lower snow levels. The higher terrain of the Sierra Nevada and
northern California mountains are likely to see 1-2 feet of snow
accumulation.

Meanwhile, lingering convection along a frontal boundary in the
Southeast on Tuesday could cause high rain rates for some
possibility of flash flooding there, especially in areas that see
heavy rain during the days 2-3 time period early in the week. A
Marginal Risk is in place across the Deep South. Meanwhile in the
Northeast, models have been waffling on how much precipitation
there could be, and recent trends have been for lower rain and
higher elevation/northern snow amounts for Tuesday-Wednesday. Then
by Thursday and Friday, the surface low ejecting from the West and
the amplified upper pattern should lead to increasing showers and
thunderstorms across the Plains and Mississippi Valley. The Storm
Prediction Center has already delineated an area of potentially
severe convection for parts of the southern half of the Plains on
Thursday. Some snow is possible on the backside of the low in the
north-central U.S. into later next week, but with considerable
uncertainty in placement and amounts of wintry weather for now.

Overall troughing in the West will lead to cooler than normal
temperatures there for much of next week, with highs around 10-20
degrees below normal. The coolest anomalies are likely to be
across the northern Plains though, where temperatures will range
from 10 to 30 degrees below average depending on the placement and
day, equating to highs in the 20s to 30s. Meanwhile the Southeast
could see a warm Tuesday morning before a cold front comes through
and brings temperatures nearer to average midweek. But as ridging
extends from a Gulf of Mexico upper high, relative warmth should
rebuild across the southern/central Plains Thursday and spread
into the Mississippi Valley Friday and the East by Saturday, with
highs generally 10-15F above average and lows around 15-20F warmer
than normal.


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

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 PM EDT Sun Mar 26 2023

Valid 12Z Wed Mar 29 2023 - 12Z Sun Apr 02 2023

...Overview...

A low pressure system just offshore of California as the period
begins Wednesday morning could lead to some coastal rain and
mountain snow continuing across California into Wednesday and
Thursday. The upper trough and associated surface low is forecast
to push eastward through the latter part of the week and emerge
into the Plains. Thus precipitation will spread across the
Intermountain West Thursday and then into the central U.S.
Thursday-Friday. Rain and thunderstorms that could cause severe
weather and flash flooding are likely through much of the Plains
and Mississippi Valley, while wintry weather could affect the
north-central U.S. on the backside. As this system pushes east,
another upper trough is forecast to drop into the Northwest by
next weekend.


...Model Guidance/Predictability Assessment...

Recent model guidance is reasonably agreeable on the synoptic
scale through much of the medium range period. Trends have been
for a slightly weaker but still notable surface low near the
California coast for Wednesday, with good consensus on its
position. Meanwhile on Wednesday model trends have continued for a
well offshore and suppressed Atlantic low. As the West Coast upper
low tracks southeast into the West and east into the central U.S.
Thursday-Friday while ridging amplifies ahead of it stemming from
a Gulf of Mexico upper high, models show differences well within
typical spread for this timeframe. GFS runs and even the 06Z GEFS
mean indicated an embedded upper low within the trough by late
Friday into Saturday as it lifts into the east-central U.S.,
unlike the ECMWF/CMC that just show a potent shortwave. Again,
these are relatively minor differences but they are associated
with variations in the surface low placement and the amounts/axis
of precipitation that could be snow across the north-central U.S.
to the northwest of the surface low around Friday. Shortwaves
behind this main feature are more variable and could affect
periods of upper ridging behind it. By the weekend another larger
scale trough with possibly an embedded upper low is forecast to
come southeast into the Northwest. While there are some
differences in the timing and depth of this feature depending on
how the energy digs, true outliers were not really noted other
than perhaps the new 12Z CMC that was somewhat flat across the
Pacific Northwest as it splits energy differently. The WPC
forecast was thus based initially on a blend of the 00Z
deterministic guidance and then gradually increased the
proportions of ECMWF ensemble mean and less so the GEFS mean as
the period progressed to reduce the impacts of individual models
varying.


...Weather/Hazards Highlights...

As the period begins Wednesday, the surface and upper low just
offshore of California will be directing an (albeit somewhat weak)
atmospheric river into California. This plume of moisture is
likely to affect southern California on Wednesday before pushing
south into Mexico. Meanwhile the considerable upper divergence and
somewhat steep lapse rates caused by the upper low so nearby could
cause scattered thunderstorms across the central California coast
through Wednesday into Thursday. Precipitation amounts shown by
the models are fairly weak, but some ingredients for heavy
rainfall rates are in place so a Marginal Risk of excessive
rainfall was added for day 4/Wednesday. Meanwhile in the higher
terrain of the Sierra Nevada, additional snow is likely through
midweek, and snow should spread into the Intermountain West and
Rockies as well through Thursday. Then by late week into the
weekend, another east Pacific/western Canada trough should direct
moisture more into the Northwest this time, though still could
affect northern California, with lower elevation rain and mountain
snow possible in those areas.

As the first trough and low system from the West eject into the
Plains for the latter half of the week, precipitation will spread
into the central and then eastern U.S. before clearing out by next
Sunday. Strong to severe thunderstorms are possible in the
southern half of the Plains Thursday and into large portions of
the Mississippi Valley on Friday per the Storm Prediction Center's
extended outlook. The day 5/Thursday experimental Excessive
Rainfall Outlook also indicates a couple of Marginal Risk areas in
place. One is in the Southern Plains where moisture and
instability will be abundant and could cause high rain rates ahead
of a cold front. The instability axis will also push farther north
into the vicinity of a warm front centered in and around Iowa, so
flash flooding is possible there as well. Moderate to heavy rain
is forecast to shift into the eastern U.S. late week, though there
has been some model variety in amounts. Meanwhile on the backside
of the low, a round of snow is possible in the north-central U.S.,
though the positioning and amounts of notable snow totals will
have to be refined with time. Windy conditions also could be a
threat across the southwestern to south-central U.S. and
progressing eastward toward the Ohio Valley with time behind the
cold front.

Troughing in the West will lead to cooler than normal temperatures
there for much of next week, with highs around 10-20 degrees below
normal. The coolest anomalies are likely to be across the northern
Plains though, where temperatures will range from 10 to 30 degrees
below average depending on the placement and day, equating to
highs in the teens to 30s and lows near or even below 0F. After a
near average Wednesday in terms of temperatures elsewhere, ridging
extending from a Gulf of Mexico upper high should cause relative
warmth to rebuild across the southern/central Plains Thursday and
spread into the Mississippi Valley Friday and the East by
Saturday, with highs generally 10-15F above average and lows
around 15-25F warmer than normal. A few record warm low
temperatures could be tied or set, but record highs may be limited
to Florida.


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

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
412 PM EDT Mon Mar 27 2023

Valid 12Z Thu Mar 30 2023 - 12Z Mon Apr 03 2023

***Strong low pressure to produce some severe thunderstorms,
episodes of heavy rainfall, and windy conditions across portions
of the Plains and Midwest late week into the weekend***

...Synoptic Overview...

Latest guidance shows fairly progressive upper level mean flow
across most of the lower 48 between Gulf of Mexico/northwestern
Caribbean ridging and a Hudson Bay upper low, while gradually
amplifying North Pacific/Gulf of Alaska flow should ultimately
reload the long-term West Coast mean trough after departure of an
initial western U.S. trough late this week. This leading western
trough should support lee cyclogenesis over eastern Colorado
Thursday night and a vigorous low pressure system will likely
continue northeastward through the Great Lakes and southeastern
Canada during the weekend. Meanwhile, the next upper level
trough/closed low amplifying from the Gulf of Alaska should reach
the Pacific Northwest by Saturday-Sunday and support a multi-day
period of enhanced rain/mountain snow from northern/central West
Coast through the northern half of the Rockies. A leading cold
front crossing the western U.S. will help to reinforce the cool
weather pattern, with the northern part extending farther east in
wavy fashion across the northern tier and eventually central
Plains.


...Model Guidance/Predictability Assessment...

The primary guidance discrepancy continues to involve latest GFS
runs leaning to the slow side of the envelope as the system
ejecting from the West/Plains tracks through the Great Lakes by
early Saturday and continues across southeastern Canada into
Sunday. The GEFS mean, as well as other means and operational
models, generally support the upper low opening up a little
earlier and the surface system progressing somewhat faster than
seen in the GFS. The new 12Z GFS does nudge a tad faster than the
00Z/06Z runs from about late Saturday onward. Behind this system,
guidance trends are starting to resolve a better defined northern
Plains into Upper Great Lakes wave around Sunday-Monday but with a
fair degree of spread for the track. The ensemble means provide a
reasonable intermediate solution. Finally, the latest operational
models and means compare reasonably well for the amplifying West
Coast trough from the weekend into early next week relative to
typical spread/error ranges with forecasts 5-7 days out in time.
A model/mean blend offers a good representation of this upper
trough and leading surface front. Combining these considerations,
the updated forecast started with a 00Z/06Z operational model
composite early in the period and then transitioned to a
combination of models and 06Z GEFS/00Z ECMWF means. The forecast
reduced operational GFS weight during the time of the model's
lower probability depiction of the storm crossing the Great Lakes.


...Weather/Hazards Highlights...

The ejecting western U.S. upper trough along with its low pressure
system tracking northeastward from the central High Plains late
Thursday onward will produce a variety of significant weather late
this week into the weekend. Precipitation will expand across the
central and then eastern U.S. with strong to severe thunderstorms
possible in the southern half of the Plains Thursday and into
large portions of the Mississippi Valley in the warm sector of the
low on Friday based on recent outlooks from the Storm Prediction
Center. The Day 4 (12Z Thursday-12Z Friday) Excessive Rainfall
Outlook shows a Marginal Risk area across portions of the Upper
Midwest, with the daytime update expanding the northern extent to
accommodate latest guidance but keeping in mind the occasional
northward bias that guidance can have (favoring maintenance of the
existing southern part). Guidance shows both moisture and
instability pushing northward in the vicinity of a leading warm
front and trailing wavy front with cold/stationary segments with
multiple rounds of convection possibly leading to some instances
of flash flooding. Swaths of moderate to heavy rain should reach
the east-central U.S. by late week, though guidance continues to
disagree with precise locations of highest totals. Currently the
best signal for locally enhanced QPF (with a reasonable
combination of moisture and instability) exists from near Arkansas
into portions of the Ohio/Tennessee Valleys, with sufficient
confidence to enlarge the prior Marginal Risk area during the Day
5 period (12Z Friday-12Z Saturday). Improved guidance clustering
for heaviest totals in future runs, especially if overlapping
areas that have had heavy rain recently, would help to increase
confidence enough to resolve any possible embedded Slight Risk
area. Meanwhile a band of snow is possible in the deformation
zone on the northwest side of the surface low, most likely from
South Dakota through parts of Minnesota and eventually the
northern Great Lakes. Positioning and magnitude of snow
accumulations will have to be refined with time as models get a
better handle on the system's evolution. The tight pressure
gradient around this storm system will also produce breezy to
windy conditions from the southwestern to south-central U.S. and
then progressing eastward to varying degrees across a decent
portion of the eastern U.S. Reloading of upper troughing along
the West Coast by the weekend and early next week will support
multiple days of rain/mountain snow (some locally moderate to
heavy) from the Pacific Northwest and northern California into the
Rockies, with the moisture shield pushing gradually farther
southeast with time.

Persistent upper troughing across much of the western U.S. will
lead to cooler than normal temperatures across the region for most
of this forecast period. Best potential for highs around 10-20
degrees below normal will be Thursday into Friday as the first
upper trough passes through and then over north-central areas by
Sunday-Monday as the next trough settles in. The northern Plains
will also be quite cold versus normal with some highs 15 to 25
degrees below average depending on the placement and day, equating
to highs in the 20s to lower 30s, and lows in the 0s to low 10s
across much of North Dakota for the end of the week. Upper level
ridging extending from a Gulf of Mexico upper high should result
in warm and humid conditions to rebuild across the
southern/central Plains Thursday and spread into the Mississippi
Valley Friday and the East by Saturday, with highs generally 5-15F
above average and lows around 15-25F warmer than normal. A few
record warm low temperatures could be tied or set.

Rausch/Hamrick

Hazards:
- Heavy rain across portions of California and the Pacific
Northwest, Fri-Sat, Mar 31-Apr 1.
- Heavy rain across portions of the Great Lakes, the Upper
Mississippi Valley, and the Northern
Plains, Thu-Fri, Mar 30-Mar 31.
- Heavy rain across portions of the Middle Mississippi Valley, the
Lower Mississippi Valley, the
Southern Appalachians, the Ohio Valley, and the Tennessee Valley,
Fri, Mar 31.
- Heavy snow across portions of the Pacific Northwest and the
Northern Great Basin, Fri-Sat, Mar
31-Apr 1.
- Heavy snow across portions of the Northern Rockies and the
Northern Great Basin, Sat-Sun, Apr
1-Apr 2.
- Heavy snow across portions of the Central Rockies and the
Central Great Basin, Thu, Mar 30 and
Mon, Apr3.
- Heavy snow across portions of the Northern Plains and the
Northern Rockies, Thu, Mar 30 and
Sat-Sun, Apr 1-Apr 2.
- Heavy snow across portions of the Northeast, the Great Lakes,
the Upper Mississippi Valley, and
the Northern Plains, Fri, Mar 31.
- Severe weather across portions of the Central Plains and the
Southern Plains, Thu, Mar 30.
- Severe weather across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee
Valley, the Great Lakes, the Middle Mississippi Valley, the Upper
Mississippi Valley, the Southern
Plains, and the Ohio Valley, Fri, Mar 31.
- Flooding possible across portions of the Southeast, the Middle
Mississippi Valley, and the Ohio
Valley.
- Flooding occurring or imminent across portions of the Middle
Mississippi Valley, the Lower
Mississippi Valley, and the Ohio Valley.
- Flooding likely across portions of the Middle Mississippi
Valley, the Lower Mississippi Valley,
and the Ohio Valley.
- High winds across portions of the Southern Rockies, the Central
Plains, the Southern Plains, and
the Southwest, Thu-Fri, Mar 30-Mar 31.
- High winds across portions of the Middle Mississippi Valley, the
Great Lakes, and the Upper
Mississippi Valley, Sat, Apr 1.
- Enhanced wildfire risk across portions of the Central Plains and
the Southern Plains, Thu, Mar 30.
- Enhanced wildfire risk across portions of the Southern Plains,
Fri, Mar 31.
- High winds across portions of mainland Alaska, Fri-Sun, Mar
31-Apr 2.


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

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Tue Mar 28 2023

Valid 12Z Fri Mar 31 2023 - 12Z Tue Apr 04 2023

***Strong low pressure to produce some severe thunderstorms,
episodes of heavy rainfall, and windy conditions across portions
of the Plains and Midwest late week into the weekend***

...Synoptic Overview...

The main weather story will be the strong low pressure system
developing across the Central Plains and the Midwest to close out
the work week. As the upper trough from the western U.S. ejects
over the western High Plains, lee cyclogenesis will commence over
eastern Colorado Thursday night and a well organized low pressure
system will evolve over the Central Plains along a rather strong
frontal boundary. Severe storms, heavy rainfall, and gusty winds
will be making weather headlines going into Friday and persisting
into early Saturday. This system will then move in a general
northeastward direction through the Great Lakes by Saturday and
then to southeastern Canada by Sunday. 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 over the West by 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 may produce
another surface low developing over the central/southern Plains
early next week, with strength and position determined by depth
and timing of the supporting dynamics.


...Model Guidance/Predictability Assessment...

The updated forecast started with a composite of 06Z/00Z
operational models for late this week into the weekend and then
trended toward a late-period even mix of operational models and
06Z GEFS/00Z ECMWF means, with the operational components split
among the 00Z and 12Z/27 ECMWF runs along with switching GFS input
more to the 00Z run based in light of differences/guidance
comparisons.

Over the past day the guidance has trended somewhat closer
together for the storm tracking through the Great Lakes by
Saturday, with latest consensus holding onto a closed or nearly
closed upper low as seen in recent GFS runs but with timing
somewhat faster than earlier GFS runs but a little slower than the
ECMWF. The 12Z CMC is now on the slower side of this majority
cluster. Behind this system, guidance has held onto using leading
Pacific energy tracking along the U.S.-Canadian border to support
a surface system reaching near Lake Superior by next Monday. Most
GFS runs and the 12Z CMC are on the slower side of the spread
while ECMWF runs have tended to be on the fast side, with an
intermediate/ensemble mean solution holding steady. Developing
differences with upstream Pacific/Alaska flow late in the period
start to influence progression of the upper trough moving into the
West early next week. Latest GFS/ECMWF runs have shown quite a
bit of waffling for specifics, with the 00Z GFS and new 12Z GFS
comparing somewhat better to the means than the flatter/faster 06Z
run, and an average of the past two ECMWF runs looking more
appealing than either one on its own. Thus a
multi-model-run/ensemble blend provided the best large scale
representation of the western trough aloft late in the period.


...Weather/Hazards Highlights...

The most impactful weather during this forecast period is expected
on Friday in association with the strengthening low pressure
system across the Plains and Midwest, and March will not be going
out like a lamb here. Perhaps the greatest concern will be the
elevated threat of severe thunderstorms in the broad warm sector
extending from the greater Chicago metro area to the ArkLaTex
region based on the latest Storm Prediction Center outlook. A
combination of both strong kinematics and instability parameters
will create a favorable environment of severe storms with
increasing wind shear and thunderstorm updraft potential, and this
is something that will need to be closely monitored in the days
ahead as the event enters the short range. In addition to the
intense convection, widespread windy conditions are likely to
develop across a broad expanse of the Plains and Midwest as the
surface pressure gradient tightens, with gusts in excess of 40 mph
expected behind the cold front. There has also been a trend for a
band of moderate to locally heavy snow from southern South Dakota
to southern Minnesota to the northern Great Lakes, along the
expected deformation band northwest of the main surface low. The
potential exists for some 6-12 inch totals across parts of this
region. Swaths of heavy rainfall are also likely farther south
from the Ohio Valley to the Deep South, but the relatively
progressive nature of this storm system should keep rainfall
totals from becoming extreme. Fairly intense rain rates for a
short duration of time could still lead to localized issues
though. These considerations and lack of strong guidance
clustering for location(s) of highest rainfall totals merit only a
Marginal Risk of excessive rainfall in the Day 4 Excessive
Rainfall Outlook (12Z Friday-12Z Saturday), though will continue
to monitor any emerging trends that could help to resolve any
embedded Slight Risk area. There is a lingering Marginal Risk
area near the Gulf Coast on Day 5 (12Z Saturday-12Z Sunday) for
what is left of the Day 4 activity over the Southeast plus
possible localized maxima farther west, as the front settles
along/just south of the Gulf Coast.

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 possible at higher
elevations. Significant snow may reach the Sierra Nevada by early
next week. Showers and thunderstorms may return to locations from
the Deep South to the Ohio Valley again on Tuesday as the next
storm system gets better organized across the central Plains.

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. The best potential
for highs 15 to 25 degrees below normal will be Friday across the
Dakotas as the first
upper trough passes through, and then over a broader expanse from
the West Coast to the Dakotas early next week as the second trough
settles in. Scattered record cold highs may be possible. Upper
level ridging extending from a Gulf of Mexico upper high should
encourage warm and humid conditions rebuilding across the
south-central U.S. to spread into the Mississippi Valley Friday
and the East by Saturday, with highs generally 5-15F above average
and lows around 15-25F warmer than normal. After a very brief
cooling trend, above normal temperatures should again spread from
the central U.S. on Sunday into the rest of the East by
Monday-Tuesday. A few record warm low temperatures could be tied
or set, and next Tuesday may offer the possibility for some record
highs over the South.

Rausch/Hamrick

Hazards:
- Heavy rain across portions of California and the Pacific
Northwest, Fri-Sat, Mar 31-Apr 1.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Middle
Mississippi Valley, the Southern Appalachians, the Upper
Mississippi Valley, the Great Lakes, and
the Ohio Valley, Fri, Mar 31.
- Heavy rain across portions of the Ohio Valley, Sun-Mon, Apr
2-Apr 3.
- Heavy snow across portions of California, the Central Great
Basin, the Pacific Northwest, and the
Northern Great Basin, Fri-Tue, Mar 31-Apr 4.
- Heavy snow across portions of the Pacific Northwest, Fri-Sat,
Mar 31-Apr 1.
- Heavy snow across portions of the Northern Rockies and the
Northern Great Basin, Sat-Sun, Apr
1-Apr 2.
- Heavy snow across portions of the Central Rockies and the
Central Great Basin, Mon-Tue, Apr 3-Apr
4.
- Heavy snow across portions of the Northern Plains and the
Northern Rockies, Sat-Tue, Apr 1-Apr 4.
- Heavy snow across portions of the Central Plains, the Great
Lakes, the Upper Mississippi Valley,
and the Northern Plains, Fri, Mar 31.
- Heavy snow across portions of the Northeast, Sat, Apr 1.
- Severe weather across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee
Valley, the Great Lakes, the Middle Mississippi Valley, the Upper
Mississippi Valley, the
Southeast, the Southern Plains, and the Ohio Valley, Fri, Mar 31.
- Flooding possible across portions of the Southeast and the Ohio
Valley.
- Flooding occurring or imminent across portions of the Middle
Mississippi Valley, the Lower
Mississippi Valley, and the Ohio Valley.
- Flooding likely across portions of the Southeast, the Middle
Mississippi Valley, the Lower
Mississippi Valley, and the Ohio Valley.
- High winds across portions of the Central Plains, the Northern
Plains, the Great Lakes, the
Southern Rockies, the Middle Mississippi Valley, the Upper
Mississippi Valley, the Southern Plains,
and the Southwest, Fri, Mar 31.
- Enhanced wildfire risk across portions of the Southern Plains,
Fri, Mar 31.
- Enhanced wildfire risk across portions of the Southern Plains,
Mon, Apr 3.
- High winds across portions of mainland Alaska, Fri-Sun, Mar
31-Apr 2.


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

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

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.
storm.


...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).

Rausch/Hamrick



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

Hazards:
- 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
3.
- 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
Valley.
- 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
Valley.
- 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
at:

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