Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
419 PM EDT Sat Apr 01 2023

Valid 00Z Sun Apr 02 2023 - 00Z Tue Apr 04 2023

...There is an Enhanced Risk of severe thunderstorms over parts of the
Lower Great Lakes, Central Appalachians, and the northern Mid-Atlantic...

...Heavy snow over parts of the Cascades and Northern Central Rockies...

...There is a Slight Risk of excessive rainfall over parts of the Southern
Plains/Lower Mississippi Valley on Sunday...

A front extending from the Northeast roughly southwestward to the
Central/Western Gulf Coast will create showers and severe thunderstorms
over parts of the Northeast. Therefore, the SPC has issued an Enhanced
Risk of severe thunderstorms over the Lower Great Lakes, Central
Appalachians, and the northern Mid-Atlantic through Sunday morning.

The hazards associated with these thunderstorms are frequent lightning,
severe thunderstorm wind gusts, hail, and a few tornadoes.

Moreover, the upper-level energy associated with the storm will produce
snow and rain over parts of the Great Lakes and Ohio Valley, ending later
Saturday evening. Overnight Saturday, snow will develop over parts of the
Northeast and into the Central Appalachians, ending by late Sunday morning.

Meanwhile, along the southern half of the front, showers and severe
thunderstorms will develop over parts of the Southeast. Therefore, the SPC
has issued a Slight Risk of severe thunderstorms over parts of the
Southeast through Sunday morning. The hazards associated with these
thunderstorms are frequent lightning, severe thunderstorm wind gusts,
hail, and a few tornadoes. The rain will end overnight Saturday over the
Southeastern portion of the U. S.

On Sunday, the front over the Gulf Coast will move northward as a warm
front. Moisture pooling along the boundary will produce heavy rain.
Therefore, the WPC has issued a Slight Risk of excessive rainfall over
parts of the Southern Plains/Lower Mississippi Valley from Sunday into
Monday morning. The associated heavy rain will create mainly localized
areas of flash flooding, with urban areas, roads, and small streams the
most vulnerable.

Moreover, a front extending from the Northern High Plains southwestward to
Northern California will move eastward to the Great Lakes to the Central
Plains and then to the Central Rockies by Monday evening. The energy
associated with the boundary will aid in procuring coastal rain and
higher-elevation snow over parts of the Pacific Northwest and Northern
California through Sunday morning. In addition, snow will develop over
parts of the Northern Intermountain Region through Sunday morning, too.

On Sunday morning, weak onshore flow and additional upper-level energy
will create additional coastal rain and higher-elevation snow over the
Pacific Northwest and Northern California through Monday evening. In
addition, the energy will produce heavy snow over the Cascades through
Monday. By Sunday afternoon, snow returns to the Northern Intermountain
Region, continuing into Monday. Waves of low pressure move along the front
producing snow over parts of the Northern/Central Rockies and Great Basin
from Sunday into Monday.

Additionally, on Sunday, as the low pressure associated with the system
moves into the Upper Midwest, light snow will develop over parts of the
Upper Midwest into Monday. As the storm moves into Michigan, light rain
and snow develop over the Upper Great Lakes from Sunday afternoon into
Monday. Furthermore, rain will develop along the front on Monday afternoon
into Monday evening from parts of the Northeast to the Ohio Valley.
Showers and thunderstorms will return to the Southeast on Monday.


Ziegenfelder



Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Sat Apr 01 2023

Valid 12Z Tue Apr 04 2023 - 12Z Sat Apr 08 2023

...Blizzard continues across the northern Plains and Upper Midwest
into Wednesday night...
...Heavy rainfall and severe thunderstorms from the South into the
Midwest Tuesday, persisting rest of the week over the South...
...Winter cold for the West and North-central U.S. next week to
starkly contrast summer heat that shifts east from the South
through the East/Southeast through midweek...

...Synoptic Overview...

Energetic closed upper low will move east-northeast over the
north-central Rockies and spill over the north-central High Plains
Tuesday before further strengthening as it turns northeast and
lifts over eastern South Dakota Tuesday night and Minnesota
Wednesday. Winter cold, broad/heavy swaths of snow and high winds
to the north of the track of the powerful low pressure system make
for widespread blizzard conditions. This is in stark contrast to
widespread convective warm sector showers/thunderstorms that
develop Tuesday afternoon from northeast Texas into the Midwest
which includes a threat for severe weather with a Mid-South
Tuesday per the Storm Prediction Center (SPC). Upper ridging over
the Gulf Coast builds northward over the eastern U.S. through
Wednesday and supports anomalous warmth ahead of the cold front
from the large Plains storm. This pattern should lead to the
stalling of the trailing front near the Gulf Coast at least into
the weekend. Frontal wave enhancements with the ejection of
southern stream upper energies should focus convergence/convection
and potential training/flash flooding issues, especially with the
front aligned with the upper flow across the moist and unstable
lower Mississippi Valley in the favorable right entrance region of
the upper jet. Accordingly, the experimental WPC medium range
Excessive Rainfall Outlook (ERO) expands the Slight Risk threat
area for Wednesday.

...Model Guidance/Predictability Assessment...

Confidence remains well above normal for the main weather threats
next week. Forecast clustering is best Tuesday-Thursday with the
06 UTC GFS and 00 UTC ECMWF/UKMET/CMC (with the CMC dropping off
on Day 4) provides a good forecast basis that is well supported by
ensembles. Forecast spread slowly increases heading into next
weekend, particularly with the placement and strength of a
reinforcing trough over the Intermountain West Wednesday into
Thursday along with potential for a positively-tilted trough late
next week off southern California with some possibility on it
becoming a cutoff low including with 12 UTC guidance. This lends a
gradual transition to a preference for the more run to run
consistent GEFS/ECENS ensemble means along with the 13 UTC
National Blend of Models (NBM). There continues to be a gradual
southward trend in QPF (toward the Gulf Coast) over the south
Wednesday to Friday with 12 UTC guidance.

...Weather/Hazards Highlights...

Blizzard north-central High Plains through the Upper Midwest peaks
Tuesday night and continues into Wednesday. Areas farther east may
see brisk to strong winds even if to a less extreme degree. There
is also another substantial threat of strong to severe storms in
the expansive warm sector, with the Storm Prediction Center
highlighting and area over the Mid-South on Tuesday. Numerous
showers and thunderstorms are likely from the Gulf Coast to the
Midwest Tuesday, continuing next week over the South as
reinforcing southern stream trough energies suggest a continued
advection of copious Gulf moisture and instability, especially
with a wavy/stalling front. Accordingly, the experimental WPC
medium range Excessive Rainfall Outlook (ERO) expanded a "Slight
Risk" threat area over the lower Mississippi Valley to portions of
the Tennessee Valley Wednesday.

A pronounced temperature contrast will persists 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 shifting from the southern Plains/Gulf
Coast through much of the eastern states. Tuesday night-Wednesday
night look to be the coldest stretch versus normal over the
West/Plains with some areas seeing highs as much as 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 are expected over the West during the first
half of the week. Farther east in the warm sector,
Wednesday-Thursday should see some daily records, with warm lows
tending to be more numerous than record highs until the cold
frontal passage.

Jackson


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

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Sat Apr 01 2023

Valid 00Z Sun Apr 02 2023 - 00Z Sun Apr 09 2023

The closed upper low associated with an deep surface low off to
the northwest of Hawaii has finally begun to slowly lift north and
away from the northwestern Islands. The majority of the showers
and thunderstorms associated with a trailing front may linger into
the weekend over the western islands within a plume of deeper
moisture. The central and eastern Islands will continue to be on
the southwestern periphery of the subtropical high through most of
the forecast period, and as the low lifts north well away from the
state, the high then builds back westward centered near 35 degrees
north. Accordingly, trades should then become more easterly going
into early next week as the ridge axis builds in to the north, and
there will likely be in increase in showers over most of the
Islands as a weak upper trough works into and lingers over the
region next week that may act to pool moisture and instability.
Prefer a composite of reasonably well clustered model guidance for
a pattern that seems to have good ensemble support.

Schichtel

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
809 PM EDT Sat Apr 01 2023

Day 1
Valid 01Z Sun Apr 02 2023 - 12Z Sun Apr 02 2023

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Sat Apr 01 2023

Day 2
Valid 12Z Sun Apr 02 2023 - 12Z Mon Apr 03 2023

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHEAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY...

The closed low over southern CA (as of 18z Sat) will track into
the Southern Plains on Sunday and be responsible for an area of
organized convection Sunday afternoon and night. Model agreement
in the overall synoptic setup is pretty high. The aforementioned
mid level shortwave combined with an upper jet to the north will
provide the large scale ascent. This forcing will interact with a
lifting warm front, with upwards of 40 kts of 850mb flow resulting
in pretty good moisture transport/convergence and PWs around the
climatological 90th percentile. QPF differences amongst the models
are most likely mainly driven by different handling of the
convective evolution. Cells will form Sunday afternoon over
portions of northeast TX into southeast OK, and should evolve into
an organized area of convection fairly quickly. Mean wind fields
would suggest an east northeastward progression of this
convection. However as convection organizes it should tend to
build into the low level jet and track along the instability
gradient. This would support more of a east southeast and eventual
southeast progression of the most intense convection. Corfidi
vectors and thickness lines also support this east southeast to
southeast movement. For this reason we continue to lean away from
the guidance that has more of a east to northeast progression of
the heaviest rainfall. Guidance such as the 12z HRRR, ARW and Gem
Reg seem to have the more realistic evolution based on these
thoughts.

The system as a whole will be progressive, limiting the higher end
QPF/flood potential. However some east to west training seems
reasonable given the broad moisture transport along the warm
front, and this scenario is supported by some of the 12z HREF
members. It seems likely that we will see a swath of 2-4" of rain
somewhere from northeast TX towards the AR/LA border and into
central MS, although at the moment 5"+ probs from the HREF are
zero (indicative of the upper bound cap due to the progressiveness
of the system). Still think this supports an isolated to scattered
flash flood risk, so the Slight risk will be maintained. The area
was adjusted a bit north over northeast TX, and then south over MS
to account for the aforementioned expected east southeast movement
of stronger convection.

Chenard

Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Sat Apr 01 2023

Day 3
Valid 12Z Mon Apr 03 2023 - 12Z Tue Apr 04 2023

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL IN AND AROUND
SOUTHERN AL, SOUTHWEST GA AND THE FLORIDA PANHANDLE...

19z Update: No changes made to the Marginal risk. Organized
convection should be ongoing at 12z Monday across the area. What
happens the rest of the day remains a bit uncertain, but some
chance we see continued convective activity with potential
training/backbuilding. The better forcing leaves the area, but
850mb moisture transport persists and some guidance does have a
training signal. The GFS remains too dry, with something closer to
the 12z GEM Reg, FV3CAM and ECMWF preferred...which all depict
2-3"+ totals in spots. We may eventually need to give
consideration to a Slight risk upgrade across portions of southern
AL into southwest GA, but given relatively high FFG and some
lingering uncertainty with convective details, thought leaving the
Marginal was good for now and we can continue to reassess with
future updates.

Chenard

...Previous Discussion...

While there are differences amongst the guidance mass fields,
there is a general signal for a moisture plume with precipitable
water values at or above 1.5" to become stuck vaguely near the FL
border with AL and GA. Instability, low-level inflow, and
effective bulk shear appear sufficient for convective
organization. The flow should be fairly unidirectional with
height from the west-southwest, leading to concerns for cell
training. With low-level inflow slightly convergent, cell mergers
can't be ruled out either. The low- to mid-level frontogenesis
seen on Sunday should be exiting to the east and northeast. The
guidance spread in amounts is fairly wide, with the 00z NAM the
driest and the 00z ECMWF the wettest, showing local amounts of 5".
Soil moisture across portions of southern AL and the FL Panhandle
and Big Bend is elevated, and rainfall during the day Saturday
(and possibly Sunday) could lead to further saturation. The model
guidance has a general signal for 1-3" in this area, which could
fall as quickly as an hour or two. Considering the above, a
Marginal Risk area was added for this region.

Roth

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
458 PM EDT Sat Apr 01 2023

Valid 00Z Sun Apr 02 2023 - 00Z Wed Apr 05 2023


...Pacific Northwest to the northern High Plains...
Days 1-3...

...A major winter storm will produce heavy snow and strong winds
from the Intermountain West to the northern High Plains early next
week...

A leading shortwave that brought periods of snow from the
mountains of the Pacific Northwest to the northern Rockies will
continue to move east of the northern Rockies and into the High
Plains tonight. In its wake, a well-defined cold front will
continue to settle south and east across the region, with snow
levels forecast to tumble to its north. Even as the leading wave
moves east of the region, periods of snow are forecast to continue
through Sunday across the Northwest into the northern Rockies as
an upper low settling south along the coast of British Columbia
directs a steady stream of energy across the region. This energy
will begin to carve out a deeper trough across the region.
Additional heavy accumulations are likely, especially for the
Cascades, with impactful accumulations expected along the major
passes as well.

By late Sunday and continuing through Monday, a strong shortwave
will dig southeast through the broader scale trough, carving out
an anomalously deep trough centered over the Great Basin by late
Monday. By late Monday, the model consensus shows -2.5 std dev
500mb height anomalies centered over the Great Basin. Heavy snow
and strong winds are likely to develop along a strong baroclinic
zone following an impressive low developing over eastern Utah on
Monday. This will mark the onset of what are expected to be heavy
snow accumulations along the Utah ranges. Meanwhile, increasing
ascent and moisture advection will support snows east of the
Rockies, with amplifying low level easterly winds supporting heavy
snows
developing over southeastern to south-central Wyoming. By late
Monday, WPC probabilities indicate that snow accumulations of 6
inches or more will be common, with localized heavier totals
likely across the region.

By late Monday and continuing into Tuesday, models show the upper
trough continuing to amplify with a closed low developing over the
central Rockies. Strong upper forcing, along with low-to-mid
level frontogenesis on the northwest side of a powerful surface
low redeveloping over the central Plains will support moderate to
heavy snow stretching northeast from the central High Plains
toward the Upper Midwest on Tuesday. In addition to the heavy
snow, strong pressure gradient will generate strong, gusty winds
across the region. WPC probabilities indicate that by late
Tuesday snowfall totals are likely to exceed a foot in many
locations. These include the northern Utah and south-central
Wyoming mountains and the High Plains from southeastern Wyoming
northeastward into the Nebraska Panhandle and western South Dakota.

Heavy snow amounts are likely to extend farther to the northeast
as the storm continues to track toward the Upper Midwest beyond
the end of the period. See below for the latest Key Messages for
this event.

Meanwhile, energy embedded within northwest flow on the backside
of the trough will continue to support periods of snow across the
Northwest, with additional heavy accumulations possible,
especially for the Oregon Cascades late Monday into Tuesday.

The probability for ice accumulations greater than 0.10 inch is
less than 10 percent.

Pereira

...Key Messages for Apr 3-5 Winter Storm...

--Heavy Snow in Excess of One Foot Likely
Confidence continues to increase in a swath of heavy snow in
excess of 12 inches, which could challenge some April snow records
in the Dakotas and northwest Minnesota. Avalanches and significant
impacts from snow load are possible in the Intermountain West,
particularly in portions of Utah.

--Blizzard Conditions Likely in the Northern Plains
Strong winds and heavy snow will create whiteout conditions at
times Tuesday and Wednesday, leading to dangerous to impossible
driving conditions and considerable disruption to daily life.

--Life Threatening Cold for Anyone Stranded
Wind chills should fall to near or below zero during the blizzard
in the Northern Plains, which could be life-threatening to anyone
stranded.

--Damaging Winds on Warm Side of System
Widespread gusts in excess of 50 MPH will spread from the
Southwest and Four Corners Monday, to the Plains Tuesday, and
Upper Midwest Wednesday. This may lead to power outages, wind
damage, and blowing dust, even outside of thunderstorm activity.

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Sat Apr 01 2023

Valid 12Z Tue Apr 04 2023 - 12Z Sat Apr 08 2023

...Blizzard continues across the northern Plains and Upper Midwest
into Wednesday night...
...Heavy rainfall and severe thunderstorms from the South into the
Midwest Tuesday, persisting rest of the week over the South...
...Winter cold for the West and North-central U.S. next week to
starkly contrast summer heat that shifts east from the South
through the East/Southeast through midweek...

...Synoptic Overview...

Energetic closed upper low will move east-northeast over the
north-central Rockies and spill over the north-central High Plains
Tuesday before further strengthening as it turns northeast and
lifts over eastern South Dakota Tuesday night and Minnesota
Wednesday. Winter cold, broad/heavy swaths of snow and high winds
to the north of the track of the powerful low pressure system make
for widespread blizzard conditions. This is in stark contrast to
widespread convective warm sector showers/thunderstorms that
develop Tuesday afternoon from northeast Texas into the Midwest
which includes a threat for severe weather with a Mid-South
Tuesday per the Storm Prediction Center (SPC). Upper ridging over
the Gulf Coast builds northward over the eastern U.S. through
Wednesday and supports anomalous warmth ahead of the cold front
from the large Plains storm. This pattern should lead to the
stalling of the trailing front near the Gulf Coast at least into
the weekend. Frontal wave enhancements with the ejection of
southern stream upper energies should focus convergence/convection
and potential training/flash flooding issues, especially with the
front aligned with the upper flow across the moist and unstable
lower Mississippi Valley in the favorable right entrance region of
the upper jet. Accordingly, the experimental WPC medium range
Excessive Rainfall Outlook (ERO) expands the Slight Risk threat
area for Wednesday.

...Model Guidance/Predictability Assessment...

Confidence remains well above normal for the main weather threats
next week. Forecast clustering is best Tuesday-Thursday with the
06 UTC GFS and 00 UTC ECMWF/UKMET/CMC (with the CMC dropping off
on Day 4) provides a good forecast basis that is well supported by
ensembles. Forecast spread slowly increases heading into next
weekend, particularly with the placement and strength of a
reinforcing trough over the Intermountain West Wednesday into
Thursday along with potential for a positively-tilted trough late
next week off southern California with some possibility on it
becoming a cutoff low including with 12 UTC guidance. This lends a
gradual transition to a preference for the more run to run
consistent GEFS/ECENS ensemble means along with the 13 UTC
National Blend of Models (NBM). There continues to be a gradual
southward trend in QPF (toward the Gulf Coast) over the south
Wednesday to Friday with 12 UTC guidance.

...Weather/Hazards Highlights...

Blizzard north-central High Plains through the Upper Midwest peaks
Tuesday night and continues into Wednesday. Areas farther east may
see brisk to strong winds even if to a less extreme degree. There
is also another substantial threat of strong to severe storms in
the expansive warm sector, with the Storm Prediction Center
highlighting and area over the Mid-South on Tuesday. Numerous
showers and thunderstorms are likely from the Gulf Coast to the
Midwest Tuesday, continuing next week over the South as
reinforcing southern stream trough energies suggest a continued
advection of copious Gulf moisture and instability, especially
with a wavy/stalling front. Accordingly, the experimental WPC
medium range Excessive Rainfall Outlook (ERO) expanded a "Slight
Risk" threat area over the lower Mississippi Valley to portions of
the Tennessee Valley Wednesday.

A pronounced temperature contrast will persists 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 shifting from the southern Plains/Gulf
Coast through much of the eastern states. Tuesday night-Wednesday
night look to be the coldest stretch versus normal over the
West/Plains with some areas seeing highs as much as 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 are expected over the West during the first
half of the week. Farther east in the warm sector,
Wednesday-Thursday should see some daily records, with warm lows
tending to be more numerous than record highs until the cold
frontal passage.

Jackson


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