Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
317 PM EDT Thu Apr 25 2024

Valid 00Z Fri Apr 26 2024 - 00Z Sun Apr 28 2024

...An active weather pattern for much of the Plains into the Mid to Upper
Mississippi Valley regions...

...Thunderstorms to bring heavy rains, localized flash flooding and severe
weather to portions of the Plains...

...An elevated to critical fire weather threat across the Southern High
Plains...

..Cooler than average temperatures expected from the Rockies to the West
coast and from the Mid-Atlantic to the Northeast, while much above average
temperatures spread from the Southern Plains to the Great Lakes...


An active weather pattern expected across the mid section of the nation
from the Plains into the Mid to Upper Mississippi Valley. Two strong
storms expected to produce a variety of spring time weather over the next
several days across these regions. Thunderstorm activity occurring across
portions of the Central Plains, Lower Arkansas and Lower Missouri Valleys
Thursday afternoon will be expanding northward into the Northern
Plains/Upper Mississippi Valley region and southward into the Southern
Plains as the first of two strong lows to affect these regions begins to
deepen across the Central High Plains and move northeastward. There is
the likelihood of severe weather across much of the Central to Southern
High Plains from Thursday afternoon into Thursday night/early Friday along
and ahead of a strengthening frontal zone. This severe weather threat
will then push farther to the east during the day on Friday into eastern
portions of the Central to Southern Plains, Lower Missouri and Lower
Arkansas River Valleys as the strong cold front also pushes eastward. In
addition, heavy rains from the expected thunderstorm activity poses the
threat of localized flooding from this afternoon through Friday,
especially across the eastern portions of the Central to Southern Plains
into the into Lower Missouri and Lower Arkansas River Valleys. In the
wake of the first strong storm pushing northeastward into the Northern
Plains/Upper Mississippi Valley on Saturday, where it will produce
potential for moderate to heavy rainfall amounts, a second storm will
begin to deepen across the Central High Plains. Another round of
thunderstorms, heavy rains, flash flooding and severe weather is again
possible across the Southern Plains beginning Saturday afternoon and
continuing into Sunday.

In contrast to the wet, stormy weather across large portions of the mid
section of the nation, windy and dry conditions are expected across the
Southern High Plains from southeast Colorado, the Texas-Oklahoma Panhandle
region, southward through West to Southwest Texas and eastern to
southeastern New Mexico. The combination of the windy conditions and low
relative humidities will support a prolonged period of elevated to
critical fire weather conditions from Thursday through the weekend.

A frontal boundary moving off the northeast Pacific into the Pacific
Northwest this evening will keep conditions wet across the Pacific
Northwest and Northern Rockies tonight. This wet weather and high
elevation snows are then expected to spread into the Great Basin and
Central Rockies on Friday.

Temperatures are expected to be below average across most areas from the
Rockies to the West coast over the next few days. Much above average
temperatures Thursday across the Central and Northern High Plains will be
replaced by much cooler temps by the beginning of the weekend. Much above
average temperatures expected from the Southern Plains, northeast the
Mississippi Valley, Ohio Valley and into the Great Lakes over the next two
days, while cooler,slightly below average temperatures expected from the
Mid-Atlantic into the Northeast.

Oravec

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 25 2024

Valid 12Z Sun Apr 28 2024 - 12Z Thu May 02 2024

***Severe thunderstorms and heavy rain expected west of the lower
and Mid-Mississippi Valley on Sunday, moving into the lower
Mississippi Valley on Monday***


...General Overview...

The medium-range period will likely begin with a rather active
pattern Sunday morning as a low pressure system tracks northeast
across the central Plains with severe thunderstorms from the
central Plains eastward to the lower to mid-Mississippi Valley into
Monday. The upper pattern appears to become more zonal later next
week as the central U.S. trough lifts out and a moderately strong
trough passes through the Pacific Northwest and reaches into the
northern Plains. It appears that a deeper trough will edge into
the West Coast by midweek while Gulf moisture will tend to increase
and expand across the southern Plains.

...Guidance/Predictability Assessment...

The morning model guidance suite features good overall agreement
across the U.S. through much of the medium-range period. Models are
unanimous in lifting the upper trough and low pressure system
northeastward away from the Great Plains early next week but
solutions gradually show more diversity afterward as a moderately
strong upper trough moves through the Pacific Northwest into the
northern Plains. This is due to uncertainty on how fast the upper
trough will lift out of the Plains and how much the Pacific
Northwest trough will interact with the central U.S. trough.
Despite the uncertainty on the trough interactions, the ensemble
means are agreeing well that a more zonal pattern will be
established across the northern tier states midweek next week while
a deeper upper trough will edge toward the West Coast.

The WPC medium-range forecast package was based on a general model
compromise
of 40% from the 00Z ECMWF/EC mean, 40% from the 06Z GFS/GEFS, and
20% from the 00Z CMC/CMC mean, and leaning toward the ensemble
means by Days 6 and 7.


...Weather/Hazards Highlights...

The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems to develop from the ArkLaTex
region to Missouri, and there is a good chance of training
convection given the slow overall progression of the frontal
boundary in conjunction with parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
is maintained from eastern Texas north-northeast across Arkansas
into southern Missouri where the QPF signal is highest in the
model guidance, where a multi-model signal for some 3-5 inch
totals is indicated. Storms training over the same areas with
locally higher totals are possible. There is still a good chance
for a future upgrade to Moderate Risk for portions of this region
if these model trends continue. The WPC forecast for QPF remains on
the lower end of the guidance spectrum given the influence from
the NBM. A Slight Risk area is also maintained on Day 5 centered
over northern Louisiana and into portions of adjacent states,
generally southeast of the Day 4 outlook area. The convergence
boundary is likely to linger across the region on Monday and fire
new rounds of convection, followed by an abatement in the coverage
and intensity of the convection going in Tuesday over this region.
The latest guidance has generally placed the highest QPF farther
north. The Slight was kept farther south in favor of the previous
ERO for this area.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse of the country east of the
Rockies. Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday with readings 5-15 degrees below average, before things
moderate going into early next week.

Kong/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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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
https://www.wpc.ncep.noaa.gov/#page=ovw

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Thu Apr 25 2024

Valid 00Z Fri Apr 26 2024 - 00Z Fri May 3 2024

The subtropical high that will initially to the north of the state
around 30-35N will shift to the northeast by this weekend.
East-northeasterly trade winds are expected to veer more to the
east or east-southeast as the high retreats and a col develops
within the subtropical ridge axis. The ensemble guidance has
trended stronger with an inverted trough and potential closed low
in the vicinity of the far northwestern Islands by Monday.

This pattern will favor precipitation chances each day for the
favored east-facing terrain, and conditions will remain mainly dry
for southwestern portions of the Islands. The aforementioned
trough over the far northwestern Islands and its accompanying
surface front will likely be blocked by the subtropical ridge and
remain northwest of the state, keeping the most impactful weather
well offshore through at least the middle of next week.

Hamrick

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Thu Apr 25 2024
Day 1
Valid 12Z Thu Apr 25 2024 - 12Z Fri Apr 26 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
PLAINS AND MISSISSIPPI VALLEY...

16Z update... The latest hi-res guidance is suggesting multiple
hours of rainfall rates up to 2 inches/hour to pass through
southeast Nebraska and northeast Kansas. 3-hr FFGs over this part
of the region are as low as 2 inches which given the new hi-res
trends, could reach or exceed soil saturation. The Slight Risk area
was expanded to the northeast to cover more of southeast Nebraska
and northeast Kansas. Meanwhile, latest observations and model
trends supported the small trimming of the backside of the Slight
Risk across portions of Oklahoma and central Kansas. The best
potential for the highest amounts and rainfall rates of 1.5-3
inches/hour remain across eastern Kansas to the borders of
Oklahoma/Arkansas/Missouri/Kansas.

Campbell

Convection will be ongoing at 12z this morning across portions of
the central and southern Plains. There remains some spread within
the 00z HREF guidance whether to favor a northern training axis
across portions of KS and MO, or a southern axis from northeast OK
into northwest AR. At this point it remains a bit unclear which
axis will become the dominant one, but both will likely see some
upscale convective development this morning within an area of
increasing moisture convergence in the 850-700mb layer. Storm
motions will favor some training and backbuilding, and thus some
flash flood risk will probably exist this morning from KS into
western MO, and from northeast OK into northwest AR.

Stronger mid and upper level forcing will eject east out of the
Rockies tonight, which will trigger additional convective
development over the Plains. Over KS and OK this convection should
be quite progressive off to the east. However high rainfall rates
are likely, and so any areas that see heavy rain from the first
round of convection this morning/afternoon could potentially see
areas of flash flooding tonight. Otherwise the activity should be
quick enough to pose only an isolated flash flood risk. There is a
better chance of a convective training tonight closer to the warm
front near the KS/NE border, which could drive an isolated to
scattered flash flood threat.

Overall will continue with a broad Slight risk that stretches from
near the NE/KS border southeast into northwest AR. This covers
both the expected convection this morning/afternoon, and the
development expected tonight with the arrival of stronger forcing
from the west.

Chenard

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Thu Apr 25 2024
Day 2
Valid 12Z Fri Apr 26 2024 - 12Z Sat Apr 27 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
THE SOUTHERN PLAINS INTO THE LOWER TO MID MISSISSIPPI VALLEY...

21Z update... Overall the setup for this period has not changed
much, just minor shifts of the QPF footprint across the Plains,
Midwest and Mississippi Valley. There will be some overlap of the
heavy rains from the Day 1 period and where some of the higher
amounts are expected for this period, particularly across Missouri,
Oklahoma and Arkansas. This will elevate the threat for local
flooding concerns. Minor reshaping of the Slight Risk to a more
southwest-northeast orientation was made with this update along
with an expansion into east-central Missouri.

Campbell

In what is shaping up to be an active stretch of excessive
rainfall potential, Friday may end up being a relative minimum of
flash flood impacts. The first system will be rapidly ejecting
northeast across the Plains and upper MS Valley. Given the quick
forward motion and the fact that the system will be moving east of
the stronger instability with time, tend to think any flash flood
risk will stay localized in nature from the central/northern
Plains into the upper Midwest.

The southern extent of the system may pose a slightly greater flash
flood risk, but even this remains uncertain. Convection should be
ongoing Friday morning across portions of TX/OK/AR/MO, although the
intensity and organization of this activity remains unclear. The
convection will be outrunning the surface front by this time
resulting in a gradual weakening of lower level convergence. In
the upper levels the forcing is also on a decline, so quite
possible activity is weakening Friday. However with plenty of
moisture and instability in place, and little reason for much
eastward progression of convection...any activity that is able to
persist and/or intensify during the day could end up pretty slow
moving and thus capable of producing flash flooding. Thus opted to
maintain a Slight risk from northeast TX into southwest MO to
account for this threat...while also accounting for the fact that
some of these areas may be more sensitive depending on the rainfall
that occurs Thursday and Thursday night. Also worth noting our
machine learning ERO also has elevated probabilities over
approximately this same area...likely indicative of the lingering
favorable ingredients in place.

Chenard

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Thu Apr 25 2024
Day 3
Valid 12Z Sat Apr 27 2024 - 12Z Sun Apr 28 2024

...A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
OKLAHOMA...

21Z update... Areal averages of 2 to 4.25+ inches expected from the
Southern Plains to the Mid/Upper Mississippi Valley as convection
really ramps up during this period. the 72-hr QPF footprint over
this region will be in the 2 to 6 inches range with the highest
amounts focused over eastern Oklahoma to southwest Missouri. The
latest models and WPC forecast trended QPF higher further south across
portions of Oklahoma and eastern Texas, as well as, the girth of
the QPF axis. As such the size of the Moderate Risk area was
expanded west-east and southwest-northeast. With the southward
trend, the Slight Risk was also expanded further south into
eastern Texas and a smidgen northeast further into central Iowa.
Convection near the Front Range trended a bit further west so in
turn, minor adjustments of the Marginal Risk in northeast Colorado
was made.

Campbell

A significant rainfall event appears likely Saturday night across
portions of north central TX into central/eastern OK. Large scale
forcing really ramps up Saturday night with the approach of the mid
level trough and 250mb upper jet streak. With strong ridging to the
east, these features lift more northward than eastward during the
overnight hours, resulting in a prolonged period of impressive
upper level divergence centered over Oklahoma. The persistence of
this large scale forcing is typically indicative of a favorable
training convective setup.

In the lower levels we have a very strong 850mb jet in excess of
50 kts resulting in impressive moisture transport and convergence
near a slow moving cold front. This low level flow is nearly equal
and parallel to the deep layer mean flow, which typically supports
a backbuilding convective risk. The expectation is that with deep
layer mean flow nearly parallel to the low level boundary,
convective cells will tend to train and also backbuild into the
strong low level jet.

Convection should become intense and organized enough to develop
a stronger cold pool resulting in some eastward cell progression
with time. This eastward progression is the main wild card in
determining the magnitude of the flash flood risk with this event.
We do think there will be some eastward progression, but the
persistent forcing and strong low level jet both will be opposing a
significant eastward push...and thus tend to think we will see
enough persistence of convection to result in an organized flash
flood threat. Convection will be capable of 2-3"/hr rainfall, and
thus it will not take much persistence to start getting some
significant rainfall totals. While widespread 5"+ totals may not
occur, swaths of totals exceeding 5" are expected, which should
result in an increasing, and locally significant, flash flood
threat.

Model guidance is in decent agreement for a day 3 forecast, all
generally focusing the highest swath of QPF from north central TX
into central/eastern OK. Although, as would be expected with a day
3 forecast, there is still some uncertainty on where exactly the
highest QPF ends up, as the swath of the most excessive amounts
will likely be rather narrow. The current placement of the MDT risk
is where the best overlap in ingredients and the model QPF
consensus resides. To the north into southeast KS, some expansion
may eventually be needed depending on antecedent rainfall over the
next couple days leading up to Saturday night. Meanwhile some
expansion to the south southwest of the current risk area is a
possibility...as the south and southwest flank of convection is
often a favored region for more prolonged training/backbuilding in
these type of events.

Across eastern KS into northwest MO and southern IA locally
excessive rainfall is also possible. But in general the
environmental ingredients are not as favorable for a prolonged
period of heavy rain, and thus a Slight risk should suffice. A
Marginal risk extends westward across NE into northeast CO
along/near the low track where convection near the warm front may
result in a localized flood risk.

Chenard

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 25 2024


The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems to develop from the ArkLaTex
region to Missouri, and there is a good chance of training
convection given the slow overall progression of the frontal
boundary in conjunction with parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
is maintained from eastern Texas north-northeast across Arkansas
into southern Missouri where the QPF signal is highest in the
model guidance, where a multi-model signal for some 3-5 inch
totals is indicated. Storms training over the same areas with
locally higher totals are possible. There is still a good chance
for a future upgrade to Moderate Risk for portions of this region
if these model trends continue. The WPC forecast for QPF remains on
the lower end of the guidance spectrum given the influence from
the NBM. A Slight Risk area is also maintained on Day 5 centered
over northern Louisiana and into portions of adjacent states,
generally southeast of the Day 4 outlook area. The convergence
boundary is likely to linger across the region on Monday and fire
new rounds of convection, followed by an abatement in the coverage
and intensity of the convection going in Tuesday over this region.
The latest guidance has generally placed the highest QPF farther
north. The Slight was kept farther south in favor of the previous
ERO for this area.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse of the country east of the
Rockies. Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday with readings 5-15 degrees below average, before things
moderate going into early next week.

Kong/Hamrick

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 25 2024


The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems to develop from the ArkLaTex
region to Missouri, and there is a good chance of training
convection given the slow overall progression of the frontal
boundary in conjunction with parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
is maintained from eastern Texas north-northeast across Arkansas
into southern Missouri where the QPF signal is highest in the
model guidance, where a multi-model signal for some 3-5 inch
totals is indicated. Storms training over the same areas with
locally higher totals are possible. There is still a good chance
for a future upgrade to Moderate Risk for portions of this region
if these model trends continue. The WPC forecast for QPF remains on
the lower end of the guidance spectrum given the influence from
the NBM. A Slight Risk area is also maintained on Day 5 centered
over northern Louisiana and into portions of adjacent states,
generally southeast of the Day 4 outlook area. The convergence
boundary is likely to linger across the region on Monday and fire
new rounds of convection, followed by an abatement in the coverage
and intensity of the convection going in Tuesday over this region.
The latest guidance has generally placed the highest QPF farther
north. The Slight was kept farther south in favor of the previous
ERO for this area.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse of the country east of the
Rockies. Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday with readings 5-15 degrees below average, before things
moderate going into early next week.

Kong/Hamrick

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
435 PM EDT Thu Apr 25 2024

Valid 00Z Fri Apr 26 2024 - 00Z Mon Apr 29 2024


...The West...
Days 1-3...


A series of impulses approaching the PacNW dig southeast tonight to
Friday, which builds a substantial longwave trough over the Great
Basin. This trough then shifts east, closing into a low over the
Four Corners early Saturday before swinging northeast through CO
through Saturday night and into the Dakotas Sunday. Pacific
moisture streaming in ahead of this trough makes for a broad areas
of higher elevation snow to develop across much of the
Intermountain West on Friday. Day 1 PWPF for >6" are 50-90% over
the OR Cascades which sees the most direct lift of Pacific
moisture as this trough crosses tonight (with snow levels dropping
from 6000ft to 5000ft), and generally 40-80% above snow levels of
6000-8000ft over the higher Great Basin ranges in NV and UT as
well as the Absarokas and Wind Rivers.

As the developing low shifts east over the Four Corners Friday
night, the heavy snow focus shifts to the Rockies from CO through
southwest MT. Lee- side cyclogenesis downstream of the low develops
over southeast CO late Friday which focuses flow of Gulf moisture
into the north- central Rockies which provides additional ascent
through upslope flow and periods of enhanced fgen, potentially
overlapping a deformation axis in the Central Rockies, to produce
heavier snowfall rates exceeding 1"/hr at times. Snow levels in the
Rockies will remain generally elevated, primarily 8000 ft, but
with steepened lapse rates beneath the cold trough and some areas
of enhanced ascent, snow is possible into the 6000ft elevation
range. Day 2 PWPF for >8" is 50-90% over the Wind Rivers, Front
Range, and portions of the San Juans and more like 30-70% for the
rest of the higher terrain between southwest MT, UT, and central
CO. The pivot to a northeast direction over CO late Saturday makes
a potential for persistent banding and substantial snowfall at
elevation with 2-3ft likely in the higher terrain of the Wind
Rivers and Front Range.

The low shifts onto the Plains Sunday with a deformation axis
possibly bringing accumulating snow to the High Plains and a
notable reduction in rates and coverage to the Rockies. PWPF for
>4" is generally 40-70% over the CO Rockies into southern WY.

The next low tracks from the southern Gulf of Alaska Saturday night
bringing moderate precip to the PacNW with snow levels around
4000ft. Day 3 PWPF for >4" is 30-80% in the North Cascades of WA.



The probability of significant icing is less than 10 percent.


Jackson

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Thu Apr 25 2024

Valid 12Z Sun Apr 28 2024 - 12Z Thu May 02 2024

***Severe thunderstorms and heavy rain expected west of the lower
and Mid-Mississippi Valley on Sunday, moving into the lower
Mississippi Valley on Monday***


...General Overview...

The medium-range period will likely begin with a rather active
pattern Sunday morning as a low pressure system tracks northeast
across the central Plains with severe thunderstorms from the
central Plains eastward to the lower to mid-Mississippi Valley into
Monday. The upper pattern appears to become more zonal later next
week as the central U.S. trough lifts out and a moderately strong
trough passes through the Pacific Northwest and reaches into the
northern Plains. It appears that a deeper trough will edge into
the West Coast by midweek while Gulf moisture will tend to increase
and expand across the southern Plains.

...Guidance/Predictability Assessment...

The morning model guidance suite features good overall agreement
across the U.S. through much of the medium-range period. Models are
unanimous in lifting the upper trough and low pressure system
northeastward away from the Great Plains early next week but
solutions gradually show more diversity afterward as a moderately
strong upper trough moves through the Pacific Northwest into the
northern Plains. This is due to uncertainty on how fast the upper
trough will lift out of the Plains and how much the Pacific
Northwest trough will interact with the central U.S. trough.
Despite the uncertainty on the trough interactions, the ensemble
means are agreeing well that a more zonal pattern will be
established across the northern tier states midweek next week while
a deeper upper trough will edge toward the West Coast.

The WPC medium-range forecast package was based on a general model
compromise
of 40% from the 00Z ECMWF/EC mean, 40% from the 06Z GFS/GEFS, and
20% from the 00Z CMC/CMC mean, and leaning toward the ensemble
means by Days 6 and 7.


...Weather/Hazards Highlights...

The overall synoptic environment will be quite conducive for
multiple episodes of excessive rainfall across portions of the
central and lower Mississippi River Valley. There will likely be
multiple mesoscale convective systems to develop from the ArkLaTex
region to Missouri, and there is a good chance of training
convection given the slow overall progression of the frontal
boundary in conjunction with parallel flow to the trailing frontal
boundary. For the Day 4 period Sunday, the existing Slight Risk
is maintained from eastern Texas north-northeast across Arkansas
into southern Missouri where the QPF signal is highest in the
model guidance, where a multi-model signal for some 3-5 inch
totals is indicated. Storms training over the same areas with
locally higher totals are possible. There is still a good chance
for a future upgrade to Moderate Risk for portions of this region
if these model trends continue. The WPC forecast for QPF remains on
the lower end of the guidance spectrum given the influence from
the NBM. A Slight Risk area is also maintained on Day 5 centered
over northern Louisiana and into portions of adjacent states,
generally southeast of the Day 4 outlook area. The convergence
boundary is likely to linger across the region on Monday and fire
new rounds of convection, followed by an abatement in the coverage
and intensity of the convection going in Tuesday over this region.
The latest guidance has generally placed the highest QPF farther
north. The Slight was kept farther south in favor of the previous
ERO for this area.

Elsewhere across the U.S., widespread moderate to locally heavy
rain is expected from Minnesota to northern Michigan on Sunday as
the surface low lifts northeastward, and a Marginal Risk area is
planned to account for that on the Day 4 outlook. Colder
temperatures moving in across the Intermountain West and the
Rockies behind this storm system will likely result in continuing
snow showers for the higher mountain ranges of Wyoming and
Colorado, although becoming lighter. Rain and mountain snow is also
likely to make a return to the Pacific Northwest for the beginning
to middle of next week as the next shortwave trough arrives. By
Wednesday, showers and storms could once again increase in coverage
from Texas to the Central Plains.

Temperatures will also be making weather headlines as a major
warm-up is expected for a wide expanse of the country east of the
Rockies. Highs are expected to rise well into the 80s from the
Central/Southern Plains to the Ohio Valley and then reaching the
East Coast by Monday, perhaps reaching 90 degrees in some cases.
These readings are on the order of 10-20 degrees above normal for
late April, and there may be some daily record highs set. Overnight
lows will also be summer-like with lows only falling into the 60s
for many of these same areas. A modest cool-down is likely by mid-
week from the Great Lake to the Ohio Valley and Northeast, and
still remaining warm and humid across the south-central U.S. to the
Carolinas. The opposite holds true for the Intermountain West on
Sunday with readings 5-15 degrees below average, before things
moderate going into early next week.

Kong/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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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
https://www.wpc.ncep.noaa.gov/#page=ovw