Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 PM EDT Fri Apr 11 2025

Valid 12Z Mon Apr 14 2025 - 12Z Fri Apr 18 2025

...Overview...

Guidance agrees rather well for a leading northern stream upper
trough and surface low/frontal system that will affect the central
through eastern U.S. during the first half of next week. This
system will bring mostly light to moderate precipitation on Monday
along with potentially severe storms in the Upper Ohio Valley, with
a period of brisk winds from the Plains into the Northeast. The
western ridge/eastern trough pattern early-mid week should promote
warm temperatures over the West and cool weather over the East.
From about Wednesday onward there is rapidly increasing spread for
the evolution of the next shortwave trough in the series. Somewhat
more guidance shows this energy feeding into yet another amplified
eastern upper trough by next Friday, leading to another round of
rain spreading across the central and eastern U.S. mid- late week,
while mean ridging persists over the West. However there is a
meaningful minority that shows the energy digging into the West
instead of farther eastward, obviously with major differences in
the surface/precipitation pattern and temperature anomalies.
Meanwhile a weakening southern stream upper low should reach the
Southwest by Tuesday with a larger scale upper low lurking offshore
southern California for the rest of the week (depending on flow
details over the western U.S.).


...Guidance/Predictability Assessment...

With the latest guidance clustering well in principle for the
leading central-eastern U.S. upper trough and associated system,
the primary focus of decision-making today regards the significant
guidance divergence that takes place behind the first trough.
Looking at available data through the 00Z/06Z cycles, there was a
pronounced trend in GFS/GEFS runs toward recent ECMWF/ECens
solutions depicting a more amplified eastern U.S. upper trough by
late in the week with low pressure gravitating toward the
central/upper Great Lakes as of early Friday. The 00Z CMC was a bit
westward but similar in principle while the 00Z CMCens and UKMET
means fit into this theme albeit in slightly weaker fashion. Some
CMC/ECens ensemble members provided a first suggestion of a very
different evolution however, with a handful of each digging a lot
more trough energy into the West. The 00Z ICON also fit into this
scenario. 00Z/06Z ML (machine learning) models showed a dramatic
split as well, with a couple (including multiple ECMWF AIFS runs)
opting for more western troughing versus the other ML models plus
the 00Z AIFS mean favoring the eastern trough.

Based on the relatively greater proportion of guidance depicting
the eastern trough scenario by late week, which would also
represent some persistence of the overall mean pattern, forecast
preferences by the latter half of next week trended to a blend of
the 00Z ECMWF/CMC and their ensemble means. This led to an early
Friday Great Lakes surface system close to the depth recommended by
the cluster of ML models with that solution. 00Z/06Z GFS runs and
the GEFS mean differed enough from other solutions in the cluster
for details to exclude from the forecast. An operational model
blend provided a good starting point earlier in the week.

New 12Z guidance adds further confusion to the late-week forecast,
with the ECMWF and CMC both flipping to the western trough
scenario but the ICON adjusting to an intermediate idea of a
Plains/central Rockies upper trough by next Friday. On the other
hand the 12Z GFS has adjusted very close to the preferred forecast
described above and the general surface pattern of the 12Z GEFS/06Z
UKMET means are similar to or a bit slower versus preference.


...Weather/Hazards Highlights...

A surface low tracking from the Upper Great Lakes Monday through
southeastern Canada Tuesday and its trailing cold front will
support some precipitation across the east-central and eastern U.S.
Monday-Tuesday. An upper trough will provide dynamical support and
some instability should pool in the Upper Ohio Valley to
potentially produce severe thunderstorms, with damaging winds as
the primary threat, per the Storm Prediction Center. Rain rates
could possibly reach an inch per hour around Ohio/West
Virginia/Pennsylvania, but these should be short-lived as these
storms are fast moving and north/east of where heaviest rainfall
has occurred in recent weeks. However some non-GFS models are
showing a little more of a signal now for locally enhanced
rainfall. This is a very small-scale area and a few days out in
time so the Days 4-5 EROs maintain no risk areas, but typical
terrain sensitivity and trends seem to merit some monitoring over
future cycles into the short range. On the backside of the low,
temperatures could be cold enough for snow in the U.P. of Michigan
Monday and into higher elevations of the Adirondacks and Green and
White Mountains into Tuesday. Flow behind the northern tier storm
should produce strong and gusty winds over the northern/central
Plains into Monday, with some brisk winds reaching into the Great
Lakes/Northeast thereafter.

A weakening upper low reaching the Southwest by Tuesday may
produce some very scattered and light precipitation. Then as
surface low pressure develops in the central High Plains and moves
east, rain is forecast to spread across the central Plains to
Middle Mississippi Valley for midweek. There is still uncertainty
with how heavy this rainfall will be and the forecast will continue
to be refined with time. Northern stream energy could also produce
light precipitation over the Great Lakes region Wednesday, and
these features may combine to produce an expanding area of rainfall
with varying intensity over the eastern half of the country
Thursday- Friday. Depending on how deep the supporting upper trough
and possible embedded low become toward the end of the week, it
could become cold enough to produce some snow over the Upper Great
Lakes. Note that there is a minority potential for an alternate
pattern evolution which may lead to less southward extent of
precipitation over the East and at the same time greater coverage
of rain and higher elevation snow over parts of the West/Rockies
(versus the current relatively dry forecast). Continue to monitor
forecast updates for any significant trends in the most likely
scenario.

Mean ridging aloft will favor warmer than average temperatures
over the West and expanding into the Plains early-mid next week (up
to plus 10-20F or so anomalies for highs), while the upper trough
moving into the East will bring cooler temperatures over that part
of the country (highs up to 10-15F below normal over parts of the
Great Lakes into Appalachians). Warmer than normal temperatures are
also likely from southern Texas into the eastern U.S. on Monday
ahead of the leading cold front. Forecast confidence rapidly
declines by Thursday-Friday. Current forecast preferences would
maintain very warm temperatures over the West, as well as the
southern half of the Plains into Thursday before frontal passage,
while the East would trend below normal again by next Friday.
However there is some potential for a cooler trend over parts of
the West and less cooling farther east.


Rausch/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 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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Sat Apr 12 2025

Valid 12Z Tue Apr 15 2025 - 12Z Sat Apr 19 2025

...Overview...

Initially, an upper level trough will be moving across the eastern
U.S. and a closed upper low will be positioned offshore over the
eastern Pacific, with ridging in between over the Intermountain
West. By the second half of next week, the eastern trough will
shift into the Atlantic followed by the upper ridge, making way for
an energetic upper low that is expected to dive south across the
West. This low is forecast to interact with the low/trough over the
eastern Pacific and eject energy northeast towards the Plains. At
the surface, a couple of cold fronts will push across the East
Tuesday into Wednesday, supporting precipitation chances from the
Great Lakes to the Mid-Atlantic and Northeast, then the focus for
precipitation will shift to the Western and Central U.S. as a
strong frontal system moves southeast across these regions.
Portions of the Rockies could see notable snowfall from this system
Wednesday through Friday. Then by next weekend, this frontal system
is expected to become elongated, stretching from the Southwest to
the Northeast, and there may be a risk of heavy rainfall from the
Southern Plains to the Ohio Valley.


...Guidance/Predictability Assessment...

Model guidance had been split on the evolution of northern stream
energy in the West next week, with some solutions bringing energy
south and some pushing it to the east. Today, all available
deterministic, ensemble, and AI model guidance are depicting the
energy taking a southward track into the Western U.S., which has
resulted in significant changes to the forecast since yesterday
afternoon. The frontal evolution Thursday through Saturday has
changed dramatically, which will result in large changes to the
sensible weather forecast. Most notably, the probability of
snowfall in the Rockies has increased Wednesday through Friday, and
a wetter pattern is favored late next week from the Southern
Plains to the Ohio Valley.

For WPC's afternoon forecast, a blend of the deterministic 06Z GFS
and 00Z ECMWF/CMC/UKMET was used for the first two days, then
ensemble means from the 06Z GEFS and 00Z ECENS were added in
increasing amounts through the rest of the period. The GFS and
ECMWF were fairly agreeable with the exception of timing and
placement of some features late in the period, and they were also
in line with available AI guidance. The CMC and UKMET also showed
good agreement, but deviated a bit from the general consensus on
how to handle northern stream energy across the northern tier late
next week. For this reason, the GFS and ECMWF were given stronger
weight in the WPC forecast blend than the CMC and UKMET.


...Weather/Hazards Highlights...

At this time, no risk areas were introduced to the Day 4 (Tuesday)
and Day 5 (Wednesday) Excessive Rainfall Outlooks. Precipitation
amounts are forecast to be modest early next week, with little to
no risk of flash flooding.

A surface low tracking through southeastern Canada and its
trailing cold front will support some precipitation from the Great
Lakes to the Mid-Atlantic and Northeast on Tuesday, some of which
may linger into Wednesday for the Interior Northeast. Temperatures
on the backside of the low could be cold enough for snow at higher
elevations of the Adirondacks and Green and White Mountains. Gusty
winds will also be possible with this system from the
Midwest/Great Lakes to the Northeast and northern/central
Appalachians. Conditions will dry out across the East mid-week as
high pressure moves in behind the system.

A weakening upper low will be positioned over the eastern Pacific
on Tuesday with troughing extending into the Southwest, which may
support isolated to scattered precipitation for the Four Corners
states. More significant precipitation chances will arrive on
Wednesday as the energetic upper low dives southward into the West.
Precipitation will spread from the Northern Rockies on Wednesday,
to the Great Basin and Central Rockies on Thursday, and into the
Four Corners region by Friday. The probability of accumulating snow
has increased across the Rockies with this forecast, and some
locations could receive notable snowfall from this system.

As the energetic upper low dives south, a smaller portion of the
northern stream energy will continue east, trailing along the
northern tier of the nation. This will support precipitation
chances from the Northern Plains to the Midwest and Great Lakes
Thursday and Friday. By Saturday, an elongated frontal system is
expected to stretch from the Southwest to the Northeast with shower
and thunderstorm chances spanning the entire length of the
boundary. Southerly flow ahead of the boundary should push warm,
moist air into the South-Central U.S., which could create a threat
of heavy rain from the Southern Plains to the Mid-Mississippi and
Ohio Valleys next weekend. Due to increased sensitivity to rainfall
across the Mississippi and Ohio Valleys, rainfall next week could
cause additional flooding issues for these regions. However, at
this time, this wetter solution is still uncertain. The forecast
details will likely change over the next few days and should be
closely monitored to assess any possible impacts.

Initial mean ridging aloft will allow for above normal temperatures
in the West, spreading into the Plains by mid-week. Generally,
temperatures are forecast to be 10-20 degrees above average, with
highs in the 90s in the Desert Southwest Tuesday and Wednesday and
in the Central and Southern Plains on Thursday. Cooler than average
temperatures are likely in the Great Lakes and Ohio Valley on
Tuesday and into the Eastern U.S. on Wednesday and Thursday. Lows
should be 5-10 degrees below average and highs 10-15 below average.
After that, below average temperatures are expected to develop
southward across the West underneath the upper low while above
normal temperatures gradually shift towards the East and
Southeast.


Dolan/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 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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Sun Apr 13 2025

Valid 12Z Wed Apr 16 2025 - 12Z Sun Apr 20 2025

...Overview...

As the medium range period begins Wednesday, an upper low will be
moving across southeastern Canada with troughing extending south
across the Eastern U.S. and upper ridging will be in position
across the Plains. Upstream, an energetic trough over western
Canada is expected to begin nudging into the Northwest while a
Pacific upper low meanders east towards the Coast of California.
The trough is forecast to dive southwards across the West during
the second half of next week and form a closed low over the
Southwest. Cooler temperatures and increased precipitation chances
are expected with this trough/low, including the potential for
heavy snow in the Northern/Central Rockies Wednesday and Thursday.
Meanwhile, a northern stream trough is forecast to swing across
north-Central and northeastern U.S., accompanied by a strengthening
surface low pressure system and widespread precipitation chances
from the Midwest to the Northeast. By next weekend, the frontal
system will become elongated and settle across the Southern Plains
and Middle/Lower Mississippi Valley. This set up could result in
heavy rainfall, and will continue to monitor this potential.


...Guidance/Predictability Assessment...

After a significant pattern change over the past couple of days,
models have now stabilized on the overall pattern described above
for mid to late next week. All available model guidance over the
past 24 hours has consistently shown upper level energy diving
south across the West and forming a closed low over the Southwest.
Overall, model agreement is good, but there are some differences in
the details, such as how the low moving south across the West will
interact with energy moving east from the Pacific and
timing/position of the late week northern stream trough.

For the western low, the 00Z CMC and UKMET solutions fall east of
where the 00Z ECMWF and 06Z GFS have the low, but the eastern
position is closer to the ensemble mean positions from the latest
GEFS/ECENS/CMCE. The 00Z ECMWF is on the southern edge of model
spread, but the 12Z GFS trended south, closer to the ECMWF
solution. Overall, a solution in the middle of the east/west spread
seemed reasonable with a slightly southward bias towards the ECMWF
solution. Once the trough/low reaches the Southwest it should
interact with Pacific energy from the Pacific low. Models are
showing potential for some Pacific energy to be ejected northeast
across the Central U.S. towards the Midwest, which could enhance
precipitation Friday into Saturday.

For the northern stream trough, there is quite a bit of spread
among the different model solutions. The 06Z GFS seemed to be the
farthest outlier from the general consensus, with a slower and more
southwards track. The 00Z GFS was closer to the ECMWF solutions,
which falls in line with the ensemble mean solutions as well.
However, the 12Z GFS held on to the slower and southern trend. For
now, a solution closer the the means was favored, but there is
potential for this to change in future iterations of the forecast.

WPC's afternoon forecast blend consisted of purely deterministic
guidance from the 06Z GFS and 00Z ECMWF/CMC/UKMET for the first two
days (Wednesday and Thursday). For the rest of the period, the 06Z
GFS was phased out and the 00Z GFS was phased in, and ensemble
means from the GEFS and ECENS were added in increasing amounts.


...Weather/Hazards Highlights...

There will likely be some lingering precipitation in the Northeast
on Wednesday under the upper trough axis, and a shortwave could
produce some modest rain across the Mid-Mississippi Valley.
However, a rainfall totals should stay well below excessive
rainfall thresholds, so there are no risk areas on the Day 4
Excessive Rainfall Outlook.

More significant precipitation is expected across the West with
the combining energies from the upper lows. Precipitation chances
will spread from the Northern Rockies Wednesday-Thursday to the
Central Rockies and Southwest Thursday-Friday. With the cold upper
trough, accumulating snow in higher elevations is likely, with the
heaviest snow expected in the higher elevations of Wyoming and
southern Montana. Precipitation amounts have trended up slightly in
the Sierra Nevada and across the Great Basin, including some
higher elevation snow in the Sierra and Wasatch. Some precipitation
is forecast to continue in the Four Corners states into next
weekend.

As the upper low dives south in the West, a smaller portion of the
northern stream energy will continue east, trailing along the
northern tier of the nation with an accompanying surface low
pressure system. This will support shower and thunderstorm chances
from the Northern Plains to the Midwest on Thursday. Locally heavy
rain rates may be possible in thunderstorms, but storms should be
moving quickly with the progressive low pressure system which would
limit any flooding concerns. For this reason, there are no risk
areas on the Day 5 Excessive Rainfall Outlook.

Rain chances will continue east into the Great Lakes region on
Friday and the Northeast and Mid-Atlantic on Saturday. Meanwhile,
the tail end of this frontal system combining with a front ahead of
the slow moving Southwest upper low could support a focus for
heavy rain from the Southern Plains to the Mid-Mississippi Valley,
with modest rainfall chances extending into the Ohio Valley as
well. Some areas could overlap with areas of the Ohio and
Mississippi Valleys that may still be sensitive from recent
flooding, but fortunately the axis of the heaviest amounts through
Saturday is expected to be to the west. Even so, runoff from these
areas could flow into the Mississippi River, could exacerbate
ongoing flooding issues in some areas. The forecast details could
change over the next few days and should be closely monitored to
assess any possible impacts.

Initial upper ridging across portions of the Interior West and
Plains will allow for above normal temperatures there. Temperatures
are generally forecast to be 10-20 degrees above average, and even
up to 25 degrees above normal in the Central and Southern Plains on
Thursday with highs in the 90s from Texas to Kansas. Cooler than
average temperatures are likely in the East on Wednesday and
Thursday. Lows should be 5-10 degrees below average and highs 10-20
degrees below average. After that, below normal temperatures are
expected to develop southward across the West underneath the upper
low while above normal temperatures gradually shift towards the
East, becoming more limited to the Southeast next weekend.


Dolan/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 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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 PM EDT Mon Apr 14 2025

Valid 12Z Thu Apr 17 2025 - 12Z Mon Apr 21 2025


...Heavy rainfall and flooding possible in parts of the central
U.S. by the weekend...

...Overview...

Starting Thursday a vigorous upper trough will be traversing
through the Northwest as southern stream troughing setups up over
the Southwest. These two features will combine to yield an upper
low over the Great Basin region late in the week and with time,
pivot to the south and east through the weekend. Cooler
temperatures along with increased potential for precipitation, some
of which may be heavy snowfall for the Northern/Central Rockies
through Friday. In addition, there will be northern stream trough
advancing through the north-central and northeastern U.S.
accompanied by a low pressure system, as an elongated frontal
system stretches from the northern tier southwestward through the
south-central U.S. late week into the weekend. Rain and
thunderstorms are expected with this feature along with the
possibility of severe storms. Heavy rainfall and possible flooding
to develop across the south-central U.S where moisture streaming
ahead of the Southwest Upper Low will interact with frontal systems
over the region. The greatest potential will be over the weekend.



...Guidance/Predictability Assessment...

The latest runs of guidance maintain the synoptic pattern from
above while hanging on to some of the tendencies observed from the
the previous forecast package. The use of a multi-model approach
maintained a sense of continuity and reduced some of the minor
differences with the timing and location of the northern and
southern stream troughing. As previously noted, the GFS is hanging
on to a slow progression of the trough/low over the Great
Basin/Southwest which impacts the QPF over the Central/Southern
High Plains whereas the other guidance favors QPF more to the south
and east of the expected frontal positions. The CMC has trended
somewhat toward the GFS solution however, the ECWMF is providing
the favored placement and associated details at this time.

The WPC forecast was based on a blend of the deterministic
guidance using the 00Z ECMWF, 06/12Z GFS, 00Z CMC, and 00Z UKMET
initially while light weighting of the ECWMF and GEFS means were
incorporated for the weekend and into early next week to temper
the model differences.


...Weather/Hazards Highlights...

Strong upper-level energy will provide support for moderate to
heavy precipitation across parts of the West, stretching from the
Northern/Central Rockies and High Plains across the Intermountain
West into the Sierra Nevada. Colder air aloft will likely lead to
accumulating snow in the higher elevation, particularly heavy
across
Wyoming and southern Montana with some areas of snow for the
Wasatch and Sierra. Some precipitation is forecast to continue in
the Four Corners states into the weekend, with possibly multiple
days of snow in the Colorado Rockies.

Farther east, the northern stream upper trough and a surface low
pressure system will traverse the north-central Plains and Midwest
on Thursday, supporting shower and thunderstorm activity. The
Storm Prediction Center has identified these areas as having a
severe weather risk. Given the progressiveness of the low, the
locally heavy rain will have limited potential for flooding.
Individual thunderstorms should move quickly but there may be
repeated rounds moving west to east somewhere in the vicinity of
Lower Michigan and/or Indiana/Ohio. With antecedent dry conditions
and uncertainty with the axis of potential heavy rain there will
not be an area for the Excessive Rainfall Outlook however will
continue to monitor flooding potential. Farther south, the tail end
of the frontal system in the Southern Plains should help to focus
moisture advection ahead of the Southwest upper low. Some rain and
storms become likely by Friday evening or night over parts of Texas
and Oklahoma, with some likely lesser amounts over
Arkansas/Missouri. By Saturday heavy rain is likely to continue in
the Southern Plains, and this should warrant ERO areas, but this is
beyond the Day 5 ERO period. The surface low and frontal system is
expected to shift northeast by Sunday which will allow the rain
and thunderstorms to spread into the Central/Southern Plains and
the Middle/Lower Mississippi Valley. Heaviest rainfall amounts are
likely to be west of the most sensitive areas of the Mississippi
Valley and Ohio Valley from recent flooding. However, some rain
atop recently flooded areas, and runoff from other areas into these
rivers, could exacerbate ongoing flooding issues in some areas.
The forecast details could change over the next few days and should
be closely monitored to assess any possible impacts.

Initial upper ridging across the Plains will allow for above
normal temperatures there on Thursday. Above normal highs by 20-25
degrees will raise highs into the 90s from Texas to Kansas.
Meanwhile cooler than normal temperatures, especially for highs,
are likely to spread across the Interior West Thursday and Friday
under the upper trough. Warmer than average temperatures are
forecast to moderate and shift east into late week and focus across
the southeastern U.S. by Sunday.


Campbell/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 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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
236 PM EDT Tue Apr 15 2025

Valid 12Z Fri Apr 18 2025 - 12Z Tue Apr 22 2025


...Heavy rainfall and flooding possible in parts of the central
U.S. by the weekend...


...Overview...

A potent upper trough developing an embedded upper low will be in
place over the Interior West Friday and pivot east over the
weekend. Cooler temperatures and increased precipitation chances
are forecast with this developing low, including snow in the
central Rockies into Friday and Saturday. Meanwhile a northern
stream upper trough will advance through the Midwest to Northeast
late week, along with a surface low and an elongated front that is
forecast to stretch from the northern tier southwestward through
the south-central U.S. late week into the weekend. This will lead
to rain and thunderstorm chances, including possible severe
weather. Moisture streaming in ahead of the Southwest upper low
interacting with frontal systems atop the south-central U.S. will
lead to some heavy rainfall and flooding potential there, beginning
Friday but with rising potential over the weekend. Farther east,
warm upper ridging will take hold over the Southeast.


...Guidance/Predictability Assessment...

The 00Z/06Z suite of model guidance remains in reasonably good
agreement regarding the evolution of the large scale pattern,
including a slow-moving upper trough and closed low over the
Intermountain West and Four Corners, and a northern stream
shortwave/closed low north of the Great Lakes and the Northeast
through the early part of the weekend. Model differences become
more apparent and impactful by Sunday, however, as the closed low
reverts back to an open wave before ejecting eastward into the
Plains. Aside from the 00Z CMC, which remained quite fast and more
negatively tilted, the 00Z ECMWF, 06Z GFS, and 00Z UKMET were all
in a similar cluster of keeping the wave slower and farther south
across southern New Mexico and far western Texas. Other than the
generally minor differences in timing/strength typically seen at
these extended ranges, the 500 mb and surface evolutions through
the remainder of the period were handled roughly the same overall
by the deterministic guidance, with the wave and frontal system
consolidating and gaining latitude from the southern Plains to the
Upper Midwest. More drastic changes were seen with some of the new
12Z guidance, especially the 12Z GFS and 12Z ECMWF, which were both
much faster and farther north compared to their earlier runs. The
12Z CMC on the other hand was slower and farther south, while the
12Z UKMET was similar to 00Z albeit slightly farther north. Given
the above, it's clear that the synoptic features in play still
remain quite sensitive to even small changes from run-to-run, which
thus leads to lower than average confidence overall for days 5-7.

Later in the period, another trough is expected to dig southward
across the Pacific Northwest, with the 12Z CMC and 12Z UKMET more
aggressive compared to their previous runs and the new 12Z GFS and
12Z
ECMWF (the latter which was more aggressive at 00Z). A general
blend depicted broad troughing for days 6 and 7, which is a fair
compromise for now.

The WPC forecast was based on a blend of the deterministic
guidance using the 00Z ECMWF, 06Z GFS and to a lesser degree the
00Z UKMET and 00Z CMC. Gradually included some ensemble mean
guidance and increased the means to half by the end of the period
to temper the individual model differences. Overall, this resulted
in a slightly slower and farther south trend in the progs compared
to continuity.


...Weather/Hazards Highlights...

Precipitation is likely across the Four Corners states and nearby
on Friday-Saturday, with support from the trough/low aloft. Some
snow is possible in the Wasatch and the Mogollon Rim on Friday
before the trough moves east, and the central Rockies could see
snow pile up both Friday and Saturday. Then another trough pushing
into the Northwest by early next week could spread some modest rain
and higher elevation snow particularly to the northern
Rockies/High Plains.

Farther east, a surface low pressure system will traverse the
Midwest/Great Lakes on Friday, supporting shower and thunderstorm
activity in that area and southwest along the trailing front. The
Storm Prediction Center indicates a severe threat from the Upper
Ohio Valley through the Mid-Mississippi Valley and Southern Plains.
There may be some locally heavy rain on Friday and Friday night
with this convection. There may be some flooding concerns from the
south-central Plains into the Mid-Mississippi Valley, where storms
may train by Friday night as the front starts to become more west-
east oriented. Maintained a Marginal Risk for the Day 4/Friday ERO
for this potential. By Saturday, the slow pivot of the upper low,
the consolidating frontal system, and precipitable water anomalies
over the 90th percentile are likely to cause widespread heavy rain
of 3+ inches, with locally higher amounts. A Slight Risk of
excessive rainfall stretches from north-central Texas across
Oklahoma and into southwestern Missouri (clipping southeast Kansas
and northwest Arkansas) for Day 5/Saturday. A broader Marginal Risk
surrounds the Slight and is drawn across much of the Ohio River
where streamflows remain high. By Sunday there remains some model
spread in the timing and placement of the upper and surface lows
and thus where rainfall will focus, but broadly rain and
thunderstorms chances are likely from the southern and central
Plains into much of the Mississippi Valley. The heaviest rainfall
is likely to be west of the most sensitive areas of the Mississippi
Valley and Ohio Valley from recent flooding. However, some rain
atop recently flooded areas, and runoff from other areas into these
rivers, could exacerbate ongoing flooding issues in some areas, so
continue to monitor. Rain chances spread farther east by Monday.

Late this week, temperatures will be below average especially in
terms of highs in the Interior West underneath the upper trough.
These should moderate toward normal by early next week, though
temperatures in the Northwest may end up below normal by a few
degrees. Meanwhile farther east, above average temperatures by 10
to 20 degrees are likely from the southern Plains into much of the
eastern half of the U.S. on Friday. The primary cold front will
push above normal temperatures toward the Northeast/Mid-Atlantic on
Saturday but remaining over the Southeast as an upper ridge sets
up. The Southeast should remain warm into early next week, with
expansions of above average temperatures northward at times.


Miller/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 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