Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Wed Jun 18 2025

Valid 12Z Wed Jun 18 2025 - 12Z Fri Jun 20 2025

...Severe thunderstorm risks for the Midwest & lower Great Lakes on
Wednesday, & the Mid-Atlantic States Thursday...

...Fire weather concerns and/or significant heat for portions of the West,
Rockies, & Central High Plains through Friday...

...Heat builds in the East through Thursday...

The weather maker for the eastern half of the country through Friday will
be a progressive upper level disturbance and cold front pushing across the
Plains and the East. A wave of low pressure wave in the Plains is
forecast to intensify and track northeast through the Midwest on
Wednesday, which brings a threat of severe thunderstorms and flash
flooding from the southern Plains across the Midwest/Ohio Valley and into
the Great Lakes. The Appalachians, Mid-Atlantic states, and New England
states will see increasing heat through Thursday as a ridge of high
pressure briefly builds across the region and a warm front lifts north of
the area. Record high temperatures...in the mid 90s...are possible in
southern New England on Thursday. Once the cold front nears the East on
Thursday, more widespread severe weather would be possible within the
increasingly hot and humid air mass across the Mid-Atlantic States and New
England. A waning area of thunderstorms is expected with time as a cold
front leads to cooling and dries things out, clearing the Midwest by
Thursday and the Mid-Atlantic and New England states by Friday. The Gulf
Coast and Southeast maintain scattered showers and thunderstorms for the
remainder of the work week.

A deep layer cyclone moves southeast with time out of the northeast
Pacific, with the center moving into the Pacific Northwest on Friday. It
will drive a cold front east and south through the Pacific Northwest and
Montana by Friday morning. The combination of windy and dry conditions
brings an elevated fire weather threat across interior portions of the
Northwest on Wednesday (where Red Flag Warnings are in effect), which
shifts into the Great Basin on Thursday and Friday (Red Flag Warnings are
in effect for much of Utah). Significant heat expands across the West
into the Central High Plains on Wednesday through Friday ahead of the cold
front as the ridge rebuilds ahead of the deep layer cyclone, threatening
daily record high temperatures across portions of the Great Basin and
western South Dakota on Thursday and from Colorado north and east into
Nebraska and South Dakota on Friday. High temperatures will remain 100F+
for the Desert Southwest through the remainder of the work week (Death
Valley could exceed 120F) where Extreme Heat Warnings remain in effect.
Heat Advisories remain in effect for southern and western fringes of the
Big Bend of western Texas on Wednesday where high temperatures of 100-110F
are forecast.

Roth/Miller


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Wed Jun 18 2025

Valid 12Z Sat Jun 21 2025 - 12Z Wed Jun 25 2025

...First significant and extremely dangerous heat wave of the
season expected from the central Plains through the Midwest to the
Northeast this weekend/early next week...


...General Overview...

A significant and extremely dangerous heat wave is expected to
start the Summer across much of the central/eastern U.S. this
weekend/early next week under an expanding upper-level ridge. A
deep upper trough is forecast to work its way across the Northwest,
eventually emerging into the northern U.S., where a rather deep
cyclone is forecast to develop this weekend. Multiple frontal waves
appear to follow as they develop and track northeast through the
central/northern Plains along a slow-moving front by early next
week bringing storm chances with potential for heavy rainfall and
severe weather. Influx of tropical moisture into the Southern High
Plains may also bring a heavy rainfall threat early next week.


...Guidance/Predictability Assessment...

Model guidance remains in above average agreement on the general
evolution of the synoptic pattern through the medium-range period.
All guidance shows that the quasi-zonal pattern in place through
late week will begin to amplify following the departure of an
upper-wave off the East Coast. A strengthening and broadening
upper-high will build over the central/eastern U.S. while an upper-
low that had been anchored over the northeastern Pacific will drop
southward with upper-troughing digging across the western U.S. Most
of the forecast uncertainty revolves around a complex surface
evolution of the leading frontal system over the Plains as the
upper-trough makes slow eastward progress with embedded short-wave
energies leading to at least a couple rounds of cyclogenesis. The
latest runs of the GFS have come into better agreement with the
ECMWF with main surface low/frontal system evolution and
progression through the weekend and early next week as the system
eventually lifts northward into Canada north of the broad upper-
ridge, with support from EC and GFS means and AI guidance as well.
The 12Z and especially the 18Z GFS are a bit faster than this other
guidance but still cluster generally well. On the other hand, the
12Z UKMET and especially the CMC are slower in lifting the leading
surface wave northward, with further discrepancies in
amounts/footprint of associated QPF compared to the other guidance.
However, the certainty with respect to the synoptic pattern
ramifications for a significant, dangerous heatwave over the
central/eastern U.S. remain much higher, and this pattern looks to
remain in place through at least the middle of next week, with only
gradual weakening of the upper-high and modest weakening of the
upper trough.

The updated WPC forecast begins with a composite blend of the
deterministic guidance given good agreement, with the 12Z GFS used
over the 18Z GFS because of its closer clustering. The GEFS/ECens
means replace the contributions from the CMC/UKMET mid to late
period when their solutions with respect to the progression of the
central U.S. system notably diverge, and the means help to account
for growing uncertainty in smaller-scale details.


...Weather/Hazards Highlights...

A major synoptic pattern change is in store for the weekend and
into next week as an amplifying upper- level ridge over the
central/eastern U.S. shifts the storm track northward and brings a
period of drier conditions to many after unsettled weather much of
the week. Embedded impulses within the upper-ridge will trigger
convection, potentially organized, across the Upper Great Lakes to
Interior Northeast Saturday (day 4). A Marginal Risk ERO is in
place as a strong low level jet and high PWATs (up to 2 standard
deviations above the mean) support the threat of heavy rainfall and
at least isolated flash flooding. Daily showers and thunderstorms
are also expected in vicinity of the Gulf Coast as disturbances
round the south side of the ridge and with possible influence of
tropical moisture for the western Gulf Coast/south Texas. This
influx of moisture also looks to bring precipitation chances
further northwest into western Texas and the southern high Plains
by later this weekend, with heavy rainfall/flash flooding concerns
especially into Monday - Wednesday as PWATs rise upwards of 2.5-3
standard deviations above the mean.

Upstream, an energetic deep upper-trough/Pacific system and
northern stream into the West will bring increasing precipitation
chances to the Pacific Northwest and northern Rockies/Plains this
weekend in unsettled flow with moderate to heavy rainfall
potential. A Marginal Risk ERO is in place for Saturday (Day 4) for
north-central Montana given a signal for high QPF in the guidance
and the presence of strong, very moist upslope flow behind the
departing cyclone in the northern Plains. Much colder temperatures
aloft will also bring some snowfall to higher elevations of the
northern Rockies, and this precludes a higher threat for flash
flooding in the region for now despite high QPF and anomalously
high moisture. Eventual lead frontal system development over the
Plains will bring a return of thunderstorm chances to portions of
the central/northern Plains and Midwest Sunday and particularly
Monday-Wednesday with moist return flow along a slow moving frontal
boundary. Potential organized convection in southwesterly flow
rounding the ridge may bring daily heavy rainfall/flash flooding
and severe weather threats.

The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains into the
Midwest/Great Lakes by Saturday, and the Ohio Valley/Mid-
Atlantic/Northeast by Sunday thanks to an anomalous upper-level
high building overhead. Widespread Major to Extreme Heat Risk
(levels 3 and 4/4) is forecast, indicating an intensity of heat
that is extremely dangerous to anyone without adequate cooling or
hydration. Heat indices are forecast to climb into the 100-110
degree range, potentially higher, and muggy overnight lows in the
mid- to upper 70s will bring little overnight relief from the heat.
Numerous daily record high and minimum temperatures are possible.
Unfortunately, this heat wave looks to persist through at least the
middle of next week, which will increases the danger. Some
locations from the central Plains into the Upper Midwest may see
some relief by Tuesday as a cold front moves into the region. Highs
will be cooler and below average by as much as 10-20 degrees
across portions of the Pacific Northwest, Great Basin, and northern
Rockies/High Plains this weekend as an upper level trough and
associated surface cold front from the northeast Pacific
overspreads the region.

Putnam


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
317 AM EDT Tue Jun 17 2025

Valid 00Z Wed 18 Jun 2025 - 00Z Wed 25 Jun 2025

A stable and dry pattern looks to remain in place for the islands
through this week/weekend and into early next week. An area of
surface high pressure well north of the islands is forecast to
shift east- southeastward early in the period and then settle in
northeast of the islands. Trade winds will be enhanced through the
middle of this week as the high passes due north of the islands
resulting in a tighter pressure gradient. A brief period of
lighter winds should exist late this week as the high drifts away
from the islands. However, another period of gustier winds look to
return through the weekend as the high strengthens and drift back
towards the islands. Guidance suggests the high will then weaken
early next week with lighter winds expected. Any rainfall should
be limited to lighter terrain- enhanced showers mostly for
windward areas.

Putnam

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Jun 17 2025
Day 1
Valid 01Z Wed Jun 18 2025 - 12Z Wed Jun 18 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL APPALACHIANS AND THE SOUTH-CENTRAL GREAT PLAINS...

01Z Excessive Rainfall Discussion...
Greatest threat for excessive rainfall overnight continues to be
focused mainly over southeast Kansas and a small part of adjoining
states. Too early to trim more than a small part of the western
and northern periphery given on-going convection although warming
cloud top temperatures suggest model guidance is on-track for
diminishing flash flooding threat to the north and west of on-going
Moderate Risk area.

Farther west...maintained the Moderate Risk area in the Central
Appalachians given on-going convection and satellite imagery still
showing convection located upstream. The WoFS runs continue to
favor the area along and north of the Mason Dixon Line into the
late evening/early morning hours while convection elsewhere in the
eastern US fades by 04Z or so,

Bann



...Central Appalachians to the Central Gulf Coast...
Extreme thermodynamics expanding across the eastern CONUS will
produce an environment favorable for widespread convection with
heavy rainfall today and tonight.

A broad Bermuda-type ridge centered off the southeast Atlantic
coast will expand northwestward, while a shortwave trough persists
over the Mississippi/Ohio Valleys. This will accelerate the SWly
850-500mb flow which contains multiple mid-level impulses that
provide waves of enhanced ascent from the Central Gulf Coast
through the Mid-Atlantic states.

12Z CAMs remain in good agreement on diurnal expansion of
thunderstorms in a swath from Louisiana into Upstate NY, though
poorly organized with bulk shear 20-25 kts and progressive to the
northeast on 20-30 kts of mean layer wind. However, any storm will
likely contain impressive rain rates in deep Gulf-sourced moisture
with PWs up around 2" through this swath. Daily record high PW is
possible at both OKX and PIT. This high PW and deep warm cloud
depths of 13000-14000 ft will support high hourly rainfall,
particularly around south-central PA that remains a favored area
for QPF max today where a warm front is lifting.

12Z HREF neighborhood probs have 20-30% risk of of exceeding
2"/hr in south-central PA where a Moderate Risk persists. Sub-
hourly rain rates of 3-4"/hr are possible in this environment.

FFG is extremely compromised in parts of the central Appalachians
with a Slight Risk remaining for eastern KY into northern PA. The
Marginal Risk still extending all the way to the central Gulf
Coast where isolated flash flooding is ongoing.


...South-Central Plains into the Midwest...
16Z Update...
Shrank north side of Slight Risk to focus on organized convective
activity over KS (where a Moderate Risk persists) with expansion
downstream in OK and western MO.

A potent shortwave shifts across the central Rockies this
afternoon and amplifies sharply over the Plains this evening. This
should enable vigorous terrain induced convection off the Front
Range into WY with some organization as it shift east this evening.

This will be after the ongoing activity centered on KS which is
after a powerful MCS blew through last night. Impressive ascent
downstream of this shortwave will impinge into a cold front draped
across the Plains, resulting in surface low pressure development
this evening as well. This will enhance ascent locally, especially
as the LLJ ramps up to 40-50 kts, and is locally additionally
enhanced downstream of the developing low pressure, especially in
KS/OK. This LLJ will draw impressive thermodynamics northward
reflected by PWs rising above 1.75 inches collocated with MUCAPE
potentially exceeding 4000 J/kg. Where this LLJ converges both
along its nose and into the wavering surface front, convection is
expected to develop this evening, and then grow upscale and
intensify tonight. The 12Z CAM consensus is for southern KS to be
the MCS focus this evening with repeating heavy rain where earlier
activity fell, raising the threat level.


Weiss/Jackson

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Jun 17 2025
Day 2
Valid 12Z Wed Jun 18 2025 - 12Z Thu Jun 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
MICHIGAN...

...Central States/Midwest...
21Z Update...
Slight Risk introduced for the L.P. of Michigan.

A shortwave trough lifts north from northern Missouri through the
L.P. of Michigan Wednesday. This is in advance of the longer wave
trough axis shifting east from the central Plains Wednesday and in
the right entrance region of a SWly upper jet streak lingering over
the northern Great Lakes through this time. These dynamics will
allow the surface low pressure coincident with the shortwave to
deepen through its track as it crosses northern Illinois and the
L.P. of MI. This low will move along a baroclinic zone to the
northeast, dragging its accompanying cold front east into the
Midwest Wednesday afternoon and tracking over the Mid-South and
Ohio Valleys Wednesday night, leading to two main swaths of heavy
rain.

The environment along the low track will support prolonged
convergence/ascent as intensifying 850mb inflow from the Gulf will
draw higher PWs (1.75 to 2") and with sufficient instability
(MUCAPE around 1000 J/kg) northward. Within the deformation, the
850mb winds will lift a theta-e ridge northward and cyclonically
around the low pressure, producing an axis of moderate to heavy
rainfall within a modest TROWAL that will pivot northeast. The
confidence on higher rain rates have increased with 12Z HREF
neighborhood probabilities for 1"/hr rates now 40-60% over the
central/lower L.P. through the afternoon (with 2-4" likely in the
swath which warrants an introduction of a Slight Risk despite the
typically higher FFGs in MI. Rates do ramp up over northern IL and
especially over Chicago, so a Slight Risk could become warranted
for the Chicago metro should trends continue to increase.

Farther south along the front, instability is more robust with
MUCAPE progged to be 1000-2000 J/kg, promoting scattered convection
with embedded heavy rates particularly in the late
afternoon/evening over southern Missouri and Arkansas east into
Kentucky/Indiana. This area should also have ongoing activity from
tonight which will further precondition soils. Given the
progressive nature of the activity, the Marginal is maintained
with expansion over OK/northeast TX/southern AR and central KY/TN.


...Mid-Atlantic into New England...
Continued return flow around a Bermuda-type ridge off the
Southeast coast will maintain broad southwesterly flow to pump
elevated PWs northward into the Mid- Atlantic on Wednesday. PWs
reach 2" Wednesday afternoon from the DC metro up through southern
New England as a weak surface trough swings east over the Midwest.
Despite the relatively isolated to scattered nature of convection
expected, any of these torrential rain rates atop the more urban
areas could cause isolated instances of flash flooding, and the
Marginal Risk is maintained/expanded a bit into central PA where
morning activity should be occurring from overnight tonight.


Weiss/Jackson


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Jun 17 2025
Day 3
Valid 12Z Thu Jun 19 2025 - 12Z Fri Jun 20 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR AN AREA FROM
THE MID-SOUTH THROUGH INTERIOR NEW ENGLAND...

A mid-level longwave trough axis will progress eastward from the
lower/mid-Mississippi Valley to the Atlantic coast on Thursday.
This trough will push an accompanying surface cold front beneath
it, and this front is progged to reach the Eastern Seaboard by 12Z
Friday. The overlap of the front with its parent trough will drive
another strong corridor of lift through height falls/convergence,
into an environment supportive of convection with heavy rain.
Despite the rapid progression of this front, the Marginal Risk is
expanded from TN through southern AR due to potential short-
duration training of thunderstorms due to mean 0-6km winds that are
parallel to the boundary. With rain rates likely eclipsing 1"/hr
at times, this should produce stripes of 1-2" of rainfall, with
locally as much as 3" in a few locations as suggested by 12Z
consensus including the experimental RRFS which is the first CAM to
go out through Day 3. While in general this pattern suggests only
an isolated flash flood risk, there are rather vulnerable soils in
the central Appalachians, so a targeted Slight could be needed in
future updates, particularly as it gets more into the typical CAM
range.

Weiss/Jackson


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Wed Jun 18 2025


A major synoptic pattern change is in store for the weekend and
into next week as an amplifying upper- level ridge over the
central/eastern U.S. shifts the storm track northward and brings a
period of drier conditions to many after unsettled weather much of
the week. Embedded impulses within the upper-ridge will trigger
convection, potentially organized, across the Upper Great Lakes to
Interior Northeast Saturday (day 4). A Marginal Risk ERO is in
place as a strong low level jet and high PWATs (up to 2 standard
deviations above the mean) support the threat of heavy rainfall and
at least isolated flash flooding. Daily showers and thunderstorms
are also expected in vicinity of the Gulf Coast as disturbances
round the south side of the ridge and with possible influence of
tropical moisture for the western Gulf Coast/south Texas. This
influx of moisture also looks to bring precipitation chances
further northwest into western Texas and the southern high Plains
by later this weekend, with heavy rainfall/flash flooding concerns
especially into Monday - Wednesday as PWATs rise upwards of 2.5-3
standard deviations above the mean.

Upstream, an energetic deep upper-trough/Pacific system and
northern stream into the West will bring increasing precipitation
chances to the Pacific Northwest and northern Rockies/Plains this
weekend in unsettled flow with moderate to heavy rainfall
potential. A Marginal Risk ERO is in place for Saturday (Day 4) for
north-central Montana given a signal for high QPF in the guidance
and the presence of strong, very moist upslope flow behind the
departing cyclone in the northern Plains. Much colder temperatures
aloft will also bring some snowfall to higher elevations of the
northern Rockies, and this precludes a higher threat for flash
flooding in the region for now despite high QPF and anomalously
high moisture. Eventual lead frontal system development over the
Plains will bring a return of thunderstorm chances to portions of
the central/northern Plains and Midwest Sunday and particularly
Monday-Wednesday with moist return flow along a slow moving frontal
boundary. Potential organized convection in southwesterly flow
rounding the ridge may bring daily heavy rainfall/flash flooding
and severe weather threats.

The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains into the
Midwest/Great Lakes by Saturday, and the Ohio Valley/Mid-
Atlantic/Northeast by Sunday thanks to an anomalous upper-level
high building overhead. Widespread Major to Extreme Heat Risk
(levels 3 and 4/4) is forecast, indicating an intensity of heat
that is extremely dangerous to anyone without adequate cooling or
hydration. Heat indices are forecast to climb into the 100-110
degree range, potentially higher, and muggy overnight lows in the
mid- to upper 70s will bring little overnight relief from the heat.
Numerous daily record high and minimum temperatures are possible.
Unfortunately, this heat wave looks to persist through at least the
middle of next week, which will increases the danger. Some
locations from the central Plains into the Upper Midwest may see
some relief by Tuesday as a cold front moves into the region. Highs
will be cooler and below average by as much as 10-20 degrees
across portions of the Pacific Northwest, Great Basin, and northern
Rockies/High Plains this weekend as an upper level trough and
associated surface cold front from the northeast Pacific
overspreads the region.

Putnam

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Wed Jun 18 2025


A major synoptic pattern change is in store for the weekend and
into next week as an amplifying upper- level ridge over the
central/eastern U.S. shifts the storm track northward and brings a
period of drier conditions to many after unsettled weather much of
the week. Embedded impulses within the upper-ridge will trigger
convection, potentially organized, across the Upper Great Lakes to
Interior Northeast Saturday (day 4). A Marginal Risk ERO is in
place as a strong low level jet and high PWATs (up to 2 standard
deviations above the mean) support the threat of heavy rainfall and
at least isolated flash flooding. Daily showers and thunderstorms
are also expected in vicinity of the Gulf Coast as disturbances
round the south side of the ridge and with possible influence of
tropical moisture for the western Gulf Coast/south Texas. This
influx of moisture also looks to bring precipitation chances
further northwest into western Texas and the southern high Plains
by later this weekend, with heavy rainfall/flash flooding concerns
especially into Monday - Wednesday as PWATs rise upwards of 2.5-3
standard deviations above the mean.

Upstream, an energetic deep upper-trough/Pacific system and
northern stream into the West will bring increasing precipitation
chances to the Pacific Northwest and northern Rockies/Plains this
weekend in unsettled flow with moderate to heavy rainfall
potential. A Marginal Risk ERO is in place for Saturday (Day 4) for
north-central Montana given a signal for high QPF in the guidance
and the presence of strong, very moist upslope flow behind the
departing cyclone in the northern Plains. Much colder temperatures
aloft will also bring some snowfall to higher elevations of the
northern Rockies, and this precludes a higher threat for flash
flooding in the region for now despite high QPF and anomalously
high moisture. Eventual lead frontal system development over the
Plains will bring a return of thunderstorm chances to portions of
the central/northern Plains and Midwest Sunday and particularly
Monday-Wednesday with moist return flow along a slow moving frontal
boundary. Potential organized convection in southwesterly flow
rounding the ridge may bring daily heavy rainfall/flash flooding
and severe weather threats.

The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains into the
Midwest/Great Lakes by Saturday, and the Ohio Valley/Mid-
Atlantic/Northeast by Sunday thanks to an anomalous upper-level
high building overhead. Widespread Major to Extreme Heat Risk
(levels 3 and 4/4) is forecast, indicating an intensity of heat
that is extremely dangerous to anyone without adequate cooling or
hydration. Heat indices are forecast to climb into the 100-110
degree range, potentially higher, and muggy overnight lows in the
mid- to upper 70s will bring little overnight relief from the heat.
Numerous daily record high and minimum temperatures are possible.
Unfortunately, this heat wave looks to persist through at least the
middle of next week, which will increases the danger. Some
locations from the central Plains into the Upper Midwest may see
some relief by Tuesday as a cold front moves into the region. Highs
will be cooler and below average by as much as 10-20 degrees
across portions of the Pacific Northwest, Great Basin, and northern
Rockies/High Plains this weekend as an upper level trough and
associated surface cold front from the northeast Pacific
overspreads the region.

Putnam

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Wed May 7 2025

Valid 00Z Thu May 08 2025 - 00Z Sun May 11 2025


...Colorado...
Day 1...

Lingering vorticity on the western side of the departing upper low
will still trigger some light snow over the San Juans this evening
before tapering off tonight/early Thursday. WPC probabilities for
at least an additional 4 inches of snow after 00Z are low (10-40%)
above 11,000ft.

For days 2-3, the probability of at least 4 inches of snow is less
than 10%.

The probability of significant freezing rain across the CONUS is
less than 10%.

Note - this is the last regularly scheduled discussion (QPFHSD)
for the 2024-2025 winter season. Unless a significant winter
weather threat emerges, this discussion will next be updated on or
about September 25, 2025.


Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Wed Jun 18 2025

Valid 12Z Sat Jun 21 2025 - 12Z Wed Jun 25 2025

...First significant and extremely dangerous heat wave of the
season expected from the central Plains through the Midwest to the
Northeast this weekend/early next week...


...General Overview...

A significant and extremely dangerous heat wave is expected to
start the Summer across much of the central/eastern U.S. this
weekend/early next week under an expanding upper-level ridge. A
deep upper trough is forecast to work its way across the Northwest,
eventually emerging into the northern U.S., where a rather deep
cyclone is forecast to develop this weekend. Multiple frontal waves
appear to follow as they develop and track northeast through the
central/northern Plains along a slow-moving front by early next
week bringing storm chances with potential for heavy rainfall and
severe weather. Influx of tropical moisture into the Southern High
Plains may also bring a heavy rainfall threat early next week.


...Guidance/Predictability Assessment...

Model guidance remains in above average agreement on the general
evolution of the synoptic pattern through the medium-range period.
All guidance shows that the quasi-zonal pattern in place through
late week will begin to amplify following the departure of an
upper-wave off the East Coast. A strengthening and broadening
upper-high will build over the central/eastern U.S. while an upper-
low that had been anchored over the northeastern Pacific will drop
southward with upper-troughing digging across the western U.S. Most
of the forecast uncertainty revolves around a complex surface
evolution of the leading frontal system over the Plains as the
upper-trough makes slow eastward progress with embedded short-wave
energies leading to at least a couple rounds of cyclogenesis. The
latest runs of the GFS have come into better agreement with the
ECMWF with main surface low/frontal system evolution and
progression through the weekend and early next week as the system
eventually lifts northward into Canada north of the broad upper-
ridge, with support from EC and GFS means and AI guidance as well.
The 12Z and especially the 18Z GFS are a bit faster than this other
guidance but still cluster generally well. On the other hand, the
12Z UKMET and especially the CMC are slower in lifting the leading
surface wave northward, with further discrepancies in
amounts/footprint of associated QPF compared to the other guidance.
However, the certainty with respect to the synoptic pattern
ramifications for a significant, dangerous heatwave over the
central/eastern U.S. remain much higher, and this pattern looks to
remain in place through at least the middle of next week, with only
gradual weakening of the upper-high and modest weakening of the
upper trough.

The updated WPC forecast begins with a composite blend of the
deterministic guidance given good agreement, with the 12Z GFS used
over the 18Z GFS because of its closer clustering. The GEFS/ECens
means replace the contributions from the CMC/UKMET mid to late
period when their solutions with respect to the progression of the
central U.S. system notably diverge, and the means help to account
for growing uncertainty in smaller-scale details.


...Weather/Hazards Highlights...

A major synoptic pattern change is in store for the weekend and
into next week as an amplifying upper- level ridge over the
central/eastern U.S. shifts the storm track northward and brings a
period of drier conditions to many after unsettled weather much of
the week. Embedded impulses within the upper-ridge will trigger
convection, potentially organized, across the Upper Great Lakes to
Interior Northeast Saturday (day 4). A Marginal Risk ERO is in
place as a strong low level jet and high PWATs (up to 2 standard
deviations above the mean) support the threat of heavy rainfall and
at least isolated flash flooding. Daily showers and thunderstorms
are also expected in vicinity of the Gulf Coast as disturbances
round the south side of the ridge and with possible influence of
tropical moisture for the western Gulf Coast/south Texas. This
influx of moisture also looks to bring precipitation chances
further northwest into western Texas and the southern high Plains
by later this weekend, with heavy rainfall/flash flooding concerns
especially into Monday - Wednesday as PWATs rise upwards of 2.5-3
standard deviations above the mean.

Upstream, an energetic deep upper-trough/Pacific system and
northern stream into the West will bring increasing precipitation
chances to the Pacific Northwest and northern Rockies/Plains this
weekend in unsettled flow with moderate to heavy rainfall
potential. A Marginal Risk ERO is in place for Saturday (Day 4) for
north-central Montana given a signal for high QPF in the guidance
and the presence of strong, very moist upslope flow behind the
departing cyclone in the northern Plains. Much colder temperatures
aloft will also bring some snowfall to higher elevations of the
northern Rockies, and this precludes a higher threat for flash
flooding in the region for now despite high QPF and anomalously
high moisture. Eventual lead frontal system development over the
Plains will bring a return of thunderstorm chances to portions of
the central/northern Plains and Midwest Sunday and particularly
Monday-Wednesday with moist return flow along a slow moving frontal
boundary. Potential organized convection in southwesterly flow
rounding the ridge may bring daily heavy rainfall/flash flooding
and severe weather threats.

The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains into the
Midwest/Great Lakes by Saturday, and the Ohio Valley/Mid-
Atlantic/Northeast by Sunday thanks to an anomalous upper-level
high building overhead. Widespread Major to Extreme Heat Risk
(levels 3 and 4/4) is forecast, indicating an intensity of heat
that is extremely dangerous to anyone without adequate cooling or
hydration. Heat indices are forecast to climb into the 100-110
degree range, potentially higher, and muggy overnight lows in the
mid- to upper 70s will bring little overnight relief from the heat.
Numerous daily record high and minimum temperatures are possible.
Unfortunately, this heat wave looks to persist through at least the
middle of next week, which will increases the danger. Some
locations from the central Plains into the Upper Midwest may see
some relief by Tuesday as a cold front moves into the region. Highs
will be cooler and below average by as much as 10-20 degrees
across portions of the Pacific Northwest, Great Basin, and northern
Rockies/High Plains this weekend as an upper level trough and
associated surface cold front from the northeast Pacific
overspreads the region.

Putnam


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