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
334 AM EDT Wed Jun 18 2025

Valid 00Z Thu 19 Jun 2025 - 00Z Thu 26 Jun 2025

A stable and dry pattern looks to remain in place for the islands
through late this week/weekend and into the middle of next week.
An area of surface high pressure northeast of the islands is
forecast to strengthen this weekend bringing a period of gustier
trade winds through Monday as the pressure gradient tightens.
Winds should lighten into the middle of next week as the high
weakens and begins to drift north away from the islands. Rainfall
should be limited to lighter terrain- enhanced showers mostly for
windward areas.

Putnam

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1157 AM EDT Wed Jun 18 2025
Day 1
Valid 16Z Wed Jun 18 2025 - 12Z Thu Jun 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
GREAT LAKES AND THE MID-SOUTH STATES...

...Great Lakes through the Mid-Mississippi Valley...
Strung out shortwave embedded within amplifying mid-level flow
will swing northeastward today as the primary trough axis shifts
from the Central Plains to the Ohio Valley. The collocated height
falls/PVA accompanying this energy will interact with the modest
RRQ of a departing upper jet streak to help deepen a surface low
moving into the Great Lakes. This low will strengthen along the
front, leading to scattered/widespread showers and thunderstorms,
but with two focused regions of excessive rainfall -- northern
Illinois across Lower Michigan and from near Memphis into Kentucky.

The greatest risk for heavy rain capable of producing flash flooding
appears to be centered across the lower peninsula (L.P.) of
Michigan. Heavy rain is favored along a warm front ahead of the
low track, and along a deformation axis in the same region with
embedded convection (some occurring already this morning/noontime).
850mb flow ahead of the low will surge to 20-30kts, drawing PWs as
high as 1.75 inches into MI, coincident with MUCAPE nearing 1000
J/kg. This will support rainfall rates that have a moderate chance
(40-60%) of exceeding 1"/hr at times. The heaviest rain rates are
expected along the leading warm front thanks to stronger
instability this evening, and during that time the combination of
20-30 kts of bulk shear and 0-6km mean winds aligned to the front,
despite progressive speeds near 30 kts, will support rainfall that
will likely (70% chance) reach 3", and may reach as much as 5" in a
few isolated locations. This could result in instances of flash
flooding (15-30% chance of 3-hr FFG exceedance) despite generally
dry antecedent conditions, and the SLGT risk was maintained here.

Farther to the south, the cold front will be the primary mechanism
for ascent/convective development as it tracks east from the Central
Plains to the Tennessee Valley. This front will impinge upon intense
thermodynamics characterized by MUCAPE above 3000 J/kg and PWs
approaching 2 inches (>90th percentile). Thunderstorms will likely
develop along the length of this front during peak instability,
and where bulk shear exceeds 25 kts, generally from IN through AR,
clusters of more organized convection are expected. While cells
will generally move rapidly along the front, Corfidi vectors
progged to collapse to just 5-10 kts suggests some
backbuilding/short term training, which could enhance rainfall to
more than 3 inches in some areas (max ensemble rainfall is 5-7").
There is still some latitudinal spread in the axis of highest
rainfall potential between the HREF and REFS members, leading to
lower confidence in placement of heaviest rain. However, the EAS
probabilities from both ensemble clusters, while varying greatly in
magnitude, are focused generally in the same area, and atop a
region of more sensitive soils and lower FFG due to 7-day rainfall
more than 300% of normal. The SLGT risk was maintained in this area
due to the potential for this heavy rain falling atop vulnerable
soil conditions.


...Mid-Atlantic into New England...
Southwest return flow around a Bermuda-type ridge off the
Southeast coast will continue today, pumping elevated moisture
northward into the Mid-Atlantic States. PWs are forecast to reach
around 2 inches (12Z IAD sounding was 2.15" / 99th percentile /
near-record for this time of year per the ESAT). This PW will be
spread through the entire column as reflected by long-skinny CAPE
profiles among the regional soundings, indicating efficient
rainfall processes within thunderstorms that develop along a weak
surface trough skirting across the area. Both the HREF and REFS
probabilities indicate a moderate potential (30-50%) for 1"/hr
rates, which, despite generally progressive motion, could cause
axes of 2-3" of rain where multiple rounds occur (especially over
the Mid-Atlantic DC-PHL-TTN). Recent HREF/RRFS members show
potential for >4" rainfall in this urban corridor. If any of this
heavy rain falls atop these urban areas or more sensitive soils
from recent rain (where FFG is as low as 1-1.5"/3hrs), instances
of flash flooding could result. Maintained the Marginal risk here
due to the expected coverage (more isolated) though local impacts
may be significant depending on the exact placement.

Fracasso/Weiss


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1157 AM EDT Wed Jun 18 2025
Day 2
Valid 12Z Thu Jun 19 2025 - 12Z Fri Jun 20 2025

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

Mid-level trough axis initially positioned across the Mississippi
Valley will become more progressive on Thursday as it weakens in
response to an expanding ridge over the Southern Plains. As this
trough weakens and move quickly towards the Atlantic coast, a
surface cold front beneath it will additionally track eastward,
likely exiting the Mid-Atlantic and New England coasts by Friday
morning, while lingering into the Southeast. This front will
provide a focus for convective development Thursday, especially
during peak heating as downstream SW 850mb flow of 25-35 kts surges
PWs to 1.75+ inches, reflective of an environment that will support
extremely efficient rainfall within thunderstorms. This indicates
that despite the rapid frontal progression, and accompanying
forward motion of thunderstorms (0-6km mean winds 20-25 kts),
intense rainfall rates of 1-2"/hr could still produce isolated
impacts, especially where any repeating storms can occur, or if
heavier rain falls atop urban areas or more sensitive soils.

At this time no SLGT risks have been introduced as storm motions
may be more perpendicular to the front, and thus, mostly
progressive. However, there is at least a subtle signal for some
heavier rainfall across the Central Appalachians. This area is
extremely sensitive due to recent heavy rainfall (7-day rainfall
150-300 percent of normal) which has primed soils and reduced FFG
to 1-2"/3hrs. If this signal increases, a targeted SLGT risk may be
needed across these most vulnerable areas.


Weiss


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1157 AM EDT Wed Jun 18 2025
Day 3
Valid 12Z Fri Jun 20 2025 - 12Z Sat Jun 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE NORTHERN
GREAT LAKES AND PORTIONS OF THE NORTHERN ROCKIES...

...Northern Great Lakes...
Low pressure emerging from the Northern High Plains will extend a
warm front downstream and into the Upper Midwest/Great Lakes. As
this warm front lifts steadily northeast, especially the latter
half of D3 /Friday night/, it will serve as a focus for blossoming
convection. The downstream amplifying 850mb flow lifting out of the
Gulf will reach as high as 40-50 kts into the Upper Midwest, and
with the presence of the low to the west, these winds will back
steadily to the SE to surge higher PWs, approaching 1.75 inches,
into the warm front and into MN/WI. The combination of moisture
convergence and isentropic ascent invof this front will help expand
clusters of thunderstorms Friday night, leading to an axis of heavy
rain that has a modest potential (10% or less from the ECENS/SREF)
of exceeding 3 inches. Despite high FFG across this region,
isolated flash flooding could result from this rainfall.


...Northern Rockies...
Extremely anomalous mid-level low will dig into the Pacific
Northwest Friday, pushing 500mb heights to below the 00Z minimum of
the climatological database from NAEFS. Where intense height
falls/PVA combine with the increasing diffluence along the LFQ of a
Pacific jet streak, surface pressure falls will result, leading to
a deepening low pressure moving from ID into MT. The increasingly
backed low-level flow ahead of this system will cause 850mb winds
to surge out of the E at 15-25 kts, lifting favorably to upslope
into the terrain while additionally transporting a ribbon of PWs
above 1 inch into the High Plains and banking into the eastern side
of the Rockies. This will cause expanding precipitation, with
embedded rainfall rates above 0.5"/hr where a narrow corridor of
instability exists over northern MT. Locally heavy rainfall of
1-2", with locally higher amounts, will result, leading to the
potential for isolated flash flooding atop FFG that is only
1-1.5"/3hrs.

Weiss
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