Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Wed Jun 18 2025
Day 1
Valid 01Z Thu Jun 19 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...
01Z Excessive Rainfall Discussion...
The area extending from parts of the southern and eastern Great
Lakes into the Mid-South remain the primary concern for excessive
rainfall this evening and into the overnight hours. The HRRR and
HREF keep pushing showers and thunderstorms southward across parts
of the Ohio and Tennessee Valley with spotty 15 percent
neighborhood probabilities of rainfall exceeding 1-hour flash
flood guidance in parts of Tennessee. Farther north...the threat of
heavy to potentially excessive rainfall lingers as mid-level
height falls continue tracking northeastward and support from a
departing upper jet streak. In some cases..the concern arises from
repeat/training convection.
Bann
Previous Excessive Rainfall Discussion...
...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
344 AM EDT Thu Jun 19 2025
Day 1
Valid 12Z Thu Jun 19 2025 - 12Z Fri Jun 20 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL APPALACHIANS...
...Central Appalachians...
Cold front progression from the Ohio Valley through the Eastern
CONUS will lead to scattered instances of heavy convection along
and just ahead of the front during its evolution. As of now, the
highlight will be a steady forward motion of cells given the mean
field and general speed shear located within the warm sector of the
synoptically driven ascent field. Thunderstorms from eastern OH
down through the Tennessee Valley and points east will be capable
of 1-2"/hr rates within any convective development thanks to
relevant buoyancy out ahead of the surface front and deep moist
plume still running between +1 to +2 deviations above normal from
the Southeast CONUS up through New England. The greatest area of
concern remains the interior Mid Atlantic positioned between WV up
through far eastern OH and Western PA where remnant soils have been
significantly compromised over a succession of 5 straight
convective impact days. Area FFG's for 1hr indices are down as low
as 0.5/hr for exceedance with some spots even lower within the
confines of the Central Appalachians in Northern WV and the
northern Laurels in PA. The prospects for considerable rates and
training potential are lower than previous days due to the more
progressive nature of precip, but the environment is very capable
of producing rates sufficient for localized flooding in those areas
that have been hardest hit. In coordination with the local WFO's
across the interior Mid Atlantic, a targeted SLGT risk was added
for the areas with the lowest FFG's and more susceptible flash
flood capabilities.
...Mid Atlantic and Northeast...
Across the Mid Atlantic and Northeast, the front will produce some
heavy thunderstorms capable of flash flooding within the urban
corridor extending from Richmond up through NYC, however the
progressive nature of the storms should curb the worst impacts and
relegate to a more isolated threat with the urban centers the most
at risk within the nature of the setup. A quick 1-2" with locally
higher is forecast over the above I-95 megalopolis corridor, but
the threat is not anticipated to be widespread with areal average
QPF closer to ~0.5" in most areas with stripes of heavier QPF noted
in the 00z HREF blended mean output. This entire area up through
parts of New England remain firmly in a MRGL with a small chance of
upgrade over parts of the Mid Atlantic if morning CAMs indicate
more aggressive signals.
...Southeast...
Another heavy rain scenario is depicted over parts of the Lower
Mississippi into the Southeast U.S. where convection developing
overnight into a MCS will lead to heavy rain pushing south through
parts of AR/MS/AL tomorrow morning with an flanking line
potentially inducing some backbuilding/training scenarios over
Southern AR. The expected magnitude of the precip should thwart
significant flash flood concerns within the primary axis of the
complex, but a few areas could certainly be impacted enough to
produce localized flash flooding. Over the flanking side of the
complex back west, that area will need to be monitored closely due
to the backbuilding potential and slower storm motions as mean flow
is much weaker and more susceptible to this potential. A MRGL risk
is in place over the Southeast to highlight the threat.
Kleebauer
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Thu Jun 19 2025
Day 2
Valid 12Z Fri Jun 20 2025 - 12Z Sat Jun 21 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE UPPER
MIDWEST AND PORTIONS OF THE NORTHERN ROCKIES...
...Upper Midwest...
Amplified mid and upper pattern across the Western CONUS into the
Northern Plains will lead to a stout area of low pressure
developing across the Western High Plains, moving east through the
Upper Midwest as we move through Friday into Saturday morning.
South of the area will see a strong ridge pattern unfold creating
an enhanced thermal gradient pattern with a budding warm sector and
ample surface based instability with most guidance inferring
3000-5000 J/kg of SBCAPE across the area between the eastern
Dakotas over into the Upper Midwest by Friday evening. Split jet
max ejecting northeast out of the Plains will lead to increasing
ascent within the diffluent area of the jet and along the eastern
flank of the intensifying surface low. Thunderstorms will blossom
across the Eastern Dakotas and quickly advance eastward with
upscale growth thanks to the speed shear presence and strong
thermal gradient to maintain general MCS structure. Inflow around
the eastern flank of the low will aid in the overall maintenance
of the expected complex with smaller convective cells forming out
ahead and being integrated into the complex as it maneuvers through
MN. Areal QPF within the latest blend and ensemble bias corrected
forecast indicates a general 0.5-1" coverage with maxima likely to
locally exceed 2" over a short period of time within a zone
extending through Central MN into the Arrowhead. Will monitor for
backbuilding within the flanking portion of any complex which could
lead to local enhancement of precip and enhance flash flood
prospects in pockets where the MCS crosses. For now, the
progression of the MCS would favor limited training potential and
more impacts based on enhanced rates given the favorable upper
level dynamics, instability, and rich moisture pull within the
eastern side of the surface low. The previous MRGL risk was
maintained with only some minor adjustments based on QPF
distribution this forecast.
...Northern Rockies...
Guidance remains pretty locked in for the anticipated evolution of
the next disturbance entering the Pacific Northwest with convective
impacts forecast for the Northern Rockies and adjacent areas to the
east. 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. The previous MRGL risk was maintained given the
expected evolution with general run to run continuity among
deterministic and global ensemble means.
Weiss/Kleebauer
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Thu Jun 19 2025
Day 3
Valid 12Z Sat Jun 21 2025 - 12Z Sun Jun 22 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN GREAT LAKES, INTERIOR NORTHEAST, AND NORTHERN MONTANA...
...Northern Great Lakes into the Northeast...
Shortwave progression out of the Upper Midwest will ride along the
northern periphery of our expansive ridge as we move through
Saturday. Ensemble consensus pins the energy over the Northern
Great Lakes with remnant thunderstorms propagating through the
Michigan U.P. into adjacent Ontario with a break in convective
activity in the CONUS before the disturbance re-emerges over
Upstate NY and Northern New England. Some discrepancy on the
northern extent of the shortwave progression as the ECMWF bias is
further north with sights on Western ME and far northern VT/NH as
the impact points. Other guidance is suggesting a bit further south
into Upstate NY through Central New England with heavier precip
threats more likely into the central and northern Hudson Valley.
This is a period to monitor closely as flash flood impacts will be
tied to the progression of a fairly robust complex as it exits out
of Canada. QPF distribution is skewed towards heavier precip
located within North Country of NY state with some secondary maxima
over Northern New England down through the Adirondacks. Heavy rain
over the U.P. may be progressive enough to curb significant
impacts, but the eastern portion of the U.P. is the area of concern
with the vacating complex as it moves quickly through the region.
The MRGL risk inherited was adjusted slightly to account for the
uncertainty in the exact progression of the complex.
...Northern Montana...
Our potent mid-upper trough will meander over the Pacific Northwest
with a strong shortwave migrating out of the base of the trough,
eventually closing off right along the International Border to the
northeast of Glacier National. Surface low development in-of the
closed upper reflection should provide a narrow axis of convergence
just outside the eastern slopes of the Rockies generating a period
of heavy rainfall in the adjacent valleys to the east of the
mountains. Height falls across the region will be significant
creating favorable mid-level lapse rates within any convective
scheme along with ample moisture advection east of the terrain. The
threat is very much tied to the northern tier of MT where the
convergence pattern is greatest. The threat is less pronounced
further south and east comparatively, however some inference of a
few mid-level perturbations ejecting downstream over Northern WY
into Southern MT could provide a secondary area of focus for heavy
rainfall. For now, the main threat within the QPF distribution is
for locally heavy rainfall in that small zone of convergence under
the surface low formation near the border. Local 1-2" is forecast
in that area with some ensemble QPF output closer to 3" not too far
away into Canada. Targeted MRGL risk for that area east of the
terrain remains with little change from previous forecast.
Kleebauer
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 Thu Jun 19 2025
A major synoptic pattern change is in store this weekend and into
next week as an upper-level ridge amplifies over the
central/eastern U.S. and precipitation chances focus along the
periphery. A leading frontal system ahead of a deep- upper trough
over the western U.S. will become quasi-stationary northwest of the
ridge through the Midwest southwest through the central Plains.
Embedded energies in the upper flow with accompanying frontal waves
to follow look to trigger widespread convection in vicinity of the
boundary Monday-Thursday. Anomalously high moisture (2+ standard
deviations above the mean) will lead to multiple days of heavy
rainfall and flash flood potential, with a Slight Risk ERO
introduced for day 5 (Monday) centered on the Middle Missouri
Valley, and a broader Marginal Risk from the Upper Midwest
southwest through the central Plains. Some severe weather will be
possible as well. To the southwest, an influx of moisture from
Mexico, connected at least in part to tropical cyclone Erick in the
eastern Pacific, is forecast to bring an increasing chance of
enhanced rainfall into west Texas and the southern high
Plains/Rockies later this weekend and especially into Monday-
Wednesday as PWATs rise upwards of 2.5-3 standard deviations above
the mean. For this reason, portions of the southern Rockies/High
Plains have been included in a day 5 (Monday) Marginal Risk.
Elsewhere, daily showers and thunderstorms are also expected in
vicinity of the Gulf Coast as disturbances round the south side of
the ridge. Precipitation chances (including some very high
elevation snow) will linger through Monday for the northern Rockies
under the influence of the deep upper-trough.
The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains/Midwest/Great Lakes
into the Ohio Valley/Mid-Atlantic/Northeast on Sunday thanks to an
anomalous upper-level high building overhead. Heat will intensify
for portions of the interior South as well. Widespread Major to
Extreme Heat Risk (levels 3 and 4/4) is forecast, indicating an
intensity and duration 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, with 110-115
possible for portions of the Upper Ohio Valley and eastern
Carolinas/southern Mid- Atlantic. In addition, 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. Some locations from the central Plains into the Upper
Midwest will see some relief Monday-Tuesday as a cold front moves
into the region, and the focus for the most intense heat shifts
from the Midwest/Great Lakes into the Ohio Valley and Mid-Atlantic.
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 with a deep-upper level
trough overhead. Temperatures will moderate closer to average
through early/mid next week.
Putnam
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Jun 19 2025
A major synoptic pattern change is in store this weekend and into
next week as an upper-level ridge amplifies over the
central/eastern U.S. and precipitation chances focus along the
periphery. A leading frontal system ahead of a deep- upper trough
over the western U.S. will become quasi-stationary northwest of the
ridge through the Midwest southwest through the central Plains.
Embedded energies in the upper flow with accompanying frontal waves
to follow look to trigger widespread convection in vicinity of the
boundary Monday-Thursday. Anomalously high moisture (2+ standard
deviations above the mean) will lead to multiple days of heavy
rainfall and flash flood potential, with a Slight Risk ERO
introduced for day 5 (Monday) centered on the Middle Missouri
Valley, and a broader Marginal Risk from the Upper Midwest
southwest through the central Plains. Some severe weather will be
possible as well. To the southwest, an influx of moisture from
Mexico, connected at least in part to tropical cyclone Erick in the
eastern Pacific, is forecast to bring an increasing chance of
enhanced rainfall into west Texas and the southern high
Plains/Rockies later this weekend and especially into Monday-
Wednesday as PWATs rise upwards of 2.5-3 standard deviations above
the mean. For this reason, portions of the southern Rockies/High
Plains have been included in a day 5 (Monday) Marginal Risk.
Elsewhere, daily showers and thunderstorms are also expected in
vicinity of the Gulf Coast as disturbances round the south side of
the ridge. Precipitation chances (including some very high
elevation snow) will linger through Monday for the northern Rockies
under the influence of the deep upper-trough.
The first significant heat wave of the season is expected to be
expanding in coverage from the central Plains/Midwest/Great Lakes
into the Ohio Valley/Mid-Atlantic/Northeast on Sunday thanks to an
anomalous upper-level high building overhead. Heat will intensify
for portions of the interior South as well. Widespread Major to
Extreme Heat Risk (levels 3 and 4/4) is forecast, indicating an
intensity and duration 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, with 110-115
possible for portions of the Upper Ohio Valley and eastern
Carolinas/southern Mid- Atlantic. In addition, 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. Some locations from the central Plains into the Upper
Midwest will see some relief Monday-Tuesday as a cold front moves
into the region, and the focus for the most intense heat shifts
from the Midwest/Great Lakes into the Ohio Valley and Mid-Atlantic.
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 with a deep-upper level
trough overhead. Temperatures will moderate closer to average
through early/mid next week.
Putnam
