FOUS30 KWBC 301944
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Tue Jun 30 2026
Day 1
Valid 16Z Tue Jun 30 2026 - 12Z Wed Jul 01 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GREAT LAKES...NEW ENGLAND...OVER SOUTHWEST TEXAS AND THE
FLORIDA PENINSULA...
16Z Update: The entire forecast remained consistent in the general
placement of heavy convection with only a few changes made to
account for trends within the latest CAMs. Heavier rainfall is
likely to be confined closer to the western half of FL with the
axis of heaviest rain likely to occur west and south of SR-91 to
the coast. This allowed for trimming of the eastern fringes of the
previous MRGL risk, matching the higher probs for >3" off the
latest HREF neighborhood probabilities.
Areal coverage of the MRGL in the Northeast was trimmed to remove
northern ME and the rest of the ME coast as trends have moved away
from the shortwave progression being far enough north and less
progressive to attain any flash flooding threat.
A small expansion of the MRGL risk was made over the Sacramento
mountains in NM for account for modest probs of >1" over the more
sensitive area near Ruidoso where burn scar remnants allow for
greater run off potential. This is a low-end threat in that
vicinity, however locally heavy rainfall of 1-2+ inches/hr are
still forecast across Southwest TX into the Panhandle on the
eastern side of the dryline.
Kleebauer
..Previous Discussions...
...Southern High Plains to the Great Lakes...
There will be a risk of excessive rainfall in various places east
of the Rockies today as a deep/strong low moves slowly from
Saskatchewan to Manitoba while a broad, sprawling upper high
expands across the Southern Plains into the Mid- Atlantic and parts
of the northeastern United States. This results in broad
southwesterly flow that transports an unstable airmass with
abundant Gulf moisture into parts of the Southern High Plains
northeastward through the Great Lakes. Embedded shortwave energy
within the larger scale flow pattern will support increasingly
scattered convection with locally heavy rains and isolated runoff
issues this afternoon into tonight. The concern is especially
heightened over burn scars and dry washes/arroyos of the terrain
near the southern Rockies. The latest hi-res guidance shows the
potential for 1-3"+ of rainfall with these storms even if they
remain rather short- lived and transient due to efficient downpours
with rain rates of 1-2" per hour.
...New England...
The latest hi-res guidance supports the maintenance/renewed
development of thunderstorms in northwesterly flow over New England
and portions of Upstate New York. The more widespread/organized
nature of the convection would bring at least the risk of isolated
flash flooding with storm total rainfall of 2 or 3 inches possible
as suggested by much of the hi-res guidance. MRGL risk remains in
effect over portions of Upstate NY into northern and central New
England.
...Florida...
A cold front will be the focus for showers and thunderstorms as it
makes its way southward into the northern Florida peninsula. The
models have been maintaining their signal for convection and the
storms look to be efficient rainfall producers considering the
airmass will have nearly 2 inch precipitable water values already
in place. As a result...maintained a Marginal risk of excessive
rainfall over portions of the peninsula, the panhandle and a small
part of neighboring states.
Bann
=20
Day 2
Valid 12Z Wed Jul 01 2026 - 12Z Thu Jul 02 2026
..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER
MIDWEST...
Upper Midwest and Upper Great Lakes Regions...
20Z Update: The previous forecast remains on track with the overall
synoptic overview still very much in-line in run-to-run continuity.
Hi-res models have been initiating heavier convection across
southeastern MN with a focus on the area south of MSP towards
Rochester and neighboring areas. This is likely coincident with the
alignment of a sharp theta_E gradient oriented along a cold front
that will bisect the region from west-southwest to east-northeast
across southern MN into WI. Multiple shortwaves will ride across
the northern periphery of a ridge expanding across the eastern
CONUS leading to aided mid and upper forcing to couple with a
primed environment positioned over the Upper Midwest. Heavy
rainfall is likely with any convective core that develops leading
to localized rates of 1-2"/hr as noted via the modest hourly rate
probabilities from the 12z HREF. Neighborhood probabilities for >2"
are running between 60-90% across all of southeastern MN into
Central WI with >3" probs still a respectable 30-60% with a
bullseye located just east of Rochester, MN. This was enough of a
signal to expand the SLGT risk further southwest into the region
and generally maintain the previous forecast over WI with some
minor trimming on the northern edge of the risk as noted via trends
in a slight southward shift of the frontal alignment.
Kleebauer
..Previous Discussion..
The large scale flow changes little during the Day 2 period with
deep low pressure moving slowly from Manitoba into Ontario while a
strong and sprawling upper high remains quasi-stationary over the
eastern US (except for portions of New England). That leaves a
broad region of enhanced moisture-transport from the central and
southern portion of the Rockies front-range and nearby High Plains
to the Upper Mississippi Valley and the Upper Great Lakes region.
There was a growing overlap in the models between shortwave energy
rotating around the Canadian upper low and the deep-layered
moisture in the channel of the moist southwesterly flow across the
Upper Mississippi Valley with a corresponding increase in model
QPF. The UKMET and NAM NEST were most aggressive with their
QPF...perhaps from convective feedback...but even other models
tended to place their QPF maximum values somewhere over or near
Wisconsin. This region had precipitable water values in excess of
2.5 standardized anomalies above climatology on Wednesday
afternoon/evening when daytime ML CAPE values are forecast to be in
the 1000-2500 J/KG range. This environment should remain
sufficient to produce a few more robust downpours with the threat
for some isolated flash flooding so introduced a Slight risk area
there. A broad...unfocused Marginal extended from the Upper Midwest southwestward to the Southern Rockies foothills. Weak and
difficult-to-time shortwaves embedded within the broader flow can
easily trigger storms capable of downpours almost anywhere within
the channel.
Bann
Northeast US...
20Z Update: No changes were necessary across the Northeast U.S. as
the forecast remains steadfast from the previous update. Pockets of
heavier rain are plausible across Central NY and points north with
a general maxima between 2-3" in the hardest hit locations. Best
chance for those heavier totals are forecast over Northern New
England with prob fields indicating modest potential for such
totals over northern VT down through the Green Mountain corridor.
The MRGL risk remains in effect.
Kleebauer
..Previous Discussion..
Additional showers and thunderstorms are expected over parts of New
England in the northwest flow to the east of the ridge axis of the
upper high. Seasonably high precipitable water value should support
at least some isolated heavier downpours. Antecedent conditions may
also be more sensitive depending on the evolution of more widespread/potentially organized convection on Tuesday. No major
changes were needed to the Marginal Risk area added on Monday.
Bann
Southeast Florida...
20Z Update: MRGL risk was maintained with the current update, but
did trim back some on the western and northern edge of the previous
update. Hi-res trends were pretty aggressive across Miami proper
which correlated to elevated probs for >3" locally and even some
relevant probs (30-50%) for >5" within the latest HREF output.
This allowed for maintaining the MRGL risk with a chance at a
targeted upgrade pending further trends. Convergence pattern across
the southeast FL coast is pretty well-documented as this point in
the CAMs, so there will likely be an area that receives appreciable
rainfall in the region. Whether that settles over an urban zone or
not will dictate the potential for flash flooding as FFG's remain
high across the area.
Kleebauer
..Previous Discussion..
The front which is expected to help focus showers and
thunderstorms on Tuesday will continue to make its way into the
southern Florida peninsula on Wednesday. Despite the front
becoming weaker and more diffuse with time...the expectation is
that the boundary will still act to help focus showers and
thunderstorms in the unstable airmass...aided by convergence along
the sea breeze along with potential for sea breeze collisions.
Bann
...Louisiana...
Inverted trough will maneuver around the southern periphery of a
strengthening ridge positioned to the north leading to an
increasing convergence pattern across the southern half of
Louisiana as we move into Wednesday. Recent trends have been more
aggressive with the signature over the I-10 corridor extending
from the Lower Sabine through the Lake Charles to Lafayette, LA
areas with the latest HREF blended mean QPF output pushing closer
to 2-3" across the area. Probabilities for >3" locally are up to
40-70% within that zone along the interstate with some lower end
probs for even >5" showing up between Lake Charles and Lafayette
proper in the latest update. One positive in this setup is the area
FFG's for all 1/3/6hr thresholds are very high given the drier
antecedent soils remaining over the area. This should curb a more
enhanced flash flood scenario, but still offer a modest prospect
given the heavy totals in the deterministic outputs. In
coordination with the local LCH and LIX WFO's, a MRGL risk was
added in this forecast update to encompass the aforementioned area.
Kleebauer
=20
Day 3
Valid 12Z Thu Jul 02 2026 - 12Z Fri Jul 03 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
NORTHERN PLAINS, UPPER MIDWEST INTO THE GREAT LAKES...
...Northern Plains/Upper Midwest/Great Lakes...
20Z Update: Models maintain a general convective threat across much
of the Northern Plains into the Mid and Upper Midwest on Thursday
as the synoptic pattern continues to promote persistent
northwesterly flow around the northern periphery of a strengthening
upper ridge positioned across the Eastern U.S. The general area of
convection from ND down through northern IA and points north will
offer the threat for isolated instances of flash flooding as models
have mixed areas of QPF maxima littered across the northern tier of
the CONUS. There could be an instance where heavy rainfall
intersects areas hit the previous period and offer a better
opportunity for flash flooding, however judgment on any targeted
upgrades would need to be assessed after the previous period's
rainfall. Will refrain an upgrade at this time and maintain
continuity with a broad MRGL risk over the Northern Plains to Upper
Midwest with a minor expansion northwest into central ND to
account for the latest precip forecast indicating heavier
convective potential back over the area.
Kleebauer
..Previous Discussion..
A broad region of west southwesterly mid to upper level flow is
expected to persist during the Day 3 period across the Northern
Plains into the Upper MS Valley and Great Lakes. The area should
still be located between an eastern closed upper high and a mean
western trough, both of which are in the process of weakening by
Saturday morning. Broadly diffluent mid- to upper-level flow
associated with embedded shortwave energy moving northeastward
within the west-southwest mid to upper level will support active
convection, possibly organized, in an axis of slightly above
average moisture across these regions. Only subtle changes were
made to broad marginal risk areas which were already issued
covering the period spanning from Thursday into early Friday. Confidence remains low with respect to where convection may become organized
and produce heavy rainfall and isolated runoff issues, possibly
linked to the changing behavior of the flow across portions of the
Central and Eastern US/Canadian border and ridge strength and
orientation in the eastern US.
Bann
=20
Day 4 and Day 5
Valid 12Z Fri Jul 03 2026 - 12Z Sun Jul 05 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE
NORTHERN PLAINS, MID TO UPPER MS VALLEY, GREAT LAKES, CENTRAL
APPALACHIANS, AND NORTHERN MID-ATLANTIC...
...2000Z Update...
On both days 4 and 5, both Marginal Risk areas were expanded a bit,
based on the latest 12Z probabilistic data (including GEFS and CMC
6/12/24hr QPF 2/3/5 inch exceedance probabilities. Did broaden the
areas a bit farther to the south on both days, basically 'casting a
wider net' to account for the latitudinal variability in the
guidance, and with the expectation that evolving MCS activity and
areas of potential cell training will be able to slip farther into
the ridge where low-level lapse rates will be quite high.
Hurley
Previous discussion...
The west southwesterly mid to upper level flow that has been
persistent across the Central to Northern Plains into the Upper MS
Valley and Upper Lakes region will begin to become more westerly
from the Northern Plains, eastward across the Lakes and into the
Northeast. Broadly diffluent mid to upper level flow associated
with shortwave energy moving east northeastward in this west
southwest to westerly mid to upper level will support active
convection, possibly organized, in an axis of slightly above
average moisture across these regions. Broad marginal risk areas
were depicted both day 4 and 5 to cover the current model spread
for locally heavy rains and isolated runoff issues. Concerns are
that with the low level flow will becoming increasingly westerly
across these regions from day 4 into day 5, there will be
potential for convection training for a period, likely late
afternoon into the early hours each day, along and just south of
the west to east oriented frontal zone expected to be moving slowly
southward across the northern tier from the Upper MS Valley into
the Lakes.
Oravec
=20
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5FgCA-DiL7Rrq0K35dIM-LD9eMImE6_T_GVJznF3g3ld= 7OCof94vqWJnP8YeSra40cYh99ZLeml-hjTvu4hStz9jXSE$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5FgCA-DiL7Rrq0K35dIM-LD9eMImE6_T_GVJznF3g3ld= 7OCof94vqWJnP8YeSra40cYh99ZLeml-hjTvu4hSuJbUCfc$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5FgCA-DiL7Rrq0K35dIM-LD9eMImE6_T_GVJznF3g3ld= 7OCof94vqWJnP8YeSra40cYh99ZLeml-hjTvu4hS7b26adU$=20
$$
=3D =3D =3D
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* Origin: Capitol City Weather Station (1:2320/127)