FOUS30 KWBC 051952
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
352 PM EDT Sun Jul 5 2026
Day 1
Valid 12Z Sun Jul 05 2026 - 12Z Mon Jul 06 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN
PENNSYLVANIA THROUGH SOUTHEAST NEW YORK...
...Ohio Valley into the Mid-Atlantic & Northeast...
Impressive plume of tropical moisture extending from the Gulf Coast
through Southern New England will produce an environment favorable
for heavy rainfall today. 12Z RAOBs from PIT/IAD/OKX all measured
PWs between 1.75 and 1.95 inches, well above the 90th percentile
for the date and nearing daily-records. This is suggestive of the
tropical airmass, and weak lapse rates within a saturated column
with freezing levels nearing 14,000 ft point towards an environment
which will support heavy rainfall in all thunderstorms today.
Forcing for ascent into this environment will become increasingly
robust through the day as well. A front analyzed by WPC draped from
Illinois to Long Island will oscillate north/south today as a
stationary front, along which waves of low pressure will ripple
eastward, aided by shortwaves pushing eastward within the flow.
These waves will not only provide enhanced ascent, but also force
locally accelerated moist inflow and shear to create clusters of
more organized convection with heavier rainfall. This is reflected
by both HREF and REFS probabilities that exceed 40% for 2"/hr
rainfall rates, this morning/aftn in the OH VLY and then this
evening for the Mid-Atlantic states. With Corfidi vectors aligned
to the mean 0-6km wind, backbuilding/training of echoes is likely,
so corridors of heavy rain exceeding 3" are likely (60-80% chance)
with more than 5" possible (30-50%) chance.
The greatest risk areas for the heaviest rain are focused in SE
MI/NW OH as well as eastern PA/northern NJ/southeast NY where HREF probabilities for 8"/24hrs show low but meaningful (5-10%)
probabilities. While soil moisture according to NASA SPoRT is well
below normal in the former (0-40cm soil moisture in the 10th
percentile), it is much more saturated in PA/NJ. Adding in the
urban influences across PA/NJ/NY, the inherited MDT risk still
appears needed, and has been expanded northeast into far southeast
Upstate NY to account for latest trends. At this time, New York
City appears to remain just west of the heaviest rainfall so was
excluded from the MDT risk area, but otherwise, it appears likely
that numerous impacts from flash flooding will occur today in this
area, with locally significant events possible.
...Southern Plains and Gulf Coast through the Tennessee Valley...
Broad mid-level trough will remain aligned SW to NE from Texas
through Kentucky through today. Within this trough, several weak
mid-level impulses are progged to rotate E/NE through the flow,
providing locally enhanced ascent within an already unstable
atmosphere characterized by widespread MUCAPE around 3000 J/kg. At
the surface, a weak cold front will drop southeast, reaching along
a line from Kentucky to the Red River Valley of the South by this
evening before stalling. The overlap of the weak impulses on this
baroclinic gradient will help create ripples of low pressure, and
this extra lift will help create scattered thunderstorms today.
PW anomalies of +1 (to locally +1.5) sigma will support heavy
rainfall rates of 1-3"/hr, which through weak storm motions (0-6km
mean winds of just 5-10 kts and variable direction) will create
areas of heavy rainfall capable of producing at least isolated
instances of flash flooding. Both the HREF and REFS 24-hr
neighborhood rainfall probabilities show scattered areas of greater
than 30% chance for at least 3" of rain in a large area, but the
weak shear to support generally pulse convection should limit more widespread/organized amounts to this level. In general, the
inherited MRGL risk was maintained with only cosmetic adjustments.
However, an expansion west of the MRGL was created along the Red
River Valley near the OK/TX border for some potential multi-cell
development exhibiting short-term training tonight.
...Florida Peninsula...
After coordination with WFOs MLB/JAX, added a small MRGL risk for
the eastern third of the Florida Peninsula for today. Ridge of high
pressure centered just west of the state will produce generally
weak mean flow, but with subtle upper diffluence. Generally SW
winds will help convection track slowly northeast into the
aftn/eve, which will likely result in sea-breeze collisions on the
Atlantic Coast later today with storms stalling/regenerating in the
pulse environment. PWs above 2" will support 1-3"/hr rain rates
(30-50% chance for 2"/hr from both the REFS and HREF), which
through stalling/slow motions could result in areas of 3-5" of
rainfall. Should any storms stall across the more urban areas or
atop soils more sensitive from 24-hr rainfall as much as 4",
instances of flash flooding could result.
Weiss
=20
Day 2
Valid 12Z Mon Jul 06 2026 - 12Z Tue Jul 07 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE COASTAL MID-ATLANTIC FROM DELAWARE TO CONNECTICUT...
...Mid-Atlantic and Northeast...
Another active day of heavy-rain producing convection is expected
Monday as waves of low pressure ripple along a latitudinally
wavering stationary front causing multiple rounds of training
thunderstorms.
At 12Z Monday /start of D2/ this front is progged to be generally
aligned west to east from central OH through central NJ, although
some variation in this placement is likely due to model
uncertainty. Two distinct shortwaves moving along this front will
help track dual waves of low pressure eastward, each of which will
locally enhance ascent (one across western PA, the second from NJ
into southern New England). Aloft, broad troughing will persist
across New England, leaving pinched almost zonal flow towards the
Mid-Atlantic, while weak jet energy leaves modest RRQ diffluence in
its wake. This synoptic lift will occur within robust
thermodynamics characterized by PWs over 2" and MUCAPE rising to
500-1000 J/kg with an intense gradient expected along the
aforementioned front. At the same time, moist 850mb inflow will
become locally backed and accelerated (still to a modest 15-20 kts)
to impinge and isentropically ascend the boundary. Together, these
pose a significant risk for heavy rainfall capable of producing
flash flooding.
Although there remains typical uncertainty into the exact evolution
of heavy rain on Monday/Monday night, the threat appears to be
increasing for flash flooding. The high-res CAMs are in good
agreement that there will be impressive amounts of rainfall (3-6"
with embedded much higher totals above 8" as reflected by the REFS
and HREF PMM) but the placement varies considerably. This suggests
the probabilistic output is critical for evaluating the excessive
rainfall outlook, and the recent HREF and REFS 5"/24hr neighborhood probabilities reach above 40% for coastal New England, Long Island,
and south through the DelMarVa. In these areas 24-hr probabilities
for 8" from both ensemble systems also are notable (20-40%). With
the impressive thermodynamics in place, and robust persistent
forcing tapping into this, rainfall rates at times reaching 2-3"/hr
combined with aligned mean wind/Corfidi vectors which are parallel
to the boundary will drive training/backbuilding to support these
heavy rainfall amounts.
While FFG exceedance probabilities are somewhat modest when
compared to the rainfall probabilities (locally 25-40% chance),
some of these areas will be experiencing heavy rainfall on D1 which
will contribute to the increasing vulnerability on D2. After
coordination with the affected WFOs, a MDT risk was raised for
portions of eastern PA, NJ, New York City, and southern CT where
confidence is highest in training heavy rainfall leading to
numerous flash flood instances, some of which could be significant.
A bit farther west, a secondary area of low pressure interacting
with the same thermodynamic environment will produce streaks of
heavy rain producing convection from western PA through the
vicinity of Washington, D.C. While uncertainty is a little higher
in this area as to the coverage, speed, and intensity of the
thunderstorms, both the HREF and REFS depict a 20-40% chance of
2"/hr rain rates with at least short-term training potential. FFG
across western PA is quite low (1-1.5"/3hrs) and HREF/REFS
exceedance potential is elevated as a result. Farther south into
the D.C. area, FFG is higher, but these intense rates atop more
urban regions could still pose a flash flood concern so a SLGT
risk was added across these areas.
...ArkLaTex east through the Carolinas...
A slow moving cold front will drop slowly southward, reaching a
line from southern Arkansas through eastern Tennessee by Tuesday
morning before stalling. This front will sit within a plume of
overlapping elevated PWs (1.75 to 2.00 inches) and MUCAPE
(1000-2000 J/kg) to support hourly rainfall of 1-2" with higher
short-term rates. 0-6km bulk shear is progged to be minimal (less
than 20 kts) so storms that form will likely be of the pulse
variety. However, weak Corfidi vectors of just around 5 kts aligned
both to the mean wind and the front will allow for repeating rounds
and some short-term training of these intense rainfall rates.
Additionally, pulse convection may redevelop along outflows and
through collisions, suggesting that some places may experienced
multiple rounds of heavy rainfall during primarily the peak-
heating hours of Monday. This setup is still supportive of the
inherited MRGL risk, and only cosmetic adjustments were made to
account for the recent guidance.
Weiss
=20
Day 3
Valid 12Z Tue Jul 07 2026 - 12Z Wed Jul 08 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN PLAINS...
...Northern Plains...
A shortwave cresting the expanding ridge centered over the Four
Corners will translate steadily eastward from central MT early D3
to western MN by the end of the forecast period. This shortwave
will drive downstream PVA and height falls while concurrent but
modest RRQ diffluence in the tail of a distant jet streak helps
enhance synoptic lift. At the surface, a wavering boundary with a
wave of low pressure moving along it will try to shift north in
response to subtly increasing southerly low-level flow, with the
resulting isentropic ascent aiding lift across the region. This
robust ascent will act upon PWs that will surge to 1.25 to 1.75
inches, or around +2 sigma, collocated with a plume of MUCAPE
exceeding 2000 J/kg.
Together, this will manifest as increasing thunderstorm development
most of the day on Tuesday, with activity moving steadily from west
to east across MT, while secondary development occurs in the
Dakotas along the front itself. Mean storm motions should generally
be around 20 kts to the E/NE, but increasing bulk shear to 40-50
kts and aligned Corfidi vectors suggests some backbuilding or
training of clusters will develop. Hourly rainfall as much as
0.75"-1.0"+ is likely, which could create locally 2-3" of rainfall
as reflected by modest (5-15% chance) of 3"/24 hrs. This rain will
occur atop sensitive soils due to recent heavy rainfall, and 3-hr
FFG is as low as 1-1.5"/3hrs. The inherited SLGT risk was modified
to account for the recent UFVS first-guess fields, with the MRGL
also adjusted for recent model trends and soil vulnerabilities.
...Mid-Atlantic States...
Scattered to widespread thunderstorms will develop during the aftn
beneath a broad mid-level trough that will remain entrenched over
the area. Weak impulses within the weak flow combined with the
typical Piedmont trough and other lingering boundaries will be the
focus for convection initiation, followed by boundary interactions
and mergers leading to additional clusters during peak heating. In
general, these storms should be of the pulse variety and move E/NE
on 15 kts of 0-6km mean wind. However, the impressive
thermodynamics in place (PWs over 1.75 inches overlapping MUCAPE of
1000-2000 J/kg) will support rainfall rates of 1-2"/hr, through
which any short-term training or repeating rounds could lead to
instances of flash flooding.
...Eastern Massachusetts & Rhode Island...
A wave of low pressure will be moving south of Rhode Island at the
start of D3 /12Z Tuesday/ will gradually translate east through the
morning before exiting by the afternoon. Although there is some
spread in the departure speed of this wave, there is enough overlap
in the model QPF early Tuesday to add a small MRGL risk for eastern
MA, RI, and the Cape/Islands. While additional rainfall D3 may be
modest (10-30% chance of 1+"), lingering rates will remain
impressive within the high PW airmass, and this will be falling
atop soils saturated from what is expected to be heavy rainfall on
D2. The small MRGL risk was added to encompass areas with the
highest D3 probabilities atop the heaviest QPF footprint from D2.
Weiss
=20
Day 4 and Day 5
Valid 12Z Wed Jul 08 2026 - 12Z Fri Jul 10 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN GREAT LAKES WEDNESDAY...
20z Update: Only minor changes needed to the inherited risk areas.
There is some uncertainty regarding the convective mode and extent
of training on Wednesday over the northern Great Lakes, but the
multi-model consensus supports a max rainfall axis in line with
our ongoing Slight risk. Thus see no reason to deviate from the
ongoing forecast.
On day 5 we did expand the Marginal risk a bit further west over
the Plains as shortwave energy riding over the Western U.S. ridge
and an upper level jet streak should support organized convection
moving off the High Plains. As mentioned below, there will probably
be an embedded Slight risk or two on day 5 as we get closer and
confidence increases on the location, but a broad Marginal risk
will suffice for now.
Chenard
...Previous Discussion...
A seasonably moist, unstable airmass will be in place along the
northern side of an upper-ridge building over the western to
central U.S. early next week. An upper-level wave rounding the top
of the ridge will help trigger scattered to widespread thunderstorm
development along a frontal boundary through the northern
Plains/Upper Midwest Tuesday with ongoing/additional storms
spreading into the Upper Great Lakes Wednesday. Storms will likely
focus ahead of an eastward moving surface wave along the boundary
with clustering/upscale growth potentially leading to a more
organized system. Typical uncertainty on the exact location and
coverage of convective development remains a concern particularly
as the storm evolution Tuesday will likely impact storm
development/evolution Wednesday. However, there remains good
consensus amongst the deterministic model guidance on areal average
rainfall totals in the 1-2" range, locally 3"+, supporting the
threat for scattered flash flooding. A Slight Risk of Excessive
rainfall is in place from east-central MN into northern WI and the
UP/northern LP MI, with the potential for areal adjustment of the
risk in subsequent outlooks.
The embedded shortwave energy will help to subtly deepen/expand
troughing more broadly across the the Midwest and adjacent areas on
Thursday. The southward shift of stronger upper-flow aloft into
the central Plains east through the Middle Mississippi/Ohio Valleys
and Lower Great Lakes will bring more scattered thunderstorm
chances across the region. Seasonably high instability and moisture
pooling along a southward progressing cold front will support
locally heavy rainfall bringing the threat for at least isolated
instances of flash flooding, and a broad Marginal Risk of Excessive
Rainfall has been outlined. A targeted Slight Risk may eventually
be necessary with more confidence in the frontal position as storm
motions may tend to run generally parallel to the boundary helping
to lead to prolonged/repeated rounds of rainfall.
Putnam
=20
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-O4QmvqeGEkMTA5U6uMkL05VuNekeYpIix1N2FjbkcmY= PQWLikYmHv7XUNL7JQji74Sm1LdPRWtNDytnDTXeoOEfkos$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-O4QmvqeGEkMTA5U6uMkL05VuNekeYpIix1N2FjbkcmY= PQWLikYmHv7XUNL7JQji74Sm1LdPRWtNDytnDTXecT_FQq4$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-O4QmvqeGEkMTA5U6uMkL05VuNekeYpIix1N2FjbkcmY= PQWLikYmHv7XUNL7JQji74Sm1LdPRWtNDytnDTXeePD189Q$=20
$$
=3D =3D =3D
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* Origin: Capitol City Weather Station (1:2320/127)