Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Tue Aug 4 2026
Day 1
Valid 2125Z Wed Aug 05 2026 - 12Z Wed Aug 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN ARIZONA, THE MID ATLANTIC, AND MIDWEST...
...Southwest/Southern High Plains...
The Slight Risk still looks reasonable and was maintained with only
minor adjustments across far southeast Arizona within a broader
Marginal. Typical terrain features and burn scars will be
particularly vulnerable to flash flooding concerns.
Weak energy aloft could undercut the broad Southwest upper ridge
to the south and provide support for enhanced convection this
afternoon and tonight. The combination of 1500-3000 J/kg MUCAPE
and above average moisture transport into the region (as shown by 4+
standardized anomalies greater than climatology for 850-700 mb
moisture flux from the GFS and 2+ standardized anomalies from the
ECMWF) should support rainfall rates above 1"/hour. Slow westward
motion will contribute to enhanced rainfall amounts.
...Southeast to Southern/Central Appalachians into the Mid-
Atlantic States...
2130Z Update: Have included a Slight Risk across much of central-
eastern VA, along with a small portion of north-central NC. Much of
this is related to the ongoing activity -- organized, slow-moving
convective clusters that lie within a ribbon of difluence aloft
(downstream of the H5 closed low), with strong deep- layer
moistening within an evolving Warm Conveyor Belt (WCB). TPW values
are between 2.2-2.4" along and south of the surface warm/stationary
boundary, quite sufficient for optimal warm rain processes as
MLCAPEs average between 1000-1500 J/Kg. MRMS shows 3-6+ inches of
rain within the last 3 hours from this activity. Expect the leading
edge of the convection to diminish somewhat as it heads into a
more stable environment across northern VA-southern MD later this
evening (strong S-N TPW gradient); however, additional spokes of
convection are expected to flare at least into the early evening
hours across the Slight Risk area. The latest (18) HREF shows
>2"/hr rainfall rate probabilities dropping below 50% over the
Slight Risk area by 2300Z.
Hurley
Previous discussion..
Steep low-to mid-level lapse rates and a moisture rich atmosphere
underneath a meandering upper low will support daytime and evening
thunderstorms that pose an isolated risk of flash flooding in the
region. The CAM guidance available this morning still depict a
broad area of 1000-2000 J/kg MUCAPE (locally higher) with morning
soundings showing 2 inch precipitable water values hugging the
coastal areas and 1.75 to 2.0 inch amounts extending westward to
near the Appalachians. Pockets of wet antecedent conditions could
exacerbate flooding concerns, while rugged terrain and urban areas
are also vulnerable.
...Central Plains into the Upper Midwest...
2130Z Update: Have hoisted a Slight Risk across a small portion of
southeastern NE along with southern IA, based on the latest
observational trends along with short term CAM trends, including
the 18Z HREF QPF exceedance probabilities. Current organized QLCS
segments upstream are moving into an environment with 1.7-1.9" TPWs
and 2000-3000 J/Kg of MUCAPE. Thermodynamically, the ingredients
for heavy rainfall is most certainly there; the risk for excessive
rainfall will ultimately come down to persistence/duration. Given
the slow frontal progression, with hints already of some repetitive
convection aligning more W-E, much of the latest mesoscale guidance
(CAMs) are showing 3-5+ inches of additional rainfall after 00Z,
with multiple rounds of elevated >1"/hr probabilities per the 18Z
HREF, i.e. between 23-04Z, and again 04-12Z overnight.
Hurley
Previous discussion..
A moderately strong trough advancing through the northern tier of
states will send a cold front through the Upper Midwest today and
into the Plains later tonight. Ahead of this system moisture and
instability will pool across the region an when coupled with the
right entrance region of the upper level jet there will be enhanced
ascent for rain/thunderstorms development. The front's axis of
orientation will generally be west to east which should be
supportive of training convection. Hi-res guidance has a general
consensus of 24 hour accumulations around 3 inches; however given
the recent drier period the threat for excessive rainfall and flash
flooding impacts may be minimal thus maintained a Marginal Risk.
The only modification was to trim the Marginal risk area that was
now in a more stable post-frontal environment.
Bann/Campbell/Tate
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Tue Aug 4 2026
Day 2
Valid 12Z Wed Aug 05 2026 - 12Z Thu Aug 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL PLAINS TO MIDDLE MISSISSIPPI VALLEY...
2030Z Update...
Few changes needed. Numerical guidance continues to shift the focus
for heavy rainfall and associated risk of flooding impacts
southeastward during the period. Little reason to make changes
given such consistency in the large-scale guidance.
Bann
Previous Discussion...
...Central Plains to Mid/Upper Mississippi Valley...
The upper trough and associated cold front described in the Day 2
discussion will reduce to a snail's pace while providing an axis
for moisture to pool and thunderstorms to focus. A Slight Risk for
an elevated threat for excessive rainfall was maintained given
some potential overlap with rain the previous day affecting
antecedent conditions. There has been more model spread in the
position of heaviest rain, but general consensus is along line from
northeast Kansas to the Chicago vicinity.
...Southern to Central Appalachians into the Northern Mid-
Atlantic...
Whatever is left of the upper level trough across the eastern U.S.
should devolve into a shear line by midweek. However, a moist and
unstable environment (PWs greater than the 75th percentile in an
already moist season of the year) will continue and expand
northwestward as the upper energy shifts. Scattered rainfall with
high rain rates can be expected thus maintaining a Marginal Risk
for excessive rainfall and local flash flooding potential. Convection
may once again be enhanced over portions of the Florida Peninsula,
but given a likely rainfall focus over the less sensitive areas of
the Everglades westward, will not introduce a Marginal at this
point.
...Southwest/Southern High Plains...
There will be a persistent influx of moisture along the southern
periphery of the Southwest upper high, although its been noted that
there is a less focused area for where higher QPF will occur. A
Marginal Risk remains for much of Arizona and New Mexico for
isolated flooding and runoff issues.
Campbell/Tate
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Tue Aug 4 2026
Day 3
Valid 12Z Thu Aug 06 2026 - 12Z Fri Aug 07 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE
SOUTHWEST THROUGH THE CENTRAL/SOUTHERN PLAINS, MIDWEST, & EAST...
2030Z Update...
No changes needed to the Marginal risk area extending from the
Southwest US through parts of the Central/Southern Plains eastward
into parts of the Eastern US.
Bann
Previous Discussion...
...Central Plains into the Lower Missouri Valley...
Another round of organized convection is expected to fire up along
the southward moving cold front. During the overnight hours,
moist, southerly flow will be increasing over the frontal boundary
which will lead to locally heavy rainfall, potentially accumulation
around 2.5 inches.
...Lower Lakes, Ohio Valley into the Northern Mid-Atlantic...
A slow-moving frontal boundary expected to persist as shortwave
energy track east along the southern edge of the Westerlies,
helping to accentuate lift in the high PW axis in the vicinity of
this front. Moderate to locally heavy rain totals expected with
hourly rain amounts up to 2.5" possible, supporting at least
isolated runoff issues in urban areas and places with some degree
of soil saturation.
...Southern to Central Appalachians...
A broad Marginal Risk covers the Central to Southern Appalachians
for widespread scattered convection. Not a lot of confidence in
details, but with PW values expected to remain in the 1.5-1.75"+
range, hourly rain amounts to 2.5" could lead to runoff issues,
particularly in urban areas and within sharp relief.
...Southwest/Southern High Plains...
A Marginal Risk was maintained for much of the Southwest and
Southern Rockies for monsoonal convection. The ridge placement
across the southern Great Basin during the time frame along with
some backing off in the moisture return on the guidance led to some
reduction in the Marginal Risk area across southern Nevada. While
there is continued low confidence with details, locally heavy rains
with hourly amounts up to 2" could lead to isolated runoff issues.
Campbell/Roth
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Tue Aug 4 2026
Day 4 and Day 5
Valid 12Z Fri Aug 07 2026 - 12Z Sun Aug 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE LOWER AND MID MISSISSIPPI VALLEY EAST AND NORTHEAST INTO THE
MID ATLANTIC AND NEW ENGLAND, ACROSS THE UPPER MISSISSIPPI VALLEY,
AND OVER THE SOUTHWEST...
2000 UTC Update: Fairly minor changes made to the Days 4 and 5
EROs, based on the latest (12Z) operational and ensemble model
guidance, both the deterministic and probabilistic QPFs. For the
most part this resulted in a tightening of the Marginal Risk areas.
Hurley
Previous discussion...
...Lower Lakes, Ohio Valley into New England...
An axis of high PW values...1.50-1.75"+ expected to continue to
stretch from the Lower MS Valley, northeastward into New England
in the southwest flow between the western Atlantic upper ridge and
the broad mean trof across the Great Lakes into the OH Valley.
Shortwave energy in this southwest flow will help accentuate lift
in this high PW axis, supporting widespread scattered convection
across these areas. There may be better organization to the
convective activity across the Lower Lakes/OH Valley region in the
vicinity of a slow moving frontal boundary expected to stretch west
southwest to east northeast across this area. The risk level was
maintained at marginal, but with FFG values relatively low across
the eastern Lakes/Northern Mid-Atlantic, an upgrade is possible,
especially as more hi res guidance becomes available.
...Southern to Central Appalachians...
A broad marginal risk is depicted through the Central to Southern
Appalachians for the last week period for widespread scattered
convection. Not a lot of confidence in details, but with PW values
expected to remain in the 1.5-1.75"+ range, localized hourly rain
amounts of 1-2"+ could lead to runoff issues, particularly in
urban areas and within areas of steep terrain.
...Upper Mississippi Valley...
Additional shortwave energy riding west to east along the southern
edge of the westerlies will increase convective activity day 5 in
the vicinity of a strengthening west to east oriented frontal
boundary stretching from the Northern Plains into the Upper
Mississippi Valley. The low level southerly to southwesterly flow
is expected to strengthen into this front, increasing PW values to
1.50-1.75"+ and supporting heavy to locally excessive rainfall
totals in what may be an area of organized convection. The
marginal risk area was drawn to encompass the current spread in
model qpf axes.
..Southwest...
No significant changes to the broad marginal risk area across the
Southwest for monsoonal convection both day 4 and day 5. While
there continues to be low confidence with qpf details, locally
heavy rains and isolated runoff issues will continue in the axis of
above average PW values expected across this area.
Oravec
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Tue Aug 4 2026
Day 4 and Day 5
Valid 12Z Fri Aug 07 2026 - 12Z Sun Aug 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE LOWER AND MID MISSISSIPPI VALLEY EAST AND NORTHEAST INTO THE
MID ATLANTIC AND NEW ENGLAND, ACROSS THE UPPER MISSISSIPPI VALLEY,
AND OVER THE SOUTHWEST...
2000 UTC Update: Fairly minor changes made to the Days 4 and 5
EROs, based on the latest (12Z) operational and ensemble model
guidance, both the deterministic and probabilistic QPFs. For the
most part this resulted in a tightening of the Marginal Risk areas.
Hurley
Previous discussion...
...Lower Lakes, Ohio Valley into New England...
An axis of high PW values...1.50-1.75"+ expected to continue to
stretch from the Lower MS Valley, northeastward into New England
in the southwest flow between the western Atlantic upper ridge and
the broad mean trof across the Great Lakes into the OH Valley.
Shortwave energy in this southwest flow will help accentuate lift
in this high PW axis, supporting widespread scattered convection
across these areas. There may be better organization to the
convective activity across the Lower Lakes/OH Valley region in the
vicinity of a slow moving frontal boundary expected to stretch west
southwest to east northeast across this area. The risk level was
maintained at marginal, but with FFG values relatively low across
the eastern Lakes/Northern Mid-Atlantic, an upgrade is possible,
especially as more hi res guidance becomes available.
...Southern to Central Appalachians...
A broad marginal risk is depicted through the Central to Southern
Appalachians for the last week period for widespread scattered
convection. Not a lot of confidence in details, but with PW values
expected to remain in the 1.5-1.75"+ range, localized hourly rain
amounts of 1-2"+ could lead to runoff issues, particularly in
urban areas and within areas of steep terrain.
...Upper Mississippi Valley...
Additional shortwave energy riding west to east along the southern
edge of the westerlies will increase convective activity day 5 in
the vicinity of a strengthening west to east oriented frontal
boundary stretching from the Northern Plains into the Upper
Mississippi Valley. The low level southerly to southwesterly flow
is expected to strengthen into this front, increasing PW values to
1.50-1.75"+ and supporting heavy to locally excessive rainfall
totals in what may be an area of organized convection. The
marginal risk area was drawn to encompass the current spread in
model qpf axes.
..Southwest...
No significant changes to the broad marginal risk area across the
Southwest for monsoonal convection both day 4 and day 5. While
there continues to be low confidence with qpf details, locally
heavy rains and isolated runoff issues will continue in the axis of
above average PW values expected across this area.
Oravec
