Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
156 PM EDT Sat Jul 19 2025
Day 1
Valid 1747Z Sat Jul 19 2025 - 12Z Sun Jul 20 2025
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS
MAINLY FOR PORTIONS OF KENTUCKY...
Upgraded to a Moderate Risk area over a portion of Western/northern
Kentucky were deep, organized convection was growing in areal
coverage with increasingly intense rainfall the storms were moving
towards an area with wet soils and lowered flash flood guidance.
Refer to the Mesoscale Convective Discussion 0757 for further
details about the environmental conditions.
Bann
16Z Excessive Rainfall Discussion Update...
No major changes needed in the big picture. Was able to trim a bit
of territory from the Slight Risk over parts of the
Appalachians/Mid Atlantic where some drier air has filtered in from
the north. A tight gradient in deep moisture remains and the 12Z
run of the HREF continues to paint a corridor with neighborhood
probabilities of 3 inch rainfall and low-end probability of 5
inches of rainfall to the south from convection later today and
through the evening. As a result...did not tighten up the gradient
quite as much as entirely possible given the probabilistic nature
of the outlook. Also made a minor extension in Nebraska to account
for somewhat higher exceedance probabilities just to the southwest
of our previous outlook. Beyond that...few if any changes were
made.
Bann
...0830Z Excessive Rainfall Outlook...
Corn Belt/Ohio Valley/Mid-Atlantic States/Mid-South...
Ample moisture exists regionally. Some of this is due to the
synoptic pattern, with the Westerlies stronger than and south of
July norms which is allowing for greater effective bulk shear and
thunderstorm organization. Some of the moisture influx is also due
to the flow around the retrograding 3 sigma warm core ridge for
mid- July moving into the eastern Gulf. Additional moisture is
being imported from the direction of the former tropical
disturbance. Regardless of the source, precipitable water values
are forecast to crest at or above 2.25". ML CAPE could exceed 4000
J/kg due to daytime heating. Portions of IA, IL, and KY have the
potential for backbuilding convection both Saturday morning and
Saturday night/Sunday morning. Across IA, there is a question about
how much overlap convection dropping in from the north this
morning would have with convection Saturday night/Sunday morning.
Within such an environment, hourly rain amounts to 4" are possible,
with local amounts to 8". At the moment, these amounts are not
explicitly forecast by much of the guidance, with the 00z HREF/18z
RRFS showing minimal potential for 5"+ amounts, centered across IA.
However, the high resolution NAM and Canadian Regional show local
totals in the 6" ballpark. Large swaths of the region have had
well above average rainfall during the past week, saturating soils.
Since there's a bit of uncertainty, coordination with DMX/Des
Moines IA and DVN/Davenport IA have left the risk area as a high-
end Slight. However, should cells train for 2+ hours downstream of
existing instability pools, localized Moderate or High Risk
impacts cannot be ruled out.
Southwest/Southern Rockies...
Enough moisture is available for scattered monsoon convection again
on Saturday. Hourly amounts to 2" are possible due to diurnal
heating, which would be most problematic in urban areas, dry
washes/arroyos, or burn scars.
Roth
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
156 PM EDT Sat Jul 19 2025
Day 2
Valid 12Z Sun Jul 20 2025 - 12Z Mon Jul 21 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST, SOUTHERN APPALACHIANS, & NORTHERN PLAINS...
...Midwest, Ohio Valley, & Southern Appalachians...
High moisture for Saturday persists into Sunday -- precipitable
water values eclipsing 2.25" -- with the core of the instability
pool more significant across portions of the Ohio Valley on Sunday
as warming at 700 hPa occurs across the Central Plains, slowly
strengthening a mid-level capping inversion. Effective bulk shear
should remain sufficient for convective organization. Inflow off
the instability pool could lead to backbuilding, so the potential
for 4" amounts in an hour and local 8" totals remains (the 00z NAM
advertised 7"). There's not enough confidence on where the higher
amounts will materialize to upgrade to a Moderate Risk, but a
higher end Slight Risk appears to exist from in and near southern
IL into KY, TN, southern WV, and westernmost VA. Localized Moderate
or High Risk impacts cannot be ruled out.
...Northern Plains...
Much of North Dakota will be at the nose of a potent low level jet
across the area. A subtle shortwave in the upper level jet may be
all it takes to initiate a line of storms across the region,
though there may be two separate rounds: one in the morning and a
second Sunday night. There is considerable uncertainty both with
storm intensity and receptivity of the ground to the heavy
rainfall. Used the recent guidance to trim some of the Slight Risk
area away. Like continuity, believe this is a lower end Slight
Risk.
Southwest/Southern Rockies...
Enough moisture is available for scattered monsoon convection on
Sunday. Hourly amounts to 2" are possible due to diurnal heating,
which would be most problematic in urban areas, dry washes/arroyos,
or burn scars.
Roth/Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
156 PM EDT Sat Jul 19 2025
Day 3
Valid 12Z Mon Jul 21 2025 - 12Z Tue Jul 22 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN ROCKIES, PLAINS, OHIO VALLEY, & SOUTHEAST...
Surface boundaries/low pressure areas/upper level disturbances are
on this move this period, which along with warming temperatures at
700 hPa/increased mid- level capping across portions of the
Central Plains and IA should broadly limit QPF and flash flood
potential. Wherever cells can manage to train/merge, hourly rain
amounts up to 3" with local totals to 6" would be possible across
the Plains, Ohio Valley, and Southeast, while hourly amounts up to
2" and local totals to 4" would be possible across the Southern
Rockies and Southwest. At the moment, it appears any flash flooding
would be on an isolated to widely scattered basis. In the
Southwest and Southern Rockies, burn scars and dry washes/arroyos
would be most at risk. Anywhere within these regions, urban areas
would be of most concern.
Roth
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Sat Jul 19 2025
It remains the case that an axis of unsettled weather will remain
in place across the Upper Midwest and also the Southeast U.S. for
the beginning to middle of the week. Thunderstorm complexes
traveling around the northern periphery of the big upper high will
likely produce localized areas of heavy rainfall, potentially
exceeding an inch per hour or more. Therefore, a broad Marginal
Risk area extends from the eastern Dakotas to the western Great
Lakes on Tuesday where a cold front will be intersecting a warm and
humid airmass to the south. There is a good chance that a Slight
Risk could eventually be needed in later outlooks as confidence on
the main QPF axis becomes more certain. Across the Deep South and
northern Florida, a lingering stationary front will help focus deep
moisture with a potential wave of low pressure developing along it,
with some 1-3 inch rainfall totals possible for some areas.
Therefore, a Marginal Risk area is valid here for both Tuesday and
Wednesday.
Heat will once again make weather headlines for much of next week
across a large portion of the southern and central U.S. with a
large upper high becoming anchored over the Mid-South. Widespread
major impacts on the Heat Risk scale are expected from the Central
Plains to the Southeast states early in the week, and these higher
impacts then reach the Midwest and Ohio Valley by mid to late week.
This will be due to widespread highs in the lower 90s to low 100s
for many of these areas, in combination with dewpoints well into
the 70s, and overnight lows remaining uncomfortably warm. This will
likely have some staying power beyond this forecast period based
on the latest week two outlook from the Climate Prediction Center
from the Central Plains to the Gulf Coast region.
Elsewhere across the nation, there should be just enough monsoonal
moisture in place across eastern Arizona and much of New Mexico,
and probably extending into southern portions of Colorado, and
given the potential for some isolated slow moving storms, a
Marginal Risk is in place for both Tuesday and Wednesday. Across
the East Coast region, a cold front is forecast to clear the
Northeast and the Mid-Atlantic region through Tuesday, and
bringing a higher quality airmass after all of the heat and
oppressive humidity lately and lower rain chances. However, the
heat will likely return towards the end of the week as the Canadian
surface high moves offshore and a more southerly flow commences.
Hamrick
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Sat Jul 19 2025
It remains the case that an axis of unsettled weather will remain
in place across the Upper Midwest and also the Southeast U.S. for
the beginning to middle of the week. Thunderstorm complexes
traveling around the northern periphery of the big upper high will
likely produce localized areas of heavy rainfall, potentially
exceeding an inch per hour or more. Therefore, a broad Marginal
Risk area extends from the eastern Dakotas to the western Great
Lakes on Tuesday where a cold front will be intersecting a warm and
humid airmass to the south. There is a good chance that a Slight
Risk could eventually be needed in later outlooks as confidence on
the main QPF axis becomes more certain. Across the Deep South and
northern Florida, a lingering stationary front will help focus deep
moisture with a potential wave of low pressure developing along it,
with some 1-3 inch rainfall totals possible for some areas.
Therefore, a Marginal Risk area is valid here for both Tuesday and
Wednesday.
Heat will once again make weather headlines for much of next week
across a large portion of the southern and central U.S. with a
large upper high becoming anchored over the Mid-South. Widespread
major impacts on the Heat Risk scale are expected from the Central
Plains to the Southeast states early in the week, and these higher
impacts then reach the Midwest and Ohio Valley by mid to late week.
This will be due to widespread highs in the lower 90s to low 100s
for many of these areas, in combination with dewpoints well into
the 70s, and overnight lows remaining uncomfortably warm. This will
likely have some staying power beyond this forecast period based
on the latest week two outlook from the Climate Prediction Center
from the Central Plains to the Gulf Coast region.
Elsewhere across the nation, there should be just enough monsoonal
moisture in place across eastern Arizona and much of New Mexico,
and probably extending into southern portions of Colorado, and
given the potential for some isolated slow moving storms, a
Marginal Risk is in place for both Tuesday and Wednesday. Across
the East Coast region, a cold front is forecast to clear the
Northeast and the Mid-Atlantic region through Tuesday, and
bringing a higher quality airmass after all of the heat and
oppressive humidity lately and lower rain chances. However, the
heat will likely return towards the end of the week as the Canadian
surface high moves offshore and a more southerly flow commences.
Hamrick
