Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Fri Jun 27 2025
Day 1
Valid 16Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL APPALACHIANS...
...Central Appalachians...
A more focused thunderstorm/heavy rainfall threat is expected
through the central Appalachians today as very moist flow interacts
with the terrain ahead of a 'back-door' cold front passing through
the Mid-Atlantic that will become quasi-stationary throughout the
day. Of particular concern is the prospect suggested by some of the
12Z hi-res guidance (HRRR and HREF) that initial storms over parts
of western Maryland/West Virgina Panhandle/northwestern Virginia
will cluster/organize and move slowly southward along the
instability gradient ahead of the stalling front. Updated 12Z HREF
probabilities are between 40-60% for rainfall of 3"+, with a
focused area of 20-30% of 5"+ across the West Virginia Panhandle.
Efficient rainfall rates of 1-2.5" per hour can be expected given
PWATs upwards of 2" per 12Z PBZ sounding. Much of this region
remains more sensitive to additional rainfall not only due to the
typical terrain impacts but a number of recent heavy rainfall
events keeping FFGs low, with scattered to potentially numerous
instances of flash flooding possible.
...Northern NY-New England...
The suite of 12Z operational models and ensemble runs continues a
trend started during the day on Thursday of shifting the focus for
heavy rainfall to remain north of the international border. Even
though there are some variances on the possible MCS path which
could still result in an MCS clipping the northern portion of New
York and New England...it should fall in a region where Flash Flood
Guidance is higher than adjacent areas so the Slight Risk was
removed and the Marginal Risk area was removed from the upper
Hudson Valley and southward.
...Southern Plains into the Mississippi Valley and Southeast...
Another typical Summer day of scattered thunderstorms is expected
broadly from the Southeast through the Mississippi Valley and west
along a surface trough through the southern Plains given seasonable
instability with daytime heating and a passing upper- wave. Pulse-
type thunderstorms will have the ability to produce quick efficient
bursts of heavy rainfall (1-3") and the risk for some mostly
isolated urban flooding, especially where any storms
develop/congeal along residual outflows.
...Northern Plains...
A quick moving shortwave across the northern and central tier of
the CONUS will lead to thunderstorm activity capable of locally
heavy rainfall, especially if convection can grow upscale into a
more organized MCS as indicated by some of the 12Z hi-res model
guidance. However, prospects for flash flooding still seem to be
limited given the progressive nature of the shortwave
trough/possible MCS. A quick 1-3+" is likely anywhere over parts of
the eastern Dakotas and across central Minnesota.
...West Texas into New Mexico...
Continued threat of widely scattered thunderstorms across far West
Texas into New Mexico again over an area that will have seen
several days of heavy convective impacts with compromised Flash
Flood Guidance. Local 1- to 2-inch amounts are possible in the
period with the highest threat likely over the Sacramento's down
through the Guadalupe Mountains and adjacent valleys. A Marginal
risk was maintained to cover for the threat.
Putnam/Bann
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Fri Jun 27 2025
Day 2
Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHERN PLAINS AND UPPER MIDWEST, THE NORTHEAST, AND SOUTH-
CENTRAL NEW MEXICO...
...Northern Plains and Upper Midwest...
Next approaching upper shortwave trough, with a 90kt upper level
jet streak on the lee side, will generate a compact area of fairly
robust, transient deep-layer forcing over the outlook area into
Saturday night. MUCAPEs are expected to soar within the warm sector
prior to the surface cold frontal passage. Given precipitable
water values getting near 1.75 inches...storms which form within
the unstable airmass will be capable of producing rainfall rates in
excess of 1 inch per hour and areal average rainfall amounts of 1
to 3 inches...especially once low- level inflow accelerates to
between 30 kts and 40kts at 850 mb ahead of the approaching front
with the potential for upscale/organized growth into one or more
MCSs. The storm/mesoscale nature of the threat leads to uncertainty
of a more focused corridor of higher risk, but a Slight Risk may
be necessary particularly over the Upper Mississippi Valley if
trends remain consistent in the guidance.
...Northeast...
There continues to be an increasing concern for heavy to
potentially excessive rainfall to develop across western
Pennsylvania and surrounding areas as the frontal boundary sags
southward and taps into the pooled PW values of 1.5-2". The latest
model guidance are showing local maximums upwards of 2 inches
possible and the ERO first guess supports expanding the Marginal
Risk from eastern Pennsylvania further west into eastern Ohio, West
Virginia and western Maryland. Further north, widespread
convective activity across southeastern Canada north of the warm
front looks to move into portions of northern New England. While
guidance indicates the potential for 1-2" of rainfall totals across
the region, the less robust convection on the northern side of the
front should keep any flooding issues isolated.
...Southeast to the Mississippi Valley and adjacent southern
Plains...
Similar to day 1, scattered pulse thunderstorms are expected
across a broad warm sector as seasonable instability develops with
daytime heating from the Southeast west through the Mississippi
Valley and into the adjacent southern Plains. High precipitable
water values (~2", 2 standard deviations above the mean) will once
again lead to highly efficient rain rates of 1-2" per hour,
possibly as high as 3" per hour, which is more than enough to lead
to isolated flash flooding concerns despite the generally limited
thunderstorm duration.
...New Mexico...
Yet another day of thunderstorms is expected across portions of
southern New Mexico and west Texas with locally heavy rainfall
(1-2") possible. QPF trends (coverage, intensity) are more isolated
compared to day 1 with the moist south to southeast low-level
upslope flow likely resulting in more localized areas of heavier
rainfall focused across the Sacramento and Guadalupe Mtns south
through the Trans-Pecos. The flash flood potential is expected to
remain isolated.
Putnam/Bann
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Fri Jun 27 2025
Day 3
Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING OVER
PORTIONS OF THE CENTRAL UNITED STATES...
There is a Marginal Risk of excessive rainfall over portions of
the central United States from the western Great Lakes south
through the Mississippi Valley and west into the central/southern
Plains and southern Rockies. Showers and thunderstorms are expected
both along and well-ahead of a cold front and trailing surface
trough/dryline as an upper-level trough approaches from the west.
Mechanisms to help focus convection becomes less defined ahead of
the front but deterministic guidance indicates widely scattered
rainfall totals of 1-3" are possible in an atmosphere characterized
by precipitable water values in excess of 1.5 inches over all but
the plains near the Central and Southern Rockies to in excess of 2
inches east of the Mississippi. Surface waves along the front may
help to focus/organize convection and lead to a more concentrated
threat. This is supported by localized maxima in the ensemble
means/probabilities in the central Plains/Missouri Valley to the
Upper Mississippi Valley region, but with low confidence in exact
location at this point. Therefore, a broad Marginal Risk has been
maintained for now.
Putnam/Bann
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Fri Jun 27 2025
Widespread thunderstorms with favorable moisture/instability and
right entrance region upper jet lift will fuel locally strong/heavy
convective downpours likely to form ahead of the broad but shallow
upper trough and a surface frontal boundary working southeastward
over the Midwest on Monday. An elongated WPC Marginal Risk
Excessive Rainfall Outlook (ERO) area is located along and ahead
of the front from the Ohio/Tennessee Valleys, Mid/Lower Mississippi
Valley, and the south-central Plains Day 4/Monday. The front will
continue to push onward Tuesday, leading to a wet day from the
Northeast/Mid- Atlantic back through the Appalachians and into the
South Tuesday where a Day 5 Marginal Risk ERO is drawn. These
areas will dry out and and moderate post-frontal, but activity will
linger as the front slows across the South/Southeast into mid-late
next week. Even before the front approaches, scattered
thunderstorms are likely farther south in the broad warm sector as
well. There will be less forcing for organization and sustaining of
storms across the southern tier away from the upper jet, but
instability could allow for heavy rain rates that may cause non-
zero chances of localized flash flooding, but that are likely
dependent on smaller scale boundaries and are less predictable at
this point. One area of focus with a growing model signal for some
heavier rain is across the central to eastern Gulf Coast region.
Will monitor if there will be flash flooding concerns there, but it
would have to battle with very high flash flood guidance.
Monsoonal moisture with some connection to possible Pacific
tropical development is likely to increase next week in the
Southern/Central Rockies and High Plains with southerly flow under
the upper ridge, thus increasing coverage of rain amounts in
storms. Marginal Risks are planned for the southern Rockies/High
Plains Day 4/Monday and Day 5/Tuesday. Areas like the Sacramento
Mountains, where the steep terrain and burn scars cause the area to
be particularly sensitive to rain, seem likely most vulnerable to
rain causing potential flash flooding, especially with wet
antecedent conditions there.
Elsewhere, showers and storms may develop over parts of the Great
Basin Monday and toward the Northern Rockies by Tuesday. Downstream
shortwave energy translations support increasing rain/convection
chances over the north-central U.S. Wednesday into Thursday as
moisture/instability pool along/overtop a retreating front.
Temperatures are forecast to be around 5-10 degrees above average
across the Midwest/Great Lakes early next week, while the southern
half of the Plains to Southeast can expect typical summer heat.
HeatRisk shows some Major (level 3 of 4) areas in these regions,
indicating heat levels that affect anyone without effective cooling
and/or adequate hydration. Temperatures and dewpoints will
decrease behind the cold front as it progresses southeast. Farther
west, building heat is expected next week as an upper ridge takes
hold. Temperatures in the Northwest are likely to be 10-15 (locally
20) degrees above normal, for highs nearing 100F. In the Desert
Southwest, temperatures a few degrees above already high averages
will equate to 100s and 110s. Moderate to Major HeatRisk is shown
for much of the Interior West peaking Monday-Tuesday.
Santorelli/Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Fri Jun 27 2025
Widespread thunderstorms with favorable moisture/instability and
right entrance region upper jet lift will fuel locally strong/heavy
convective downpours likely to form ahead of the broad but shallow
upper trough and a surface frontal boundary working southeastward
over the Midwest on Monday. An elongated WPC Marginal Risk
Excessive Rainfall Outlook (ERO) area is located along and ahead
of the front from the Ohio/Tennessee Valleys, Mid/Lower Mississippi
Valley, and the south-central Plains Day 4/Monday. The front will
continue to push onward Tuesday, leading to a wet day from the
Northeast/Mid- Atlantic back through the Appalachians and into the
South Tuesday where a Day 5 Marginal Risk ERO is drawn. These
areas will dry out and and moderate post-frontal, but activity will
linger as the front slows across the South/Southeast into mid-late
next week. Even before the front approaches, scattered
thunderstorms are likely farther south in the broad warm sector as
well. There will be less forcing for organization and sustaining of
storms across the southern tier away from the upper jet, but
instability could allow for heavy rain rates that may cause non-
zero chances of localized flash flooding, but that are likely
dependent on smaller scale boundaries and are less predictable at
this point. One area of focus with a growing model signal for some
heavier rain is across the central to eastern Gulf Coast region.
Will monitor if there will be flash flooding concerns there, but it
would have to battle with very high flash flood guidance.
Monsoonal moisture with some connection to possible Pacific
tropical development is likely to increase next week in the
Southern/Central Rockies and High Plains with southerly flow under
the upper ridge, thus increasing coverage of rain amounts in
storms. Marginal Risks are planned for the southern Rockies/High
Plains Day 4/Monday and Day 5/Tuesday. Areas like the Sacramento
Mountains, where the steep terrain and burn scars cause the area to
be particularly sensitive to rain, seem likely most vulnerable to
rain causing potential flash flooding, especially with wet
antecedent conditions there.
Elsewhere, showers and storms may develop over parts of the Great
Basin Monday and toward the Northern Rockies by Tuesday. Downstream
shortwave energy translations support increasing rain/convection
chances over the north-central U.S. Wednesday into Thursday as
moisture/instability pool along/overtop a retreating front.
Temperatures are forecast to be around 5-10 degrees above average
across the Midwest/Great Lakes early next week, while the southern
half of the Plains to Southeast can expect typical summer heat.
HeatRisk shows some Major (level 3 of 4) areas in these regions,
indicating heat levels that affect anyone without effective cooling
and/or adequate hydration. Temperatures and dewpoints will
decrease behind the cold front as it progresses southeast. Farther
west, building heat is expected next week as an upper ridge takes
hold. Temperatures in the Northwest are likely to be 10-15 (locally
20) degrees above normal, for highs nearing 100F. In the Desert
Southwest, temperatures a few degrees above already high averages
will equate to 100s and 110s. Moderate to Major HeatRisk is shown
for much of the Interior West peaking Monday-Tuesday.
Santorelli/Schichtel
