Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
849 PM EDT Thu Jun 26 2025
Day 1
Valid 01Z Fri Jun 27 2025 - 12Z Fri Jun 27 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE CENTRAL PLAINS, MIDWEST, & GREAT LAKES...
An upper level trough will pivot eastward across the Upper MS
Valley and Upper Great Lakes region Thursday night into early
Friday. Enhancing the deep-layer forcing will be the curved 90kt
upper level jet streak that will be skirting the U.S.-Canadian
border. Ahead of the upper shortwave trough/surface front --
850-700 mb moisture flux anomalies are noteworthy (1.5-2.0 standard
deviations above normal), as is the 0-6km bulk shear values
(35-45+ kts). This will likely continue to support more widespread,
organized convective line segments into the overnight across the
elongated Slight Risk area, with embedded mesocyclones possible.
When compared to continuity, cleared the former western portions of
the risk areas based on radar reflectivity trends and 18z HREF
output.
...Mid Atlantic & Upper Ohio Valley...
Relatively light (generally 20kt or less) deep-layer shear with
a near upper level high overhead between a retrograding TUTT cell
in the Southeast and Westerlies to the north has caused a Florida-
like situation to unfold today, with outflow boundaries moving in
from many directions of the compass, which has caused CIN to set in
across much of the region. The most interesting aspect has been a
synoptically enhanced sea breeze, a possible cold front that
cleared portions of the Eastern Shore this afternoon and evening
and has led to patches of stratus in its wake over portions of NJ
& DE. The 18z HREF has significantly overforecast early evening
convection in the DC area in the hours leading up to this
discussion's issuance. With convective coverage becoming more
isolated due to the broad CIN development, dropped the risk in the
region to Marginal. The 18z HREF indicates that the threat of heavy
rainfall on an isolated basis should end by midnight, holding on
the longest across portions southern PA, the Virginias, and near
the shores of Chesapeake Bay.
...New Mexico...
Isolated to scattered thunderstorms across the Southern High Plains
and the Texas Big Bend should maintain at least some threat for
flash flooding given wet antecedent conditions following a wet
multi-day convective period. Remaining elevated moisture and
sufficient buoyancy will maintain the diurnally driven
thunderstorms through roughly 05z, based on the 18z HREF output.
Heaviest thunderstorms will be capable of 1-2" with the peak QPF
max probably closer to 3". The previous MRGL risk was maintained,
but trimmed on its western side per radar trends and the 18z HREF
output.
Roth/Hurley
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Fri Jun 27 2025
Day 1
Valid 12Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL APPALACHIANS AND NEIGHBORING MID ATLANTIC...
...Northern NY-New England...
The suite of 00Z operational models and ensemble runs continued 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.
At the same time...introduced a Slight risk area over portions of
the central Appalachians where model signals have been growing for
enhanced rainfall amounts near the terrain. With a westward
propagating cold front encountering the terrain... the higher
amounts suggested by the latest HRRR runs seems reasonable and was
placed near the axis of heaviest rainfall from the WPC
deterministic QPF.
...Northern Plains...
A quick moving shortwave across the northern and central tier of
the CONUS will lead to scattered thunderstorm activity capable of
locally heavy rainfall. Prospects for flash flooding seem to be
limited given the progressive nature of the shortwave trough which
should help focus the convection. A quick 1-3+" is likely anywhere
over parts of the eastern Dakotas and across central Minnesota.
This threat remained within the lower end of the MRGL risk
threshold and will be monitored closely.
...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.
Bann
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM 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 mainly
Saturday night. later in the period (especially Sat 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 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.
...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.
...New Mexico...
Maintained a targeted Marginal Risk area over/near the Sacramento
Mtns, particularly in vicinity of burn scars. QPF trends
(coverage, intensity) are similar to Day 1, with the moist south to
southeast low-level upslope flow likely resulting in a
concentrated area of heavier rainfall across the Sacramento Mtns
and eastern foothills. The flash flood potential is expected to
remain isolated/localized.
Bann
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM 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 between the western Great Lakes and the
Southern Rockies. Any showers or thunderstorms which form along or
ahead of the front may be able to produce rainfall rates high
enough to result in flash flooding. Away from the upper
trough...mechanisms to help focus convection becomes less defined
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.
Ensemble guidance depicted isolated to widely scattered rainfall
amounts of 1 to 3 inches but little coherence in placement between
the ensemble runs. Opted to highlight a broad but generally
unfocused Marginal risk area .
Bann
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
310 AM 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 Monday. An elongated WPC Marginal Risk Excessive
Rainfall Outlook area (ERO) 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 has been introduced. 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 eastern
tropical 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 and 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.
Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
310 AM 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 Monday. An elongated WPC Marginal Risk Excessive
Rainfall Outlook area (ERO) 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 has been introduced. 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 eastern
tropical 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 and 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.
Schichtel
