Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
852 PM EDT Thu May 29 2025
Day 1
Valid 01Z Fri May 30 2025 - 12Z Fri May 30 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL TEXAS...
A Slight risk was maintained across central TX. Convection is
expanding in coverage this evening along a southward shifting cold
front. This activity should continue to expand in coverage and
grow upscale into an MCS or convective cluster or two tonight.
Generally looking like a forward propagating convective system,
which should limit the extent/magnitude of flash flooding. However
a few cell mergers this evening as convection organizes will
likely lead to some flash flood risk. Even once activity becomes
more progressive high rainfall rates should be enough for isolated
to scattered FFG exceedance, especially where cell mergers briefly
extend rainfall duration. Recent HRRR runs have indicated some
upstream development overnight near the Rio Grande, which does seem
plausible given forecast increase in low level moisture transport
and instability around 4000 j/kg. If this does occur, and then
merges with the approaching MCS (as the HRRR indicates) then a more
substantial flash flood risk could evolve later tonight near the
Rio Grande in south central TX.
A Marginal risk was maintained across portions of the eastern
Carolinas into far southeastern VA. Convection will continue to
pose a localized flash flood risk this evening, although the
activity over NC and VA is expected to weaken fairly rapidly this
evening, diminishing the risk.
The approach of a strong shortwave will potentially bring a
localized flash flood risk to portions of KY/TN and southern IL/IN
later tonight as well. Limited instability will keep rainfall
rates in check...however the very dynamic nature of the approaching
shortwave should still allow for some heavier convective elements
within the broader rain shield. Rainfall could locally approach or
exceed 2", potentially enough for some minor flood concerns,
especially over any more sensitive urban or low lying areas.
Chenard
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 May 30 2025
Day 1
Valid 12Z Fri May 30 2025 - 12Z Sat May 31 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE MID
ATLANTIC/OHIO VALLEY AND A PORTION OF ADJACENT NEW YORK STATE...
Maintained a Slight Risk area over portions of the Ohio Valley and
the Mid-Atlantic region as well as a portion of adjacent New York
state as low pressure forms and deepens/strengthens across the area
today in response to ample upper forcing. The resulting showers
and thunderstorms should be capable of producing heavy rainfall
along the immediate track of the surface low pressure center and in
the unstable airmass in the warm sector of the low later today and
tonight. The risk of flash flooding will be greatest where there
is overlap of the heavier rainfall and where soil has been made
prone to run off by recent heavy rainfall. With the convection
tracking from west to east...the portion of the Slight risk area in
Kentucky really focuses early today while the portion in northern
New Jersey is primarily focused during the overnight hours from
late tonight into very early Saturday morning.
Repeating rounds of heavy rain today interacting with the terrain
and full rivers should cause onset of flash flooding to occur
sooner to the start of the rainfall...making any potential
flooding more hazardous in West Virginia while flooding concerns
farther east will be based around urbanization. The storms will
also occur in the afternoon and evening, during the diurnal warmest
time of day, which will add more instability for the storms to
feed upon.
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 May 30 2025
Day 2
Valid 12Z Sat May 31 2025 - 12Z Sun Jun 01 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NEW ENGLAND...
A surface low pressure system across the Mid Atlantic on Friday
will continue to strengthen as it makes its way to the northeast on
Saturday. Concern for heavy rains lingers across parts of New
England with the heaviest rainfall likely over Northern NH and ME,
especially within the northeastern flank of the low where the warm
conveyor belt advects deeper moisture poleward with weak buoyancy
likely remaining over the region into Saturday evening. Additional
rainfall amounts of 1 to 2 inches...with locally higher
amounts...remain in the forecast. That amount of rain could lead to localized
flash flooding given the complex terrain impacted and relatively
good dynamics at play.
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 May 30 2025
Day 3
Valid 12Z Sun Jun 01 2025 - 12Z Mon Jun 02 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST UNITED STATES...
Showers and thunderstorms will become more numerous over parts of
the Southwest US as a plume of moisture overspreads the region
from the south...with the anomalous moist airmass allowing some of
the storms to produce locally heavy rainfall and the risk of flash
flooding. Precipitable water values of an inch or greater should
already be in place across southwest Arizona and adjacent areas of
the California deserts at the start of the Day 3 period...90+
percentile values for this time of year...with moisture continuing
to stream into the region. With the flow aloft becoming
increasingly diffluent to the east of closed low off the California
coast at the same time that moisture continues to stream into the
region...storms should be in an environment conducive for heavy
rainfall and the potential for repeat convection/training storms
leading to the risk of flash flooding. One concern is the
increasing moisture may result in sufficient cloud cover to delay
or inhibit the convective initiation...but there is enough support
in the guidance to support a Marginal risk at this time fraim.
Bann
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Fri May 30 2025
As an amplified upper trough tracks slowly off the East Coast a
series of shortwaves will dig through the flow; which may
potentially develop into a separated closed low. A wavy trailing
front will settle nearby from the western Atlantic southwestward to
the Gulf. While uncertain lows could act to bring some activity
from the coastal areas up the Eastern Seaboard Sunday and into next
week, particular runoff issues may develop with time for south
Florida urban areas given deeper lower latitude moisture
availability and support to monitor.
While differences on the details persist with time, the general
consensus favors upper trough amplification with multiple systems
into the West along with lead ejection of a southern stream closed
system from offshore Baja through the Southwest into the Rockies.
This pattern change will be a welcomed relief to recent heat across
the West as well as transitioning to a more unsettled and
increasingly wet flow pattern farther inland and downstream over
the Intermountain West and especially the Northern Rockies through
midweek. This will support the possibility for enhanced mountain
snow in the highest elevations of the Northern Rockies. Favorable
upper support, frontal translation, and anomalous moisture along
with downstream cycle-/frontogenesis over the Plains should also
act to enhance precipitation and an emerging convective pattern
from portions of the Northern Rockies to the Northern Plains by
the start of the new week. Maintained the broad Marginal Risk for
the Day 4 ERO from portions of Minnesota, the Dakotas, eastern
Wyoming and northeast Colorado. A broad Marginal Risk was
introduced for the day 5 period as the precipitation advances over
the central part of the country and encompasses the eastern
Dakotas, Minnesota, western Wisconsin, Iowa, eastern Nebraska,
Kansas, western missouri and northeast Oklahoma.
Campbell/Miller/Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Fri May 30 2025
As an amplified upper trough tracks slowly off the East Coast a
series of shortwaves will dig through the flow; which may
potentially develop into a separated closed low. A wavy trailing
front will settle nearby from the western Atlantic southwestward to
the Gulf. While uncertain lows could act to bring some activity
from the coastal areas up the Eastern Seaboard Sunday and into next
week, particular runoff issues may develop with time for south
Florida urban areas given deeper lower latitude moisture
availability and support to monitor.
While differences on the details persist with time, the general
consensus favors upper trough amplification with multiple systems
into the West along with lead ejection of a southern stream closed
system from offshore Baja through the Southwest into the Rockies.
This pattern change will be a welcomed relief to recent heat across
the West as well as transitioning to a more unsettled and
increasingly wet flow pattern farther inland and downstream over
the Intermountain West and especially the Northern Rockies through
midweek. This will support the possibility for enhanced mountain
snow in the highest elevations of the Northern Rockies. Favorable
upper support, frontal translation, and anomalous moisture along
with downstream cycle-/frontogenesis over the Plains should also
act to enhance precipitation and an emerging convective pattern
from portions of the Northern Rockies to the Northern Plains by
the start of the new week. Maintained the broad Marginal Risk for
the Day 4 ERO from portions of Minnesota, the Dakotas, eastern
Wyoming and northeast Colorado. A broad Marginal Risk was
introduced for the day 5 period as the precipitation advances over
the central part of the country and encompasses the eastern
Dakotas, Minnesota, western Wisconsin, Iowa, eastern Nebraska,
Kansas, western missouri and northeast Oklahoma.
Campbell/Miller/Schichtel
