Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sat Jun 7 2025
Day 1
Valid 01Z Sun Jun 08 2025 - 12Z Sun Jun 08 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE OHIO RIVER
VALLEY AND MID-SOUTH INTO THE SOUTHEAST...
01Z Update...
...Midwest and Central Appalachians...
Thunderstorms will continue develop in advance of an eastward
moving wave currently along the MO/IL border. This activity should
mainly form along the warm front currently extending from StL
through southern IN and organize a bit in the warm air advection
regime. PW increases behind the front to around 1.75", above the
90th percentile for early June, along with tall, skinny CAPE
profiles per model soundings that will make for efficient, low-
topped convection and scattered flash flood events. Of particular
concern will be the potential for flash flooding overnight from
central IN along the mid-upper OH Valley through WV. Southwest
low- level inflow increases over the terrain in the very moist
environment with the right entrance region of an upper level jet
streak providing divergence aloft. Locally significant flash
flooding will be possible given the terrain and relatively wet
antecedent conditions of the Slight Risk area.
...Mid-South through Southeast...
Forward propagating MCS pushes east over SC this evening with fast
motion. The leading cells that developed ahead of the line when it
was over GA are not occurring as much over SC, so the associated
flash flood threat is low overnight.
The next line of activity has developed across south-central AR and
is moving close to its orientation axis, causing repeating cells.
This will continue until enough cold pool can develop to begin a
propagation southeast into LA and over north-central MS/AL which
continues rest of the overnight. Despite dry antecedent conditions
and high FFG, the Slight Risk is maintained for potential for 2-4"
rainfall with high hourly rates and potential scattered instances
of flash flooding.
...Southern Plains...
Third consecutive night of supercells from the south-central High
Plains developing and shifting southeast. Expanded a Marginal Risk
from North Texas to these cells based on current motion and CAM
guidance like recent runs of the RRFS which maintain this activity
through tonight. This swath is mainly between the heaviest rain
from last night, but there is an isolated flash flood threat as
this activity propagates southeast.
...Northeast...
Low pressure has shifted well east of New England bringing rainfall
with it. Some heavy rain remains along the front over Long Island,
though the rates are not excessive. The EROs in the Northeast have
been removed.
Lamers/Jackson
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sat Jun 7 2025
Day 2
Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL
APPALACHIANS AND MID ATLANTIC... AS WELL AS THE SOUTHERN PLAINS...
...Central Appalachians into the Mid-Atlantic...
The heavy rain and associated flash flood threat is likely to be
ongoing across portions of the region at the beginning of the
outlook period (12 UTC Sunday). Model guidance today has generally
begun to focus the QPF signal across the region such that there is
much better consistency between the global ensembles and hi-res
ensembles (both RRFS experimental ensemble and HREF operational).
Therefore, confidence was sufficiently high to go with a relatively
big departure from the existing more focused Marginal Risk area,
and go with a broad Slight Risk. The biggest change was to areas of
eastern Virginia and central Maryland, which previously had ERO
probabilities of less than 5 percent, but hi-res guidance is now
consistently showing some localized maxima in excess of 3 inches
into the coastal plain.
Greatest concern within the Slight Risk area is in the Allegheny
Mountains, Potomac Highlands and Laurel Highlands of northeast
West Virginia, the Maryland Panhandle, far southwest Pennsylvania,
as well as the Shenandoah Valley and Blue Ridge Mountain region of
far northwest Virginia. These areas have been very wet lately, with
30-day rainfall double to triple the normal amount, and a
significant portion of the same area received between 1 and 4
inches of rain in the past day or so.
Rainfall may be enhanced in these areas by a subtle southeasterly
low-level jet that should increase between 06 UTC and 18 UTC Sunday
due to a developing low level cyclone ahead of an eastward
propagating mid-upper level wave. If the low becomes situated near
the OH-WV border by the beginning of the outlook period, which has
been a trend over the past couple model cycles (along with a deeper
low overall), the LLJ would be likely to be enhanced. This may
create orographic enhancement to the rainfall and could help some
convective features and bands persist for a greater duration where
the orographic enhancement is most pronounced. Any convection is
likely to be low-topped, with model forecast soundings showing a
high melting level (above 12,000 feet) and a low equilibrium level
(between -10C and -20C), with PWs above the 90th percentile for
early June. This would be likely to lead to dominance of
efficient, warm rain processes with little to no ice present in the
cloud. This could support rapidly developing flash flooding where
convective features can persist.
Meanwhile, further east into the coastal plain and I-95 urban
corridor from Richmond to Baltimore, models have also converged on
an increased heavy rainfall threat. In these areas, greater
instability will be present -- enough to support organized clusters
of thunderstorms that could produce very heavy rain rates at times.
The heavy rain should be less persistent as compared to the
mountainous areas, but that would be offset by higher instantaneous
rain rates. Therefore, these areas were also included in the Slight
Risk and could see some flash flooding impacts.
...Southern Plains to the Southeast...
Fewer changes were made to the existing Day 2 outlook from the
Southern Plains into the Gulf Coast region. A Slight Risk remains
centered on North Texas and southern Oklahoma, and many models now
show a rainfall maxima in excess of 3 inches somewhere in the
area. Although a forward propagating MCS may develop with time,
there is enough signal in the model guidance for a corridor of
enhanced QPF that some training of intense convection seems
possible. This would be most likely either via (1) individual cells
and clusters developing near the front ahead of the advancing
convective line and subsequent cell mergers, or (2) slowing or
stalling of the convective line on the southwest periphery of the
developing cold pool. If either of these scenarios develops, flash
flooding would be possible via heavy rainfall sustained for a
couple hours at any one location.
Although the Gulf Coast is not in a Slight Risk at this time, it
will need to be monitored, as some (but not all) recent hi-res
model runs show significant localized rainfall extremes in excess
of 6 inches. An examination of individual model runs indicates this
would be most likely where convective outflows interact with the
coastal convergence zone.
Lamers
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sat Jun 7 2025
Day 3
Valid 12Z Mon Jun 09 2025 - 12Z Tue Jun 10 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS A LARGE
PORTION OF THE SOUTHERN AND EASTERN UNITED STATES...
Very few changes were made to the existing Marginal Risk, which
encompassed a broad area in the southern and eastern United States
along and ahead of a slowly advancing cold front. The air mass
ahead of the front will be characterized by above normal PWs and
widespread moderate to strong instability. Therefore, a day with
abundant areas of active convection containing relatively high
rain rates is expected. Confidence is not very high at this time in
the detail, particularly where concentrated areas of heavy rainfall
and/or localized extreme events may occur. However, based on
today's model guidance, this seems most likely in the following
locations, where a Slight Risk upgrade may eventually be needed:
1. Eastern Great Lakes and Central Appalachians. Instability is
projected to be more limited in these areas, but recent rainfall
may lead to wet conditions in advance, and there is better model
consensus on areas of over 1 inch QPF.
2. The Gulf Coast. A combination of strong instability and high PWs
would support organized convection and high rain rates, but there
is less model agreement on placement.
3. West Texas into Northeast New Mexico. PWs will be increasing and
quite anomalous (over the 90th percentile) along with fairly
strong instability. These areas will be removed from stronger mid-
upper level flow, likely leading to overall slower storm motions.
Lamers
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Sun Jun 8 2025
A trailing frontal boundary draped generally west to east across
the South will continue to provide focus for numerous showers and
thunderstorms through most of next week. Guidance continues to
converge of central Texas into Oklahoma for multiple days of heavy
rainfall, with parts of this area already primed from recent
rainfall. Accordingly, the Days 4 and 5 Excessive Rainfall Outlooks
(valid Wednesday and Thursday) show slight risk areas across this
region. Intentionally kept the slight risks (and surrounding
marginal risks) broad given some lingering uncertainties in exactly
where possible convective complexes track and the location of
heaviest rain. If the forecast materializes though, it is possible
a moderate risk area may be needed at some point in the future. By
Thursday and Friday, this front should lift north pulling the
heavier rains out of Texas, but continuing for parts of Oklahoma
into the middle Mississippi Valley, eventually moving into the Ohio
Valley and East next weekend.
A shortwave interacting with a frontal boundary across the
northern tier will bring showers and storms across parts of the
northern Rockies into the Upper Midwest. Moisture anomalies should
be above the 90th percentile in especially Montana, supporting a
Marginal Risk on the Wednesday and Thursday ERO. Additionally,
convection is likely to move through the north- central U.S. along
the cusp of the instability gradient and thus the Marginal Risk
also extends east into the Upper Midwest.
A heat wave during the short range period over the West should
moderate by the start of the medium range period, though above
normal temperatures may continue across the West through the
period. Daytime highs generally could be 5 to locally 15 degrees
above normal. Otherwise, the rest of the country looks near normal
or within a few degrees of normal depending on quick systems moving
through.
Santorelli
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Sun Jun 8 2025
A trailing frontal boundary draped generally west to east across
the South will continue to provide focus for numerous showers and
thunderstorms through most of next week. Guidance continues to
converge of central Texas into Oklahoma for multiple days of heavy
rainfall, with parts of this area already primed from recent
rainfall. Accordingly, the Days 4 and 5 Excessive Rainfall Outlooks
(valid Wednesday and Thursday) show slight risk areas across this
region. Intentionally kept the slight risks (and surrounding
marginal risks) broad given some lingering uncertainties in exactly
where possible convective complexes track and the location of
heaviest rain. If the forecast materializes though, it is possible
a moderate risk area may be needed at some point in the future. By
Thursday and Friday, this front should lift north pulling the
heavier rains out of Texas, but continuing for parts of Oklahoma
into the middle Mississippi Valley, eventually moving into the Ohio
Valley and East next weekend.
A shortwave interacting with a frontal boundary across the
northern tier will bring showers and storms across parts of the
northern Rockies into the Upper Midwest. Moisture anomalies should
be above the 90th percentile in especially Montana, supporting a
Marginal Risk on the Wednesday and Thursday ERO. Additionally,
convection is likely to move through the north- central U.S. along
the cusp of the instability gradient and thus the Marginal Risk
also extends east into the Upper Midwest.
A heat wave during the short range period over the West should
moderate by the start of the medium range period, though above
normal temperatures may continue across the West through the
period. Daytime highs generally could be 5 to locally 15 degrees
above normal. Otherwise, the rest of the country looks near normal
or within a few degrees of normal depending on quick systems moving
through.
Santorelli
