Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
842 PM EDT Mon Jun 2 2025
Day 1
Valid 01Z Tue Jun 03 2025 - 12Z Tue Jun 03 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS...
...Central Plains...
The Slight Risk area was trimmed southeastward out of the Sand
Hills and behind the line of storms currently bisecting Nebraska.
As expected, the storms across Nebraska are barely moving, and are
producing rain rates to 3 inches per hour in otherwise normally dry
areas. Thus, the Slight remains in place for central and much of
eastern Nebraska. When the storms begin to move, likely as the line
interacts with a second progressive line of storms across west
Kansas, they should propagate eastward, so areas west of the line
should remain with relatively little rainfall.
The surrounding Marginal across Minnesota was trimmed as the storms
in that area are very progressive. While there may be some
redevelopment of shower activity later tonight, it is not expected
to result in any flooding concerns.
The Marginal in west Texas and western Oklahoma remains largely
intact as potential backbuilding of the line could result in
localized training, which may produce an isolated flash flood or
two.
The Slight across south Florida has been downgraded with this
update as the peak rainfall rates from storms have come way down as
the storms have congealed into a larger MCS, but with relatively
low embedded rainfall rates. Most areas seeing rates below an inch
per hour should preclude anything other than isolated flash
flooding through the evening.
Wegman
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
531 AM EDT Wed Jun 4 2025
Day 1
Valid 12Z Wed Jun 04 2025 - 12Z Thu Jun 05 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT BASIN AND SOUTHWEST, THE MIDDLE MISSISSIPPI VALLEY, AND
COASTAL SOUTH CAROLINA...
...Southwest and Four Corners into Central/Southern High Plains...
Another active day of showers and thunderstorms expected as the
upper low over northern Baja (that helped produce localized 2-3"
totals over the past 24 hours across portions of CA/NV/AZ border
region) fills and ejects northeast atop the Four Corners. The
accompanying ascent will move into continued anomalous PWs which
will exceed the 99th percentile (per NAEFS), associated with
remnant moisture from former T.S. Alvin. This will fuel widespread
convection capable of localized rainfall rates of 0.5"-1.0"/hr (or
at times even higher, per 00z HREF 40-km neighborhood 1"/1-hr
exceedance probs as high as 20-30%). Storms will likely move slowly
beneath the upper trough, leading to a longer duration of localized
heavy rainfall. Given prevailing 1-hr Flash Flood Guidance of
0.5"-1.0" from the CA/NV/AZ border region into the Four Corners
region, these rainfall rates may have locally significant impacts
to sensitive terrain features (such as slot canyons and dry washes)
or urban instances of flash flooding could result. While the overall
coverage of flash flooding should be somewhat modest (i.e. isolated
to widely scattered), decided to introduce a relatively large SLGT
given the continued highly anomalous moisture, the overachieving
nature of the convection over the past 24 hours, and the relatively
high exceedance probabilities from the CAMs. The main limiting
factor may be instability, given the prevalence of cloud cover this
morning which could significant limit diurnal heating. However, HREF
mean suggests at least 500-1000 J/kg of SB CAPE, and the ensemble
max is as high as 1000-2000 J/kg (should significant erosion of
cloud cover occur, the higher-end may be realized in spots).
Farther east into the Central/Southern Rockies and High Plains,
Flash Flood Guidance is generally higher and uncertainty remains
high with regard to any substantial convective organization. While
HREF exceedance probs are relatively high (20-30% for 3" threshold)
over the TX Panhandle, the FV3 is an overall outlier to the rest of
the ensemble. A targeted SLGT upgrade may be necessary later today,
should models come into better agreement on organized convection.
...Southern Plains, Lower-Mid Mississippi Valley, Great Lakes...
The cold front over the central CONUS will continue on its trek
eastward today, but will start to slow and become aligned more west
to east as its tail gets pulled northward by an approaching
shortwave over the Four Corners region. Shortwaves embedded within
the flow will continue to race northeast, especially from Missouri
to Michigan, which is where the greatest concentration of t'storms
is expected. Storm motions along the front are likely to be
progressive, lifting off to the northeast on 0-6km mean winds of
20-30 kts, but weaker Corfidi vectors aligned both to this mean
wind and the front suggests a potential for training. A SLGT risk
was introduced for southeast MO into southern IL, where HREF
exceedance probs for 3" and 5" thresholds are concentrated (30-60%
and 10-30%, respectively). Much of these totals may occur over a
relatively short period of time, as 1-2"/hr rainfall rates locally
train/repeat over the same areas.
Farther south into the Southern Plains, thunderstorms from this
morning should tend to wane over time, but will present a localized
flash flood threat through about 15z (with the HREF indicating some
potential for redevelopment after 00z, though FFGs are much higher
in this region).
...Southeast...
An inverted surface trough crossing the northern FL Peninsula with
an accompanying mid-upper low (centered near the Big Bend) will
shift northeast along the FL/GA/SC coasts, having already drawn
substantial tropical moisture northward (along with accompanying
showers and thunderstorms). While the NHC continues to indicate a
10% probability of tropical or sub-tropical development in
association with this feature, heavy rainfall is increasingly a
concern (whether or not a circulation ultimately forms, though a
non-tropical low is expected to). While the bulk of the heavy
precipitation is still expected to occur mainly offshore of (with
the most significant HREF signal offshore of SC, specifically),
there are concerns that prolonged heavy rainfall could impact
portions of the coastline. A SLGT risk was introduced to coastal
portions of SC, where rainfall totals in excessive of 5" are most
likely to occur (per HREF exceedance probs of 20-30%, which is also
in-line with the corresponding 10-yr ARI and co- located with the
best EAS probs, indicating relatively good spatial agreement as
well). This includes the relatively sensitive Charleston metro
area, and any localized flooding impacts may be exacerbated by
high tide. Outside of this specific area, locally heavy rainfall
could result in more isolated instances of flash flooding across
much of FL and adjacent portions of southeast AL, southern and
central GA, and into more of SC/NC (depending with the northern
extent of the MRGL largely dependent on timing differences with the
northward progression of convection). Local 3" exceedance probs
are relatively high throughout this region (20-60%), though absent
of significant convective organization these totals should largely
be below the relatively high FFGs that prevail (which are as high
as 4-5" over 6-hr).
Churchill
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
845 PM EDT Tue Jun 3 2025
Day 2
Valid 12Z Wed Jun 04 2025 - 12Z Thu Jun 05 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST, MIDDLE MISSISSIPPI VALLEY, SOUTHERN PLAINS, THE FOUR
CORNERS/DESERT SOUTHWEST, AND THE SOUTHEAST...
...2030Z Update...
Changes to the Day 2 ERO for this cycle were relatively minor.
Expanded the Four Corners Marginal Risk on the western side to
encompass parts of eastern California and southern Nevada. HREF
probabilities for exceeding 3 and 6 hour FFG guidance are scattered
through much of the Southwest once again Wednesday. However, the
HREF mean etc. shows lower instability compared to today (Tuesday)
and support aloft is not quite as strong, so held off from a Slight
Risk, but expect possibly isolated to scattered flash flooding, but
possibly less focused. Another area to watch for a potential
Slight is the southern High Plains, for nocturnal convection that
may produce heavy rain rates before 12Z Thursday, but looks to ramp
up specifically Thursday/Day 3 period. Meanwhile, expanded the
Marginal Risk in south-central Texas for some Wednesday morning
ongoing convection. The Southeast to Florida Marginal Risk remains
similar to the previous outlook.
Tate
...Previous Discussion...
...Four Corners into Central/Southern High Plains...
Another active day of showers and thunderstorms expected as the
upper low over northern Baja fills and ejects northeast atop the
Four Corners. The accompanying ascent will move into continued
anomalous PWs which will exceed the 99th percentile (per NAEFS).
This will fuel widespread convection capable of localized rainfall
rates of 0.5"/hr (or at times higher). Storms will likely move
slowly beneath the upper trough, leading to a longer duration of
heavy rain. Although total rainfall will be modest in most areas
(as reflected by relatively low 24-hr probability from ECENS/GEFS
for 1" exceedance), where the heavy rain impacts sensitive terrain
features or urban areas instances of flash flooding could result.
Probabilities have also increased a bit (particularly from the new
00z ECENS suite) further east into the Central/Southern High
Plains and the MRGL risk has been expanded accordingly. Should
models come into better agreement, additional expansion may be
needed further south into West TX (and with additional CAM guidance
and agreement, an upgrade to SLGT may also be needed).
...Southern Plains and Mid-Mississippi Valley to Great Lakes...
The cold front from D1 will continue its trek eastward on
Wednesday, but will start to slow and become aligned more west to
east as its tail gets pulled northward by an approaching shortwave
over the Four Corners region. Shortwaves embedded within the flow
will continue to race northeast, especially from Missouri to
Michigan, which is where the greatest concentration of
thunderstorms is expected on D2 (though some models are also
indicated potential for isolated convective development farther
southwest into portions of the Southern Plains). Storm motions
along the front are likely to be progressive, lifting off to the
northeast on 0-6km mean winds of 20-30 kts, but weaker Corfidi
vectors aligned both to this mean wind and the front suggests a
potential for training. As rainfall rates peak above 1"/hr within
favorable thermodynamics, this could result in stripes of heavy
rainfall with ensembles indicating 10-40% chance of exceeding 1"
and up to 10% probabilities for exceeding 2" (with the new ECENS
being the most aggressive). The inherited MRGL risk was maintained
(and expanded a bit southwest) with this update.
...Southeast...
Guidance continues to be somewhat aggressive with
a wave of low pressure potentially developing along an inverted
trough shifting northeast along the FL/GA/SC coasts. While NHC
continues to indicate a 10% probability of tropical or sub-tropical
development with this feature, regardless of whether a circulation
forms or not, there continues to be increasing confidence that
heavy rain will spread across the FL Peninsula and then rotate
onshore the GA/SC coasts on Wednesday. There also has been a clear
model trend of potential increased convective development farther
inland to the FL Panhandle and into southeast AL and southwest GA
(likely due to a stronger closed low and the associated dynamics),
so the MRGL was expanded to reflect this. With PWs progged to
exceed 2", above the 90th percentile, supported by warm cloud
depths that may exceed 15,000 ft, efficient rainfall rates of
1-2"/hr will be likely in any showers/thunderstorms. It certainly
remains possible that the heaviest rainfall in association with the
potential surface low will remain just offshore, but impressive
moisture convergence from Jacksonville, FL to Charleston, SC should
support waves of heavy rainfall regardless of development of this
system. Additionally, plentiful tropical moisture across the rest
of the FL Peninsula and a shortwave continuing to pivot across the
Gulf could enhance rainfall over much of Florida Wednesday, and the
MRGL was maintained accordingly (with the exception of the FL
Keys, which were removed due to model consensus that convection
will be pulling away northward by 12z Weds).
Churchill/Weiss
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
531 AM EDT Wed Jun 4 2025
Day 3
Valid 12Z Fri Jun 06 2025 - 12Z Sat Jun 07 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF
OKLAHOMA...
...Southern Plains...
Convection looks to remain active in the Southern Plains from
overnight Thursday into Friday morning, fueled by a 30-40 kt low-
level jet and likely ongoing MCS(s). In addition, the trailing
frontal zone is unlikely to move much as the upper-level pattern
remains blocky. Models indicate that another shortwave could fuel
yet more organized convective coverage into Friday night, this time
originating from the northern stream and digging southeastward from
the central Rockies/High Plains. The LLJ should reinvigorate once
again, and this is a recipe for heavy rainfall with training and
repeating over many of the same areas a distinct possibility. While
there is a fair amount of spread in the global guidance at this
range with QPF output, the consensus cluster is pretty well
situated over central OK (with some solutions suggesting farther
eastward progress of high totals into portions of northwest AR and
southwest MO). Maintained the inherited SLGT risk over the best
ensemble signal (where 00z GEFS/ECENS 2" and 3" exceedance probs
overall quite well). As confidence increases, the SLGT risk region
may expand (with potential for a targeted Moderate upgrade in
subsequent outlooks, depending largely on how much rainfall
transpires on Thursday and how well QPF on Friday overlaps).
...MS/TN/OH Valleys into Great Lakes and Appalachians...
Moisture looks to continue to pool along a meandering front in
this blocky pattern, which may continue to lead to locally heavy
rain across the Lower-Middle MS Valley and OH/TN Valleys toward
the Lower Great Lakes region. The MRGL was maintained and adjusted,
and subsequent targeted SLGT(s) may be necessary with increasing
overall PWs and the potential for localized totals beginning to add
up from multiple days. In addition, expanded the inherited MRGL
risk eastward into much of the Appalachians, as models come into
better agreement that better moisture and subsequent convection
will start to move into those more sensitive areas.
Churchill
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
220 AM EDT Wed Jun 4 2025
A non-tropical low is expected to develop offshore the Southeast
coast prior to the extended. The National Hurricane Center is
monitoring this feature for the potential to transition into a
subtropical or tropical low. Deepest moisture may stay offshore
and uncertainty is high, but there is a chance of some heavier
rainfall along the coast.
Pooled moisture across the central U.S. will help convection fire
up along a slow-moving and wavy front that will stretch from the
Northeast and Ohio Valley states down to the Southern Plains.
Locally enhanced rainfall will be supported thanks to steady
advection from the Gulf coupled with shortwave/jet. Conditions
will be favorable for hourly rates of 1 inch/hour or greater. WPC
has a broad Marginal Risk spanning from the Plains to the Great
Lakes/Northeast into the weekend. Within the Marginal is a smaller
area highlighted with a Slight Risk of excessive rainfall mainly
for Oklahoma, but also into the adjacent counties of Arkansas and
southwest Missouri. The southern trailing tail of the elongated
boundary will stall and weaken over the southern Plains. Dynamic
upper closed low/trough digging into the north- central U.S. from
the weekend into early next week will spawn fronto/cyclo genesis,
with baroclinicity rejuvenated more broadly again that may act to
spread heavy rainfall focus across the Mid- South and Tennessee
Valley then down across the Mid- Atlantic and the South/Southeast.
Summer heat will build across the Interior Northwest/West and into
the Desert Southwest with establishment of mean upper ridging over
the weekend into next week. Maximum temperatures over the interior
Northwest may range upwards to 20-25F degrees above normal. Areas
from south Texas into the Gulf Coast will also experience rising
temperatures, cresting upwards of 105F by the weekend over South
Texas to push heat index values dangerously upwards to 110-115F.
Please take heat safety precautions such as increased water intake
and more time in air conditioned areas to avoid heat exhaustion
and heat stroke. See weather.gov/heat for more information on
safety tips and resources.
Campbell/Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
220 AM EDT Wed Jun 4 2025
A non-tropical low is expected to develop offshore the Southeast
coast prior to the extended. The National Hurricane Center is
monitoring this feature for the potential to transition into a
subtropical or tropical low. Deepest moisture may stay offshore
and uncertainty is high, but there is a chance of some heavier
rainfall along the coast.
Pooled moisture across the central U.S. will help convection fire
up along a slow-moving and wavy front that will stretch from the
Northeast and Ohio Valley states down to the Southern Plains.
Locally enhanced rainfall will be supported thanks to steady
advection from the Gulf coupled with shortwave/jet. Conditions
will be favorable for hourly rates of 1 inch/hour or greater. WPC
has a broad Marginal Risk spanning from the Plains to the Great
Lakes/Northeast into the weekend. Within the Marginal is a smaller
area highlighted with a Slight Risk of excessive rainfall mainly
for Oklahoma, but also into the adjacent counties of Arkansas and
southwest Missouri. The southern trailing tail of the elongated
boundary will stall and weaken over the southern Plains. Dynamic
upper closed low/trough digging into the north- central U.S. from
the weekend into early next week will spawn fronto/cyclo genesis,
with baroclinicity rejuvenated more broadly again that may act to
spread heavy rainfall focus across the Mid- South and Tennessee
Valley then down across the Mid- Atlantic and the South/Southeast.
Summer heat will build across the Interior Northwest/West and into
the Desert Southwest with establishment of mean upper ridging over
the weekend into next week. Maximum temperatures over the interior
Northwest may range upwards to 20-25F degrees above normal. Areas
from south Texas into the Gulf Coast will also experience rising
temperatures, cresting upwards of 105F by the weekend over South
Texas to push heat index values dangerously upwards to 110-115F.
Please take heat safety precautions such as increased water intake
and more time in air conditioned areas to avoid heat exhaustion
and heat stroke. See weather.gov/heat for more information on
safety tips and resources.
Campbell/Schichtel
