Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1210 PM EDT Wed Jun 4 2025
Day 1
Valid 16Z 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...
...16z update...
The development of an earlier-than-usual cumulus field over parts
of east-central AZ/west-central NM, where an area of shallow
instability is in place along with a relatively fast moving upper
jet (75-85kts), could support short fused convection this morning.
The marginal risk area was expanded on its southern periphery to
account for this. The slight risk areas over the Midwest and South
Carolina were expanded to account for an uptick in qpf in the
latest global/hires guidance. The Midwest slight was expanded
northwestward across Illinois and Indiana while the Southeast
slight risk was expanded northward to encompass the entire South
Carolina coast.
Kebede
...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
1210 PM EDT Wed Jun 4 2025
Day 2
Valid 12Z Thu Jun 05 2025 - 12Z Fri Jun 06 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTH-CENTRAL PLAINS...
...Intermountain West to Central/Southern Plains...
Thursday/Day 2 should see a similar pattern as Wednesday/Day 1,
with a broad positively tilted trough axis across the West and
shortwaves moving through. Pacific moisture (continuing to be over
the 90th percentile for PWs, and as high as the 99th percentile,
per NAEFS) will stream northeastward just ahead of the trough to
produce scattered convection across the central Great Basin toward
the central Rockies, where the Marginal Risk has been maintained
(and adjusted to the latest data).
Farther east, an initial shortwave will force convection in the
southern High Plains tonight into Thursday morning, then a renewed
low-level jet (30-40 kts at 925-850mb) will push moisture and
instability a bit farther north into Oklahoma/Kansas Thursday
night. This will likely sustain convection (or perhaps reinitiate
convection from a remnant MCV) that originates in CO/NM, leading
to heavy rain rates (that potentially persist and repeat over the
same areas). While there continues to be spread in the guidance
regarding whether there are ultimately two separate areas of
convection (one near the TX Panhandle and Permian Basin and another
near the KS/OK border) or one more consolidated area of convection
(likely somewhere inbetween), have maintained and adjusted the
associated SLGT risk (which is centered near the highest ECENS 2"
and 3" exceedance probs). Further refinements are expected with the
addition of the remainder of the CAM suite later today (and could
result in higher confidence of upper-end SLGT probabilities, should
CAMs come into relatively good agreement).
...Ohio/Tennessee Valleys and Lower Great Lakes...
Moisture pooling along a meandering front may lead to loclatestally
heavy rain across the Mid-Lower MS Valley and OH/TN Valleys toward
the Lower Great Lakes region. A Marginal Risk was adjusted
eastward across this region from prior cycles, owing to trends in
the placement of the frontal zone. Still considered a Marginal Risk
stretching into northern New England near/ahead of the front where
above normal moisture and instability are likely, but have judged
model QPFs remain not too heavy. There is likely a non-zero
probability for localized flash flooding, which will continue to be
monitored.
...Southeast/Carolina Coast...
A non-tropical low pressure system is forecast to be tracking just
onshore in the Carolinas on Thursday, and models continue to
indicate significant rainfall totals mainly just offshore in
association with tropical moisture. While this system is most
likely to remain frontal/baroclinic in nature, there is still a
low-end chance (near 10% per the NHC) of a tropical or sub-tropical
low consolidating within the persistent tropical convection offshore.
Even though the heaviest rainfall totals are forecast to stay
offshore, wraparound moisture is expected to stream into coastal
areas with PWs near the 95th percentile (per NAEFS). Have
maintained a MRGL risk for the new Day 2, owing to uncertainties
with regard to how things ultimately develop, but current ensemble
probs (available CAMs and GEFS/ECENS) suggest 2-3" areal averages
for the NC coast (which has the greatest chance of being locally
upgraded to a SLGT with subsequent updates). Farther west and south
of the low, lack of instability and focused low-level moisture
transport looks to limit rain rates and subsequent totals (though
lingering flooding may still be ongoing from D1 rainfall).
Churchill/Tate
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1210 PM 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
256 PM EDT Wed Jun 4 2025
A frontal system will be working through the Northeast at the
start of the period Saturday, with above average moisture (likely
from the Gulf and Atlantic) and instability pooling along and ahead
of it. This should produce some convection possibly with heavy
rain rates over an inch per hour that could cause flash flooding
concerns over typically sensitive areas like terrain in the
Northeast. Thus a Marginal Risk is in place in the Day 4/Saturday
ERO in eastern New York into northern New England. This trend was
farther north than than the previous outlook showed.
This front will stretch back through the Lower Ohio/Tennessee
Valleys, Lower Mississippi Valley, and into the southern Plains.
Ample moisture and high instability is likely across this southern
tier with upper level support at the base of the trough. Rain and
thunderstorms are likely to be widespread with these parameters in
place. The Storm Prediction Center continues to show the potential
for severe weather Saturday across the south-central Plains east
into the Southeast. Meanwhile there is a threat for flash flooding
in much the same areas, but perhaps reaching the southern
Appalachians. The Day 4/Saturday ERO indicates a Marginal Risk,
with an embedded Slight along the Red River into the Ark-La-Tex
where convection may be ongoing Saturday morning, with another
round Saturday night. This Slight was shifted just a bit south
compared to the previous issuance per newer guidance. Did think it
was best to break the Day 4 Marginal Risk that previously stretched
across the central/northern Appalachians and remove those areas,
as rain there is generally expected to be less than half an inch
and not cause flash flooding concerns.
Into Sunday, the front will progress more quickly offshore of the
Northeast, but linger across the southern tier, pressing slightly
southward especially in the Southeast. A Day 5 Marginal Risk is in
place across the Lower Mississippi Valley and Southeast, with an
expansion back west across the southern Plains where models
indicate yet another MCS. Will continue to monitor if/how heavy
rain overlaps with previous days, with the ground being more
sensitive in areas where there has already been heavy rain ,
leading to enhanced flooding concerns. In other words, eventual
upgrades to Slight Risks are certainly possible especially where
antecedent conditions allow for it, and if/where models converge on
placement of heavy rain rates.
Meanwhile, another frontal system will track across the
Midwest/Great Lakes for some modest rain there over the weekend,
reaching the Northeast by Monday and Tuesday. The current forecast
continues to show the leading front dissipating while this
secondary front becomes dominant. The second front settling south
will once again promote rain and thunderstorms across the southern
Plains and Southeast through the first half of next week as the
moisture and instability lingers.
The trough aloft centered in the east-central U.S. will generally
lead to average to slightly below average temperatures there.
However, southern Texas will be a few degrees above already hot
averages, reaching well into the 100s with heat indices possibly
above 110F. But the largest temperature anomalies will be across
the Northwest U.S. through the weekend into early next week
underneath mean upper ridging. Temperatures are forecast to be 15
to 25 degrees above average across much of the Northwest, with
highs reaching well into the 90s in interior areas. Even cities
like Seattle look to reach the mid to upper 80s. Above normal
temperatures will stretch into the central Great Basin, and the
Desert Southwest can expect temperatures well into the 100s to 110
degrees. For safety information, see weather.gov/heat.
Tate
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Wed Jun 4 2025
A frontal system will be working through the Northeast at the
start of the period Saturday, with above average moisture (likely
from the Gulf and Atlantic) and instability pooling along and ahead
of it. This should produce some convection possibly with heavy
rain rates over an inch per hour that could cause flash flooding
concerns over typically sensitive areas like terrain in the
Northeast. Thus a Marginal Risk is in place in the Day 4/Saturday
ERO in eastern New York into northern New England. This trend was
farther north than than the previous outlook showed.
This front will stretch back through the Lower Ohio/Tennessee
Valleys, Lower Mississippi Valley, and into the southern Plains.
Ample moisture and high instability is likely across this southern
tier with upper level support at the base of the trough. Rain and
thunderstorms are likely to be widespread with these parameters in
place. The Storm Prediction Center continues to show the potential
for severe weather Saturday across the south-central Plains east
into the Southeast. Meanwhile there is a threat for flash flooding
in much the same areas, but perhaps reaching the southern
Appalachians. The Day 4/Saturday ERO indicates a Marginal Risk,
with an embedded Slight along the Red River into the Ark-La-Tex
where convection may be ongoing Saturday morning, with another
round Saturday night. This Slight was shifted just a bit south
compared to the previous issuance per newer guidance. Did think it
was best to break the Day 4 Marginal Risk that previously stretched
across the central/northern Appalachians and remove those areas,
as rain there is generally expected to be less than half an inch
and not cause flash flooding concerns.
Into Sunday, the front will progress more quickly offshore of the
Northeast, but linger across the southern tier, pressing slightly
southward especially in the Southeast. A Day 5 Marginal Risk is in
place across the Lower Mississippi Valley and Southeast, with an
expansion back west across the southern Plains where models
indicate yet another MCS. Will continue to monitor if/how heavy
rain overlaps with previous days, with the ground being more
sensitive in areas where there has already been heavy rain ,
leading to enhanced flooding concerns. In other words, eventual
upgrades to Slight Risks are certainly possible especially where
antecedent conditions allow for it, and if/where models converge on
placement of heavy rain rates.
Meanwhile, another frontal system will track across the
Midwest/Great Lakes for some modest rain there over the weekend,
reaching the Northeast by Monday and Tuesday. The current forecast
continues to show the leading front dissipating while this
secondary front becomes dominant. The second front settling south
will once again promote rain and thunderstorms across the southern
Plains and Southeast through the first half of next week as the
moisture and instability lingers.
The trough aloft centered in the east-central U.S. will generally
lead to average to slightly below average temperatures there.
However, southern Texas will be a few degrees above already hot
averages, reaching well into the 100s with heat indices possibly
above 110F. But the largest temperature anomalies will be across
the Northwest U.S. through the weekend into early next week
underneath mean upper ridging. Temperatures are forecast to be 15
to 25 degrees above average across much of the Northwest, with
highs reaching well into the 90s in interior areas. Even cities
like Seattle look to reach the mid to upper 80s. Above normal
temperatures will stretch into the central Great Basin, and the
Desert Southwest can expect temperatures well into the 100s to 110
degrees. For safety information, see weather.gov/heat.
Tate
