Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Mon Jun 2 2025
Day 1
Valid 16Z Mon Jun 02 2025 - 12Z Tue Jun 03 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS AS WELL AS THE SOUTHERN FLORIDA PENINSULA...
...Four Corners through the Central Plains...
The CAMs have shifted just a bit north/east today with the axis of
heaviest rain, owing to subtle evolution changes in the upper
pattern. The combination of ascent through height falls,
convergence along the southeast advancing front, and increased
ascent in the vicinity of a developing low pressure will help focus
convection with heavy rainfall into favorable thermodynamics.
The high-res ensemble camps (both 12Z HREF and 06Z REFS) are both
still quite aggressive with suggesting more than 3 inches of rain
across portions of Nebraska and into IA/MN/SD, as far north as the
Coteau des Prairies. The greatest risk for excessive rainfall
appears to be across Nebraska, still, however, as convection along
the cold front initiates and then builds SW into the greater
thermodynamics as the low evolves, leading to enhanced isentropic
ascent into the boundary. Fortunately, the area of greatest
exceedance probabilities (50-80% chance of 3+ inches from the HREF
and REFS) overlaps the Sandhills which are not a favorable flash
flood location, or otherwise this event could necessitate a
targeted upgrade. Still, with locally as much as 5" of rain
possible thanks to slow moving/backbuilding rain rates of 1-2"/hr,
at least scattered instances of flash flooding are expected, and
the SLGT risk was maintained with only modest cosmetic
adjustments.
Farther Southwest, the ejecting upper low advancing into a region
of elevated instability and extremely anomalous PWs (NAEFS PWs the
maximums in the 06Z CFSR database) will promote heavy rain
producing convection over the Four Corners, especially during peak
heating. Storm motions will be weak in this area beneath the upper
low, so as rain rates which may reach 1"/hr (10-20% chance) leading
to 15-min rainfall that could reach 0.25-0.5 inches. Should any of
these cells, which could be widespread, move across sensitive
terrain features like slot canyons, instances of flash flooding
could result, and the MRGL risk has been maintained.
Additionally, a wave of low pressure developing in the lee of the
Southern Rockies will likely push additional moderate to heavy
rainfall across eastern CO late tonight, and while this round will
most likely be less intense due to weaker instability, localized
additional flash flooding is possible if the rain occurs atop of
primed soils from earlier convection.
...West Texas into Texas Panhandle and western OK...
The surface trough/dry line will focus convective development this
aftn/eve as diurnal heating pushes instability to 1000-3000 J/kg.
This robust CAPE will work in tandem with PWs exceeding 1.5" as SW
return flow reaches 30+ kts, to produce favorable thermodynamics
for heavy rain containing thunderstorms. The guidance continues to
vary widely with both the timing and spatial coverage of
thunderstorms today, but low-level convergence moving into the
thermodynamics should support at least scattered convection along
this boundary as it pushes east into tonight. While uncertainty is
low as far as coverage, it is high that at least a few storms will
fire along this boundary, and these will rapidly intensify within
this environment. Storm motions of generally 10-15 kts to the WSW
will be aligned strongly right of the Corfidi vectors to suggest at
least some training is possible as storms re-develop into the more
robust instability before tracking ENE. Additionally, increasing
bulk shear to 25-30 kts this evening may help organize storms into
clusters, and the high-res indicates the greatest chance for an MCS
type of event will be into western OK tonight. Although some parts
of this region have more vulnerable soils due to recent heavy
rainfall, the generally scattered nature of convection along with
uncertainty in placement suggests the MRGL risk remains accurate,
and this was only adjusted slightly for new guidance.
...South Florida and the Florida Keys...
Near record PWs across southern Florida will produce an environment
favorable for excessive rainfall today. PWs are progged to reach
above 2.2 inches, which would be a daily record for MFL according
to the SPC sounding climatology. This moisture will combine with
MUCAPE of 2000-3000 J/kg to provide extreme thermodynamics to
support intense rainfall rates in any thunderstorms, which are
expected to be widespread today. The primary mechanisms for ascent
will be a weakening front stalled across the southern Peninsula, as
well as a potent shortwave moving across the Gulf and towards the
area, with subtle diffluence in the tail of a jet streak over the
Atlantic additionally contributing lift. This all suggests
widespread convection this aftn/eve, which is supported by the high
res CAMs. Within these storms, rainfall rates of 2-3"/hr or more
are likely (40-60% chance of exceeding 2"/hr according to both HREF
and REFS), which through training or repeated rounds could produce
3-6" of rainfall, with local amounts potentially approaching 8" as
reflected by the HREF probabilities. Any amounts above 5" would
likely be where multiple rounds occur, but also where storms slow
or move chaotically due to boundary interactions and storm mergers.
While this part of Florida typically takes a lot of rain to flood,
this setup does support a more pronounced flash flood risk today.
Despite FFGs that remain around 4"/3hrs, exceedance of this
criteria is possible, especially over urban areas that do not drain
as efficiently. The focus today is expected to be across the
Keys and Gold Coast of FL, and this is where the SLGT risk is
focused and has been modestly adjusted for new guidance. However,
the MRGL risk encompasses much of the southern peninsula where any
of these slow moving heavy rain producing thunderstorms could
result in runoff and instances of flash flooding.
Weiss
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Mon Jun 2 2025
Day 2
Valid 12Z Tue Jun 03 2025 - 12Z Wed Jun 04 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
CENTRAL UNITED STATES AS WELL AS SOUTH FLORIDA AND THE FLORIDA KEYS...
...Texas to the Great Lakes...
An active day of convection is likely on Tuesday as a cold front
sags across the Heartland, providing the focus for widespread
showers and thunderstorms. This front will be pushed southeast in
response to an amplifying northern stream trough which will dig
across the CONUS as far south as Texas. This will drive height
falls across the region, with embedded shortwave impulses racing
northeast, and a poleward arcing jet streak downstream of the
primary trough axis combining to provide additional ascent. This
deep layer lift will work into robust thermodynamics characterized
by an overlap of PWs above the 99th percentile (NAEFS) and a ribbon
of MUCAPE exceeding 2000 J/kg, surging northward on 30-50 kts of
850mb flow emerging on return flow from the Gulf.
The CAMs continue to be in excellent agreement in the coverage of
convection on Tuesday despite some temporal and spatial differences
owing to timing of the front. Despite these modest differences,
there is good agreement among the REFS and HREF ensembles to
suggest widespread 1"/hr rain rates from the northern TX Hill
Country all the way to the eastern Missouri Valley (probabilities
exceeding 50% across this entire area). Although mean 0-6km winds
of 20-30 kts indicate progressive storm motions, this flow aligned
to the front and combined with Corfidi vectors that collapse and
veer to the NE indicate a high potential for redevelopment to the
SW into the more intense thermodynamics and training of cells to
the northeast. Where this occurs, total rainfall exceeding 3" is
likely (>60% chance in HREF/REFS) and 5" is possible (>40% chance),
with even the global ensembles suggesting a 10-30% chance for 3" in
this same region. The inherited SLGT risk was tailored for this new
guidance, with the biggest adjustment being an extension SW into
the Hill Country of TX where convection that develops along the
tail of this front will likely feature slow storm motions and
backbuilding to produce heavy rainfall.
Although heavy rainfall is also likely in convection that develops
northeast into the Upper Midwest and Great Lakes, storms should be
more progressive and the Corfidi vectors suggest less opportunity
for training, so only a MRGL risk is needed north of Iowa.
...South Florida and the Florida Keys...
Shortwave trough over the Gulf may amplify enough to become a weak
closed low Tuesday and then spin nearly in place as it gets
suppressed beneath a Bermuda- type ridge to its northeast. This
will maintain modest synoptic ascent across Florida, but some
enhancement is likely as a jet streak over the Atlantic tails back
to the SW, placing the favorably diffluent RRQ overtop the
peninsula. This forcing will combine with continued, albeit
weakening, low-level convergence along a decayed front/surface
trough, to result in another day of widespread showers and
thunderstorms. PWs in place will again be greater than 2 inches,
above the 90th percentile according to NAEFS, combining with 1000
J/kg of CAPE to produce robust thermodynamics to support rainfall
rates of 2"/hr at times. There continues to be some uncertainty in
the coverage of convection, as well as placement, among the various
CAMs, somewhat lowering the confidence into D2. However, after
heavy rain anticipated D1, any additional rainfall D2 could quickly
become problematic and lead to instances of runoff and flash
flooding, especially in urban areas. The inherited MRGL and SLGT
risks were tailored slightly to encompass the highest probabilities
of 1+" and 3+" on D2.
Although not included in a risk area at this time, some of the
guidance has become a bit more aggressive with a wave of low
pressure developing along an inverted trough aligned to the east
coast of Florida. If this low were to develop a bit more rapidly or
track farther west, some heavy rain could move onshore the
northeast Florida coast before 12Z Wednesday.
...Four Corners...
A MRGL risk was expanded westward from the Central Plains to the
UT/NV/AZ borders with this update. The guidance has become more
aggressive with showers and thunderstorms blossoming during the
aftn/evening as forcing intensifies from broad divergence
downstream of a closed low filling and moving into the Desert
Southwest, producing ascent atop a wavering frontal boundary
positioned over the region. This lift will impinge into favorable
thermodynamics with PWs reaching above 0.75 inches into a bubble of
MUCAPE of 750-1000 J/kg. Mean storm motions will be weak, generally
around 5 kts, so with rainfall rates which have a 5-15% chance of
exceeding 1"/hr, these slow motions could result in locally as much
as 1" of rainfall in a short period of time. If this occurs over
sensitive soils, urban areas, or terrain features, instances of
flash flooding could result.
Weiss
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Mon Jun 2 2025
Day 3
Valid 12Z Wed Jun 04 2025 - 12Z Thu Jun 05 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST, THE FOUR CORNERS, AND THE SOUTHEAST COAST...
...Four Corners...
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 according to
NAEFS. This will fuel widespread convection with rainfall rates of
0.5"/hr, or at times higher, likely., and 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
(24-hr probability from the ECENS/GEFS for 1" peaks around 25%),
where the heavy rain impacts sensitive terrain features or urban
areas, or should heavier rain impact the wetter soils in the CO/NM
high plains, instances of flash flooding could result.
...Mid-Mississippi Valley to Great Lakes...
The cold front from D2 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 D3. 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 for which the
SREF/ECENS/GEFS ensembles indicate have a 20-30% chance of
exceeding 1", with some low-end probabilities (5% or less) of
exceeding 3". The MRGL risk was split, with the Central Plains
removed from the risk on D3 due to a more progressive front and
some NVA behind impulses, but also extended a bit northeast to
reach the Canadian border for isolated flash flood potential.
...Southeast Coast...
Guidance has become more aggressive with a wave of low pressure
potentially developing along an inverted trough shifting northeast
along the FL/GA/SC coasts. While NHC has placed a 10% probability
of tropical or sub-tropical development on this feature, regardless
of whether a circulation forms or not, there is increasing
confidence that heavy rain will spread across the FL Peninsula and
then rotate onshore the GA/SC coasts on Wednesday. With PWs in the
vicinity 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 is possible that the heaviest rainfall 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, and although EFI is
modest, it does capture the region of greatest potential at this
time range. 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 risk was expanded from Winyah Bay, along the coastal
plain of GA/SC, and across much of the FL Peninsula.
Weiss
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Jun 2 2025
Heavy rainfall may impact portions of the Southeast Coast thanks
to a compact low under a closed weakness aloft. NHC is monitorring
development sub-tropical potential of this feature. Deepest
moisture
may stay offshore and uncertainty is high, but there is a chance
of some heavier rainfall along the coast. Accordingly, a Marginal
Risk of excessive rainfall shifts Thursday into Friday from far
northern Florida up through the coastal Carolinas as the low lifts
slowly up the coast in warm and moist Gulf Stream waters.
Numerous Showers and thunderstorms will focus along a slow-moving
and wavy front that will stretch from the Northeast and Ohio Valley
states down to the southern Plains. Gulf moisture pooling over the
region and shortwave/jet support will help prime the environment
for embedded heavy rain potential. Slow translation and deep
moisture could lead into some locally quite heavy totals, but local
focus details are proving quite varied in guidance from run to
run. Accordingly, a Day4/Thursday and Day 5/Friday WPC Marginal
Risk area for excessive rainfall and flash flooding remains
depicted for this region, with a smaller and less certain Slight
Risk area focused over Oklahoma for Friday. The southern trailing
tail of the elongated boundary will stall over the southern Plains,
eventually with baroclinicity rejuvenated more broadly again over
the central U.S. by ample northern stream system reinforcement that
may also act to spread main heavy rainfall focus across the Mid-
South and Tennessee Valley.
Meanwhile, enhanced rain and thuinderstorms will also spread
across the Northeast late week and the weekend as the northern
portion of the front advances, eventually shifting southward
through the Mid-Atlantic toward the Southeast later weekend into
next Monday.
Initially, below normal temperatures will be in place across the
Rockies and Plains on the backside of the frontal boundary. As the
frontal progresses, temperatures will begin to moderate by the end
of the week and into the weekend. Some of the warmest year to date
temperatures will be across much of the Eastern U.S. With daily
readings climbing into the upper 80s to lower 90s there will be a
Moderate level of HeatRisk. Care should be taken to protect
yourself from the hottest part of the day. Areas of south Texas
will see rising temperatures through the late week into the
weekend, cresting 105F by next weekend along the Rio Grande. This
may push heat index values over 110F.
Heat Safety -- take 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.
Schichtel/Campbell
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Jun 2 2025
Heavy rainfall may impact portions of the Southeast Coast thanks
to a compact low under a closed weakness aloft. NHC is monitorring
development sub-tropical potential of this feature. Deepest
moisture
may stay offshore and uncertainty is high, but there is a chance
of some heavier rainfall along the coast. Accordingly, a Marginal
Risk of excessive rainfall shifts Thursday into Friday from far
northern Florida up through the coastal Carolinas as the low lifts
slowly up the coast in warm and moist Gulf Stream waters.
Numerous Showers and thunderstorms will focus along a slow-moving
and wavy front that will stretch from the Northeast and Ohio Valley
states down to the southern Plains. Gulf moisture pooling over the
region and shortwave/jet support will help prime the environment
for embedded heavy rain potential. Slow translation and deep
moisture could lead into some locally quite heavy totals, but local
focus details are proving quite varied in guidance from run to
run. Accordingly, a Day4/Thursday and Day 5/Friday WPC Marginal
Risk area for excessive rainfall and flash flooding remains
depicted for this region, with a smaller and less certain Slight
Risk area focused over Oklahoma for Friday. The southern trailing
tail of the elongated boundary will stall over the southern Plains,
eventually with baroclinicity rejuvenated more broadly again over
the central U.S. by ample northern stream system reinforcement that
may also act to spread main heavy rainfall focus across the Mid-
South and Tennessee Valley.
Meanwhile, enhanced rain and thuinderstorms will also spread
across the Northeast late week and the weekend as the northern
portion of the front advances, eventually shifting southward
through the Mid-Atlantic toward the Southeast later weekend into
next Monday.
Initially, below normal temperatures will be in place across the
Rockies and Plains on the backside of the frontal boundary. As the
frontal progresses, temperatures will begin to moderate by the end
of the week and into the weekend. Some of the warmest year to date
temperatures will be across much of the Eastern U.S. With daily
readings climbing into the upper 80s to lower 90s there will be a
Moderate level of HeatRisk. Care should be taken to protect
yourself from the hottest part of the day. Areas of south Texas
will see rising temperatures through the late week into the
weekend, cresting 105F by next weekend along the Rio Grande. This
may push heat index values over 110F.
Heat Safety -- take 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.
Schichtel/Campbell
