584
FOUS30 KWBC 100033
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
833 PM EDT Sun Jun 9 2024

Day 1
Valid 01Z Mon Jun 10 2024 - 12Z Mon Jun 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN HIGH PLAINS...

...20Z Update...

...Lower Missouri Valley and the Ozarks to Lower Mississippi Valley
and Mid-South...
Issued a special Day 1 ERO update to remove the Slight Risk which
had been in effect across far northern AR into southern MO.
Observational and mesoanalysis trends show the area that was in the
Slight Risk is now behind the front, north of the ML CAPE gradient
with minimal if any deep-layer instability left. Focus for
convection will be south (AR, western TN, and northern MS-AL);
however based on the latest CAM guidance/trends, along with the
fact that these areas didn`t get the deluge of rain areas farther
north did late last night/early today, the risk will likely be more
isolated/localized (i.e. Marginal) than otherwise.

Hurley

...Previous Discussion...

...Southern High Plains...
Very few changes made across this region. Convection is likely to
develop along the west Texas dryline on north and west into the New
Mexico and Colorado Front Ranges. The southern Sangre de Cristo
Mountains in northern New Mexico remain highlighted for a higher
end Slight for flooding, as unusual moisture pumping into all these
areas are likely to cause storms to form over recent (2022) burn
scars in this area. Locally significant flash flooding will be
possible. The storms that form over NM are expected to congeal into
an MCS over west Texas tonight, which could cause locally higher
rainfall totals exceeding 3 inches. Dry soils over nearly all of
the Slight risk area should help preclude significant flash
flooding...and as such no upgrades were considered.

...Northern High Plains...
A ribbon of higher moisture (PWs > 1") will develop through the
High Plains, into portions of eastern WY and far southeast MT.
Daytime convection developing with the robust heating combined with
this higher moisture may lead to a few/isolated instances of heavy
rainfall and flash flooding. There is a slight (20 percent) signal
in the HREF probabilities for 3" totals over northeast WY with
amounts 1-2" more likely through the Marginal Risk area.

...Southern Florida...
An increasing moist environment (PWs approaching 2-2.25") combined
with the daily sea/land breezes will lead to robust and slower
moving deep convection across both the Gulf and Atlantic coasts of
southern Florida. Intense rain rates (2-3"/hr) at times will be
possible and could pose a localized, mainly urban, flash flood
threat during the afternoon/evening hours.

Wegman/Taylor


Day 2
Valid 12Z Mon Jun 10 2024 - 12Z Tue Jun 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
PORTIONS OF THE NORTHERN PLAINS, SOUTHERN HIGH PLAINS AND TEXAS,
AND SOUTHERN FLORIDA...

...20Z Update...

...Northern Plains...

No significant changes were made. The flash flooding threat remains
lower-end Marginal across the northern Plains, where the inherited
Marginal Risk area was trimmed out of eastern ND and northwestern
MN with this update. The western Plains are difficult to flash
flood and moisture availability will be a significant limiting
factor in any convection into the Dakotas. Nonetheless some
training storms are possible, which could cause isolated instances
of flash flooding in flood-sensitive areas. This area could be
considered for Marginal Risk removal with future updates.

...Southern High Plains...

The Marginal Risk area was expanded north and west to include the
Sangre de Cristos and southern Colorado Rockies with this update.
Rainfall overall will be much lesser in coverage and intensity
Monday, but with these areas likely to see some isolated to widely
scattered flash flooding today, think by Monday additional rainfall
may lead to a Marginal flash flooding threat again. No major
changes were made towards Texas, where dry line convection should
also be much reduced in coverage compared with today, but here also
may take advantage of more sensitive soils as a result of today`s
convection to cause new isolated flash flooding again Monday
afternoon.

...South Florida...

Moisture will continue building from south to north across south
Florida on Monday. Convective coverage should be greater than today
on Monday, particularly along the sea breeze fronts on both sides
of the Peninsula. Ongoing moderate to locally severe drought will
significantly limit any potential for flash flooding, but
increasing moisture and continued slow storm movement, possibly
over urban areas, will result in isolated instances of flash
flooding, and a bit further north up the Peninsula into portions of
central Florida on Monday afternoon.

Wegman

...Previous Discussion...

...Northern Plains...
A shortwave trough and a cold front will move through the region.
Ahead of this feature, a ribbon of higher moisture will be
advancing northward and will be characterized by PWs between
1-1.5". Along with MLCAPE values above 1000 J/kg, there is good
overlap of the moisture, lift, and instability to support rounds of
thunderstorms by afternoon/evening. With cell mergers and boundary
interactions, an isolated flash flood threat can`t be ruled out
with potential for isolated 1-2"/hr rain rates that could cause
flash flooding, so a Marginal Risk was introduced.


...Southern High Plains and Texas...
A forming closed low straddling NM/TX border will slowly settle
east/southeast through the period and across the entire region
there should be fairly high moisture remaining in place (PWs
1.25-1.75") that will support scattered thunderstorms. The focus
will be on the Texas Panhandle southward into west-central Texas
where totals may approach 1-3".

...Southern Florida...
Deep tropical moisture characterized by PWs well above 2-2.5",
near 2.7", will overspread much of southern Florida, drawn
northward by the larger scale troughing dipping down into the
Southeast U.S. by late Monday into Tuesday morning. With a frontal
boundary lingering over the region, this will act as the focus for
slower moving and intense thunderstorms. Placement/coverage of
heaviest rainfall is still a bit uncertain, though the latest/00Z
guidance is favoring the southwest FL coastal areas for the
potential for several inches. With the very dry conditions in
place leading up to this, the Marginal Risk was maintained to
highlight potential for isolated instances of flash flooding,
primarily for the most vulnerable locations including urban areas.

Taylor


Day 3
Valid 12Z Tue Jun 11 2024 - 12Z Wed Jun 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN
FLORIDA...

...20Z Update...

In coordination with KEY/Key West, FL; MFL/Miami, FL; TBW/Tampa,
FL; and MLB/Melbourne, FL forecast offices, a Slight Risk upgrade
was introduced with this update for much of southern Florida. An
air mass with anomalous moisture to 3 sigma above normal (PWATs
above 2 inches) will move into south Florida on Tuesday and persist
through much of the week. For Tuesday, the flash flooding concerns
are largely tied to where there was flooding today and Monday. The
deep moisture will bring periods of heavy rainfall across the
Peninsula. Widespread 1 to 3 inch totals with locally higher
amounts as high as 5 inches are possible on Tuesday. The guidance
is in general agreement that the higher totals will be along the
west coast from Ft. Meyers south. However, even the slightly lower
forecast totals into the east coast could still cause local
flooding concerns, particularly in urban areas.

The Drought Monitor shows much of the Lake Okeechobee area, as well
as Tampa to Ft. Meyers, as well as the Treasure Coast are all in
severe drought. These very dry antecedent conditions will certainly
preclude a lot of flooding. Hence, urban areas and those areas
harder hit by storms today and Monday will be the most vulnerable
to flooding come Tuesday when everyone is hit with locally heavy
rainfall. Thus, while this is a lower-end Slight, the widespread
nature of the heavy rainfall (and this being just the start of a
multi-day heavy rainfall event), think flooding will be more widely
scattered in southern Florida, necessitating the upgrade.

...North-Central Texas...

The Marginal Risk in the area was shifted a bit west with this
update in keeping with the latest guidance. Storms will be widely
scattered but this area of Texas has been hard hit in recent weeks
to the last month, so isolated flash flooding is certainly
possible...including into the Metroplex. It`s possible a targeted
Slight may be needed with future updates with more certainty and
CAMs guidance pinpointing where the heaviest rainfall will be.

Wegman

...Previous Discussion...

...Southern Florida...
By mid-week, confidence in more widespread unsettled/stormy weather
increases across the Keys and southern Florida as the deep tropical
moisture remains in place and a lingering surface boundary resides
in the region. PWs are forecast to be well above 2.5" and could
approach daily max values by Wednesday. Across the 00Z guidance
suite, rainfall amounts are higher compared to earlier in the week
with the potential for another round of deep, slow moving
convection producing several inches and intense rain rates. The
greatest focus remains on the Keys and southwest FLorida, but the
threat extends to the southeast coast and into portions of central
Florida as well. For now, will maintain the Marginal RIsk but will
need to monitor conditions if repeating daily rounds start to
saturate the soils by mid week, necessitating an upgrade to Slight
at some point.

...Southern Plains...
The aforementioned shortwave trough will slide east/southeast
through Texas and Oklahoma during the period. This extra source of
lift combined with the already moist environment in place, PWs
above 1.5", and the expected source of higher instability should
contribute to scattered/numerous areas of thunderstorms by
afternoon/evening. At this point, model agreement in the placement
of the heaviest rainfall (northern TX/southern OK) is pretty good
and overall amounts line up well among the various deterministic
and ensemble guidance (for 1-2", locally 3"). At this point, the
Marginal Risk looks good but could see a targeted Slight upgrade at
some in the next few updates as confidence in amounts and locations
become clearer.


Taylor

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt