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FOUS30 KWBC 081959
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
359 PM EDT Sat Jun 8 2024

Day 1
Valid 16Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN MISSOURI...

...16Z Update...

No major changes were needed with this update. Latest CAMs continue
to suggest a Moderate Risk event across portions of southern
Missouri starting late this afternoon and continuing into tonight.
There remains some uncertainty as to where the axis of heaviest
rainfall will set up, with the Moderate Risk area remaining a good
average of the guidance. Unfortunately given the forcing will be
along a nearly stationary boundary set up across the Ozarks of
Missouri, until the storms start forming along that boundary later
today there`s unlikely to be much change as to where the heaviest
rain will set up. There remains considerable concern that once the
storms begin forming and training along the boundary/front, there
will be multiple hours of training thunderstorms moving along that
boundary, as a southwesterly-oriented LLJ pumps moisture and
instability into the front, and dry north to northeasterly flow
north of the front helps to keep the front in place. Thus, the
Moderate risk remains a very good forecast given the potential for
significant impacts. Should the storms grow stronger, move slower,
or train for longer, it`s possible a narrow area along the boundary
may have High risk-level impacts, but certainty as to where that
will be is way to low for any further upgrades. It`s probable with
the 01Z update that the MDT may need to be adjusted a bit from its
current placement, as the event should be underway by then.

A secondary maximum in forecast precipitation is expected over
western Kansas as well tonight, as storms that form further north
and east into eastern Colorado track and merge over western Kansas.
The western extent of the supporting LLJ over the TX/OK Panhandles
should support potentially backbuilding storms, but it should not
as robust totals as further east into Missouri due to faster storm
motion. The Slight risk area was expanded a bit north and west to
cover the northeastern corner of Colorado with a bit better
agreement in the guidance.

Wegman

...Previous Discussion...

...Eastern Kansas, Missouri, and Mid Mississippi Valley...

A Moderate Risk (Level 3 of 4) was introduced for this forecast
cycle for portions of southern Missouri where rounds of
thunderstorms through early Sunday are likely to produce several
inches of rainfall in a short period. Scattered to numerous
instances of flash flooding are likely, with localized significant
flooding possible.

As of early this morning, a slow-moving MCS is advancing through
far eastern Kansas and western Missouri and is expected to weaken
some as it moves across Missouri by the beginning of the forecast
period at 12Z. It will however likely lay out an outflow boundary
west to east across far southeast Kansas through southern Missouri
which will become the main focus for additional thunderstorm
development later in the period.

By late afternoon, the increasing moisture impinging on this
boundary (PWs 2"+, 2-3 std above normal) and modest amounts of
instability (MUCAPE 2000-3000 J/kg) is likely to ignite another
round of deep convection. This activity is likely then to
train/repeat west to east as the flow becomes increasingly parallel
to the expected storm motions. This will favor some intense rain
rates and high totals due to the combination of the favorable
ingredients and training flow pattern. Several repeating rounds
are possible, particularly over southwest to south-central MO. The
HREF probabilities have continued to trend higher this cycle, the
24-hr 5" probabilities are exceeding 50 percent across southwest
MO and there are slight signals (10-15 percent) for hourly totals
in excess of 3" for several hours later this afternoon/evening.

The primary forecast uncertainty is placement, with some
north/south differences between the various hi-res models still at
this forecast lead time and is likely tied to how this morning`s
convection plays out and where the effective boundary ends up
settling. The consensus is for somewhere across far southeast KS
through Missouri, though some deterministic solutions are a bit to
the north.


...Eastern Colorado to Kansas...

The combination of robust heating, a modest amount of moisture, and
an approaching shortwave trough will ignite a few rounds of intense
thunderstorms later today initially over Colorado before evolving
into an organized complex over western Kansas. Intense rain rates
and some localized/slight threat of training could result in
scattered instances of flash flooding.

Convection initiation over the Front Range will be driven by the
sufficient heating and shortwave trough moving through, and
gradually the storms will move into a more moist environment (PWs
getting closer to 1-1.25") that will help them grow upscale into
an MCS. The latest HREF probabilities are moderate/high for 1"
hourly totals (above 60 percent) across northern/northeast CO and
even reach 20-25 percent for 2" hourly totals before increasing to
above 50 percent across western Kansas when the larger MCS is
likely to set up. For 24-hr rainfall totals, the HREF points to
western KS for the greatest threat of at least 3 inches (above 40
percent) where the Slight Risk skews toward the higher end of the
probability range (25-40%). By evening, the MCS should be rolling
through Kansas at a faster clip but still will have enough
environmental ingredient support to maintain the Slight for intense
rain rates above 2"/hr at times and isolated/scattered instances
of flash flooding.

Taylor

Day 2
Valid 12Z Sun Jun 09 2024 - 12Z Mon Jun 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEAST COLORADO, NORTHEAST NEW MEXICO, AND THE TEXAS
PANHANDLE AS WELL AS MUCH OF THE OZARKS OF MISSOURI AND ARKANSAS...

...20Z Update...

...Southern High Plains...

In coordination with ABQ/Albuquerque, NM and PUB/Pueblo, CO
forecast offices, the Slight risk inherited for some of the Plains
area east of the Front Range and Sangre De Cristos was expanded
north and west to include those ranges, adjacent valleys, and
associated burn scars. The meteorology remains little changed, but
CAMs guidance covering the entire period suggests that while most
storms will form immediately downrange of those aforementioned
mountains, moisture will get into the mountains and valleys to the
west, resulting in some convection in and west of the mountains.
Thus, the Slight was expanded.

There is particular concern around the Hermits Peak fire burn scar
northwest of Las Vegas, New Mexico. The forecast of 1-3 inches of
rain from convection may cause significant flooding in the area.
This area is in a higher end Slight and continued increases of both
coverage and intensity of convection in the area in and around the
southern Sangre de Cristo range may require a future Moderate Risk.
For now the convection appears to be a bit too scattered so impacts
as of now appear too limited for a MDT. We will continue to
monitor the trends in the CAMs in the area.

...Ozarks...

The heavy rainfall event ongoing from Day 1 tonight is expected to
continue into the morning hours of Sunday. Rainfall amounts of up
to 1.5 inches are possible after 12Z/7am CDT, which would continue
any ongoing flooding across the area. There`s good agreement that
the rainfall will quickly weaken with the diminishing of the LLJ,
so this Slight Risk upgrade is expected to only be for the morning,
and should be removed with the midday update.

...Southeast Florida...

A small Marginal Risk area was introduced with this update for
expected moisture-laden sea breeze convection Sunday afternoon
occurring over the urban I-95 corridor. An isolated instance or 2
of flash flooding can`t be ruled out should the convection form and
persist over an urban area.

Wegman

...Previous Discussion...

...Southern Plains to Central High Plains...

Scattered to numerous thunderstorms are expected to develop across
the region during the period, with a Slight Risk (Level 2 of 4) of
excessive rainfall and flash flooding. A frontal boundary is
forecast to be draped across the region, from eastern New Mexico
through the Texas Panhandle. With that, a very anomalous pool of
moisture will bank up against the terrain with PWs forecast to be
above 1.5", which is 2-3 std above normal. A shortwave trough
coming out of northwest Mexico is forecast to reach the region by
the period, and this will help drive the more widespread
convection, particularly over eastern NM. The latest model
guidance continues to highlight potential for several inches (1-3")
over eastern NM into parts of the TX Panhandle and with that and
the environmental ingredients for more intense rain rates, the
Slight Risk was only adjusted minimally from the previous forecast.

...Mid Mississippi Valley...
The frontal boundary draped across the region along with favorable
amounts of moisture will support isolated to scattered
thunderstorms, with storms likely ongoing at the start of the
period across Missouri that move eastward and weaken through the
day. By later in the period, loosely organized convection is likely
but without any strong focus, the Marginal Risk was maintained for
potential of localized 1-1.5" totals.

Taylor


Day 3
Valid 12Z Mon Jun 10 2024 - 12Z Tue Jun 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHERN PLAINS, SOUTHERN PLAINS, AS WELL AS SOUTH FLORIDA...

...20Z Update...

No major changes were made with this update. All Marginal Risk
areas are expected for the CONUS for Monday. The Marginal for the
northern Plains was extended north to the Canadian border with the
potential for a few training storms in generally flood-resistant
North Dakota and northwest Minnesota. The southern Plains Marginal
remains in place with little in the way of signal for persistent
heavy rain...rather it looks like typical dry line convection will
develop in the region Monday afternoon.

A Marginal Risk area was introduced for southern Florida. Despite
most of the state remaining well below average for precipitation,
this will start a multi-day rainfall event as deep tropical
moisture moves across the state along a stalled frontal boundary.
While the coverage of rain will be more extensive Monday than
Sunday...no significant forcing mechanisms will be around to
organize the convection into anything likely to produce any more
than isolated flash flooding.

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 to Southern Plains...
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".



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