Quantitative Precipitation Forecast
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000
FOUS30 KWBC 132027
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 PM EDT Wed Mar 13 2024

Day 1
Valid 16Z Wed Mar 13 2024 - 12Z Thu Mar 14 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NORTHEASTERN KANSAS AND NORTHWESTERN MISSOURIT...

...16Z Outlook Update...
Morning model guidance (particularly CAMs) depict a scenario for
developing (and initially slow-moving) convection to form along a
warm front along and north of the I-70 corridor in northeastern
Kansas/northwestern Missouri this afternoon. Models also generally
grow the developing convection upscale, promoting cell mergers and
eventual transition into one or two forward-propagating linear
segments through the night.  This evolution should prolong rain
rates in certain spots - allowing for local 1-2 inch/hr rates and
2-3 inch rainfall totals to materialize where training is most
pronounced.  Given the scenario, a targeted Slight Risk area (15%
or greater flash flood probabilities) was introduced where the
most likely axis of heavier rainfall is expected to develop
primarily between 22-06Z.  A broader Marginal Risk area was
maintained for this outlook, but was expanded northeastward into
more of northern Illinois/Indiana where recent guidance depicts
potential for localized training of deep convection to materialize
tonight.

See the previous discussion below for more information.

Cook

...Previous Discussion...

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS...LOWER MISSOURI VALLEY AND MID-MISSISSIPPI
VALLEY...

A stationary frontal boundary is expected to drape southwest to
northeast from eastern portions of the Central Plains into the
Lower Missouri Valley and Mid Mississippi Valley regions.   The
low level southerly flow is expected to re-strengthen into this
front late Wednesday into Wednesday night/early Thursday, with
850-700mb mb moisture flux anomalies increasing to 1 to 2 standard
deviations above the mean by early Thursday morning.  This will
support potential for an increasing area of organized overrunning
convection along and to the north of this front, with potential
for localized areas of training or more than one batch of
convection moving over the same area.    The marginal risk area
fits well with where the HREF neighborhood probabilities are high
for 1"+ totals day 1 from northeast Kansas/southeast Nebraska,
across northern Missouri, southern Iowa and northwest Illinois.
While the HREF 1"+ probabilities are high over a large area, the
EAS probabilities are showing a much smaller area of probabilities
of over 40% along the Iowa/Missouri border area, suggesting poor
hi res model overlap of 1"+ areas.  2"+ HREF neighborhood
probabilities are showing a very small area of high probabilities
over the Iowa/Missouri border area, and low EAS probabilities for
2"+ amounts.  Hourly probabilities for 1"+ totals during the 0000
to 1200 UTC period are generally less than 20%.  At the moment,
the risk level is kept at marginal with hourly FFG values mostly
1.5" and greater.  Changes to the previous outlook were to
elongate it approximately 100-120 nm to the east and west and to
narrow it on the north end by about 60 nm.

Oravec


Day 2
Valid 12Z Thu Mar 14 2024 - 12Z Fri Mar 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS AREAS FROM
NORTHEAST TEXAS INTO THE MID-SOUTH AND MISSOURI OZARKS...

...21Z Outlook Update...
Westward and northward expansions of the ongoing Slight Risk area
were made for this update amid substantial model spread and
uncertainty.  Early in the D2/Thu period (around 12-15Z), models
depict potential for training convection to focus along a warm
frontal zone across northern Illinois/Indiana.  That activity will
be heavily modulated by the eventual eastward movement of
convective complexes late in the D1 forecast period.  That
activity should maintain isolated flash flood potential through
the morning, although a weakening trend in convection is expected
after 15Z.

Later in the D2 period, a southward-moving cold front is expected
to provide a focus for scattered to numerous thunderstorm
development from the Red River in southern Oklahoma into
southwestern Missouri.  Models vary substantially with respect to
development and upscale growth of this activity, and rising
geopotential heights throughout the forecast period over the front
and warm sector raise concern that convective coverage may be
sparse in some parts of the Slight Risk area.   However, storms
are expected to develop and foster local cell mergers/training to
support flash flood potential.  The highest potential for flash
flooding should reside from southeastern Oklahoma into southern
Missouri (including much of the Ozarks) where areas of 2 inch/hr
rain rates are expected to materialize.

Some uncertainly also exists with respect to upscale growth of
convection and downstream rainfall potential across portions of
the ArkLaTex, central Arkansas, and the Mid-South.  The Slight
risk area continues to depict potential for at least localized
flash flood potential through the overnight hours depending on the
eventual evolution of upstream convective complexes that form in
the 19Z-00Z timeframe. Portions of Mississippi and northeastern
Louisiana were trimmed from the inherited Slight as it appears
less likely that deep convection will materialize in these areas
during the 00Z-12Z period (per 12Z models).

The Marginal risk area was expanded southwestward across central
Texas with the expectation that scattered thunderstorms could
focus along a cold front in that area late Thursday and
train/repeat, boosting local rain rates.  The Marginal risk area
was also expanded northeastward across the Ohio Valley with the
expectation that isolated to scattered, fast-moving storms could
train and promote isolated areas of 1+ inch/hr rain rates from
afternoon through the overnight hours.  A low-end risk of similar
activity extends as far northeast as southern New York State after
00Z Fri, although confidence in this scenario was too low to add
Marginal probabilities at this time.

See the previous discussion below for more information.

Cook

...Previous discussion...

The low level southerly flow is expected to once again strengthen
significantly late Thursday into early Friday across the eastern
portions of the Southern Plains into the Lower Arkansas and Lower
Mississippi Valleys downstream of the strengthening closed low
over the Southern Great Basin. 850-700 mb moisture flux anomalies
and PW anomalies rise to 2 to 2.5+ standard deviations above the
mean along and ahead of the associated cold front pushing
southeast through the Southern Plains into the Lower Arkansas
Valley. There is a strong model signal for heavy precipitation
from northeast Texas, southeast Oklahoma, northern Louisiana, much
of Arkansas, northwest Mississippi, far western Tennessee, far
southeast Missouri, far southern Illinois and far western Kentucky
in a region of favorable large scale conditions, strong frontal
convergence, well defined upper difluence, late Thursday into the
early hours of Friday.   Similar to the past few model
cycles,there continues to be north-south model spread with respect
to where the max convective qpf axis will set up.  The NAM
continues to be the northern outlier, the EC and EC mean, the
farthest south and the GFS, GEFS mean and UKMET in between.  The
slight risk continues to be drawn to encompass the current model
spread, with only some minor changes from the previous outlook for
this period.  The slight risk is across areas that have had below
average precip over the past few weeks and subsequently relative
high FFG values.   The heaviest precip totals over the past few
weeks and the most saturated soils area well to the southeast of
the slight risk area across portions of the South and Southeast.
Given this and the continued spread in the max qpf axis, the risk
was kept at slight for the time being.

Oravec




Day 3
Valid 12Z Fri Mar 15 2024 - 12Z Sat Mar 16 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EAST TEXAS,
ACROSS THE LOWER MISSISSIPPI VALLEY AND INTO PORTIONS OF THE
SOUTH...

...21Z Outlook Update...
An uncertain convective/flash flood scenario is expected to
continue into the D3/Fri forecast period.  Ongoing convection
(potentially extending from northeast Texas through the Mid-South)
is expected to migrate/propagate southeastward into and through
the Slight Risk area primarily during the morning hours.  Varying
model solutions suggest that whatever remaining low-level
boundaries/remnant convection should reach portions of the central
Gulf Coast and southeast Texas by midday despite substantial
ridging aloft over the area.  The low-level boundary in central
Texas has potential to aid in renewed convective development later
in the afternoon, and could result in a few instances of
training/cell mergers and increased rainfall rates.  Strong
consideration for removing the Slight was given, although enough
of a convective signal remains in the model guidance to keep
existing Marginal/Slight areas along with some geographical
restriction especially across the southern Appalachians and
southeastern Tennessee.

Cook

...Previous Discussion...

The surface frontal boundary pressing southeastward day 2 into the
Southern Plains, Lower Arkansas Valley and Mid Mississippi Valley
will begin to accelerate to the southeast day 3 through the
Tennessee Valley and Lower Mississippi Valley, moving slower to
the south into the Southern Plains.  An axis of anomalous PW
values, 1.5 to 2.5+ standard deviations above the mean will
accompany this southeastward moving front day 3.  This and the
continued overall favorable large scale conditions ahead of this
front will support another day of potentially widespread heavy
precip along and ahead of the front.  There is the typical amount
of spread with respect to the max qpf axis, but overall model
consensus for potentially heavy rains.  The day 3 qpf axis does
move back over areas of Mississippi, Alabama and Georgia that have
had above average precip over the past week or two, resulting in
higher stream flows and greater soil saturation.  There were not a
lot of changes made to the previous broad slight risk area,
extending it slightly farther to the west across northeast Texas
to cover the model spread. The northern portion of the marginal
risk area over the Northeast was cutback to the Central
Appalachians to better fit the latest model qpf.

Oravec


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


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