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FOUS30 KWBC 120051
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
851 PM EDT Tue Jun 11 2024

Day 1
Valid 01Z Wed Jun 12 2024 - 12Z Wed Jun 12 2024

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

A Slight risk was maintained for central and southern FL.
Additional heavy rainfall is moving into southern FL this evening
after a relative lull. Confidence on the exact details remain
low...the HRRR has shown considerable run to run differences, and
is not necessarily a great match to observations. Thus little
confidence in the HRRR QPF output through the overnight period.
With that said, based on radar/satellite trends would expect to see
an additional round of heavy rainfall over southern FL. Based on
the overall model consensus, think the most probable outcome is
less rain that what we saw earlier in the day, but enough to
potentially cause a few additional flash flood
concerns...especially over any more sensitive urban areas. However,
can not rule out localized significant rainfall amounts and flash
flooding overnight given the tropical airmass in place.

A Marginal risk was maintained over portions of central and
southern TX. Cell mergers over southeast TX may result in a
localized flash flood risk through the evening hours. Most
indications are that the well defined MCV over central TX will
help trigger some additional convective development later tonight
into early Wednesday. Not expecting this activity to be too robust
or organized, but could see just enough development to drive an
isolated flash flood threat.

Chenard


Day 2
Valid 12Z Wed Jun 12 2024 - 12Z Thu Jun 13 2024

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

...20Z Update...

Continuity was maintained for all the risk areas with only some
minor adjustments necessary as the general pattern evolution
remains consistent from run-to-run to limit any notable changes.
The heavy rain across the southern half of the Florida Peninsula
will continue with the best flash flood threats confined to the
coastal urban corridors, especially over southwest FL from St
Petersburg down through Naples. 12z HREF signals are still fairly
robust with neighborhood probabilities for at least 5" in totals
for the period running between 70-90% within the aforementioned
corridor along the Florida Gulf Coast. Waves of heavy rain will
move inland off the adjacent Gulf with general rates running
between 1-2"/hr within heavier cells with some localized 3-4"/hr
rates possible based on the probabilistic fields of the HREF and
upper quartile of the NBM. The multi-day event will lead to
heightened concerns for flooding, but pure flash flooding will
still remain within the SLGT risk category thanks to the elevated
FFG`s that are climatologically favored over the Peninsula. The
urban areas are the most likely to see any flash flood risks due to
impervious surfaces with the sandy soils likely to absorb much of
the rain during the period, especially with any small breaks in the
precip shield.

The other areas of concern across the Midwest and Texas are
generally MRGL with local rainfall totals likely within the 1-2"
range in the affected areas with maxes more around 3" for each
region in question. Convection over the Midwest will have the most
dynamical support with the approach of a shortwave trough and
associated cold front that will enhance surface forcing along with
the favored upper pattern. The progressive nature of the precip
will deter higher end impacts, however some backbuilding is
plausible over southern MN into northern IA that could enhance
local totals towards that upper threshold mentioned previously.
This is noted on a few hi-res deterministic and falls within the
90-99th percentile of outcomes in the blend. Considering this is
more localized, the threat remains on the MRGL level with a chance
at a targeted upgrade pending short term convective evolution.
Further south, pulse convection will occur with the passage of a
weak mid-level vorticity maximum that will swing southeast around
the eastern flank of a mid-level ridge that will shift eastward
from the Southwestern U.S. A few spots could see a quick 1-2" of
rainfall, but will be highly localized. Considering the rainfall
from the previous period, some places could still be wet and more
conducive for flooding concerns. This is highly contingent on what
falls this evening and there`s a chance this risk area is voided,
or shrinks in size.

Kleebauer


...Previous Discussion...

...Southern Florida...

The stalled front will sag a little to the south during this period
but the heavy rain will persist across South Florida. PW values of
2 inches will hold steady across the peninsula and will maintain
very efficient rain and rain rates across the nearly saturated
rural and urban areas. Areal averages will again be 2 to 4 inches
with local maxes up to 8 inches possible. A Slight Risk for
Southern Florida and the Keys remains in effect along with a
Marginal Risk for Central Florida. The nature of this multi-day
event with storm total rainfall amounts potentially rising into the
double digits, there may be the need for an upgrade in future
updates.

...Texas...

Convection will continue to shift south and east while reducing
areal coverage during this period. Most of the thunderstorms will
focus across eastern portions of the Hill Country and points east.
While amounts are on the lower end the recent rains will have
increased soil saturation thus lowering the amount of rain needed
to become problematic. The Marginal Risk was maintained for an
isolated threat for flooding concerns for portions of central and
eastern Texas toward the Mid and Upper Coast.

...Upper Mississippi Valley...

A Marginal Risk was introduced for portions of Minnesota, Wisconsin
and Iowa where soils have been nearly saturated from multiple
instances of recent rainfall. Showers and thunderstorms are
expected to accompany a passing cold front through the northern
tier states, potentially spreading 1 to 3 inches over the sensitive
area and may lead to isolated areas of flooding.


Campbell


Day 3
Valid 12Z Thu Jun 13 2024 - 12Z Fri Jun 14 2024

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

...20Z Update...

No changes were necessary for the previous D3 issuance as model
continuity maintains the areas over the central Midwest and Florida
as the primary areas of note for flash flood concerns. Recent bias
corrected QPF across the southern FL Peninsula remains aggressive
with totals approaching 2-4" across the southwest urban corridors
with 1-3" expanding further inland. This will likely lead to some
areas in FL seeing over 12" of precipitation in the span of 3-days,
a substantial amount even with a consideration for it being in
Florida. Rates are still a factor in maintaining the area in a SLGT
risk as the FFG`s, while expected to decrease, will likely remain
within the 2.5-3"/hr range for any expected flash flood threat
keeping the threat tied to the coast for greater impact. As of now,
there was not enough of a signal to warrant an upgrade.

The central Midwest through IL/IN will see the pattern evolve
upstream to overhead by Thursday afternoon and evening with a
shortwave progression bisecting the region along with a cold front
moving through on the base of a low moving through the northern
Great Lakes in to Ontario. Local totals of 2-3" are possible across
parts of the aforementioned area with the heaviest rain likely
tied to convection along the frontal boundary. The threat is still
a question mark on the latitudinal extent of the precip field as
much of the setup is contingent on the placement of the front.
Ensemble guidance is generally impacting northern IL down into the
central portion of IL/IN, so there was no reason to deviate from
the previous forecast. Thus, the MRGL was maintained over the same
general area from the past forecast.

Kleebauer


...Previous Discussion...

...Florida...

Little change in the environment and pattern across FLorida.
Thunderstorms will continue to focus across South Florida and the
Keys bringing another 1 to 3 inches to the area. WPC has 3-day
forecast accumulation of 2 to 12 inches from north to south across
the peninsula with isolated higher amounts. A Slight Risk is in
place from Tampa Bay to Melbourne metros and south to the Keys. A
Marginal Risk area covers central Florida.

...Midwest...

Thunderstorms will pass from the Upper Mississippi Valley into the
Midwest/western Ohio Valley as the cold front progresses eastward.
Areal averages of 1 to 3 inches will be possible across this part
of the country where recent rains have left soils nearly saturated.
Rain may become excessive and lead to isolated instances flooding.
A Marginal Risk was maintained from the previous day 4 forecast and
spans from eastern Iowa/northeast Missouri to southwest Michigan
and northern Indiana.

Campbell

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