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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0036Z Jul 08, 2024)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
835 PM EDT Sun Jul 7 2024

Day 1
Valid 01Z Mon Jul 08 2024 - 12Z Mon Jul 08 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
COASTAL TEXAS...

01Z Update...

...TC Beryl for Coastal Texas into Louisiana...

Beryl still has a landfall forecast prior to 12Z Monday on the
middle TX Coast (please see the NHC website for the latest
information) with the outer bands already pushing onshore early
this evening. Initially dry air is wrapping into the system but
this is expected to diminish later tonight and as the eyewall moves
onshore, the threat of flash flooding will increase quickly. Not a
lot of change was needed to the Day 1 ERO (through 12Z Monday) with
only minor tweaks to the western side of the risk areas to tighten
up the gradient some as the track guidance is clustering really
well and there is evidence of a tighter western gradient to the
precipitation at least tonight. The Moderate Risk remains in place
for the potential for considerable urban and flash flooding. In
terms of rainfall potential, the latest guidance, including 18Z
HREF, suggests narrow/localized totals near the center/landfall between
6-7" likely (HREF mean) with some potential for locally higher
amounts around portions of Matagord, Brazoria, and Fort Ben
counties.


...Southern Plains to the central High Plains and to the Upper
Midwest...

Along a frontal boundary and as a shortwave trough digs across the
region, late afternoon convection has fired up across the Front
Range of CO and is slowly moving east/southeast. Initially nearly
stationary storms will pose a flash flood risk for the potential
for intense rain rates above 1"/hr and the latest guidance is
keying on this activity congealing/organizing into several line
segments as it moves south/east. Localized 2-3" totals through
tonight will be possible and some of this could cause isolated to
scattered instances of flash flooding.

Down into the Texas Panhandle and Oklahoma, convection already
developing along the warm front will slowly train/repeat over
similar areas into tonight. Localized higher end rainfall amounts
of 2-4" will be possible, most likely over south-central OK for the
potential of scattered flash flooding.

Farther north, greater synoptic forcing is present with the upper
trough extending from an upper low over northern MN to the
southwest over the central Dakotas and extending to the central
High Plains. A few areas of organized convection early this evening
will continue pressing east/northeast across Iowa, southeast MN,
and western WI as well as a secondary area over eastern MO. Some of
this activity will wane/diminish after peak heating and
instability erodes, but a lingering threat into the night will
persist and could pose an isolated flash flood risk. The latest
HRRR runs show some redevelopment overnight across central MO that
could repeat over some areas and bring some locally higher rainfall
amounts.

...Southeast...
The stalled frontal boundary and very moist airmass in place will
continue to bring slower moving thunderstorms capable of producing
very intense rain rates over the next several hours (late evening),
particularly for portions of eastern GA and central SC. See the
latest WPC Mesoscale Precipitation Discussion 585 for more details
on this heavy rainfall threat tonight.

Taylor


Day 2
Valid 12Z Mon Jul 08 2024 - 12Z Tue Jul 09 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR MOST OF
EASTERN TEXAS...

21Z Update...

...East Texas through Arkansas...

12Z HREF consensus along with the 18Z HRRR feature feature a
considerable swath of heavy rain ahead and east of the Beryl track
which starts from just inland from the Middle TX coast at 12Z Mon.
An areal average of 3-8" is featured from the upper TX Coast (from
inflow bands right of the track) and in the inner core rainfall
north from Houston-Bryan TX then into southwest AR and far
southeast OK. The Moderate Risk is expanded a bit more northeast
through the rest of TX as well as farther east toward the LA border for
the inflow bands right of the track. At least locally considerable
impacts can be expected. Fortunately this is a fairly progressive
system per NHC forecast forward speed of at least 10kt. Given
increased confidence in the heavy rain swath extending through
western/central AR and far eastern OK warrants expansion of the
Slight Risk up to the MO/AR border. A trend in the track to the
right continues and will need to be monitored in future outlooks,
especially considering how much inflow into the Ozark
terrain/topographical enhancement will occur.

Elsewhere, tropical moisture from Beryl into a cold frontal
boundary draped over the southern Plains should focus scattered
heavy rainfall over much of OK into the TX Panhandle where a
Marginal Risk is maintained/expanded into northwest TX.


...Southeast...

Convection in proximity to the lingering frontal boundary within PW
anomalies of 2 to 3 sigma will persist over the southern
Appalachians, much of GA, southern SC and northeast FL where a
Marginal Risk is maintained. Recent rains have increased soil
saturation levels, so this additional activity allows a threat for
isolated flash flooding.


Jackson


Day 3
Valid 12Z Tue Jul 09 2024 - 12Z Wed Jul 10 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS THE MIDDLE
MISSISSIPPI VALLEY...

...Mid-South through Midwest...

Beryl is expected to quickly phase with an upper trough as it lifts
northeast from Arkansas Tuesday. A swath of heavy rainfall is
expected to persist through this extratropical transition with the
12Z GFS/ECMWF in good agreement with another shift to the right
with the track which is in line with NHC forecasts. 3-6 inches over
southeast MO, south-central IL to central IN (along with an
additional 1.5" or so over northern AR) warrants a Slight Risk that
includes the St. Louis metro. Increased confidence in central Gulf
coast precip, but limited inflow banding between the coast and the
remnants over the Mid-South warrants trimming the Marginal Risk on
the south side, while the more progressive and right trend in the
track warrants bringing the Marginal Risk into western OH.

...Southwest...

Monsoonal moisture feeds over eastern AZ through the southern
Rockies warranting maintenance of the Marginal Risk for most of
New Mexico, southeast Arizona into southern Colorado with
particularly considerations for burn scars and areas that have
seen ample rainfall recently.

...Southeast...

Maintained the Marginal Risk over southern Georgia through the
northern FL Peninsula given the abundant moisture over the region
and diurnal forcing for locally heavy rainfall, especially for
northeast Florida. General consensus of 12Z guidance continues to
suggest 1 to 2 inches with local maximums of 3 to 4+ inches.


...Northeast...

Some moisture from the Southeast and ahead of Beryl interacts with
a front over the Northeast. Guidance is rather light with activity
mainly in New England, so for now the Marginal Risk was trimmed
back to north of NYC.


Jackson

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