044
FOUS30 KWBC 062012
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 PM EDT Sat Jul 6 2024

Day 1
Valid 16Z Sat Jul 06 2024 - 12Z Sun Jul 07 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE
CAROLINAS...

...Southern states and Eastern Seaboard...

Cold front over the eastern Great Lakes and through the
Appalachians will continue eastward today with its southern extent
draped across the Southeast/South back across Texas and into New
Mexico. This slow-moving/stationary boundary will be the focus for
areas of heavy rainfall today across the Southeast (eastern Georgia
northeastward across the Carolinas) where a Slight Risk of
excessive rainfall is outlined. An expansive Marginal Risk area
spans from New Mexico eastward along and north of I-10 to northern
Florida then northward along I-95 to Maine.

Within the Slight Risk area, an impressive overlap of instability
and moisture is noted across this region...with MUCAPE likely over
2000 J/kg and PWs well above normal around 2.25" (approaching
climatological 99th percentile values). Mean wind flow will be weak
(<10 kts) supporting heavy rainfall in some locations and
afternoon sea breezes will focus developing thunderstorms inland.
12Z HREF neighborhood probabilities show values of 1-hr QPF > 2"/hr
around 30-70% this afternoon/early evening and >3"/hr around 30%.
This would cause a flash flooding threat not only in urban areas
but also in the hillier areas in western parts of the Carolinas.
Farther norther, trimmed the Marginal Risk outline in the Mid-
Atlantic where column moisture is lacking but left the area in the
Northeast which will be out ahead of the front near better dynamics
and with lower FFG values.


Along the Gulf Coast, extended the Marginal Risk through the
western Florida panhandle where high PWs and weak winds in the
lower half of the atmosphere will support some isolated/scattered
thunderstorms with heavy rainfall in some areas. Back across Texas,
higher PW values will be streaming/pooling over the west-east
orientated slow- moving/stationary front thus increasing the
potential for higher rainfall rates within the isolated to
scattered convection. Into NM, moisture will be decreasing to the
northwest but will still be sufficient in southeastern areas to
suppose isolated heavy rainfall. Areas in and around burn scars
will be especially vulnerable.


...Plains...

Connected the previously separated Marginal Risk outlines across
the TX Panhandle to link into the area through the Plains. A mid-
level shortwave or weakly-closed low is expected to dig
southeastward within the long wave trough over the central U.S.
this afternoon. Although modest moisture will be present, there
will be support for broad ascent and increased forcing to suggest
the potential for heavy rainfall rates of 1 to 2 inches/hr across
the region per the recent 12Z HREF. SPC notes a Slight Risk for
severe weather in the central Plains for activity this
afternoon/evening, within the Marginal Risk in the ERO.

Fracasso/Campbell


Day 2
Valid 12Z Sun Jul 07 2024 - 12Z Mon Jul 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
KANSAS AND OKLAHOMA AS WELL AS THE CENTRAL AND SOUTHERN COAST OF
TEXAS...

...Coastal Texas and Louisiana...

The latest (15Z) NHC forecast track for Beryl has remained
generally consistent from the 09Z forecast, which positions Beryl
just offshore the mid-Texas coast early Monday. Outer bands will
wrap into the coast from South Texas up along the coast into far
southwestern Louisiana, though the bulk of its precipitation shield
will lie in the Day 3 period. Maintained the previous Slight Risk
outline right along the coast due to the expected heavier rainfall
to be moving onshore very early Monday. Future adjustments in the
track of Beryl may shift the ERO areas a bit, depending on its
evolution in the next 24-36 hours.

...Southern and Central Plains...

Organized convection is likely over portions of KS and OK Sunday
into Sunday night. 12Z CAM guidance still shows quite the
impressive model QPF agreement/signal; thus, forecast confidence is
above average with this event. Interestingly the pattern appears
to favor a rather progressive convective complex...and PWs are not
forecast to be overly high either. The impressive QPF from the
models, while somewhat surprising, is likely indicative of the very
strong mid/upper level forcing and low level frontal convergence
in play. A look at layer IVT suggests we may start to see some low
level connection to the moisture plume ahead of Beryl, so this is
certainly something to keep an eye on and could act to enhance
rainfall efficiency. Either way this is a solid Slight risk with
higher but sub-Moderate probabilities within that outline. The
apparent progressiveness of convection keeps the risk from going
higher...but will need to continue to monitor. It has also been dry
lately in much of the region, which can increase the flash flood
threat due to hydrophobic soils. Regardless, with 12Z HREF
neighborhood probabilities of >2"/hr rainfall rates ~10-30% for
several hours Sunday afternoon and early evening, Slight Risk is
certainly warranted.

...Southeast...

With the stalled front across the region convection is expected to
persist, maintaining an isolated threat for flash flooding
concerns. PWs will remain above the climatological 90th percentile,
and layered IVT suggest we may see some mid/upper level moisture
connection to Beryl. The intrusion of tropical moisture may help
bolster rainfall efficiency in what will already be a favorable
environment for heavy rainfall rates. A Marginal Risk remains in
effect from southern Alabama to northern Florida and northward to
southeast Virginia. Some of this will be dependent on rainfall
today (Saturday) and if there is any overlap.

Fracasso/Campbell


Day 3 Valid 12Z Mon Jul 08 2024 - 12Z Tue Jul 09 2024

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

The National Hurricane Center has Beryl forecast to make landfall
during the first few hours of this forecast period somewhere up the
coast from Corpus Christi, TX (please see the NHC website for the
latest information). The guidance continues to suggest a fairly
compact storm, therefore the QPF swath is expected to be relatively
narrow and oriented N-S as the storm lifts northward across
eastern Texas. The highest QPF amounts will still follow the track
or slightly east of the path through this period. A reasonable
analog is Tropical Storm Bill (2015) which recurved a bit farther
west than what Beryl is expected to do. Max QPF with Bill was ~15"
within a broad area of 3-6" or so. Latest WPC areal average QPF of
3 to 7 inches can be expected with maximums climbing into the
double digits. The Moderate Risk was maintained for this period
from Coastal Texas into eastern Texas. A Slight Risk spans the
coastline from south of Corpus Christi to east of Lake Charles and
northward into southwest Arkansas. A Marginal Risk covers from
South Texas to central Louisiana and from the Texas/Oklahoma
Panhandles to Southern Missouri, tied to the frontal boundary to
the north. Model spread increases toward the end of this period and
the recent guidance showed a quickening trend with Beryl, but this
still fit well within the Slight Risk outline into Arkansas. Note
that the placements of the Excessive Risk areas will largely be
dependent on the NHC track so stay tuned for future adjustments.

...Southeast...

Lingering boundary in the Southeast will again act as a focus for
convection on Monday, and maintained the Marginal Risk here. With
additional showers and thunderstorms expected over recent wet
soils, the threat for isolated flooding concerns will remain
elevated for this part of the country, despite the lower QPF signal
in the guidance. Will gain more insight once we move into the CAM
window, and also with better clarity on the speed of recurvature of
Beryl.

Fracasso/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