574
FOUS30 KWBC 061557
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1157 AM 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 oulined. 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 isloated 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 throught 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, OKLAHOMA, AS WELL AS THE CENTRAL AND SOUTHERN COAST OF
TEXAS...

...Coastal Texas and Louisiana...

The latest guidance and NHC forecast track for Beryl has trended
further north/east from the previous forecast. That positions Beryl
just offshore South Texas with the bulk of its precipitation
shield hugging the Southeast Texas Coast and into southern
Louisiana. This track adjustment prompted an expansion of the
Slight Risk to the Houston Metro and the Marginal Risk to include
southwest Louisiana. The storm motion and compact storm structure
is forecast to keep the heaviest precip focused along the coast.
The latest guidance continues to favor higher QPF along and points
right of the storm track. There is still some uncertainty in the
northern extent of the track as some guidance continues to fall
even further north of the current forecast, so this forecast is
subject to shifts in the exact location of the Slight and Marginal
Risk areas, but likely still confined to the coastal plain.

...Southern and Central Plains...

Organized convection is likely over portions of KS and OK Sunday
into Sunday night. Quite the impressive model QPF signal...with
both good run to run continuity and model to model agreement. 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. Thus
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 the apparent progressiveness of convection
keeping the risk from going higher...but will need to continue to
monitor.

...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
north to southeast Virginia.

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 this period somewhere up the coast from Corpus Christi,
although the forecast track is subject to further adjustments. The
guidance continues to suggest a fairly compact storm therefore the
QPF swath is expected to be relatively narrow 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.
Areal average of 3 to 7 inches can be expected with maximums
climbing into the double digits. A Moderate Risk was raised 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. The placements of
the Excessive Risk areas will largely be dependent on the NHC track
so stay tuned for future adjustments.

...Southeast...

Convection will persist near the stalled frontal boundary with the
potential for heavy rainfall rates. 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. Therefore a Marginal Risk remain in effect.

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