213
FOUS30 KWBC 082016
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Mon Jul 8 2024

Day 1
Valid 16Z Mon Jul 08 2024 - 12Z Tue Jul 09 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF NORTHEAST
TEXAS INTO SOUTHWESTERN ARKANSAS...

...Special 2030Z Update...

Cleared the ERO risk areas across southeast Texas where significant
rainfall with Beryl has ended. The Marginal in the Southeast was
expanded into portions of southeast Virginia due to ongoing
convection, as well as into north central New Mexico for ongoing
convection.

Wegman

...Previous Discussion...

...16Z Update...

No huge changes, but several noteworthy ones to highlight for this
midday update:

First the good news. The risk areas are being trimmed on the
southwest side of Beryl`s circulation along the Upper Texas Coast.
The northerly flow of drier air will continue as a northwesterly
offshore wind along the coast through the afternoon. This should
notably tamp down the potential for convection in the area, with
even lesser chances that the convection that does form can produce
flash flooding given the low expected rainfall rates. Thus, despite
obviously rock bottom FFGs from Beryl, the lack of additional
rainfall lends confidence to full downgrades to zero behind Beryl`s
circulation. With the heaviest rainfall now clear of Houston
proper, the ERO was downgraded accordingly. Any additional rainfall
in Houston will be over the next hour or two and will be much
lighter in comparison to this morning`s rain due to the bands
southwest of center are weakening due to dry air entrainment.

Now the not so good news. Starting in eastern Oklahoma...increasing
moisture convergence from the southeasterly flow ahead of Beryl`s
center will clash with the predominant northerly flow over much of
the state. PWATs across eastern Oklahoma now well ahead of Beryl
are generally above 1.5 inches. Thus, with ample moisture in place
now and more to come, a front is expected to intensify across
eastern Oklahoma that with peak diurnal heating will lead to a line
of strong thunderstorms capable of heavy rainfall. There is
considerable uncertainty as to how quickly this line of storms will
move...but the clashing air masses tends to keep it slow.
Thus...expect a narrow area of heavier rainfall totals in eastern
Oklahoma. For this reason, the Slight with Beryl was expanded
northwest for this potential.

Further along to the north and east, the inherited Slight risk area
was expanded well to the north and east to include the southern
third of Missouri with this update. An expanding jet streak over
the northern part of the state will put the southern part of the
state in the favorable right entrance region. This will result in a
rapidly expanding precipitation shield with Beryl as it approaches
tonight. With rain, heavy at times, moving in earlier than
previously forecast, the Slight was expanded accordingly.

No big changes were made on the eastern side of the risk areas as
southerly flow now and through tonight as the storm`s center lifts
northward will mean favorable southerly flow off the Gulf continues
behind the circulation. This will keep moisture and instability
advecting across Louisiana, so the threat remains largely the same.

The daily convection across much of the Southeast will also
continue today, including across the Carolinas. The Marginal was
expanded, primarily in deference to the potential for another round
of daily afternoon isolated cells forming, especially at the head
of Pamlico and Albemarle Sounds in North Carolina...though recent
rainfall supports an isolated flash flooding risk once again across
the Southeast, even if the coverage today will be notably lower
than previous days.

A Marginal Risk area was added for portions of west Texas with the
ongoing storms near Midland and expected renewed daily convection
in flood sensitive areas of eastern New Mexico.

Wegman


Day 2
Valid 12Z Tue Jul 09 2024 - 12Z Wed Jul 10 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST AS WELL AS FOR THE CENTRAL GULF COAST...

...2030Z Update...

...Midwest...

Several notable changes were made with this afternoon`s update. As
regards the Slight Risk area associated with Beryl...guidance is
notably faster with spreading the rain shield associated with Beryl
northeastward into the Midwest. Note this isn`t an increase in
forward speed of Beryl`s circulation...but rather an expansion of
the precipitation shield. This is largely due to better interaction
with a 90 kt jet streak`s right entrance region, as well as
frontogenesis as southeasterly flow ahead of Beryl runs into the
front. Thus, the Slight was expanded. There`s a bifurcation in the
Slight across Indiana. The precipitation to the north from St.
Louis northeast to Lake Michigan is expected to be in the form of a
persistent deformation zone associated with the aforementioned
front. Instability will be very limited in this area. Thus, much of
the precipitation will either be elevated convection or a
stationary band of light to moderate rain resulting in a swath of
3-5 inch rainfall totals. Meanwhile further south along the Ohio
River, there will be much more instability resulting in stronger
storms capable of much heavier rain...but less distinct forcings
more directly driven by chaotic outflow boundaries will mean the
storms will be much more scattered, with breaks in the rain at
times in between storms. It`s probable somewhere within the Slight
Risk area will see Moderate Risk level impacts, especially with the
tropical moisture moving in with Beryl...but given consistent track
changes...generally south and east...and significant uncertainty as
to the nature of the heavy rain in any one area, no Moderate Risk
upgrades are included with this update, but could very well be
considered with future updates.

...Gulf Coast...

The inherited Slight for the southwestern Louisiana Gulf Coast was
shifted and expanded well to the east with this update...to include
New Orleans, Gulfport, Mobile and Pensacola. This is in line with
the latest shifts in the track of Beryl...bringing its associated
cold front (as it undergoes extratropical transition) further east
along the Gulf Coast. Storms in this area will still have access to
the entirety of the Gulf as far as moisture influx...and with the
front stalling in the Slight Risk area, training convection is
likely. There`s significant uncertainty both with storm track and
the speed of cell movement, but the abundant moisture should allow
any stronger storms to overcome the otherwise very high FFGs along
the Gulf Coast, with the front likely supporting training. Thus in
coordination with LIX/New Orleans, LA and MOB/Mobile, AL forecast
offices, the Slight risk upgrade was introduced. Meanwhile further
west, drier air is now expected to reach the Gulf Coast in
southwest Louisiana, prompting the downgrade in that region.

...Marginal Risks...

New Mexico: Isolated to widely scattered convection is likely to
form along the mountains once again Tuesday afternoon, which could
very well move over flood-sensitive areas.

Rio Grande of Texas: Convection that forms along the mountains of
Mexico will have enough of an eastward push that some may cross
into the Del Rio and Eagle Pass areas.

Florida: Daily diurnal storms are likely once again due to
collisions of sea breezes as well as any outliers associated with
the stalled front along the north Gulf Coast.

Southern Appalachians: Storms are likely to form in the deep
tropical moisture indirectly associated with Beryl with the
mountains acting as the primary forcing. Numerous flood sensitive
areas in western NC may support flash flooding with any slow moving
or stationary storms.

New England: Deep tropical moisture pumping north well ahead of
Beryl will make for anomalous PWATs across New England. The
Appalachians of this region may also act as forcing for widely
scattered thunderstorms capable of heavy rainfall.

Wegman

...Previous Discussion...


...Mississippi Valley and Midwest...

Beryl is still expected to quickly phase with an upper trough and
surface front to the north while in transition to being extra
tropical. This should lead to the potential for heavy rain to
blanket part of the central U.S. causing flash flooding concerns
from Arkansas to Indiana during this period. Some of the highest
QPF amounts of 3+ inches are likely to focus over the Ozarks
region and points northeast to the Illinois/Indiana border. Areal
averages are expected to be around 2 to 4 inches with local
maximums upwards of 8 inches. A Slight Risk extends from central
Arkansas to western Indiana. A Marginal Risk stretches from the
central Gulf Coast northward to southern Michigan. Again, an
future adjustments will likely be dependent on the track for
Beryl.

In addition, some of the CAMs hint that some type of southwest to
northeast band could set up along or just inland of south-central
Louisiana coast to produce a few inches of rain over some areas
that could be a little more sensitive to heavy rain impacts. A
Slight Risk area was raised for this stretch of the coastline north
to about I-10.

...Southwest...

Monsoonal moisture feeds over eastern Arizona 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...

Convection will persist during this period thanks to the abundant
moisture hanging around and diurnal forcing. Some of the guidance
continues to suggest areas of locally heavy rainfall especially
along the eastern coastline of Florida. General consensus suggests
1 to 2 inches although local maximums of 3 to 4+ inches will
certainly possible. A Marginal Risk remains in effect for portions
of central/northern Florida and southeast Georgia.

...Northeast...

Interaction of moisture ahead of Beryl and a front settling over
the Mid-Atlantic/southern New England may favor heavy rainfall
potential over this region; although guidance is rather light with
activity mainly in New England. Some focus of the convective rain
ahead of the front(s) and sufficient instability for heavy rain
rates in the northern Mid-Atlantic to Northeast favor of a Marginal
Risk.

Campbell


Day 3
Valid 12Z Wed Jul 10 2024 - 12Z Thu Jul 11 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT LAKES REGION INTO THE NORTHEAST...

...2030Z Update...

...Northeast...

Fewer changes were made to the Day 3 forecast given the inherent
uncertainties with Beryl both today and tomorrow, and with some
consistency in the guidance as well. Oddly enough the adjustment
made was generally north, or left of the previous forecast, a
change we will have to see if it will pan out. For most of Beryl`s
lifespan the forecast has nudged right of previous so that
adjustment would be unusual for Beryl`s remnants.

The inherited Slight Risk was expanded to the Maine and New
Hampshire coastline with this update. The rain shield even now has
consistently outpaced the guidance, and as such the eastward/faster
adjustment here is very normal...if the very small northward shift
is not. The heaviest rains are expected into the Adirondacks
primarily...where the mountains will provide the greatest
additional lift being oriented largely orthogonal to the WSW flow.
The Slight remains in good shape as it`s very likely given the
abundance of moisture that there will be embedded convection which
will locally increase totals. PWATs will be more than 3 sigma above
the mean, which compared with GFS climatology would break the daily
record. Thus...there will be unusual amounts of moisture available
for Beryl`s remnants to convert to rainfall. With consistency and
hopefully good CAMs support...additional upgrades to a Moderate
are at least possible.

Elsewhere in the mid-Atlantic the Marginal risk area was brought
south to include the DC-NYC I-95 corridor with this update. There
will be similarly abundant atmospheric moisture all along the
Eastern Seaboard Wednesday and Wednesday night, but the forcing
further south will be much more limited, resulting in less
widespread convection. However, given the amount of moisture in
place...even local forcings should be enough to result in some
storms, so the Marginal was expanded considering the lower FFGs in
the urban corridor.

...Marginal Risks...

New Mexico/Colorado: Same rinse and repeat forecast in this area
with the typical afternoon monsoonal convection likely to redevelop
once again Wednesday afternoon.

Central Gulf Coast: The front will remain stalled along the Gulf
Coast on Wednesday but much weaker, which should spread out the
threat while reducing the severity. The Marginal on Wednesday
roughly follows where the Day 2/Tuesday Slight is.

Wegman

...Previous Discussion...

...Midwest to Northeast...

There is still a fair amount of spread in the guidance with respect
to the evolution/track for post-tropical Beryl and exactly how
this upper level energy ejects into the overall Great
Lakes/Midwest mean trough. The flow of tropical moisture should
bring the highest precipitable water anomalies into the Lower
Great Lakes and Northeast during this period. Some PWAT anomalies
within this region will likely exceed the 90th percentile and west-
east oriented fronts north/east of post- tropical Beryl may promote
training. The exact location of the heaviest rainfall will be
dependent on the location of the frontal boundary but there is a
growing signal for a broad area to be impacted by the heavy rains.
A Slight Risk is in effect from northern Indiana to New Hampshire
while a Marginal Risk area spans from Illinois to Maine. As details
resolve and get closer in time, there may be the need to upgrade
the risk level, but at this time there is too much uncertainty.

...Central Rockies and portions of the Southwest...

Continuation of the monsoonal moisture and diurnal heating will
keep convection possible across portions of the Central and
Southern Rockies and southwest New Mexico during this period. The
inherited Marginal Risk was maintained with westward modification for
New Mexico. Rain in proximity to burn scars and other sensitive areas
that have seen ample rainfall recently will have an elevated risk
for flash flooding.

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