FOUS30 KWBC 110808
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Thu Jun 11 2026
Day 1
Valid 12Z Thu Jun 11 2026 - 12Z Fri Jun 12 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST...
.Midwest to southern Plains...
Early this morning, a frontal wave developed over the central
Plains ahead of a strong upper level trough that will lift into the
Midwest today. This wave of low pressure is forecast to surge
northeast into the Midwest and be accompanied by an area of
enhanced convection in the vicinity of the low. A strengthening low
level jet on the leading edge of this disturbance will bring a
surge of moisture (PWAT values > 2 inches) and instability (MUCAPE
3000 J/kg) into the Midwest and create a sheared environment that
will allow for organized convection with highly efficient rainfall
rates up to 2-4 inches per hour. A Slight Risk of excessive
rainfall is in effect for portions of the Midwest where the hi-res
CAMs are showing the highest rainfall totals. There was some
consideration of upgrading to a Moderate Risk for portions of Iowa,
Wisconsin, and Illinois given recent heavy rains and soil
saturation, but the highest rainfall totals today are forecast to
be displaced to the north of where the heaviest rain fell on
Wednesday, which should keep the risk of flash flooding more in
line with a high-end Slight. On the backside of the frontal wave,
the cold front will surge southeast across the central and southern
Plains this afternoon with showers and storms expected to form
along the front. Given the highly moist and unstable environment on
the warm side of the boundary, these storms will be capable of
producing high rainfall rates, but the progressive nature of the
front should help limit the risk of flash flooding. A Marginal Risk
area extends back into the southern Plains where locally heavy
rainfall may lead to isolated instances of flash flooding.
.Ohio Valley to Mid-Atlantic...
An upper level shortwave trough is expected to move southeast
across the Ohio Valley and Mid-Atlantic today, which will provide
upper level support for the development of scattered showers and
storms this afternoon. Warm, moist air will be in place across
these regions, with PWAT values generally ranging from 1.75-2
inches, which will support rainfall rates of 1-2 inches. Elevated
instability (>2000 J/kg) should allow for some deeper convective
cells that will be capable of producing locally heavy rainfall.
Isolated instances of flash flooding will be possible, especially
if heavy rain occurs in urban environments, so there is a Marginal
Risk of excessive rainfall extending from the Ohio Valley to the
Mid-Atlantic. Northwesterly upslope flow will also result in
enhanced precipitation totals along the central Appalachians that
could create isolated flooding concerns in this region as well,
which is included in the Marginal Risk area.
.Southwest Florida...
Southeasterly flow has increased PWAT values above 2 inches across
Central and South Florida, which will allow for very heavy
rainfall rates of 2-4 inches per hour in convection along the sea
breeze boundaries this afternoon. Hi-res CAMs show the Atlantic and
Gulf sea breezes colliding over Southwest Florida, which could
result in flash flooding concerns for urban areas. Therefore, there
is a Marginal Risk of excessive rainfall for urban areas along the
west coast of the Florida Peninsula from Tampa south.
Dolan
Day 2
Valid 12Z Fri Jun 12 2026 - 12Z Sat Jun 13 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN
PLAINS TO THE NORTHEAST AND FOR CENTRAL AND SOUTHWEST FLORIDA...
On Friday, an upper level trough will push across the Northeast and
drive a cold front across the eastern and south-central United
States. Scattered showers and storms are expected to develop as the
frontal boundary interacts with the anomalously warm and moist air
mass, and increased shear in the vicinity of the trough will
likely support some deeper organized convection in portions of the
Mid-Atlantic and Northeast. Moisture will pool ahead of the front,
and PWAT values are forecast to rise above 2 inches from the
southern Plains to the Northeast, which will allow for efficient
rainfall rates. Flash flood potential should be somewhat limited by
the speed of the front; however, locally heavy rainfall may lead
to isolated instances of flash flooding. Storms over the southern
Plains will move slower as the frontal boundary becomes quasi-
stationary, which may result in some areas of higher rainfall
totals. A mid-level wave is expected to move east across the
central/southern Plains Friday evening, which should lift the
frontal boundary north as a warm front and support a wave of
enhanced convection Friday night. There is still quite a bit of
uncertainty in where this area of convection will develop, but
there will likely be some enhanced flash flood potential over
portions of the central/southern Plains. Further southwest,
southeasterly flow and increasing moisture will support enhanced
showers and storms over West Texas and eastern New Mexico, which
may create flooding concerns in the vicinity of the Guadalupe and
Sacramento mountains and in burn scar areas. A Marginal Risk of
excessive rainfall stretches from the southern Plains to the
Northeast to cover these threats. Elsewhere, heavy rainfall will
also be possible in Florida where anomalous moisture will reside.
Convection along the sea breezes will have the potential to produce
very heavy rainfall that could lead to flooding concerns for urban
areas in Central and Southwest Florida. A Marginal Risk area has
been introduced to cover these threats.
Dolan
Day 3
Valid 12Z Sat Jun 13 2026 - 12Z Sun Jun 14 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL PLAINS AND MID/LOWER MISSISSIPPI VALLEY...
On Saturday, several features will come together to support a heavy
rainfall threat over the central United States. An upper level
trough will drop south into the central U.S. while several southern
stream waves move northeast into the Plains ahead of this feature.
At the surface, a warm front will lift across the south-central
U.S. while a cold front moves south across the north-central U.S.,
creating an area of strong convergence from the central Plains to
the Mid/Lower Mississippi Valley. In addition to strong synoptic
forcing, a very warm, moist, and unstable air mass will be in place,
which will support the development of numerous showers and storms
with efficient rainfall rates. These features should stall for a
period as they come together, resulting in an area of very heavy
rainfall. A Slight Risk is in effect where the heaviest rainfall
totals are expected from the central Plains to the Mid/Lower
Mississippi Valley. Locally heavy rainfall will also be possible in
showers and storms forming along the cold front in the Midwest,
and isolated flash flooding will be a concern, especially after
heavy rainfall expected on Day 1/Thursday. Locally heavy rainfall
may also be possible across West Texas and eastern New Mexico where southeasterly flow may support terrain induced precipitation. A
Marginal Risk of excessive rainfall surrounds the Slight and
extends from West Texas and eastern New Mexico to the Great Lakes.
Dolan
Day 4 and Day 5
Valid 12Z Sun Jun 14 2026 - 12Z Tue Jun 16 2026
...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND THE SOUTHEAST...
The overnight guidance continued to show a broad, amplifying trough
prevailing over over much of the eastern two-thirds of the CONUS
this period. As shortwave energy drops into the base of the
trough and further amplifies it, the associated frontal boundary
is expected to push well south into the southern Plains and lower
Mississippi Valley on Sunday. Increasing southerly flow from the
western Gulf will support deepening moisture along the front, while
upper level jet dynamics and mid-level energy provide areas of
enhanced ascent. Coinciding with the deepest moisture (PWs at or
above 2 inches) and some of the better forcing, a Slight Risk was
drawn on Day 4 from southeastern Oklahoma and northeastern Texas
over to central Mississippi. This is a southward adjustment from
the previous issuance given the overnight model trends in bringing
the front farther south.
Back to the north, low level upslope flow interacting with mid
level energy dropping into the broader scale trough is expected to
help initiate storms capable of producing locally heavy amounts
and isolated flash flooding concerns as far north as the Colorado
Rockies.
By Monday, the front is expected to move more slowly to the
south and east. As it does, moisture will continue to pool along
the boundary, with both the GFS and ECMWF showing PWs increasing
to over 2.25 inches (more than 2.5 std dev above normal) from South
Texas to southern Alabama. Given the potential for highly-
efficient, training showers and thunderstorms, heavy amounts and
flash flooding will be a likely concern across this area. A Slight
Risk was drawn where the latest guidance showed the greater
overlap between the deeper moisture and better forcing. Will
continue to monitor this area for potential upgrades, especially if
the model signal for heavy amounts continues to increase or show
successive days of heavy rainfall across the same areas.
Pereira
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/10)