943
FOUS30 KWBC 060804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu Jun 6 2024

Day 1
Valid 12Z Thu Jun 06 2024 - 12Z Fri Jun 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID ATLANTIC AND NORTHEAST...

...Mid Atlantic to Northeast...

A slow moving cold front, currently analyzed across portions of the
Ohio Valley and Appalachians, will cross through the Mid Atlantic
and Northeast today into tonight. Meanwhile, a warm front will
continue lifting northward through the Northeast this morning
before stalling or slowing across southern New England this
afternoon. The airmass will be quite moist, with the latest
guidance pointing toward PWs well above normal (exceeding 95th
percentile) with values over 1.75" from the Mid-Atlantic into
southern New England and near 1.5" across northern NY and portions
of VT/NH. This morning there should be an initial round of locally
heavy downpours with the warm front passage across southern NY and
southern New England, which could bring localized flooding concerns
with rain rates exceeding 1"/hr. A second round is then expected
for the afternoon/evening with the approaching cold front but also
could train/repeat with the warm front stalling nearby. Convective
initiation is likely between 16-18Z across western NY and PA with a
line of showers and thunderstorms moving east/northeast through
the remainder of the day.

The latest HREF probabilities for 24-hr totals of at least 2" are
spotty but show some signal exceeding 40-50 percent in locations
form eastern/northern NY and southern New England). Probabilities
for hourly totals of 1-2" are slight (under 30 percent).

Further south into the Mid-Atlantic, higher moisture ahead of the
cold front and sufficiently warm temperatures will support a line
or two of stronger showers and thunderstorms during the
afternoon/evening hours. Some of these will be capable of producing
heavy downpours, particularly from the I-95 corridor from
Baltimore to Richmond and eastward including southeast VA where the
2" HREF neighborhood probabilities are locally higher near 50
percent.

Taylor

Day 2
Valid 12Z Fri Jun 07 2024 - 12Z Sat Jun 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
EASTERN KANSAS AND WESTERN MISSOURI...

The setup continues to look favorable for a heavy rainfall event
across portions of the Southern/Central Plains Friday/Friday night.
A strong ridge of high pressure will remain anchored over
Mexico/Texas and along the periphery of this ridge, shortwave
energy is expected to ripple through out of the Rockies into the
Plains Friday afternoon/night. Meanwhile, a cold front passing
through today (Thursday) is expected to return/lift back through as
a warm front Friday/Friday night, bringing a surge of higher
moisture with it as low level flow increases. The combination of
this moisture transport, favorable dynamics (including right
entrance lift) will likely initiate a complex of thunderstorms that
then dive south/southeast along the instability gradient into
KS/MO. For this forecast cycle, the guidance remains in pretty good
agreement overall, with perhaps a nudge to the south compared to
the past 24 hours though the relative magnitude/amounts of QPF have
trended down somewhat and the latest ensemble guidance supports
lower QPF in general. There appears to be enough support to
maintain the Slight based on the environmental ingredients and
synoptic setup, but the risk probably leans toward the lower end
of the probability range for now.

Taylor


Day 3
Valid 12Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN PLAINS TO MID MISSISSIPPI VALLEY...

A wavy frontal boundary is expected to settle across portions of
the Southern Plains eastward into the Mid Mississippi Valley while
aloft the quasi zonal/northeast flow continues with periodic
shortwave energies moving through. A pool of higher moisture will
remain along/ahead of the frontal boundaries and is likely to be
characterized by PWs well above 1.5" and approaching 2",
particularly across portions of MO/AR. This higher moisture
combined with the lift/convergence and instability due to peak
heating should spark a few rounds of strong thunderstorm complexes
that track east/southeast across the risk area. There remains model
spread in placement (north vs. south) and magnitudes as well, and
some of the uncertainty will be tied to how the previous day
(Friday/Friday night) plays out but the consensus remains favorable
for an area of heavy rainfall that could lead to scattered
instances of flash flooding, especially as some of these areas are
still running above normal for soil moisture anomalies.

Further west, moisture banking against the terrain of the Front
Range combined with daytime peak heating and shortwave trough
energy moving through will lead to isolated/scattered showers and
thunderstorms, some of which will be slower moving and produce
intense rain rates and isolated/localized flash flooding.

Taylor



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