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FOUS30 KWBC 171515
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1115 AM EDT Wed Jul 17 2024

Day 1
Valid 12Z Wed Jul 17 2024 - 12Z Thu Jul 18 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN ROCKIES AND HIGH PLAINS, NORTHEASTERN TEXAS TO THE
MID-SOUTH, AND THE MID-ATLANTIC...

...Southern Plains to the Northeast...
A mid-to-upper level trough centered over the Great Lakes will
continue to amplify, pushing a cold front and accompanying pool of
deep moisture further south and east across the southern Plains,
Tennessee and Ohio valleys, the Mid-Atlantic, and the Northeast.
While locally heavy amounts producing at least isolated concerns
cannot be ruled out throughout this entire region, models continue
to signal more organized and widespread concerns for some areas.

This includes an area extending from northeastern Texas and
southeastern Oklahoma, across much of Arkansas, into the Mid-South.
Shortwave energy associated with ongoing convection across western
Kansas and the Panhandles is forecast to move east later today and
interact with a deep moisture pool (PWs ~2 inches) along the
boundary. The overnight CAMs present a notable signal for ongoing
convection extending east across Oklahoma during the early part of
the period before weakening by late morning. However, convection is
expected to redevelop in the afternoon, with some models showing
slow-moving, heavy rainfall producing storms drifting across
southeastern Oklahoma and northeastern Texas, with some additional
development further to east across Arkansas into northern
Mississippi and far western Tennessee. As is typically the case,
the CAMs differ greatly on how these storms will evolve, so
confidence in the details is limited. However, the general
consensus continues to indicate that at least locally heavy amounts
can be expected across this region, with the HREF showing
neighborhood probabilities of at least 50 percent for accumulations
of 3 inches or more within much of the Slight Risk area. The
highest probabilities center over northeastern Texas and
southeastern Oklahoma into southwestern Arkansas. The probabilities
drop off further to the east, however even lesser amounts may
prove problematic given the heavy rainfall that is already
occurring across portions of Arkansas this morning.

A Slight Risk was also maintained across portions of the Mid-
Atlantic, centered along the urban corridor from eastern Virginia
to eastern Pennsylvania and southern New Jersey. As the upper
trough shifts east, increasing southerly flow will support an
uptick in moisture along the Mid-Atlantic and Northeast seaboards.
Given the slow movement of the front, there is the potential for
numerous rounds of storms to develop and train across the region,
raising runoff concerns, especially across urbanized areas.

...Southwest to the Southern and Central Rockies and High Plains...
An upper high will remain centered over the Four Corners allowing
monsoonal moisture to funnel across the Southwest, fueling diurnal
convection and isolated flash flooding across the Southwest.

Further to the east, increasing low level easterly flow will
heighten the threat for flooding across portions of the southern
Plains into the Rockies. As the previously noted front in the
WBCQPFERDPlains slides into the region, post-frontal easterly
flow will support PW anomalies climbing to 1-2 standard deviations
across northern New Mexico and far southern Colorado. This
moisture, along with daytime heating and energy moving around the
ridge, will support developing storms, capable of producing heavy
amounts. A Slight Risk was maintained over the high terrain and
extended further to the southeast into the High Plains along a
forecast axis of significant, southeasterly low level inflow. HREF
neighborhood probabilities indicate that amounts of 1-2 inches can
be expected within this region.

Pereira

Day 2
Valid 12Z Thu Jul 18 2024 - 12Z Fri Jul 19 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN ROCKIES, SOUTHEASTERN VIRGINIA, AND EASTERN NORTH
CAROLINA...

...Southern Mid-Atlantic and the Southeast to the Southern
Plains...
The previously described front will extend from the southern Mid-
Atlantic back into the southern Plains, remaining nearly stationary
through the period. This boundary will remain a focus for deep
moisture and storm development. Models continue to indicate the
greatest concern for heavy rainfall and flash flooding will center
over southeastern Virginia and eastern North Carolina. Guidance
shows PWs around 2-2.25 inches (~2 standard deviations above
normal across this region). This moisture, along with mid-level
energy and upper jet support, is expected to generate numerous
showers and storms across the region with heavy amounts likely.

...Southwest to the Southern Rockies...
The better low level moisture flux over the southern High Plains
shifts a little further south this period, extending the threat for
scattered flash flooding further south into the southern New Mexico
mountains. Otherwise, the overall pattern and available moisture is
expected to remain largely unchanged, resulting in similar threats
for heavy rainfall and flash flooding from Day 1 into Day 2 across
the region.

Pereira

Day 3
Valid 12Z Fri Jul 19 2024 - 12Z Sat Jul 20 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN ROCKIES AND ...

...Carolinas to the Lower Mississippi Valley...
A front will linger across the region, focusing deep moisture and
more unsettled weather. For a second day, the greater threat for
organized heavy rainfall is expected to focus along the eastern
extent of the boundary. After setting a bit further south across
the eastern Carolinas, guidance shows a wave developing along the
front bringing deeper moisture back to the north. Some portions of
eastern North Carolina could see back-to-back days of heavy rain,
raising flash flooding concerns across the region.

...Southwest to the Southern Rockies...
Moisture sufficient for diurnal convection, raising at least
isolated flash flooding concerns, will remain in place. Therefore
a Marginal Risk was maintained, covering much of the same regions
as the Days 1 and 2. A Slight Risk was added to portions of
northern and central New Mexico, similar to the previous days as
well. Guidance shows another front sliding south, adding additional
moisture to the region.

Pereira


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