Quantitative Precipitation Forecast
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FOUS30 KWBC 171530
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1130 AM EDT Wed Apr 17 2024

Day 1
Valid 16Z Wed Apr 17 2024 - 12Z Thu Apr 18 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT LAKES, OHIO VALLEY AND WESTERN PARTS OF THE NORTHEAST...

...16Z Update...

Minor adjustments were made to the southern edge of the previous
MRGL issuance across the Ohio Valley into the Mid Atlantic. This
was in conjunction with the latest trends in hi-res deterministic
and the QPF footprint within the NBM. Mid-level shortwave will
rotate around the base of the closed 5H reflection over the Great
Lakes and propagate eastward over northern IL/IN/OH before pivoting
across PA by the end of the forecast cycle. Locally heavy rainfall
from progressive convection will allow for flash flood concerns
within that area bordering Lake Erie down to about I-70 where the
best forcing will occur. This will cross over an area of lower FFGs
due to recent rainfall events causing antecedent conditions to be
primed for easier exceedance thresholds. The area of focus will be
over northeast OH into western PA where even 1 and 3-hour FFG
markers are hovering around that 1-1.5" range which is very low
and a possibility within today`s setup. 12z HREF EAS probability
field is between 20-40% for exceeding 1" total rainfall between
Cleveland to Erie, aligned well with the ML algorithms from both
the GFS and ECMWF for the targeted location for best chance of
impact. As a result, did not feel there was a need to adjust the
northern extent of the risk area as it solidifies the forecast and
maintains continuity.

Across the Deep South, conditions have been fairly tame with
regards to the previously highlighted area. 12z CAMs remained "hot"
with the QPF interpretation, but radar and observational trends
negate the former runs and the newer hourly guidance is more in-
line with what is occurring which would be well below any chance of
a MRGL risk issuance. Will continue to monitor, but the threat of
flash flooding is trending closer to 0% than it is to the bottom of
the Marginal Risk threshold (5%).

Kleebauer

...Previous Discussion...

Showers and thunderstorms tracking across the Ohio Valley may
produce periods of heavy rainfall. Much of eastern Ohio and western
Pennsylvania have Low FFG which does maintain an elevated threat
for excessive rainfall and local flooding concerns. Model consensus
has accumulations less than 2 inches across this area. Multiple
rounds of convection will track through eastern portions of
Pennsylvania and into New Jersey could reach 1 inch within areas of
low FFG indices, especially in the 3 and 6-hr FFG intervals. The
Marginal Risk area that was already in effect was maintained for
this period.


Campbell/Kleebauer


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

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND MISSISSIPPI VALLEY...

A surface low pressure system and associated front will develop
across the Central Plains and advance toward the Mid-Mississippi
Valley and convection will fire off as the moist return flow from
the Gulf of Mexico drawls northward into the system. Locally heavy
rain will setup over Missouri and points southwest to central
Texas. The better concentration of the heavy rain will focus across
Missouri and surrounding locations. Recent rains have lowered some
of the FFG across this region and may have an increased
sensitivity to additional rain/heavy rain. A Marginal Risk area
covers part of northeast Texas to southern Missouri and western
Kentucky.

Campbell


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

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY...

The low pressure system will continue to have its associated front
boundary draped across the Midwest and Plains during period while
dryline sets up from the Oklahoma Panhandle to the Big Bend area.
Convection is expected to be along and south of the front over the
Southern/Central Plains and Lower Mississippi Valley with the
higher QPF near/east of the dryline in west-central Texas. The
latest guidance varies quite a bit in regard to placement and how
much will fall however consensus does suggest the higher amounts to
focus mainly over Oklahoma and a sliver of Arkansas. The
environment may be supportive for 0.50+ inch/hour rates which in
turn elevated the risk for local flooding concerns. A Marginal
Risk area spans the Big Bend area northeast to central Arkansas.


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


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