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FOUS30 KWBC 071545
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1145 AM EDT Fri Jun 7 2024

Day 1
Valid 16Z Fri Jun 07 2024 - 12Z Sat Jun 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL PLAINS...

...16Z Update...

General continuity from the previous forecast with some minor
adjustments of the SLGT risk to account for the latest forecast QPF
accompanying the expected MCS. HREF and associated CAMs are in good
agreement on the axis of heaviest precip expected from this
evenings MCS across the central plains into the Mid-Mississippi
Valley. HREF blended mean QPF is a solid stripe of 2-4" within the
zone of the MCS influence with some deterministic output entering
the 4-5" range despite the progressive nature of the complex. The
the reasoning is due to increasingly favorable low to mid-level
moisture advection occurring this evening from a developing
nocturnal LLJ that will move rich Gulf air poleward into portions
of the central plains and adjacent Mississippi Valley. Probability
fields are fairly robust for both total precip and potential rates
with the >3" neighborhood probability settling between 20-40% over
a large area encompassing southeast NE through northeast KS and
northwest MO. This was slightly better than even the overnight HREF
iteration, likely in part to the better agreement among the CAMs
members integrated into the ensemble. The prospects for rates
exceeding 2"/hr also improved with an area of 30-45% located within
the same zones above, and >3"/hr within low probabilistic means
(10-15%), so certainly not zero and statistically significant
considering the environment. As a result, the previous SLGT
inheritance was generally maintained with a focus over southeast NE
through the adjacent plains states, including KS/MO.

A quick note on the setup across ME....increasing ascent within the
confines of an approaching shortwave rounding the upper level
circulation over Ontario will induce a period of convection across
northern New England with a focus on northern NH into western ME.
After some collaboration with the local WFO`s within the impacted
area, a MRGL risk was entertained, but deemed unnecessary for the
non-zero threat of flash flooding. Area soil moisture is running
tremendously below average with much of western ME experiencing a
class 2 (Severe) drought according to the National Drought Monitor.
Outside pockets of heavier thunderstorms anchoring to the terrain
in the White Mountains and northern Appalachian front in ME that
could generate isolated flooding, much of the rainfall will be
beneficial in the areas encompassing. Thus, refrained from any
issuance, but will be an area to monitor pending the convective
evolution.

Kleebauer


...Previous Discussion...

The setup continues to look favorable for a heavy rainfall event
across portions of the Central Plains later today through tonight.
Early morning analysis showed a strong ridge of high pressure
anchored over the Four Corners into Texas while over the Central
Plains, northwest flow is present. Across the Northern Rockies,
shortwave trough energy is noted and it`s this feature that will
dive southeast into the Plains later today to help ignite a few
rounds of deep convection. In the lower levels, southerly flow in
response will bring northward anomalous moisture with the PWs
forecast to quickly rise above 1.5" through KS into southern NE.
The favorable forcing aloft with the higher moisture and expected
instability will ignite the storms and then the expectation is for
the storms to grow upscale into a MCS as it moves into portions of
Missouri and clip southwest Iowa.

The 00Z guidance has come into better agreement on the details and
expected locations of the heavy rainfall, with the 00Z HREF
neighborhood probabilities for at least 3 inches jumping to above
50 percent now for far eastern NE, northeast KS, southwest IA, and
northwest MO with a slight (10-15 percent) chance of 5" totals.
Hourly rain totals may exceed 2 inches in localized spots. The
Slight Risk was adjusted minimally to the north, to adjust toward
the latest guidance and probabilities where the setup for
training/repeating rounds is greatest.

Taylor


Day 2
Valid 12Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
EASTERN KANSAS THROUGH SOUTHERN MISSOURI...

The latest guidance continues to advertise a corridor of heavy
rainfall across portions of the Southern/Central Plains eastward
into the Mid Mississippi Valley as a cold front sags southward into
the region and low level southerly flow pushes anomalous moisture
into the boundary. Aloft, the quasi zonal flow along with an
embedded shortwave trough moving through will help bring the larger
scale forcing. This combination of higher moisture (PWs 1.5-2") and
lift along with favorable amounts of instability forecast should
support multiple rounds of thunderstorms, particularly from the
late afternoon through the nighttime hours. The latest ensemble
guidance members and deterministic models support potential for
localized 2-3" totals and rain rates 1-2"/hr at times with the
greatest potential for those higher totals over far eastern KS
through southern Missouri where the Slight Risk is highlighted.

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 3
Valid 12Z Sun Jun 09 2024 - 12Z Mon Jun 10 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF COLORADO FRONT RANGE, SOUTHERN PLAINS, AND MID MISSISSIPPI
VALLEY...

The wavy, slow moving frontal boundary is expected to reach
portions of the Southern Plains and Mid Mississippi Valley Sunday
through early Monday morning while aloft the pattern is expected to
feature quasi zonal/northwest flow. An embedded shortwave trough is
forecast to move through the region during the period, providing
the large scale forcing for ascent. Meanwhile, higher moisture
characterized by PWs > 1.5" will pool along/ahead of the surface
boundary across the S. Plains into the Mid Mississippi Valley. This
anomalous moisture, combined with the southward moving frontal
boundary and large scale lift will support thunderstorm
development early on in the period across portions of KS/MO/AR
before the focus for new development shifts westward toward the TX
Panhandle, western/central Oklahoma. The latest guidance supports
isolated/scattered 1-2" totals (based off latest ECENS/GEFS
members) and embedded higher amounts possible, especially across
TX/OK where the deeper moisture overlaps best with the instability
and forcing.

The easterly flow will also bank the higher moisture against the
terrain and lead to thunderstorm development from eastern New
Mexico through the CO Front Range where slow storm motions and/or
repeating rounds may lead to localized but intense rain
rates/totals late in the period (00Z-12Z Mon).

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