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FOUS30 KWBC 071958
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 PM 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 MUCH OF
KANSAS, MISSOURI, AND THE EASTERN COLORADO FRONT RANGE...

Previous SLGT risk area was maintained with a large expansion to
the west to include all of southern KS, curving northwest into the
eastern Colorado Front Range along with the inherited risk over eastern
KS through the southern half of MO. The combination of a southward
moving cold front in tandem with a strong mid-level shortwave
ejecting out of the central Rockies will create a primed dynamical
environment for widespread thunderstorm coverage and associated
heavy rainfall. Return flow pattern ahead of the cold front will
lead to ample low to mid-level moisture advection as noted by a
regional PWAT anomaly between 2-3 deviations above normal as
depicted by the latest NAEFS and GEFS/ECENS guidance. Deterministic
output from various models, whether CAM or global based are all
fairly bullish on the prospects of a QPF footprint of at least 2-3"
of precip over a large area correlating with the trajectory of the
shortwave with the proposed frontal positioning across the high
plains into the Mid Mississippi Valley. Individual outputs also
denote areas of 4+" in pockets across KS and MO, mainly within
areas of potentially repeating convection.

HREF probabilities are also aggressive for totals exceeding 3"
with a broad neighborhood probability of 20-40% spanning from the
eastern Front Range through southern MO. Scattered pockets of
higher probabilities upwards of 50-60% are also co-located within
the spatial coverage of the 3" markers. Even some low-end
probabilities of 10-20% for >5" are showing up within the HREF
fields, a sign of a higher potential and greater agreement for
heavy rain prospects. Rates of 2-3"/hr are increasingly likely
within the heaviest cores given both the probabilities (20-40% for
>2"/hr), and the forecasted environment signaling high MUCAPE
(2500+ J/kg) within the stout moisture advection regime. Strong
convergence pattern with flow running parallel to the cold front is
a textbook way to achieve a larger areal extent of flash flooding
concerns when coupled with the above environmental characteristics.
This has lead to the aforementioned expansion with note that some
areas will see the higher end of the SLGT risk threshold, likely
over a portion of KS or MO given the latest probabilities.

Kleebauer


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

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEAST COLORADO, NORTHEAST NEW MEXICO, AND THE TEXAS PANHANDLE...

A cold front will slowly press southward through the southern
plains with the western extent becoming elongated to the north-
south against the lee of the Rockies. Elevated moisture will pool
along the front and expand westward with PWAT indices generally
between 1.25 in the Southern Rockies and upwards of 1.75-2" across
the high plains in the Panhandle. This is a solid 2-3 deviations
above normal climatologically, a significant aspect to promote
heavy rain chances. Thermodynamically, the setup is favorable to
the south of the sagging boundary with ample diurnal heating
expected on Sunday to warrant suitable low-level lapse rates and
surface based instability. The most favorable part of the setup,
however is the dynamical nature of the expected convection as a
well organized shortwave perturbation will pivot northeast out
Mexico creating a focused large scale ascent pattern in-of the high
plains in NM and TX. Much of the deterministic output signaled a
cluster of heavy convection forming over the northern Caprock with
a general expansion to the north and east due to the progression of
the mid-level shortwave. Totals exceeding 1-2" are now cropping up
on the latest global consensus with some totals over 3" being shown
in a few ensemble members and the latest GFS. Ensemble QPF
footprint is fairly impressive at these leads considering the
forecast evolution, so the confidence for flash flooding has grown
over subsequent forecasts. There was enough of a signal to warrant
an upgrade to a SLGT risk across the Panhandle and adjacent high
plains of NM and southeast CO with MRGL risks spanning eastward
over the southern plains the Mid Mississippi Valley due to more
thunderstorms forming along just behind the cold front.

Kleebauer


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