481
AWUS01 KWNH 010801
FFGMPD
KSZ000-NEZ000-COZ000-011400-

Mesoscale Precipitation Discussion 0529
NWS Weather Prediction Center College Park MD
400 AM EDT Mon Jul 01 2024

Areas affected...southern NE...northern KS

Concerning...Heavy rainfall...Flash flooding possible

Valid 010800Z - 011400Z

Summary...Heavy rainfall with hourly rates of 1-2"/hr expected to
result in short-term (2-3 hour) localized totals of 2-3". Some
isolated instances of flash flooding are possible.

Discussion...Convection has broken out and begun to proliferate
across portions of the Central Plains early this morning, in
response to a veering and strengthening low-level jet (becoming
35-45 kts from the south to southwest at 850 mb). The associated
warm air advection and moisture flux transport is significant,
driving an impressive surge in elevated instability (indicated by
MU CAPE 3-hr increases of 600-1000 J/kg) with precipitable water
values of 1.6-1.9 inches (between the 90th percentile and max
moving average, per DDC and TOP sounding climatology). Effective
bulk shear of 30-50 kts will help to sustain/organize convection,
but 850-300 mb mean flow of 15-25 kts should keep storms moving at
a decent pace. Should more significant organization into an
mesoscale convective system occur, upwind/downwind propagation
vectors favor a much quicker storm moition (30-50 kts).

While there is some potential for localized/isolated flash
flooding due to the anomolous tropospheric moisture content and
accompanying kinematic and thermodynamic forcing (driving rainfall
rates of 1-2"/hr), the limited residence time and rather dry
antecedent conditions (per NASA SPoRT-LIS 0-1m soil moisture as
low as the 10th-30th percentile) should act to restrict the
coverage and intensity of said flash flooding. While the 00z HREF
probability matched mean (PMM) depicts short term (2-3 hr) totals
of 2-3" (near or just above associated Flash Flood Guidance), the
40-km neighborhood probabilities for 3" are surprisingly high at
15-35%. This appears to be primarily due to some of the
time-lagged (prior 12z) members of the ensemble (ARW2/NSSL and
FV3, specifically) which had more extreme QPF depictions of 4-5".
The 00z members have moved entirely away from these higher
amounts, and the shape and orientation of the QPF depiction makes
a lot more sense as well (less strongly clustered, and more spread
out and shifted eastward with the atmospheric flow, as
observational trends are bearing out). The end result is a
discounting of these outlier time-lagged members, and an
expectation for only isolated instances of flash flooding
(primarily for more sensitive localities and low-lying areas).

Churchill

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...DDC...EAX...GID...GLD...ICT...LBF...OAX...TOP...

ATTN...RFC...ABRFC...MBRFC...NWC...

LAT...LON   40979981 40909709 40099554 38689513 38269767
            38769920 38860067 39020166 39610207 40510143