795
AWUS01 KWNH 161214
FFGMPD
KSZ000-NEZ000-SDZ000-161700-

Mesoscale Precipitation Discussion 1021
NWS Weather Prediction Center College Park MD
814 AM EDT Mon Sep 16 2024

Areas affected...Southeast SD...Central NEB...North-central KS...

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

Valid 161215Z - 161700Z

SUMMARY...Persistent, stationary elevated thunderstorms continue
to produce solid rain-rates that localized totals are nearing
higher localized FFG values; suggesting flash flooding may become
possible over the next few hours.

DISCUSSION...GOES-E WV depicts stronger northern stream shortwave
and resultant MCS across the Northern Plains; a more subtle wave
is lifting northeastward along its southern flank across the
Nebraska Panhandle.  This is enhancing low level flow across the
central Plains with backed 850mb veering through 700mb at 45kts
reducing to 20kts while also becoming confluent along and just
east of 99W.  CIRA LPW and RAP TPW, show greatest ascent pattern
is just along the western gradient of the moisture axis with
1.25-1.5" values noted along it from SE SD into the northern KS
where deep layer (mainly directional) convergence is maximized.
MUCAPE appears to be sufficient at 500-1000 J/kg with axis of
greatest values along and west of the moisture axis, ideally
supporting the stronger convective ascent.  This appears to be
exhausting as the updrafts/overshooting tops are becoming a bit
less in coverage and noting a generally slow warming with the
cirrus canopies associated with the two linear clusters from SE
SDak into N NEB and again along the NEB/KS line to Lincoln county,
KS.

The concern has been/continues to be the relative zero or very
slight westward propagation of the lines allowing for localized
enhanced rainfall totals.  With deep layer steering more north;
the inflow from the 850-700mb isentropic ascent/instability axis
has been nearly equal/opposite to allow for the 1.5-2"/hr rates to
overcome the regionally above normal FFG values (given the
prolonged dry period across the region) which are about 3+"/3hrs.
As such, localized observed totals (per backyard wx stations) are
reaching 2-3" in spots, and MRMS Flash response are reaching
300-400 cfs/smi suggesting enhanced flows may be reaching near
levels typical of localized flash flooding concerns.  Given
overall trends are slowly downward, an additional hour or two will
become more likely to exceed even these higher FFGs resulting in
localized possible flash flooding conditions.

Gallina

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

ATTN...WFO...FSD...GID...ICT...LBF...OAX...TOP...

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

LAT...LON   44269842 44089772 42799758 40029761 38909767
            38569827 38689867 39079892 39909900 41439917
            42669922 43359916 43749895