AWUS01 KWNH 171135
FFGMPD
MOZ000-ARZ000-TXZ000-OKZ000-KSZ000-171630-
Mesoscale Precipitation Discussion 0890
NWS Weather Prediction Center College Park MD
734 AM EDT Sat Aug 17 2024
Areas affected...far southeast KS, eastern OK, western AR
Concerning...Heavy rainfall...Flash flooding possible
Valid 171134Z - 171630Z
Summary...A persistent MCS with training showers and thunderstorms
will persist for a few more hours this morning. Rainfall rates of
1-2"/hr will gradually weaken, but an additional 1-3" of rain is
possible which could result in instances of flash flooding.
Discussion...The regional radar mosaic depicts a persistent MCS
aligned near the OK/AR border and extending back into far
southeast KS this morning. This MCS is being driven by a weak
mid-level impulse interacting with a decaying front, now analyzed
as a trough by WPC. A modest outflow boundary from earlier
convection continues to align to the south, into which still
robust 850mb inflow measured by regional VWPs to be 25-35 kts is
converging. The overlap of this residual boundary and the nose of
this LLJ is fueling regenerating convection within a region of
elevated PWs above 1.75 inches combined with MUCAPE that, while
waning, is still analyzed by the SPC RAP to be around 1000 J/kg.
Recent radar-estimated rainfall rates from KSRX have been as high
as 1.5"/hr, and 6-hr rainfall from MRMS across this region has
been generally 2-4" leading to saturated soils and ongoing FFWs.
This MCS should gradually begin to decay in the next few hours,
although the recent HRRR and 3kmNAM may be too quick to erode
convection. Leaning more on the ARW/ARW2 output, it is likely this
MCS will gradually ease as the focus of convection drifts W/SW in
response to the veering and weakening of the 850mb LLJ. Even as
the LLJ veers, it will still originate from a ribbon of higher
MUCAPE and a bubble of warmer temperatures, suggesting continued
WAA isentropically ascending into the MCS through late morning.
Some evidence of this is already occurring as noted by fresh
convection bubbling west of the MCS across eastern OK. So even
though lightning cast probabilities are slowly falling, the
ingredients suggest there will be plentiful ascent and instability
to persist this MCS for several more hours, which is again
supported by the ARWs. This will drive rainfall rates of 1-2"/hr
at times for a few more hours, which will likely train to the
south as propagation vectors align to the convergent nose of this
LLJ.
Where the most impressive training occurs, total rainfall could
reach as much as 3", although generally should be more widespread
of 1-2". This could cause instances of flash flooding despite HREF
FFG exceedance probabilities being modest, especially where heavy
rain rates move across urban areas, or atop soils pre-conditioned
from overnight rainfall.
Weiss
ATTN...WFO...FWD...ICT...LZK...OUN...SGF...SHV...TSA...
ATTN...RFC...ABRFC...LMRFC...NWC...
LAT...LON 37549569 36929447 35769350 34689343 33819412
33879543 34219600 34649615 36439600 37369599
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