Mesoscale Precipitation Discussion 0874
NWS Weather Prediction Center College Park MD
241 PM EDT Fri Sep 21 2018

Areas affected...Northeast OK...Central/Northern AR...Far Southern
MO

Concerning...Heavy rainfall...Flash flooding likely

Valid 211840Z - 220040Z

Summary...Heavy showers and thunderstorms will become increasingly
more widespread and concentrated this afternoon and evening. Flash
flooding will become likely.

Discussion...The latest radar imagery shows showers and
thunderstorms beginning to become a bit more focused over
northeast OK and northwest AR as very moist deep layer southerly
flow advances north out ahead of a mid-level trough/low over the
southern High Plains. Meanwhile, this southerly flow is
interacting with and overrunning a strong cold front that is
slowly settling down to the south toward the Lower MS Valley.

The environment this afternoon should become increasingly
conducive for more widespread shower and thunderstorm activity as
moderate to strong diurnally enhanced instability pools up along
the front and couples with increasing moisture profiles as PWATs
increase to near 2 inches.

Facilitating the heavy rainfall potential this afternoon on the
larger scale will be an axis of stronger isentropic ascent north
of the aforementioned front, and in addition to this, the flow
aloft is expected to become increasingly diffluent. This will
certainly help sustain the elevated convective threat. South of
the front in the warm sector, there will be sufficient instability
in place for locally heavy showers and thunderstorms as well, but
the primary focus should be north of the boundary from northeast
OK east across northern AR and perhaps getting into far southern
MO as well.

The latest HRRR guidance supports as much as 3 to 5 inches of rain
with locally heavier amounts going through 00Z. Heavy rains are
already occurring over portions of northeast OK in particular and
given the additional rains this afternoon and evening, flash
flooding will become likely.

Orrison

ATTN...WFO...LZK...MEG...OUN...PAH...SGF...SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...

LAT...LON   36709168 36499046 35919003 35139015 34539086
            34199201 33819321 33539404 33329487 34179456
            35079461 35449479 35689498 35889524 35999565
            36049601 36069647 36029727 36189696 36459541
            36699332