Graphic for MPD #0760

Mesoscale Precipitation Discussion 0760
NWS Weather Prediction Center College Park MD
508 AM EDT Tue Sep 04 2018

Areas affected...Central OK

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

Valid 040905Z - 041500Z

Summary...A developing axis of training showers and thunderstorms
is likely to cause flash flooding concerns this morning across
central OK, including areas near the Oklahoma City metropolitan
area.

Discussion...The latest radar imagery shows a band of heavy
showers and thunderstorms beginning to train over the same area
across portions of central OK, including some parts of the
Oklahoma City metropolitan area and adjacent eastern suburbs. The
convection is developing within an increasingly convergent flow
pattern in the 850/700 mb layer, and all of this is associated
with the gradual northward advance of a 500/700 mb vort center.

Cloud tops have generally been cooling over the last couple of
hours, and the convection is embedded within a very moist and at
least modestly unstable airmass, with MUCAPE values of close to
1000 j/kg. Area VWP data is showing some low level speed
convergence as well with the nose of a southerly 40 kt low level
jet lifting up across central OK.

The latest HRRR guidance is strongly supportive of a N/S axis of
very heavy convective rainfall over the next several hours
extending near and east of Oklahoma City up northward to near
Stillwater. The HRRR guidance supports as much as 6+ inches of
rain going through mid morning. While this may be a bit
aggressive, the PWATS across the region are very high with values
of 2 to 2.25 inches, and this moisture axis is tied in strongly to
the nose of the rather strong low level jet. Thus, the rainfall
rates will be quite high, with amounts of as much as 3 inches/hr
possible given the highly efficient rainfall processes that will
be in place.

One other concern seen in the latest VWP data and RAP analysis is
an environment conducive for backbuilding convection along the
southern flank of the N/S training convective band. Corfidi
vectors are favoring this, and therefore the rainfall potential
may be greatly enhanced considering the degree of moisture
transport via the low level jet.

The latest thinking is that some very heavy totals of as much as 6
inches may materialize locally going through 15Z which will
respect the HRRR output. These amounts will likely cause flash
flooding. Will continue to monitor.

Orrison

ATTN...WFO...OUN...TSA...

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

LAT...LON   36999718 36909682 36729664 36189645 35679651
            34899672 34429712 34559764 35259759 35599766
            36099785 36759769


Last Updated: 508 AM EDT Tue Sep 04 2018