|WPC Met Watch|
Mesoscale Precipitation Discussion: #0405 |
(Issued at 400 AM EDT Tue Jun 30 2020
Mesoscale Precipitation Discussion 0405
NWS Weather Prediction Center College Park MD
400 AM EDT Tue Jun 30 2020
Areas affected...Far Eastern MO...Central and Southern IL
Concerning...Heavy rainfall...Flash flooding possible
Valid 300800Z - 301400Z
SUMMARY...Showers and thunderstorms are expected to expand a bit
in coverage going through the early to mid-morning hours. Some
increased threat of flash flooding will exist.
DISCUSSION...The latest GOES-16 WV satellite imagery shows a very
compact MCV over areas of far west-central IL which is focusing a
concentrated area of very heavy showers and thunderstorms.
Meanwhile, additional shower and thunderstorm activity is seen
growing in coverage farther to the south that is now moving
through southern IL. This southward extension of convection is
forming along the leading edge of stronger instability transport,
low-level speed convergence and forcing also associated with the
shortwave trough axis extending south from the MCV.
The airmass across the region is very moist with PWs around 2
inches and there is a pool of moderate to strong instability over
central and western MO that is advancing northeastward with the
aid of a 20 to 30 kt southwest low-level jet. This is expected to
at least maintain the ongoing convection over the next few hours,
with some upscale growth potential as at least modest speed
convergence remains in place along with some sharpening of a
925/850 mb trough axis over southern IL.
Hires model guidance from the 00Z HREF suite along with several
runs of the experimental WoFS guidance have been struggling with
the details of the larger scale convective evolution, but the 06Z
WoFS and the 06Z HRRR generally favor the idea of there being a
north to south axis of heavy showers and thunderstorms expanding
in coverage over the next few hours which is certainly supported
by the latest IR satellite imagery which is showing an expansion
of cooling convective tops.
Some redevelopment of convection farther back to the west over
areas of eastern MO will also be possible as a mid-level dry slot
seen in the WV imagery erodes and an additional mid-level vort
center upstream over western MO arrives.
Expect rainfall rates to be extremely heavy given the tropical PW
environment, with rates potentially reaching 2 to 3 inches/hr. As
convection evolves this morning, some of the heaviest overall
rainfall potential may be distributed in a bi-modal fashion, with
one max around the southeast flank of the MCV involving
west-central IL, and a separate max over southern IL where
stronger low-level speed convergence and instability transport
will be noted. The exact location of the heaviest rainfall totals
is hard to pinpoint, but the general thinking right now is that as
much as 3 to 5 inches of rain with locally heavier totals will be
possible going through mid-morning. Areas of flash flooding will
be possible as a result.
LAT...LON 40739126 40449013 40108926 39458827 38768783
38058780 37528808 37088844 36788891 36738962
36879016 37279048 38439075 39039120 39459182
Last Updated: 358 AM EDT Tue Jun 30 2020