Weather Prediction Center issues Mesoscale Precipitation Discussion #455 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE705
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Mesoscale Precipitation Discussion 0455
NWS Weather Prediction Center College Park MD
727 PM EDT Mon Jun 17 2024
Areas affected...Portions of the Lower to Mid Mississippi Valley
Concerning...Heavy rainfall...Flash flooding possible
Valid 172326Z - 180400Z
Summary...Showers and thunderstorms will continue to develop and
lift northward into a surface trough through the evening. Rainfall
rates within thunderstorms may peak above 2"/hr at times, creating
rainfall of 1-3" with locally higher amounts. Flash flooding is
possible.
Discussion...The regional radar mosaic this afternoon depicts
widespread showers and thunderstorms within an exceptionally moist
airmass across much of the lower to mid Mississippi Valley. These
storms are developing in response to ample fuel in the form of PWs
elevated to around 2.2 inches, above the daily record according to
the SPC sounding climatology, and MLCAPE above 1500 J/kg. This
warm/unstable airmass is further characterized by freezing levels
rising to around 14,000 ft and mid-level lapse rates that are
generally moist-adiabatic (6-7C/km) suggesting efficient warm rain
processes are dominating. Synoptic ascent is modest on the western
periphery of the building upper ridge, but weak shortwaves
embedded within the flow, some subtle low-to-mid level
convergence, and a surface trough analyzed from western TN into
northern LA are providing sufficient lift into the robust
environment to support the convection with heavy rainfall. Recent
radar estimated rainfall rates have been as high as 1-1.5"/hr, and
these are likely to continue through nightfall.
Although storm organization is likely to be minimal due to a lack
of bulk shear, the robust thermodynamics and sufficient ascent
should result in continued development of convection through and
even beyond sunset. This is reflected by most available CAMs,
although many, including the HRRR, appear to be under-doing the
convective coverage. Storms should continue to develop near the
Gulf Coast/Lower Mississippi Valley and then lift northward on
mean winds of 10-20 kts and within intensifying 850mb flow which
may reach 25-30 kts early tonight. The 850mb wind exceeding the
mean wind additionally suggests coverage will remain widespread
through the evening, and although cells will be moving quickly,
repeated rounds are possible in some areas. The greatest risk for
repeating rounds or training will be along the surface trough
where the most impressive moisture flux will focus, resulting in
enhanced lift for regenerating or merging cells. With rain rates
progged by the HREF to be 1-2"/hr, this could result in rainfall
locally exceeding 3 inches.
7-day rainfall across this portion of the MS Valley has been
minimal as noted via AHPS rainfall departures that are just around
10% of normal, which has resulted in 0-10cm RSM from NASA SPoRT
that is just around 30%. However, heavy rainfall today has
accumulated to 1-3" in some areas according to MRMS. While most of
the soils should be able to handle progressive heavy rain rates,
where training can occur, especially in the vicinity of the
surface trough, or over urban areas or soils moistened by today's
rain, isolated instances of flash flooding are possible.
Weiss
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...JAN...LZK...MEG...MOB...OHX...PAH...
ATTN...RFC...LMRFC...SERFC...NWC...
LAT...LON 36818899 36568800 35788811 34528848 33638864
32718869 31758872 31628911 31668973 31869055
32309122 32419134 33399175 34459145 35839071
36628992
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #455 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE---------------
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