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Mesoscale Precipitation Discussion: #0267 (Issued at 348 PM EDT Mon May 13 2024
) MPD Selection

 


Graphic for MPD #0267


Mesoscale Precipitation Discussion 0267
NWS Weather Prediction Center College Park MD
348 PM EDT Mon May 13 2024

Areas affected...Upper Coast of Texas into central Louisiana

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

Valid 131947Z - 140130Z

Summary...Thunderstorms developing along a stationary front will
strengthen and train to the E/NE through the evening. Rainfall
rates of 2-3"/hr will be common within these thunderstorms,
producing locally 3-5" of rain. Flash flooding is likely.

Discussion...GOES-E IR imagery this afternoon depicts rapidly
cooling cloud tops embedded within a large canopy of convective
clouds across eastern TX. These high level and cooling clouds are
a result of rapidly blossoming thunderstorms from south-central TX
into southern LA, developing primarily along a stationary front
draped near the Upper Texas Coast. Forcing for ascent is being
provided through convergence along this boundary, aided by modest
shortwaves rotating beneath the base of a mid-level trough
centered over KS, and within the favorable diffluent RRQ of a
poleward arcing jet streak. This deep layer ascent is acting upon
extremely favorable thermodynamics for heavy rain noted by SPC RAP
SBCAPE of 4000-5000 J/kg, and PWs measured by GPS of over 2
inches. This has already resulted in rainfall rates estimated by
KHGX WSR-88D of 2-2.5"/hr.

As the afternoon progresses, it is likely that thunderstorms will
continue to regenerate along this boundary within the strongest
low-level convergence as synoptic ascent remains intense. The
high-res CAMs, including the HRRR and ARWs suggest convection may
grow upscale into an MCS, which is supported by the presence of
30-50 kts of bulk shear. While this organization could eventually
result in a cold pool dominated MCS due to the extreme SBCAPE,
which would likely push convection offshore TX, until that
happens, the continued intensification and expansion of convection
will result in a continued flash flood risk. Storms that form
along the boundary will organize and train along the stationary
due to boundary-parallel 0-6km mean winds and aligned Corfidi
vectors, which with rainfall rates likely peaking at 2-3"/hr will
produce more than 3" of rain in some areas. Locally, more than 5"
of rain is possible in the next 6-hrs as reflected by HREF
probabilities for 5"/6hrs as high as 40%. The models are generally
under-initializing the current convection as well, so these
probabilities may be a bit underdone.

Additionally, this area has received excessive rain over the past
7 days as noted by AHPS rainfall departures 300-600% of normal,
especially from the Heart of Texas through the Piney Woods and
into central LA. Here, NASA SPoRT 40cm soil moisture is above the
98th percentile, indicating highly hydrophobic soils and resulting
in FFG as low as 0.5"/3hrs which should easily be exceeded in some
areas. The greatest risk for flash flooding will be in urban areas
or atop these most sensitive soils, but anywhere these impressive
rain rates train will likely lead to rapid runoff and instances of
flash flooding.

Weiss

ATTN...WFO...HGX...JAN...LCH...LIX...SHV...

ATTN...RFC...LMRFC...WGRFC...NWC...

LAT...LON   31779158 31559103 31159090 30519110 30219135
            30099226 29969337 29729402 29449464 28989534
            28869562 28739587 28889617 29299628 30179568
            31129391 31689238

Download in GIS format:    Shapefile
 | KML


Last Updated: 348 PM EDT Mon May 13 2024



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