Post by SKYSUMMIT on May 4, 2021 13:48:55 GMT -6
Mesoscale Precipitation Discussion 0153
NWS Weather Prediction Center College Park MD
342 PM EDT Tue May 04 2021
Areas affected...Ext Southeast TX...Central LA...Southern MS...
Concerning...Heavy rainfall...Flash flooding likely
Valid 041940Z - 050100Z
SUMMARY...Trailing edge of convection filling in with potential
for increased rainfall totals due to training through evening.
DISCUSSION...GOES-E Visible and regional RADAR mosaic denote
continued convective development and expansion from far SE TX and
north of I-10 in LA. This is response to destabilization but also
increased orthogonal convergence with increased surface flow from
the sea-breeze as the shortwave exits and the surface pressure
trof trails more flat with further distance from the trailing cold
front. Flow off the Gulf is a tad more moist/unstable with sfc
Tds in the low to mid-70s and MLCAPEs of 2000-3000 J/kg stretching
across S LA/S MS along/ahead of the boundary. While the broad
southerly flow 85H will slowly veer it will continue to provide
strong moisture flux convergence to maintain/expand the convection
further, while flow aloft will generally steer cells along in an
easterly fashion resulting in training convection. CIRA LPW
denotes very moist airmass pooled along the axis with 1" in the
sfc-850, but still and additional .75" in the 850-7H layer
suggesting further broadening of the updrafts with broad
entrainment to keep rainfall efficiency on average at 2"/hr with
likely some stronger cells perhaps yielding localized 3"/hr rates.
As a result, 3-5" totals are likely with greatest values further
east into NE LA/S MS due to duration of the training, perhaps even
result in a spot or two of localized 6" totals.
While FFG values are in more typical ranges for the season, of
3"/hr & 4"/3hr along/south of I-10; AHPS 2-week anomalies
supported by 0-40 cm soil saturation of 70-80% along the northern
half of MPD area of concern suggests a slight greater concern
across this area versus areas from Lake Charles to Baton Rouge
where ground conditions may be a bit drier and less prone to flash
flooding from these expected rainfall totals. As such, flash
flooding is considered possible further west where drier ground
conditions exist...through by late evening becoming more likely
further north and east into S MS by 00z.
Gallina
