Mesoscale Precipitation Discussion 0256
NWS Weather Prediction Center College Park MD
151 PM EDT Mon May 31 2021
Areas affected...West Texas through North-Central Texas
Concerning...Heavy rainfall...Flash flooding possible
Valid 311750Z - 312300Z
Summary...Showers and thunderstorms will continue to develop and
train along a slow moving cold front. Rainfall rates in excess of
2"/hr are likely, and an additional 1-3" of rainfall with locally
higher amounts, is forecast on top of pre-saturated soils. Flash
flooding is possible.
Discussion...The regional radar mosaic this afternoon depicts
widespread showers and thunderstorms along a cold front draped
from near Odessa to Abilene, generally along I-20. This convection
has produced 1-3" of rainfall already this morning with locally
higher amounts due to training of echoes along the front, and
flash flooding is ongoing across the area. GPS observations of PW
were as high as 1.6" in the pre-convective environment, with
MLCape south of the front analyzed by the RAP at above 1000 J/kg.
Moist low-level flow out of the south was observed by KSJT VWP to
be 20kts lifting orthogonally into the front, producing locally
enhanced ascent to persist this convection.
As the front sags southward, it will encounter even greater
instability with SBCape potentially exceeding 2000 J/kg and PWs
above 1.75", well above the 90th percentile for the date. These
extremely favorable thermodynamics will support continued
thunderstorm development, with organization likely as 0-6km bulk
shear rises above 35 kts. Additionally, cellular development
within the warm and unstable airmass south of the front should
lift N/NE on 850-300mb mean winds of 20-30 kts to merge with the
MCS, and cause briefly even higher rain rates. It is possible that
as the instability increases the MCS may begin to forward
propagate to the southeast more quickly than it has so far today.
Should this occur it would lower the flash flood potential, and
HREF exceedance probabilities for 3-hrs do fall to around 30% this
afternoon. However, with Corfidi vectors still aligned to the
boundary, there is likely to be regeneration into the better
instability SW of the front with training occurring to the east
which would continue the risk.
Morning high-res guidance differs in the evolution and spatial
extent of the heaviest rainfall. Despite some latitudinal
variation in the placement, the HREF blended mean and neighborhood
probabilities have increased with the 12Z run. This combined with
observational trends in radar and satellite imply a continued
threat for heavy rainfall with flash flooding as HREF forecast
rain rates of more than 2"/hr are likely, with training along the
front expected. This could produce an additional 1-3" of rainfall
with locally higher amounts, and with FFG locally as low as
2"/3hrs, flash flooding will remain possible.
Weiss
ATTN...WFO...EPZ...FWD...LUB...MAF...OUN...SJT...
