Mesoscale Precipitation Discussion 1068
NWS Weather Prediction Center College Park MD
858 PM EST Wed Dec 26 2018

Areas affected...Northeast TX

Concerning...Heavy rainfall...Flash flooding possible

Valid 270200Z - 270600Z

Summary...Convection training in a moist southerly flow could pose
a flash flood threat through the late evening hours.

Discussion...Regional radars showed a developing line of storms on
the nose of a 40 to 50 knot low level southerly jet (per regional
VWP) near and east of the Dallas Metroplex. The storms are forming
on line of low level convergence, and the GOES-16 clean IR loop
showed cloud top temperatures as low as -65 C with the stronger
storms. While the line itself is moving slowly eastward (per the
most recent RAP propagation vectors), the cells in the line are
tracking northeast with the 850-300 mb mean wind.

The training cells are producing hourly rainfall rates nearing
1.50 inches (per the KFWS radar), and as a closing mid level low
over the TX Panhandle moves slowly eastward, the environment
becomes increasing conducive to short term training along the
convective line. The most recent runs of the HRRR indicated the
potential for local 2.00/3.00 inch rainfall amounts with this line
segment as it moves slowly eastward across northeast TX. Based on
the low level forcing and deep moisture (with precipitable water
values near 1.25 inches, which is about two standard deviations
above the mean), these amounts seem plausible, and could occur in
less than 2 hours as the line moves slowly east.

Three hour flash flood guidance values here are fairly high
(generally above 3.00 inches), but the short term training could
produce rainfall amounts that approach these numbers. The
convection should be able to maintain itself, as 00z soundings
from CRP and BRO showed a reservoir of 2000-3000 J/KG of MLCAPE
upstream. this could allow the southern edge of the become more
active as well, as the cells track to the northeast.

Uncertainty about the extent of the training with the line could
limit the overall flash flood threat, but based on radar and
satellite trends, flash flooding is possible. In fact, the flash
flood threat could extend beyond 27/06z into more of northeast TX,
as a cold front pushes eastward into central TX.

Hayes

ATTN...WFO...EWX...FWD...HGX...SHV...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   33729507 31479548 30199703 30039800 30639799
            31399770 31969733 33379634