Mesoscale Precipitation Discussion 1047
NWS Weather Prediction Center College Park MD
1240 AM EST Sat Dec 08 2018

Areas affected...Coastal TX...LA

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

Valid 080540Z - 081200Z

Summary...Hourly totals near 2" will be possible along the TX
coast into portions of southwest Louisiana. With the potential for
repeated rounds of convection, localized flash flooding is likely.

Discussion...A stationary boundary was analyzed along the Texas
coastline into southern Louisiana as of 530z. This boundary has
been the focus for several rounds of moderate to locally heavy
rainfall since earlier in the evening. At 850 mb, 30-40 kt flow
has been overrunning this boundary with an strong axis of moisture
transport (PWATs around 1.9") directed at eastern TX gulf coast
into southwest LA. Best MUCAPE is mainly confined to the coastline
but upwards of 250 J/kg does extend inland across east-central TX.
Finally, aloft there is a large area of 250 mb diffluence with a
mid/upper level wave analyzed across south-central Texas.

Recent IR satellite trends show cloud tops continuing to cool as
convection blossoms. An uptick in radar trends has also been
noted, with HGX showing hourly rates nearing 1.5" in and around
the Houston and Galveston metro areas. Surface observations around
the area indicate hourly totals of around 1-1.25" with localized
amounts 1.5 to near 2.0".

There is high consensus and agreement in the hi-res models showing
the heaviest rainfall to fall through 12z across eastern TX gulf
coast into southwest LA. Widespread totals of 2-3" are likely with
local amounts reaching 4" possible. It is concerning that the
focus in the near term is around the Houston metro, where some of
the hi-res models indicate the highest amounts could fall. This is
where flash flooding is most likely.

As such, given the expected rates and duration of the locally
heavy rainfall, inundation flooding of urban and poor drainage
areas is likely overnight.

Taylor

ATTN...WFO...CRP...EWX...HGX...LCH...

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

LAT...LON   30939449 30759342 30509288 29829288 29819390
            29489464 28889541 28629625 28029703 28369708
            28729708 29589710 30649557