Mesoscale Precipitation Discussion 1070
NWS Weather Prediction Center College Park MD
732 AM EST Thu Dec 27 2018

Areas affected...Lower MS Valley and Southeast Texas

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

Valid 271232Z - 271732Z

Summary...Heavy rainfall, with generally minor flooding concerns,
will spread eastward across southeast TX and LA this morning.

Discussion...As of 12z an intense convective line is pushing
eastward across southeast TX and western LA. This activity is
being supported by deep layer ascent east of the northward lifting
shortwave/upper jet, and within a region of very strong low level
moisture transport and sufficient instability. With these
ingredients remaining in place this morning, the convective line
will be able to generally maintain its intensity as it moves
eastward, continuing to produce a couple hour period of heavy
rainfall.

The magnitude of the flooding threat is minimized by the forward
speed of the convective line, limiting the duration of heaviest
rainfall rates to just a couple hours at any one location. Think
this forward speed should continue through the morning
hours...before a likely slowing of the convection by this
afternoon as the better mid/upper forcing lifts well northward.

Recent observations show hourly rainfall totals exceeding 1"
within the line, with three hourly totals upwards of 2-3".
Generally think amounts of this magnitude will spread eastward
within the MPD area, with localized higher total possible. Flash
flood guidance is relatively high over this area, and thus
rainfall of this magnitude is unlikely to pose significant
flooding concerns. Thus generally thinking we see minor flooding
issues across any more susceptible locations within the MPD area
through the morning, with any more significant flooding issues
more localized in nature.

As mentioned above, the flooding threat may ramp up by this
afternoon across eastern LA into portions of MS/AL as the front
and convective axis slows its forward speed. Future MPDs are
likely to address that threat.

Chenard

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

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

LAT...LON   33049202 32999129 32649067 32149042 31479069
            30629161 30229243 29779399 29709405 29359483
            29319512 29519528 29869514 30479464 30859423
            31229376 32359278 32949232