AWUS01 KWNH 090926
FFGMPD
MSZ000-LAZ000-ARZ000-TXZ000-OKZ000-091525-

Mesoscale Precipitation Discussion 0138
NWS Weather Prediction Center College Park MD
525 AM EDT Tue Apr 09 2024

Areas affected...eastern TX into southern AR/northern LA

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

Valid 090925Z - 091525Z

SUMMARY...A relatively narrow axis of heavy rain is expected to
become better organized near or a little after 12Z with areas of
training from SW to NE focusing from portions of central TX into
the Arklatex and portions of southern AR/northern LA. 2 to 4 inch
totals are expected by 15Z, although locally higher cannot be
ruled out.

DISCUSSION...Regional reflectivity across northeastern TX showed a
weakening cluster of thunderstorms advancing past the DFW
Metroplex at 0900Z with outflow preceding it from near LNC to MKN.
To the east and southeast of the Metroplex, regional reflectivity
showed overrunning showers and thunderstorms, with a recent uptick
in intensity since 08Z. This newer activity was located to the
north of an effective stationary front which extended WNW from
southern LA into east-central TX. The recent uptick in intensity
to the north of the effective stationary front appears to be
related to an increase in elevated instability as seen in SPC
mesoanalysis of MUCAPE, due to increasing low level moisture
(sfc-700 mb) as seen on Layered Precipitable Water (LPW) imagery
from CIRA. LPW and water vapor imagery also showed the presence of
a shortwave located southeast of Big Bend, TX, advancing toward
the northeast along with higher levels of moisture in the 700-500
mb layer.

Expectations are for an increase in thunderstorms along the
leading edge of low level moisture return, focused in the 925-850
mb layer, with roughly 20-30 kt of southerly flow. The low level
convergence axis is forecast by recent runs of the RAP to extend
from near GTU to JDD to TXK at 12Z as low level wind fields
gradually strengthen ahead of an eastward advancing closed low
over AZ/NM. The 08/09Z SPC mesoanalysis showed 500 to 2000+ J/kg
ML and MU CAPE over east-central TX, with some relatively weak
areas of CIN south of the Metroplex.

The advection of low to mid-level moisture from the south into
central/eastern TX through the morning is expected to help reduce
CIN and moisten initially dry mid-levels. Simulated reflectivity
from the HRRR has been consistent with the development of an axis
of thunderstorms near the low level convergence axis, focusing the
potential for training and repeating storms from central into
northeastern TX and near the AR/LA border, perhaps developing near
or just after 12Z. Some of that development appears to be ongoing
over far northeastern TX.

Portions of this region have received an estimated 1 to 4+ inches
since 21Z (multi-sensor MRMS estimates) and the addition of an
additional 2-4 inches would result in renewed flash flood
concerns. There is some uncertainty with coverage of 2-4 inch
totals with recent HRRR cycles trending downward with QPF through
the mid/late morning, however, the setup looks favorable for heavy
rain developing later this morning with rainfall rates of 1-2
in/hr.

Otto


ATTN...WFO...EWX...FWD...JAN...LZK...MEG...SHV...

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

LAT...LON 34399209 34279117 33949073 33269098 32899165
32379342 31999465 31389616 30629763 31119805
32409683 33649463 34319279

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AWUS01 KWNH 100933
FFGMPD
MSZ000-LAZ000-TXZ000-101430-

Mesoscale Precipitation Discussion 0144...Corrected
NWS Weather Prediction Center College Park MD
532 AM EDT Wed Apr 10 2024

Corrected for minor northeastward expansion of MPD area

Areas affected...southeastern TX into central/southern LA and
southwestern MS

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

Valid 100927Z - 101430Z

Summary...Heavy rain is expected to expand eastward into portions
of south-central LA with scattered to numerous areas of flash
flooding through 14Z, some of which could be considerable to
severe with life-threatening impacts.

Discussion...A persistent area of training from the southern Piney
Woods region of TX into western LA has resulted in an areas of 5
to 10+ inches of rain over the past 12 hours, extending from
Hardin and Tyler counties into western Vernon and Beauregard
parishes. Radar imagery at 09Z showed the west to east axis of
training, occurring just north of a combined outflow/stationary
front, has begun to lift north over the past hour, ahead of an
approaching, forward propagating convective line moving east from
a Conroe to Houston to Freeport line. The VAD wind profile from
KHGX at 09Z indicated southerly winds of 30-40 kt in the 2-5 kft
AGL layer, ahead of the convective line, a 10 kt increase since
two hours earlier. The strengthening low level flow, just ahead of
a surface low and southward extending cold front near Houston, has
likely helped to shift the axis of ongoing training to the north
over the past hour.

As a potent mid-level trough over western TX continues to advance
east this morning, increased large scale ascent (including
strengthening divergence and diffluence aloft) will shift eastward
from eastern TX into western LA. An ongoing axis of elevated
convergence in the 925-850 mb layer, crossing the Sabine River
from SW to NE, is likely to be disrupted as the upper trough and
preceding convective line advance eastward this morning.
Overrunning low level flow of 30-40 kt will translate eastward
into LA over the next few hours, tapping a notable region of 1000
to 2000+ J/kg MLCAPE located off of the upper TX and LA coast,
supporting continued heavy rainfall. Mean steering flow will be
oriented from SW to NE, but west to east mean translation of the
heavy rainfall axis is expected which should result in continued
training, with rainfall rates of 1-2 in/hr, locally 2 to near 3
in/hr. Additional rainfall totals of 3-5 inches (locally higher)
are expected through 14Z, which is likely to extend a significant
flash flood threat eastward from southeastern TX into portions of central/southern LA. Any overlap of heavy rain which has fallen
over the past 12 hours will maintain a risk of considerable or
major flash flooding with the Sabine River Valley, and possibly
eastward into portions of central or south-central LA.

Otto

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

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

LAT...LON 32199146 31869063 31259029 30558992 30158962
29798980 29609040 29729173 29739326 29509480
29789521 30389498 31029423 31419344

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