MESO: Heavy Rainfall
From
Weather Alert@21:1/175 to
All on Wed Dec 30 23:37:00 2020
AWUS01 KWNH 302041
FFGMPD
TXZ000-310240-
Mesoscale Precipitation Discussion 0880
NWS Weather Prediction Center College Park MD
340 PM EST Wed Dec 30 2020
Areas affected...South-Central to Southeast TX
Concerning...Heavy rainfall...Flash flooding possible
Valid 302040Z - 310240Z
SUMMARY...Locally heavy showers and thunderstorms, with some brief
backbuilding of cells, may result in an isolated flash flood
threat going into the evening hours.
DISCUSSION...The latest WV imagery shows an upper trough digging
southeast across the Southwest U.S. which is expected to evolve
into a rather strong mid-level low center over northern Mexico by
this evening. Downstream of this over areas of south-central to
southeast TX, will be increasingly strong deep-layer southerly
flow which will foster strong warm-air/moisture advection in off
the western Gulf of Mexico. Along with this, will be rather strong
upper-level divergence ahead of the trough associated with
left-exit region jet dynamics approaching the region. Already some
areas of heavy showers and thunderstorms are situated across
portions of central to northeast TX as a strong cold front slowly
settles southeast across the region and coincides with the arrival
of this more conducive moisture transport and larger scale forcing
closer to the coastal plain.
The convective threat though may become a little more focused over
the next few hours and going into the evening time frame, and
especially over southeast TX as the front begins to slow down a
bit more in response to the approaching upstream height
falls/forcing. The boundary will also be interacting with a
greater uptick in PWs (reaching 1.25 to 1.5+ inches), stronger
low-level convergence/Gulf of Mexico inflow, and somewhat greater
instability with MUCAPE values of as much as 1000 to 1500 j/kg.
FFG values are quite high across the region, and generally there
is an ongoing moderate to severe drought. However, the rainfall
rates should increase somewhat this evening, and will likely get
up into the 1 to 1.5 inch/hr range occasionally. Several runs of
the HRRR have been advertising this, and with somewhat better
instability pooling across the southeast TX coastal plain, the
heavier rates will likely tend to verify. While these rates are
not overly high, there will be some potential for the cell
activity to develop and at least briefly backbuild over the same
area.
Going through early evening, some localized pockets of 2 to 3+
inch rainfall amounts will be possible. Generally any threat of
flash flooding will be highly localized and confined to the more
sensitive urban areas.
Orrison
ATTN...WFO...CRP...EWX...FWD...HGX...
ATTN...RFC...WGRFC...NWC...
LAT...LON 31479563 30769472 29529527 28719694 28869821
29709845 30239765 30729661
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