Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Sun Oct 21 2018
Valid 01Z Sun Oct 21 2018 - 12Z Sun Oct 21 2018
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
Valid 12Z Mon Oct 22 2018 - 12Z Tue Oct 23 2018
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE WESTERN GULF STATES...
...Western Gulf States...
Tropical moisture is expected to remain just offshore of TX and LA
during Day 2. As has been the case the past few model cycles,
there is still some model spread concerning just how much of the
moisture impacts the coast, and whether convection developing in
the moisture plume will cause flash flooding. A low level east
southeast flow aids in pushing 2.00/2.25 inch precipitable water
air toward the TX coast, mainly after 23/00z. Model soundings
showed instability remaining in the marginal range, as lift from
short wave energy rounding the western edge of the shrinking mid
level ridge over the Gulf of Mexico crosses TX during the period.
While most of the 00z model suite showed an axis of heavy rainfall
along an inverted trough pointing toward the TX coast, there
remains a fair amount of spread concerning where this occurs. A
blend of the 00z GFS/ECMWF places the axis of heaviest rainfall
between KPSX and KGLS, with 2.00+ inch rainfall amounts coming
just inland between these two points. A small Slight Risk area was
considered for this area, but given the model spread in the 00z
model suite, and the volatility of the solutions over the past few
cycles, this idea was shelved. This decision was collaborated with
A fairly large Marginal risk was extended across much of coastal
TX for Day 2 to cover the flash flood threat. The risk area was
extended across portions of interior south TX (west to the Rio
Grande River), as moisture from Willa could become involved in the
flow across this area. Most of the 00z guidance supports a locally
heavy rainfall threat here, though the 00z NAM may be too
aggressive bringing the deep moisture into TX during Day 2.
The Day 3 outlook will be updated by 0830Z.
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt