Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Tue Jun 16 2026
Day 2
Valid 12Z Wed Jun 17 2026 - 12Z Thu Jun 18 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE UPPER
TEXAS GULF COAST THROUGH SOUTHWESTERN LOUISIANA...

...Gulf Coast...

An upper level shortwave disturbance over the northwestern Gulf
will likely contribute to the development of a small surface low
or surface trough along the Texas Gulf Coast on Wednesday. This
disturbance will gradually track parallel to the coast towards the
northeast, and move into southwestern Louisiana this evening. The
exact track of the center of circulation will remain the
distinctive factor determining how much rain penetrates inland
along the Texas coast, including into the Houston Metro. Some of
the CAMs guidance has trended west with the track of the low, which
will prolong a period of heavy rain into Houston as cells ride
northwestward ahead of the low in a small but very potent band of
heavy rain. It will be potent not just because of the multiple
sources of forcing for the heavy rain, but also the sheer amount of
atmospheric moisture that will be available for the storms to tap
into. PWATs will remain exceptionally high, likely peaking in the
upper 2s as the low reaches its peak intensity this afternoon.
While the predominant southerly flow will advect some instability
into the low, extensive cloud cover will work against achieving
heavy rainfall rates in many cases. The hydrology will become
increasingly favorable for flash flooding even with less than
optimal rainfall rates as prior days' rains combine with the new
rainfall to continue lowering FFGs. The Moderate Risk was nudged
west in coordination with HGX/Houston, TX forecast office to
include all of the Houston Metro. Prolonged northwestward moving
cells in a narrow band could easily start causing flash flooding
problems over the Houston metro should the track optimize.

Further east, there is more certainty with heavy rainfall rates
impacting the area from Beaumont east into southwestern Louisiana.
Southerly flow exactly orthogonal to the coast, frictional
convergence, and then the low itself impacting the area from late
in the day Wednesday through Wednesday night will all contribute to
additional heavy rains over an area of Louisiana already hard hit
from the current rain and expected rain in the area on Day 1. The
Moderate Risk area was little changed from inherited in this area.

Further north and east, the heavy rain threat will concentrate over
the Wednesday night timeframe. As the low and associated upper
level disturbance move into Louisiana, a leading band of heavy
rain, oriented southwest to northeast, will overspread portions of
central and eastern Louisiana and continue into western
Mississippi. There is considerable uncertainty how far into
Mississippi the heavy rain gets. But it will likely extend from the
coast south of Lafayette northeast through Baton Rouge and into
southwestern Mississippi. Here too, favorable hydrology due to wet
soils from heavy rains from today/Day 1 will contribute to any
resultant flash flooding. For now, this appears to stay west of New
Orleans, but will likely be too close for comfort, and the New
Orleans Metro could see occasional heavy rain from passing cells.

...Midwest...

Very few changes were needed to the large Slight Risk across much
of the Midwest on Wednesday. A strong and impressively potent low
driving eastward from the Plains will run into increasing amounts
of deep tropical moisture as it moves into the Great Lakes. This
will contribute to increasing coverage of showers and storms, first
with its warm front from Chicago east along Michigan's southern
border, then followed very quickly in some areas by stronger storms
associated with the low's cold front. Favorable hydrology from
several bouts of heavy rain over the past week will support flash
flooding development. However, this low and its associated storms
will be racing eastward. Thus, duration of heavy rain will be very
limiting in many areas. For the corridor forming the northern half
of the Slight Risk area, heavy rain duration will be longer, as the
warm front and associated elevated convection quickly followed by
stronger convection with the cold front could allow for some areas
to see multiple hours with interspersed heavy rain through the day.
Instability may be more limited in this area however, so that will
work against heavy rains.

For the southern half of the Slight, there will be significantly
more moisture and instability for the storms to work with as they
race southeastward, so rainfall rates should be higher than further
north. However, it's likely just the cold front's storms that will
impact most areas, so it's one shot and done. Training and
backbuilding won't be a concern until you get back into Missouri
and Kansas. Once again, the soils remain wet in these areas, so it
may be enough to get widely scattered instances of flash flooding,
particularly in urban areas. As is typical this time of year, the
cold front will hang up on its southern and western periphery, as
it runs into the southwesterly low level jet. This will greatly
extend the potential for heavy rain from southeastern Kansas
through southern Missouri Wednesday night. These areas have also
been hard hit with heavy rain in recent days, as well as the
topography of the Ozarks, so the Slight remains in place there with
few changes.

Wegman


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt