Flash Flooding in Texas, June 1, 2021

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1156 PM CDT Mon May 31 2021

.AVIATION [06Z TAF Issuance]...

Rain is on the doorstep of CLL and UTS, and there remains high
confidence that a return to a stormier pattern is upon us. As far
as specific details for the next 24-30 hours, there's still not a
ton of clarity. Tonight's storms have outrun the front, and will
sag southward into the morning while generally weakening. When the
front catches up later in the day, the timing should support a new
blossoming of showers and storms over Southeast Texas, gradually
coming to an end again in the evening. Winds will be generally
south/southeasterly, gradually veering more southwesterly late in
the period for the sites further inland that will see the front
actually make it through.

&&

.PREV DISCUSSION /Issued 640 PM CDT Mon May 31 2021/...

.SHORT TERM [This Afternoon Through Tuesday Night]...

Currently, moderate low-level onshore flow has helped increase cloud
and moisture across southeast Texas. Much like yesterday, isolated
showers have developed west of I-45 where this onshore temperature
and moisture advection is the strongest. With daytime temperatures
peaking later this afternoon, expect some of these showers to
strengthen into thunderstorms that will soon diminish after sunset
when temperatures begin to cool.

Overnight, higher rain chances return as an upper-level trough digs
deeper into the Southwest US where its western flank will leave a
cutoff low over the Baja Peninsula. This cutoff low will begin our
period of prolonged wet weather this week. The remaining trough will
push a cold front across Texas overnight where it is expected to
reach our northern counties a few hours before sunrise. Hi-res
models differ on where this front will stall throughout the day,
with some deterministic solutions indicating as far south as Harris
County, but most models predict it will stay draped across our
northern counties as it dissipates through Tuesday evening. SPC has
placed Houston, Polk, and Trinity counties in a marginal risk for
thunderstorms tomorrow. With the frontal boundary stalled overhead
and breaks in the cloud cover leading to surface heating, some
strong to severe afternoon thunderstorms are possible for these
counties. With strengthening onshore flow across the rest of our
counties, isolated pulse showers and thunderstorms are also possible
tomorrow afternoon, especially in areas where breaks in the cloud
cover lead to the most daytime heating. Temperatures tomorrow will
be similar to today's with daytime highs reaching the mid-80s and
overnight lows in the very muggy 70s.

KBL

.LONG TERM [Wednesday Through Monday]...

Periods of showers and thunderstorms can be expected through much
of the long term period as a slow moving upper low currently near
the Baja California area gradually works its way toward Texas. A
series of shortwaves will be moving across the state, and with a
persistent onshore flow in place expect these currently hard to
time impulses to bring the state a lot more rain. Our area's best
chances look like they might end up at the end of the week and
especially over the weekend when the low works its way into the
state and becomes an even slower mover. The positioning of the low
and how fast (or slow?) it moves will become a major player as to
any chances of locally heavy rainfall and how much rain our area
eventually receives.

For now, in the short and long term periods combined (roughly over
the next eight days), look for widespread 2 to 4 inch rainfall
totals with isolated amounts possibly exceeding 5 inches for
potentially a large part of the area. As you well know, 2 to 4
inch rains in Southeast Texas can easily fall in a hour or less,
and if this happens over the same area over several rounds of
storms, flooding could easily become a threat. Stay tuned to the
forecasts as the week progresses (they can easily and significantly
change) and monitor how much rain falls/accumulates in and near
your area. Grounds have been wet across much of Southeast Texas
these past couple of weeks, and it will probably not take a whole
lot of additional rain to lead to flooding issues.  42

.MARINE...

Another extended period of wet weather is expected over the next week
or so, with rain chances generally on the rise through mid-week as
a series of upper-level disturbances move through the area. Winds will
generally remain out of the southeast through the period, occasionally
approaching caution levels through Tuesday and relaxing through the
remainder of the week. Over the weekend and into the start of next
week, look for an increase in winds and seas along with even better
rain chances. Elevated winds and seas will be possible in and around
the storms.  42

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  71  85  69  82  69 /  70  50  50  60  30
Houston (IAH)          72  86  71  85  71 /  20  50  40  70  30
Galveston (GLS)        77  84  76  84  76 /  20  20  30  40  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 7 AM CDT Tuesday for
     the following zones: Coastal waters from Freeport to
     Matagorda Ship Channel TX out 20 NM...Coastal waters from
     High Island to Freeport TX out 20 NM...Galveston
     Bay...Waters from Freeport to Matagorda Ship Channel TX
     from 20 to 60 NM...Waters from High Island to Freeport TX
     from 20 to 60 NM.

&&

SHORT TERM...KBL
LONG TERM...42
AVIATION...Luchs
MARINE...42