Areal Flood Warning 2, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
452 AM CDT Sat May 1 2021

.SHORT TERM [ Through Saturday Night]...

Widespread moderate to heavy rain and isolated thunderstorms will
continue to be the main concern over the next 12 to 24 hours.

Per latest water vapor satellite imagery, a broad upper-level low
is currently spinning just west of the Big Bend, TX. At the
surface, a coastal low continues to move over the Corpus Christi
area/Middle Coast, slowly moving northward into our region through
the day. The environment continues to be favorable for rainfall
early this morning. The warm front is almost stationary south of
Galveston to Victoria line, that, in combination with a strong
low-level frontogenesis maximized in the 925-825 mb layer, PWATs
near 2.0 inches and upper- level jet support; widespread rain will
continue to develop across the region. A constant weak low level
jet feed is also noted into the frontogenesis area; therefore, the
strongest rainfall rates continue to move across our
west/southwestern counties early this morning. Light rain are
expected across the entire region; however, the best focus for
moderate to heavy rain will be along and west of I-10 through late
morning. Additional rain totals of 1 to 3 inches will be
possible, locally higher. While instability looks limited (SBCAPE
<700 J/kg) due to extensive cloud cover, a few strong
thunderstorms cannot be ruled out given effective bulk shear in
the 30-45 knots range. The main focus for strong storms will be
south of a line from CLL to SGR to LBX with gusty winds as the
main threat.

As the day progresses, there could be a brief lull in
precipitation late this morning/early afternoon, mainly north of
I-10. The next round for moderate to heavy rain and isolated to
scattered thunderstorms arrives late this afternoon (between
22-00Z Sunday). Forcing and dynamics will be enhanced across the
region as the aforementioned upper low lifts northeastward into
eastern TX and the Lower MS Valley. Have leaned towards CAMS /Hi-
res models for PoPs for this period. Convection/showers will
gradually diminish from southwest to northeast by late
tonight/early Sunday morning.

Have continued with the Flash Flood Watch across much of the
region through 12Z Sunday. 05

.LONG TERM [Sunday Through Saturday]...

Drier conditions will gradually filter in on Sunday with some
lingering showers possible across our northeastern counties as the
sfc low and upper-low move out of the region. It will be warm as
southerly winds returns to the area during the afternoon hours.
Speaking of warm conditions, Monday is shaping up to be a very
warm day. 850 mb temperatures exceed the 90th percentile of NAEFS
guidance and southerly flow should bring highs in the upper 80s
and low 90s. Raised high temperatures toward the 75th percentile
of model guidance.

Another upper trough will moves into the southern Plains early
next week with a cold front passage Tuesday afternoon and evening.
Latest GFS, ECMWF and NAM continue in good agreement with this
system, brining the front by midday Tuesday and off the coast by
Tuesday evening. Scattered showers and storms are expected along
and ahead the front. With PWATs in the 2.0 inches, some locally
heavy rain cannot be ruled out. Drier weather returns by Wednesday
with an upper-ridge over the southern Plains.

05

&&

.AVIATION [06Z TAF Issuance]...

For the 01/06Z TAFs, have lowering ceilings and visibilities
overnight as SHRA/TSRA to the west work this way. Periods of
MVFR/IFR conditions could linger throughout the day on Saturday,
but breaks in the action could occur too. Last round of SHRA/TSRA
currently looks like it should move eastward across the area
Saturday night through early Sunday morning.

42

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  75  66  85  70  89 /  90  90  20   0   0
Houston (IAH)          76  67  84  71  90 /  80  80  30   0   0
Galveston (GLS)        75  71  81  74  84 /  70  80  30   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...Flash Flood Watch through Sunday morning for the following
     zones: Austin...Brazoria
     Islands...Brazos...Burleson...Coastal Brazoria...Coastal
     Jackson...Coastal Matagorda...Colorado...Fort
     Bend...Grimes...Houston...Inland Brazoria...Inland
     Harris...Inland Jackson...Inland
     Matagorda...Madison...Matagorda
     Islands...Montgomery...Northern Liberty...Polk...San
     Jacinto...Trinity...Walker...Waller...Washington...Wharton.

     High Rip Current Risk through this evening for the following
     zones: Bolivar Peninsula...Brazoria Islands...Galveston
     Island...Matagorda Islands.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION through this evening for the
     following zones: Coastal waters from High Island to
     Freeport TX out 20 NM...Galveston Bay...Matagorda
     Bay...Waters from High Island to Freeport TX from 20 to 60
     NM.

     Small Craft Advisory from 9 AM this morning to 7 PM CDT this
     evening for the following zones: Coastal waters from
     Freeport to Matagorda Ship Channel TX out 20 NM...Waters
     from Freeport to Matagorda Ship Channel TX from 20 to 60 NM.

     SMALL CRAFT SHOULD EXERCISE CAUTION until 9 AM CDT this morning
     for the following zones: Coastal waters from Freeport to
     Matagorda Ship Channel TX out 20 NM...Waters from Freeport
     to Matagorda Ship Channel TX from 20 to 60 NM.

&&

SHORT TERM...05
LONG TERM...05
AVIATION...42