Flash Flood Warning 12, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
945 PM CDT Sun Apr 28 2024

...New UPDATE...

.UPDATE...
Issued at 918 PM CDT Sun Apr 28 2024

The Tornado Watch was extended until 11pm for parts of the area.
Though isolated severe cells are occurring, and will probably
continue for a while, this appears to be transitioning to a
flooding event. Scattered cells have evolved into more of a east-
west oriented linear line...perpendicular to the 30-35kt llvl
inflow from the Gulf. IR imagery depicts a classic "<" from the
Brazos Valley across the northern 1/3 of our counties. This
implies a favorable environment for training heavy rain.
Widesrpead2-5" has fallen across northern parts, with a TRA gage
at Caney Creek @ Fryday measuring 8.24" as of this writing (and
still raining). We've seen 5 minute rainfalls of about 1/2".
Expect some very serious flooding to occur over parts of the
area...exceptionally dangerous because it is at night.

This system isn't in a hurry to go anywhere. Cold pool should
eventually nudge it south overnight into the metro area and
eventually off the coast. Have pulled the Flash Flood Watch south
into Montgomery and Liberty Counties. Have held off, for now,
adding locations further south. Reason being the low level jet
and higher PW axis should be trending eastward after midnight.
Will be closely monitoring things overnight, and cannot rule out
a further southward flood watch expansion into the metro area.
Regardless, Houston metro and coastal areas should still
anticipate some localized heavy rain and the associated impacts
(local street flooding, rises on some creeks/streams/bayous).

A very strong reminder...don't drive into water covered roadways!

47

&&

.SHORT TERM...
(This evening through Monday Night)
Issued at 405 PM CDT Sun Apr 28 2024

...TORNADO WATCH IN EFFECT UNTIL 9 PM TONIGHT...

...FLOOD WATCH IN EFFECT THROUGH MONDAY MORNING...

Light showers are currently ongoing across portions of SE Texas this
afternoon, with stronger/severe storms ongoing over portions of
Northeast Texas. SPC's mesocale analysis depicts ample instability
across SE Texas, with SFC CAPE values of 2500-4000 J/KG, 3km ML CAPE
of 5-150 J/KG. MU LIs of -6 to -8, LCL heights of 500-1000m, and
midlevel lapse rates of 6.5-7.5 DegC/km. Ample shear remains present
throughout the region as well, with Effective Bulk shear around 40-
50 knots and 3km SRH of 150-250 m2s2. 3km EHI values range from 3-5,
Supercell Composite values of 8-12, Sig Tor Parameter values of 1-2,
and Large Hail Parameter values of 8-16. Enhanced Stretching
Potential values of 1-2 are currently focused west of I-45 just
north of the US-59 corridor right now, coinciding with higher VTP
values of 2-4. Model consensus and current observations suggest
isolated/scattered shower/thunderstorm development across SE Texas
this afternoon, with a larger line/cluster of storms forming this
evening over portions of the Brazos Valley/Piney Woods along a
frontal boundary. This complex of thunderstorms should move
east/southeasterly overnight, pushing offshore Monday morning.

A Tornado Watch is in effect for areas north of the US-59 corridor
until 9 PM Tonight. These discrete storms will be capable of
producing all severe hazards, including damaging winds, large hail,
and even a few tornadoes. Additionally, these storms will also be
capable of producing locally heavy rainfall, with some models
suggesting the potential for training storms. A Flood Watch is
currently in effect across the northern third of our CWA until 10 AM
Monday. Rainfall totals will largely be up to 2" though isolated
higher amounts of 3-5" or higher will be possible. Locations outside
of the current watch areas will still be under a Marginal to Slight
Risk of Severe Weather/Excessive rainfall tonight into Monday
morning. Keep an eye on the forecast for additional updates, and be
sure to have multiple ways of receiving warnings tonight.

The severe weather & heavy rainfall threat come to an end on Monday
as this complex of thunderstorms pushes offshore. Isolated showers &
storms will be possible Monday night/early Tuesday due to lingering
moisture. Otherwise, expect much more benign weather with highs in
the 80s and lows in the 60s to lower 70s.

03

&&

.LONG TERM...
(Tuesday through next Saturday)
Issued at 405 PM CDT Sun Apr 28 2024

With an active west to southwest flow aloft, a series of
disturbances will be moving across the area through much of this
period. With precipitable water values remaining on the elevated
side, a persistent onshore flow, and a stalling cold front, look for
periods of showers and thunderstorms across the area for much of the
week, generally higher inland (up north) and lower closer to the
coast. Each day, expect high temperatures in the 80s and low
temperatures in an upper 60s to lower 70s range.  42

&&

.AVIATION...
(00Z TAF Issuance)
Issued at 559 PM CDT Sun Apr 28 2024

Shower/thunderstorm development increasing across the northern
half of Southeast Texas. Embedded strong-severe cells will be
capable of producing all wx modes (strong winds, hail, heavy rain
and isolated tornadoes). Look for this activity to become more
organized/linear this evening...eventually tracking into the
metro area overnight (6-10z) and toward the coast thereafter.
Prevailing MVFR cigs will become IFR in/near the strongest cells.
May see some fog/low cig develop once the precip passes late
tonight followed by gradual improvement into the mid-late morning
hours Mon. VFR areawide during the afternoon. 47

&&

.MARINE...
Issued at 405 PM CDT Sun Apr 28 2024

Moderate to strong onshore winds (still at around 20 knots this
afternoon) and hazardous seas (10 feet at Buoy 42019 at 2 PM CDT)
will continue through late tonight. Minor coastal flooding is expected
in vulnerable locations at times of high tide (mainly during the day
today). There is a chance of showers and thunderstorms, with the best
chances from this evening through Monday morning, and then again during
the day on Tuesday (look for higher winds/seas/bays in and near any
storms). Winds will gradually decrease late tonight into Monday, with
lingering high seas keeping conditions hazardous through much of the
day on Monday. Generally moderate onshore flow will persist through
the rest of the upcoming week.  42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)	  68  86  68  84 / 100   0  10  30
Houston (IAH)			  71  86  71  84 /  90  20  20  50
Galveston (GLS)			  72  80  72  79 /  80  90  20  50

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flood Watch through Monday morning for TXZ163-164-176>179-195-
     196-198>200.

     Beach Hazards Statement through Monday morning for TXZ436>439.

GM...Small Craft Advisory until 10 AM CDT Monday for GMZ330-335-350-
     355-370-375.

&&

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