Flash Flood Warning 32, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1148 PM CDT Mon Aug 7 2017

.AVIATION...
Most of our 06Z TAFs will start with SHRA/TSRA as activity continues
to increase in coverage. Look for MVFR/IFR ceilings and/or visibilities
in the stronger storms. Will keep VCSH in most TAFs through 18Z, but
lots of uncertainty as to how this will all evolve on Tuesday as some
activity could linger into the afternoon hours. Think much of the area
might see improving flying conditions by late tomorrow afternoon and
on into tomorrow evening.  42
&&

.PREV DISCUSSION... /ISSUED 1016 PM CDT Mon Aug 7 2017/

UPDATE...
Though the radar quieted down for several hours as the atmosphere
had been pretty well worked over in the wake of rain earlier
today, it is now beginning to spark back to life. A mesoscale
convective vortex (MCV) has been very conspicuously spinning in
the area of College Station, drifting roughly to the ESE at 15 or
so knots. Additionally, onshore flow is resuming from the coast -
the quality of this return flow is made very apparent by the
sparking of showers along the coast in the last hour or so near
what is effectively a frontal boundary between unstable Gulf air
and the depleted air from earlier today.

To date, the new showers along the SE edge of the MCV have been
only sporadically impressive. Though boasting individual cores
with instantaneous dual pol rates of 4+ inches per hour, the
surrounding areas have been pretty light, and with pretty quick
individual cell motion being pretty quick, the highest of MRMS one
hour QPE are isolated pixels a tad over 1 inch. That said - as the
influx of more unstable air continues, and flow aloft weakens and
veers to be more line parallel, these characteristics should
change for the worse.

Though performance from the CAMs lately has been pretty lousy, it
seems to have had a not awful handle on this MCV, and so am
reluctant to abandon its guidance entirely. Recent HRRR runs seem
to peg out in the 5 inch neighborhood for QPF. The experimental
HRRR time lagged ensemble shows a relatively strong signal for
exceeding 3 inches of rainfall in a 6 hour period, and a slight
hint in this convergent area for exceeding 6 inches. Though it's
not yet matched in rain occurring, think 2ish inches per hour and
isolated spots of 3-5 inches accumulation seems reasonable given
that factors should come to support heavier rainfall. This should
be capable of causing some localized flooding issues at the least.

The really big question is where the heaviest rain will come down.
With the MCV motion, this preferred area for rainfall will be
drifting slowly towards the Houston metro, with storms already
occurring in extreme NW Harris County. At this time, think the
line motion is slow enough that its location that the heaviest
rain will fall northwest of the more vulnerable urban locations.
However, a faster drop of the line, or if significant rain starts
developing in the inflow, and that scenario could change.

For further information, please visit the WPC website and read
Mesoscale Precipitation Discussion 651.

Luchs

PREV DISCUSSION... /ISSUED 258 PM CDT Mon Aug 7 2017/

MARINE...
Light/moderate southerly winds will prevail this evening/tonight but
the passage of a weak frontal boundary should produce a brief period
of very light N/NW winds early Tuesday morning. However, the onshore
flow is expected to return by tomorrow afternoon. Periods of showers
and thunderstorms are expected across the coastal waters for much of
the week as a series of disturbances move across the area. Winds and
seas will be higher in/around these storms.

Marine interests should continue to monitor the progress of Tropical
Storm Franklin as it moves westward across the Yucatan Peninsula and
into the Bay of Campeche towards the middle of the week. Franklin is
likely remain to the south of Texas, but increased swell could begin
impacting the offshore waters as early as Wednesday. Seas will range
from 4 to 7 feet by Weds night through Thurs before gradually taper-
ing off into the weekend. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      75  90  75  94  75 /  70  40  40  30  20
Houston (IAH)              76  90  75  93  77 /  70  50  30  40  20
Galveston (GLS)            80  89  81  90  81 /  30  40  20  30  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

Discussion...25
Aviation/Marine...42

Hazardous Weather Outlook
National Weather Service Houston/Galveston TX
1043 PM CDT Mon Aug 7 2017

TXZ163-164-176>179-195>200-210>214-226-227-235>238-090345-
Austin-Brazoria-Brazos-Burleson-Chambers-Colorado-Fort Bend-
Galveston-Grimes-Harris-Houston-Jackson-Liberty-Madison-Matagorda-
Montgomery-Polk-San Jacinto-Trinity-Walker-Waller-Washington-
Wharton-
1043 PM CDT Mon Aug 7 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Tonight

Thunderstorms are developing across portions of Southeast Texas.
Some of these thunderstorms will be capable of heavy downpours.
Localized street flooding where the highest rainfall rates are
realized.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Scattered to numerous showers and thunderstorms are expected across
Southeast Texas Tuesday. Some of these thunderstorms may be
capable of brief heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected.

GMZ330-335-350-355-370-375-090345-
Coastal waters from Freeport to the Matagorda Ship Channel out
20 NM-Coastal waters from High Island to Freeport out 20 NM-
Galveston Bay-Matagorda Bay-
Waters from Freeport to the Matagorda Ship Channel from 20 to
60 NM-Waters from High Island to Freeport from 20 to 60 NM-
1043 PM CDT Mon Aug 7 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Tonight

Scattered showers and thunderstorms will be possible across the
Upper Texas coastal waters through the night and some of these
thunderstorms will be capable of producing locally higher winds
and waves.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Scattered showers and thunderstorms will be possible across the
Upper Texas coastal waters into Tuesday and some of these
thunderstorms may be capable of producing locally higher winds and
waves. Tropical Storm Franklin is forecast to move westward
across the Bay of Campeche Wednesday and Thursday which may lead
to increased seas and long period swell by late in the week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
725 PM CDT MON AUG 07 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1245 PM     TSTM WND DMG     16 W HUNTSVILLE         30.67N  95.81W
08/07/2017                   WALKER             TX   BROADCAST MEDIA

            CARPORT FLATTENED WITH SOME DAMAGE TO ADJACENT
            STRUCTURE.

&&

EVENT NUMBER HGX1700315

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