Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 201342
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
742 AM CST Mon Feb 20 2017

.UPDATE...
The line of intense convection that moved into SE TX earlier this
morning has broken apart and intense convection has waned
significantly. The highest rainfall values have been out west over
Colorado, Burleson, Washington and Austin counties with about 3 to
4 inches of rain with most of that rain falling last night between
midnight and 2 AM. Flash flooding looks less likely as the
residual rain will be far less intense. Will drop the Flash Flood
Watch but still expecting periods of light to moderate rain to
linger through the mid afternoon. 43

&&

.PREV DISCUSSION... /ISSUED 549 AM CST Mon Feb 20 2017/

AVIATION...
Thunderstorms will affect most of the area this morning. The
stronger storms are expected to affect terminals between KUTS and
Houston metro through at least mid morning, and from the Houston
metro airports to KLBX and KGLS through midday. Short range models
show the potential for strong gusty winds of greater than 30 knots
and for locally heavy rainfall. Showers and embedded thunderstorms
will linger into the afternoon as well.

A front should push through SE Texas later today and tonight and
help to clear things out. Some of the guidance is suggesting at
least patchy fog formation will be possible tonight, especially
south and southeast of Houston.

40

PREV DISCUSSION... /ISSUED 259 AM CST Mon Feb 20 2017/

DISCUSSION...
At 230 AM, a line of showers and thunderstorms extended north to
south across the CWA from Crockett to Edna. The line will continue
to move slowly east while individual storms will continue to move
north northeast. At 07z, a a weak meso-high and associated cold
pool and outflow extended from about Dallas to La Grange. The
northern end of the line seems to be pushing east a bit faster
than the southern end of the line. 00z 850 mb analysis shows dew
pts between 10-11 degrees over North Texas and between 5 and 9
degrees further south but 850 mb winds were from the south at
25-35 knots so moisture levels expected to continue to increase
this morning. A weak 850 mb trough was located over SW TX. The
best 700 mb moisture was also located over N TX with a weak trough
over W TX. 300 mb winds show a diffluent pattern over E TX with a
deep trough over the 4 corners extending south into northern
Mexico. 00z models suggests that 300 mb winds will become even
more diffluent by 12z and PW values will increase to 1.70-1.80
inches. Instability is weaker over E-SE TX and the window for
severe weather appears to be closing. The primary hazard this
morning will be heavy rain. Will maintain the Flash Flood Watch
but not sure it will be needed after 18z. Instability is weaker
over E-SE TX and the window for severe weather appears to be
closing. The primary hazard this morning will be heavy rain. SE TX
will lie on the east side of the upper trough through this
evening so periods of light rain will persist this afternoon but
heavy rain is not expected after 18z.

The upper level trough axis will push east of the region tonight
and drier weather is expected Tuesday. A weak 500 mb ridge
amplifies slightly over Texas Wed/Thu so continued dry weather is
expected with unseasonably warm temperatures. Another upper level
trough will move across the central Rockies and surface low
pressure will develop in the lee of the Rockies. The sfc low will
move east and drag a cold front across the area Friday afternoon.
Slightly cooler temperatures expected for Saturday as high
pressure moves into the southern plains. Onshore winds resume
Saturday night as the surface high moves east of the region. Warm
air advection will persist on Sunday and patchy light rain will
accompany the warmer temperatures. 43

MARINE...
Caution conditions were diminishing slightly. However, inflow into
the storms over the inland areas will increase the winds over the
next 3 hours or so. Because of this, will keep the SCEC in place for
the Gulf waters through 12Z.

Otherwise, models were continuing to show thunderstorms developing
over Matagorda Bay and the Gulf waters west of Freeport this
morning. The storms should then begin affecting Galveston Bay and
areas east of Freeport late this morning into early this afternoon.
Impacts expected are strong winds. Storms could affect the marine
areas up to a 6-hour period.

A cold front will then push the rain and thunderstorms east of the
area later tonight and Tuesday. Offshore winds following the system
should persist through Wednesday. Onshore winds will return by
Wednesday night.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      72  57  76  54  79 /  90  20  10  10   0
Houston (IAH)              72  61  77  58  78 / 100  30  20  10  10
Galveston (GLS)            70  63  72  62  71 / 100  50  30  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch until 4 PM CST this afternoon for the
     following zones: Austin...Brazoria...Brazos...Burleson...
     Chambers...Colorado...Fort Bend...Galveston...Grimes...
     Harris...Jackson...Liberty...Madison...Matagorda...
     Montgomery...San Jacinto...Walker...Waller...Washington...
     Wharton.

GM...NONE.
&&

$$

Discussion...43


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