Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 201810
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1210 PM CST Mon Feb 20 2017

.AVIATION...
Rain reduced visibilities of 3 to 6 miles will continue for a least
a few more hours in the west and til 21-22z for the main hubs. VFR
this evening with a BKN MVFR deck developing across the north and
probably expanding down into CXO/IAH may even briefly go IFR up
north. In addition with light winds and wet ground may see areas of
fog develop and have added it but not going in whole hog like NAM
given the possibility of greater cloud cover which could limit
radiational cooling...but if the clouds clear up early then fog
threat will likely increase dramatically. Cold front coming through
the area Tuesday morning 14-18z should dry out the area and bring
northwesterly flow through Tuesday evening. 45
&&

.MARINE...
Hoisted SCEC for the increased offshore flow in the wake of the
morning storms. Otherwise only minor changes to track with
observations. 45

&&

.DISCUSSION...
Radar continues to trend downward with both coverage and intensity of
the rain, and a majority of the latest high resolution models keeps
this trend ongoing through the afternoon hours. Still looking for mainly
light to occasionally moderate rain for the rest of the afternoon with
all the activity gradually working its way off to the east. At this
time, all area rivers and bayous continue to respond well to today`s
rainfall. For the update, had to do some modifications mainly based
on current observations and also added some areas of fog for tonight.
Anticipate maybe needing to do some more updates as the afternoon
progresses.  42
&&

.PREV DISCUSSION... /ISSUED 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 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)      69  57  76  54  79 /  90  10  10  10   0
Houston (IAH)              69  61  77  58  78 /  90  30  20  10  10
Galveston (GLS)            68  63  72  62  71 /  70  50  20  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 3 PM CST this
     afternoon for the following zones: Coastal waters from
     Freeport to the Matagorda Ship Channel out 20 NM...Coastal
     waters from High Island to Freeport out 20 NM...Waters from
     Freeport to the Matagorda Ship Channel from 20 to 60 NM...
     Waters from High Island to Freeport from 20 to 60 NM.

&&

$$


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